10 kg Folding Sea Kayak

[IanHowick]

I'm not sure if it counts as a "wooden boat", but some of it is wood, and I'm planning to replace more of the HDPE with wood to make it lighter.

The beginning of the idea was to make a full size, expedition capable sea kayak that would fold up and fit in a bag and be light enough to take backpacking and or fit everything needed for a kayak trip within the 20-25kg airline weight allowance. Everything I need for camping can be got down to 9-10kg excluding food, fuel and the kayak, so the kayak needed to come in at around 10kg all up. I stumbled across Tom Yost's website, which provided huge amounts of inspiration and information. Yostwerks Kayak Building Manuals - Homebuilt kayaks by Thomas Yost (http://www.yostwerks.com) The problem was, all his folding designs with aluminium stringers and HDPE cross frames were at least twice my weight goal.

I started to think about carbon tube stringers and cross frames of marine ply, just making the corners where the stringers have to snap fit to the frames from HDPE. A look at carbon tube sizes and weights and a bit of calculation and it seemed the weight goal was possible in a 17 foot/ 5.2m sea kayak with PVC skin.

Some design issues quickly became apparent - I couldn't just line things up on a strongback, cut stringers to length, bash them flat and screw them into position, the tubes would have to terminate in sockets in the end frames. Some precise angles and lengths would need calculating and cutting, and every piece for the main frame would need to be drilled and finished to final dimensions before assembly. In the end I had to make my own design software (it ended up as a monster excel spreadsheet), and then figure out the design.

It all came together in the end, very pleasing to see the frame fit together and tension up to the designed rocker and then float on it's lines. Weight came in a fraction over 10kg, I have plans to replace most of the HDPE in the end frames with Paulownoa/ply /leftover carbon tube laminated up and make a lighter cockpit coaming so I think 8 and a bit kg is possible. Not as light as Micheal Storer's balsa canoe, but this one feels as though it could be loaded for an expedition and taken end over end in the surf without breaking. (Haven't tried this yet)

Quite a process and time frame to completion of the project, I now have three kids so the next project has to be a bigger boat! I'm currently in the early stages of building a Micheal Storer Goat Island Skiff and have sworn to myself I won't try and completely redesign it!

A few pictures are below, I can post some more with some more info on construction if anyone is interested.

Ian

[Bill P]

Ian, Thats' a fantastic effort. :2tsup:I'm currently working on a Yost design in the shed a Sea Otter-R so it great inspiration. I might give up and copy yours cos thats actually more like what I want!

Are you only using 3 stations and do the CF tubes 'snap' in? Is the tubing 3/4" , it looks a bit bigger. The two longitudinal wires (?) are they to place the frame in tension for stiffness? How does that work?

The PVC looks thin- I'm thinking of using 500g/m2. How did you do the coaming?

Great work.

Bill P

[anewhouse]

I'm interested.

What weight PVC skin did you use? I'm guessing that the surface area of the kayak is around 5 square metres, so the skin must be a significant part of the weight. Did you consider a nylon or polyester skin? Or don't they work well with a folding kayak?

I have a SOF the same length that is the same weight, but it doesn't fold. It is a Yost construction style with 12 mm ply forms and Paulownia stringers. However at the moment it still has the 0.1mm thick clear PVC I put on as a temporary skin. It has lasted 15 months and a few hundred kilometres, which is better than I expected.

It looks as if assembling the kayak needs one young male helper and a young female supervisor. :) Was your third child keeping lookout so your wife didn't catch you building a kayak inside the house? :p

That is an impressive piece of work.

[IanHowick]

Thanks for the interest.

Skin is 600g/m2 on the hull, 400g/m2 on the deck. There are zips most of the length of the front and rear deck, the assembled frame goes in through the rear zip opening and then everything is tensioned and zipped up. There are 5 longitudinal cords that are tightened up to maintain rocker and rigidity, I might be able to reduce that to three cords.

The main tubing is 19mm ID/21.4mm OD/1.2mm wall, the ferrules are 16mm ID/18.8mmOD/1.4mm wall made by C-Tech Carbon Tube - Round - www.carbon-tube.com (http://www.carbon-tube.com/round.php) in Auckland, NZ. There are 5 four metre long stringers (keel, 2 chines, 2 gunwales). Each is made of 4 one metre sections with a ferrule glued in one end and shock corded together. (For the Americans 19mm is about 3/4 inch, so OD of main tubes is a little bigger than 3/4 inch)

The end frames are made of HDPE and are/need to be quite strong in all directions. There are 4 intermediate frames of 12mm marine ply with a few bits of WRC laminated on where necessary. Ply frames are at the footrest position, front and rear of the cockpit and middle of the rear part of the kayak. It might be possible to design to eliminate the middle rear frame, but with the asymmetric swedish form (LCB is 54%), it's needed to hold the shape back there, and in any case helps support the rear deck in a re-entry following capsize if you don't roll. The ply frames "snap" to the carbon stringer to some extent, at the moment they are held together with velcro straps where necessary, but I plan to make two small trianglular HDPE snap connectors for each corner and screw them on either side of the ply. Details/pictures soon.

The cockpit rim is laminated from 12mm and 4mm ply and is hinged so it folds in half.

Bill P - I'd be prepared to send you a table of offsets (Similar format to Tom Yosts) if you wanted to have a go at this or a similar design. Be aware it's built around me (70kg, 175cm height), and is quite narrow (52cm beam, but waterline beam of 43.3cm which is quite narrow, tippy). It's easy for me to make adjustments to LOA, beam, waterline beam, position of footrest cross frame to suit, so if you are interested let me know your leg length, weight and desire for stability and I can fiddle things accordingly. Also, what build method are you thinking of - copy of mine with carbon, non folding wooden or aluminum tube following Tom Yost more closely.

More with pictures soon, probably on Wednesday morning.

Ian

[IanHowick]

anewhouse:

I just checked the numbers on total hull surface area, it's 4.74 m2

Multiply the hull and deck areas by the respective g/m2 and it comes out at 2.53 kg, add about another 500g for zips, velcro, flaps over same etc and the skin is about 3 kg. Haven't put it on the scales separately to check. Not sure if (presumably) coated nylon or polyester skin would work for a folder, I guess it would if you wanted an ultra light day-tripper.

Folding Kayaks by FirstLight (http://www.firstlightkayaks.com/) make the lightest/most high-tech commercial folding kayaks I have come across, they make their skins out of an unsupported urethane material which is probably very good - presumably durable enough with care if they are trusting their commercial reputation to it and stretchy as it has no polyester fabric in the structure so easier to skin. I'd guess it can be glued with the same heat activated glue that we are gluing the PVC with, this PVC glue is urethane based I believe. I haven't found a source for this kind of urethane fabric. Am away from a big city so haven't had the opportunity to go around and look at fabrics to decide if they're suitable, may have to do some looking and requesting samples online or ask the firstlight people.

Ian

[Bill P]

Hi Ian,

I’m after a folder for multi day touring that can be taken on a light aircraft and can be made for a reasonable cost. One that can be packed/unpacked reasonably easily for portages too.

Thanks for your offer of a special design, I’m thinking the Sea Otter shape & lines perhaps suits my needs more so than say a West Greenland Qajak style. Tom quotes <13.6kg for the Sea Otter, which until I saw yours I thought was very good for a home built.

I reckon your frame design is superior to Toms. The tensile strings would make that hull very stiff and I like the way they ‘tie’ the whole frame structure together. I haven’t been comfortable with just shock cord & snapping into the stations with the only ‘hard’ attachment at the stems.

I would be keen to see photos of your end stations, the tension system and your coaming. The stems areas beyond your end stations appear to have no chine or gunnel support just the ridge & keel- is that OK?

I’ts early enough in my project for me to change tack. The kids are after a chook shed anyway, so I might just pause my folder and reconsider.

Bill P

[IanHowick]

Hi Bill,

I agree that the Sea Otter design would serve your needs well. My design was the result of a long process and ideas I wanted to try out, and I'm happy with the result, but if you got out on a trip the differences would be more a matter of personal tastes than anything objective. There's actually very little difference in performance at cruising speed across the whole range of boats designed with cruising/touring in mind.

Disagree that my frame design is superior to Toms, most of the changes I made were a result of the decision to use carbon tube. It's difficult to join at the ends without fatally weakening it so the ends had to terminate in sockets in the end frames without any drilling or screwing of the carbon tube. This requirement opened up a whole can of worms in design, as to hold the tubes securely the sockets had to be at 2 to 3 times the tube diameter, which meant they had to be cut at precise angles, which meant figuring out some software to calculate the angles and a jig for the drill press to drill them... All stringers were left at 4 m length, but the end points vary due to the different curves of the gunwales,chines and keel stringers. (For this design, the chines finish 7.2mm closer to the centre at each end and the gunwales 8.5mm closer to the centre at each end than the keel stringer. This needs to be sorted with shims on the corners of the end frames or making the chine and gunwale stringers those amounts longer than the keel stringer. Lots of complication and extra weight in those end frames which isn't necessary if you have aluminum which can be screwed in at the ends. I've got some ideas as to how to make those end frames lighter but they won't be much simpler to construct, so I'd be inclined to stick to Tom's plans at the ends.

I could eliminate some cross frames and the deck ridges due to the inherent rigidity of the carbon tube that you perhaps couldn't if it was aluminum.

"The stems areas beyond your end stations appear to have no chine or gunnel support just the ridge & keel- is that OK? " That part seem fine for strength, forces beyond those end frames are minimal except for straight compression. The rear stem/rear cross frame is involved in tensioning up the skin once the frame is in place - more on this later.

My advice would be to stick with the Sea Otter design, and the overall frame construction methods of Tom's unless you want to go the carbon tube route. I wouldn't worry about the strength/security of the way Tom puts his boats together, he's built a lot of these kayaks and lots of people have put them to some serious use.

Changes I would consider worthwhile:

Make the cross frames of 12mm ply and just put triangular HDPE snap connectors on both sides of the ply at each corner. Cross frame weight will be halved, and you'll have enough HDPE for 5 or 6 kayaks left over. HDPE connectors on both sides of each corner will mean you can use longer screws that go right through the ply and bed into the other connector so they will stay in place. Others have tried putting HDPE connectors in the corners of the ply frames screwed into one side and the screws just pull out of the ply/everything becomes loose quite quickly. I'd put the screws/HDPE in with epoxy glue, it won't stick to the HDPE but it will help bed the screws into the ply. With double the connector power and triple the connector width at each corner rigidity/security should be higher and weight /cost much reduced as ply is much cheaper and half the weight of HDPE.

Tensioning strings are worth the trouble, I think, and do add to the rigidity without adding much weight. I needed them to maintain the rocker due to how I tensioned up the skin to make it smooth and fair on the bottom. Tom commented on how smooth and tight I'd got the skin for a folder, more on the secret to this in the next installment...

Ian

[Bill P]

Can't wait for the next installment Ian.

Thanks for validating my design choice- I think I I'll stick with the Sea Otter, Yost contruction. Maybe with a couple of full length stringer cables in lieu of the two rear deck tubes.

I take the point about the density of plywood vs HDPE, theres a kilo or two to be saved there. However I have some HDPP ex industrial cutting mat which I got for less than the cost of ply and I intend to that use for my frames.

If I was starting from scratch I would go ply/HDPE clips for frames as you suggest which would be stronger, lighter & cheaper.

Your tension system would preclude any need for spring clips, taping of the CF tubes? I'm keen to see more of this system.

Bill P

[keyhavenpotter]

Well done Ian, terrific effort. Buying carbon tubing when you cannot be sure of the outcome takes determination and self belief - something I lack!

Thought you might enjoy reading this article in Duckworks about a 10kg sit on top design and build.

Duckworks - A Boat Named Alice (http://www.duckworksmagazine.com/09/designs/alice/index.htm)

http://www.duckworksmagazine.com/09/designs/alice/Frame-showing-seat-s.jpg

Brian

[IanHowick]

Hi Brian, good to hear from you. "Determination and self belief" - maybe, but I also had a fair idea of what I didn't know, and the journey I'd have to take to get there.

One big plus of the folding skin on frame kayak method is if you stuff up the design, go too far out on a limb in some direction, you can always take what you learnt, redesign, pull the frame apart, make some new frames from ply, put it together with a new skin and try again, so it was knowing that that I spent $1000 on some carbon tube. (Please don't tell my wife!) It's also possible to make cheap cross frames, put them in temporarily with tape, wrap it all in polyethylene sheeting and duct tape and give it a try on the water before finalising the construction (though I didn't do this)

Spend $1000 or more on ply, timber and epoxy, glue it all together into a sailing boat, put it on the water and find it doesn't work and there's not much you can do with the result. If you do come up with something new and it actually works really well, then if you do more looking, you'll probably find you've re-created something that someone else has already designed!

I didn't do any prototyping as described above, I just built my kayak complete, put it on the water but I'd done a lot of computer modelling so I knew where the waterline and longitudinal centre of buoyancy and such like would be. I also downloaded line drawings or pictures of every kayak in the range of designs I had in mind, overlaid them with what I'd come up with and analysed where mine was different and what the consequences would be.

A kayak is also much easier than a sailboat, the kayak is purely a displacement hull, there is only so much that you can vary and get wrong.

For those who feel inspired to follow the amateur self design route, I'd still recommend caution. I'd agree with everything that real designers such as Michael Storer, Par, Ross Lillistone have said on this forum and elsewhere about the pitfalls of designing or modifying designs yourself, it's much more complicated than you think. On the other hand, all these guys started somewhere (Par at age 10 I believe).

A sailing dinghy has to work in both displacement and planing modes and transition between them, and there are the issues with lateral balance and the way things scale with size. Stability scales with the forth power of size, displacement hull speed with the square root of length, foil lift with the square of speed... There's also all the structural stuff.

If you understand all these things and lots of things I haven't mentioned/don't know about and have built and sailed half a dozen boats yourself and start from something existing that already works, and enjoy a challenge and the possibility of failure, then go for it!

I did see the article on the boat named Alice, I thought the construction out of lots of very thin tube made it very complicated and fragile, (but was dictated by a source of cheaper tubing?). Was his down to 10pounds? Mine uses only 5 longitudinal stringers which are quite solid at more than 3/4 inch dia. When I figure out simplicating the end frames and cockpit combing, it could be built quite quickly and easily. My aim was to build the strongest expedition capable boat I could at around the 10kg mark rather than the lightest possible kayak. I can stand all by weight on any one of the cross frames, and I'm sure it would be OK going end over end in big surf as long as the end didn't hit the bottom. (I'll post some pictures once I've completed sea trials at St Clair beach, Dunedin)http://farm2.static.flickr.com/1046/668645669_fc968c596c.jpg?v=0

Have to go now,

Ian

[IanHowick]

I take the point about the density of plywood vs HDPE, theres a kilo or two to be saved there. However I have some HDPP ex industrial cutting mat which I got for less than the cost of ply and I intend to that use for my frames.

Bill P

Hi Bill, you mention using "HDPP ex industrial cutting mat" Do you mean high density polypropylene, or is the last P a typo? I'd be dubious about using polypropylene for the cross frames, I had a household cutting board of polypropylene and experimented with using it for cross frames/corner snap connectors and it seemed too soft, as if it wouldn't last many cycles of having the aluminum tubes snapped into place. (But household HD polyethylene cutting boards are a good source of material if you're only using it for corner snap connectors for ply frames) What you have might be OK, but it would be worth the trouble of mocking up a couple of frame corners and checking before proceeding.

One big advantage of a folding skin on frame kayak is you can experiment and alter the frame one component at a time - you could proceed as you plan to, then later borrow a cutting board from the kitchen when your wife isn't looking, replace one of your frames with my ply - HDPE constructions and see if it's lighter/stronger/worth he trouble.

Will try and post pictures and address some of the other ideas/issues on Saturday morning.

All the best with the Sea Otter.

Ian

[keyhavenpotter]

Ian, thanks for your full and detailed replies.

I have plans for Hugh Horton's Bufflehead sailing canoe. Here is a blog of the design in build using 4mm plywood over frames, planks fitted edge to edge then inside kevlar coated and outside carbon coated.

Stacy Smith&#039;s Photos - Bufflehead 50-50 Sailing Canoe | Facebook (http://www.facebook.com/album.php?aid=6900&id=100000740013771&l=fd3bc9143e#!/album.php?id=100000740013771&aid=6900&l=fd3bc9143e&s=0&hash=d4d5de1533494aef8e6dbc96fb4d130c)

I have been thinking that to build her as a folding kayak might be possible following many of Tom Yosts methods.

My question is, that often Tom's designs have little rocker, and then when loaded on the water the rocker takes shape. If you are building to a set of plans for plywood with a fixed designed rocker how would one best approach the issue of rocker increasing as she is loaded.

Thanks,

Brian

[IanHowick]

I have been thinking that to build her as a folding kayak might be possible following many of Tom Yosts methods.

My question is, that often Tom's designs have little rocker, and then when loaded on the water the rocker takes shape. If you are building to a set of plans for plywood with a fixed designed rocker how would one best approach the issue of rocker increasing as she is loaded.
Brian

Hi Brian, I'd approach that particular problem by just ignoring it.

Most of Tom's designs have little rocker, but that's inherent in the style of the design and use. They're not designed to do a slalom. If you got in one and tried to paddle it in a circle, it would have the turning circle of an oil tanker. However, with these hard chine designs, if you tilt the hull on edge with you hips, suddenly you have a rockered hull shape in the water and it turns quite easily. Best of both worlds - straight tracking when level, if you're paddling forward and need to turn to the right you edge the hull towards the left chine and it carves a nice turn to the right. Turning on the spot similarly with even more edging supported hopefully by the sweep stroke. I'd guess most of his main designs would bend only an extra cm, two at the most when you get in them.
His Sonnet designs (hybrid inflatable/minimal frame) are different, with minimal frame, they are built with no rocker/sheer curve and bent to an appropriate rocker in the water.

Of course a sailing craft needs a lit more rocker than a paddling craft if you are ever going to tack it.

Depending on the mix of design/skinning material/skinning method it's possible to have exactly the opposite problem to it gaining too muck rocker as it is loaded - how to maintain the desired rocker and stop the hull hogging.

I think it would be possible to build the Bufflehead as a folder following Tom Yost's methods. The main thing you would have to pay attention to would be managing the forces from the sail and lee board and the righting moment to keep the boat/sail upright. I would be inclined to make the cockpit combing the main structural element of the boat - maybe from 50 mm wide 4mm ply sections with aluminium tube epoxied/glassed along top and bottom edges and the sections fitting together with ferrules on the tubes. Mast partner in the front of the cockpit combing, a beam that clamps across behind it to carry the leeboard. Maybe a couple of stays from this leeboard beam to the mast. Will try to draw and scan a picture of what I have in mind. Have a look at the Klepper website - they have been building folding kayaks with sail rigs for a long time now, Franz Romer sailed the Atlantic in one in 1928, Hans Lindeman also did the Atlantic in one of these in 1956. http://www.klepper.com/images/segel2.jpg

http://www.klepper.com/images/sailkit1.gif

There must be someone on the Solent with a Klepper with a sail rig you could look at.

You asked about designing to deal with the extra rocker when the canoe is loaded up - strange to tell, I think you will have the opposite problem if you build the Bufflehead with it's upward curving sheer line One thing you notice with all the comercial folding sea kayaks is they are built in a "two icecream cones" shape. Straight sheer line, highest in the middle and deck ridge sloping downwards towards each end. Extreme in this regard are the First Light designs. http://tpe-u.com/_cms_live/media/medias/0000/00/00/b8/47231.jpg

This is for good reasons - the bottom of a sea kayak is not a developable surface (at least in one piece), so if you want to cover it in a single piece of fabric, you need stretch and or wrinkles and or darts. The secret to a smooth underwater surface is longitudinal stretch. (If you try to stretch the material around the kayak by pulling it up tight on the gunwales, you can't get enough to smooth out all the wrinkles unless you use the light unsupported clear PVC's, but the % stretch necessary in the long direction is less) If the ends are cone shaped, the stretch along the bottom matches the stretch along the deck and the structure stays balanced/undistorted.

The traditional greenland kayak shape http://www.traditionalkayaks.com/images/imagesGREENLAND/LC.148framefwd.jpg
comes from thin but relatively wide gunwale planks which form most of the structural strength of these boats. Tie the ends of the gunwales together, push them out in the middle and flare them at the top of the gunwales and the ends will curve upwards in a nice sheer line, and the structure will hold it's shape against a lot of force.

Do the same shape in aluminium or carbon tube, and all the stringers are curving up towards the ends, and they want to be straight. Put some significant longitudinal stretch along the bottom to smooth out the skin, and they'll straighten and want to curve the other way, which is bad however you look at it.
Solutions
(1) Design as all the comercial ones do as "two icecream cones" so the structure remains balanced under tension.
(2) Stick to the Greenland shape and don't put any longitudinal stretch in the skin. Put up with some wrinkles in the hull skin, try and keep them in the area between the chines and the gunwales so they don't affect water flow too much and smooth them out with a glued dart or two as necessary. (I think this is Tom's approach)
(3) Stick to the Greenland shape but counteract all those forces trying to make the kayak bend the other way with lots of tension in cords along the deck and in an approximately parabolic shape from the bottom of the stems front and rear with the high point in the middle. (Or use inwales curving this way as is documented somewhere in Tom's sight)
(4) Use more stretchy material than the easily available PVC with polyester weave. Have a link to the people who manufacture the skin material that First Light use, I think they're in Germany.
(5)?


Have to go now, more later.

Ian

[IanHowick]

If you are building to a set of plans for plywood with a fixed designed rocker how would one best approach the issue of rocker increasing as she is loaded.

Brian
What I mean to say is I believe you could build the folding version to the same rocker as the hard-shell version on the strong back, be prepared to put some cords/straps lengthways at deck level to create tension so it holds it's shape when the skin goes on and you should be able to get a tight structure that doesn't deform much when it goes in the water and you sit in it.

As I think Mik has said in regard to his balsa canoe, end to end forces on a lightweight hull in the water are quite distributed, create less bending moment than you would think. However, moments and torsion forces from the sail to foils to movable ballast (you) holding the boat upright are much greater once you go the sail route.

Ian

[IanHowick]

Hi Everyone, I'm just figuring getting a photoset of the kayak construction up on Flickr. I might end up linking to the individual photos here with some more description/information, but in the meantime, I think this link will get you to the photos I am adding with some description alongside them.

Folding Sea Kayak - a set on Flickr (http://www.flickr.com/photos/50860028@N04/sets/72157624085895887/detail/)

Most of the photos are high enough resolution to zoom in on if you want to see any details.

Ian

[Bill P]

Thanks for the photo set Ian. Its great.

My polypropylene is indeed too soft so I reckon I will be going marine ply frames with HDPE corners.!

I like the stanchions in your rear frames and also the elegant cutout shapes. How do you find the coaming, do you think it is strong enough to support re-entry? Is there 4 holes in the cover for the bolts? How did you do the cover around the coaming- looks great but maybe fiddly to construct?

I see you have attached additional members to the 'masik'- was that for stiffness? I wouldn't mind additional pictures of the frames & coaming & seat setup. (Actually I wouldn't mind taking her for a paddle)

Also what string did you use for tension- I was thinking SS cable but you have some sort of cord?

Bill P

[scottz]

Well done! Noice work! You kickstarted those evil thougts again :-) You've got to send those pictures to Tom!

I second any recommendation for the Otter (Picasa Web Albums - Scott - Sea Otter Lau... (http://picasaweb.google.com/scott.zwanenbeek/SeaOtterLaunch2008#)). Since I finished that, I began contemplating carbon fibre stringers for the next generation but then I checked the costs locally (from sailing outfits, like Carbonfibreexpress.com.au, etc). Approximately 35m (144ft) * ~A$90 per metre = Ouch! Must have googled with the wrong terms... Anyway, I will have to stick with Aluminium and HDPE for the next one. Maybe a Sea Ranger.

Off to the Sydney Working with Wood show this friday. I will visit Trend Timbers and other merchants to try and find a suitable piece of western red cedar for a greenland paddle. Wish me luck!

Scott

[IanHowick]

Well done! Nice work! You kickstarted those evil thougts again :-) You've got to send those pictures to Tom!

Since I finished that, I began contemplating carbon fibre stringers for the next generation but then I checked the costs locally (from sailing outfits, like Carbonfibreexpress.com.au, etc). Approximately 35m (144ft) * ~A$90 per metre = Ouch! Must have googled with the wrong terms...
Scott

Hi Scott, these are the people who made up the carbon tube for my kayak:
C-Tech Carbon Tube - Round - www.carbon-tube.com (http://www.carbon-tube.com/round.php)

As you can see, about NZ$40 per metre which is a lot better than your quoted A$90 per metre. Tubes were custom made to my dimensions (main tubes 1.2mm wall, ferrules 1.4mm wall on a mandrel of 3mm less diameter, so a nice close slide fit in the main tubes, and all cut to length for me. They do high tech boat stuff too, I'm going to get them to make a mast and yard for my Goat Island Skiff.

It is possible to build a 5.2m (17ft) kayak from 20m of main tube and about 4m of the ferrule tube (25 ferrules @ 15cm each). I left out a deck stringer, so stringers were keel, two chines and two gunwales, all of 4 m length. The extra 60cm at each end is just made of light 12mm ply stem pieces.

The cost of the carbon tube for my kayak was about NZ$1000, it'd be easy to freight an order anywhere in the world as the package is only 1m long and weighs about 3 kg.

Have sent pictures to Tom Yost, must get back to him with a link to the flickr photoset, but have been busy with a new addition to the family 8 weeks ago. I believe he (Tom, that is!) is planning a motorcycle with sonnet kayak tied on the back trip around New Zealand next southern summer, so he's likely to get a chance to paddle it himself.

It would probably be possible to go down a size in tubing, the kayak I made is very stiff/solid in comparison to other folding kayaks I've seen. (One size down would be main tubing 1.2mm wall on a 16mm mandrell compared to the main tubing I used which was 1.2mm wall on a 19mm mandrell)

I did stiffness calculations on the various carbon tube sizes versus 3/4 inch aluminium, from memory the smaller size is still stiffer than the 3/4 inch aluminium, I went up a size in the carbon to make sure I'd be OK, and also as I was thinking of using the same tubing to make a 6m double kayak as the next project.

Have shelved the double kayak project in favour of the Goat Island Skiff as I realised the family was growing quicker than I could build bigger kayaks! I'd be the only one paddling with three kids under 5 in a double for quite a while yet, then when they got big enough to paddle they'd be too big to fit in one double. 15ft by 5 ft with a sail for power should be easier for getting around on the water with three kids on board for a while yet, and we can always put the folding kayak or a Sonnet double under the seat of the skiff.

Worth noting, that for day trip use, Tom Yost's hybrid Sonnet construction method makes cheap, easily built and quick to assemble kayaks at comparable weights to my carbon tube version. I have some ideas for a couple of variations on that construction style which would reduce their weight again. I'm not sure of storage room for longer distance cruising with the inflated sponsons, but I guess you could get stuff for a week in one of them, maybe not much longer. From what I understand, Tom uses his Sonnet more than any other of his boats.

Ian

[scottz]

Thanks for the info. You've given me some food for thought. We too have a new family member (6 weeks) so I'm recalculating my long term projects (and budgets :)) too.

I guess if you aren't gathering up the stringer ends at bow and stern that you don't need as much flexibility. It's not likely that we'd take these into white water, so carbon fibre should be ok. Still, its triple what I paid for aluminium, and that was for two 15' kayaks. I'm happy with the 15Kg AUW, sort of... This has only recently been challenged by those ABS rotomoulded sea kayaks (Prijon or others) which come in at 17Kg. However, my kayak fits in my boot :U

I tried to make some sponsons from the inflatables and accessories pages, however doing it 'freehand' with contact pvc glues left little runnels that I had to address. I wasn't confident that I could safely make a Sonnet. I was thinking of using a pvc pipe former and some stringers for more control of the mating process, then a Feathercraft Gemini turned up on ebay for A$1K the day I went looking. Never thought I'd own a Feathercraft.

I will have to see when we can afford to attend "Warbirds over Wanaka" or the next paraglidng festival there. I will either have to bring my floppy over or see if I can hire one there. I'd bring my kayak, if I could stop tinkering with it :roll:

I always thought Herons, Cadets or Sabots would be the way to go for us. Let us know how your GIS goes.

Ciao,
Scott Zwanenbeek

[IanHowick]

My polypropylene is indeed too soft so I reckon I will be going marine ply frames with HDPE corners!
Bill P
As you're now using some wood in the kayak, I guess that means we can continue to discuss it here!
A couple of issues: HDPE corners need to be both sides of the ply so things hold together. As the connector width is now much wider, the fact the stringer meets the frame corner at an angle becomes significant. It would be necessary to assemble the kayak with ply frames in place, clip the HDPE connectors in place each side at each corner, then drill holes for screws with everything assembled. Put all the screws through, dis-assemble frame then take each corner connector assembly apart one by on and put some epoxy glue in before reassempling each corner.
It would be possible to calculate angles at each corner and make a jig for the drill press to drill them so everything was exact, but the above should work.


I like the stanchions in your rear frames and also the elegant cutout shapes. How do you find the coaming, do you think it is strong enough to support re-entry? Is there 4 holes in the cover for the bolts? How did you do the cover around the coaming- looks great but maybe fiddly to construct?
Bill P
Cockpit coaming is laminated ply, strong enough for re-entry. It's attached front and back to the cross frames with 4 bolts which go through to embeded nuts in those frames. The bolts do indeed go through the skin. The cover around the coaming was fiddly to construct - several bits and sewing then glue. The sides of the cockpit coaming are also supported by the closed cell foam hip pads (Blue in the picture looking down on the cockpit) I'll have another look at how Tom does it - maybe it's simpler. Next time, I'd probably look at Tom's cockpit construction of Alu tube, though doing a good job of bending it can be tricky. I do have thoughts that it may be possible to eliminate the solid coaming altogether - just velcro between an upturned edge of the deck material hole and a specially constructed sprayskirt. Issues would be security against it coming off and keeping water out, while maintaining ability to pull it off quickly when needed and ease of putting it back on.


I see you have attached additional members to the 'masik'- was that for stiffness? I wouldn't mind additional pictures of the frames & coaming & seat setup. (Actually I wouldn't mind taking her for a paddle)
Bill P
Yes, there is WRC laminated on top of the masik for extra stiffness, I can stand on that frame. Will post some more detailed pictures of these parts when I get the chance.


Also what string did you use for tension- I was thinking SS cable but you have some sort of cord?
Bill P
I just used standard 4mm nylon cord. Tensioning was done with truckie hitches in the middle. Polyester would be be better with less stretch, I'd probably go to 20mm wide polyester tape so I could use the standard friction buckles and similar bits to put the tension on. I think something very low stretch like SS cable or spectra/kevlar would be unnecessary and possibly cause problems due to high shock loads transferring into the end frames. You want the cables to spread and dissapate shock loads, not concentrate them. (But I'm not sure of how forces would change with low stretch cables, maybe it could be tried, but I'd try cheap and easy first).

One change worth contemplating on almost all kayak designs is adjusting the foortest frame/bulkhead position to match your leg length, especially if it's significantly different to the designers. Sit against a wall with about the amount of padding your backrest will have between you and the wall, put your legs in the position you'll assume in a kayak, then get someone to put a box against your feet. Measure the distance to the wall, and compare it to the cockpit rear to footrest frame as designed.

If you want to move the footrest frame, you need to adjust it's profile to match the new position so you don't change the hull shape. It's possible to calculate this new profile accurately without access to the designers CAD program. If you want to move it, I can tell you how if you're mathematically inclined or otherwise tell me how much and I'll put the numbers through excel for you.

More soon, with pictures if I get the chance.

Ian

[scottz]

Erm, yes, Wood! Wood! Wood! Rhubarb... :wink:

Ian, what was the build up of your coaming? Two layers of 3mm marine ply with something inbetween? How do your coaming halves come together? Just screw to the ribs or do they interlock first? Are those T nuts under the top of your cockpit ribs?

I'm possibly looking at replacing my bent aluminium coaming (scientifically constructed btw - bow end bent around the top of a large blue plastic food barrel, stern end used two swipes of a tube bender). I definately need to implement some form of thigh bracing and might require the smaller ply coaming to provide a mount point for foam blocks. Would you have any ideas based on your current setup for adding thigh braces?

Regards,
Scott

[Bill P]

Hi all,

It is interesting that Wood is holding a worthy place in a field populated by high tensile alloys, carbon fibre tubes and assorted plastics. http://cdn.woodworkforums.com/http://cdn.woodworkforums.com/images/smilies/smile.gif Great to see truckies hitches too- best knot I ever learned.

Ian you seem a bit unhappy with your coaming. To me it appears well resolved and suitable for all purpose & heavy duty use- is it the weight?

Are your floorboards attached somehow to stop forward movement.? (The pic seems to show 2 layers of boards) is it just one 4mm hinged set on top of the CF keel & chines? (That rear cockpit frame seems to be begging for a foam backrest!)

Is your zip arrangement conventional Yost or did you manage to shave some grams there too? I 'm thinking about prefabricating the 5" zipper strip & velcro flap as one subassembly and sticking it on in one go.

Thanks for the HDPE clip alignment tip. I am seeing if I can buy some suitable 19mm moulded clips- min qty at this stage appears to be 1000!.


Bill P

[IanHowick]

Hi all,
It is interesting that Wood is holding a worthy place in a field populated by high tensile alloys, carbon fibre tubes and assorted plastics.
Bill P
Yes, wood can hold it's own against the high tech composites because it is a high tech composite - Of cellulose and lignin, with some engineering at cellular level that the human engineers can only dream of.
In some situations it won't hold it's own against carbon composite - if your beam needs to take forces in all directions (masts, kayak paddles/ oar shafts...), it needs to be a tube. CF is 10 times the strength of wood but a little over 3 times the density of wood, so the carbon ends up about one third the weight for the same strength. A 9-10kg hollow wooden mast will be around 3 kg in carbon.

But, if the main forces are in one direction, it becomes interesting, wood can in many cases keep up with the CF for beams and hull material for boats. A 45x10mm beam of Paulownia on edge is about the same weight and stiffness as a 19mm ID 1.2mm wall carbon tube, though it will break if bent in the other direction. Trick if designing lightweight is to always make the structure lower density but thicker in the direction that the force will be, add some higher density along the top and bottom of the structure with higher density wood or glass tape. Wooden venetian blinds are a good source of ready made thin strips for laminating and can be everything from low density WRC to dense, fine grained hardwood.



Ian you seem a bit unhappy with your coaming. To me it appears well resolved and suitable for all purpose & heavy duty use- is it the weight?
Bill P
I guess you're right, it does work well, concerns were probably just "is there a way to do it more simply?" and it's weight - 730g. The circumference of the cockpit is about 2 metres so if I could make something out of very light alu tube, I could save perhaps 500g. If I could find some Easton tent pole sections pre-bent to the right radius for the front curve and curves at the back corners or figure out doing it myself... Important to note that in my kayak the cockpit coaming isn't needed to help with longitudinal stiffness, but in kayaks with alu tube stringers a solid coaming locked into the cross frames and the deck ridge tubes helps with the strength/stiffness.


Are your floorboards attached somehow to stop forward movement.? (The pic seems to show 2 layers of boards) is it just one 4mm hinged set on top of the CF keel & chines? (That rear cockpit frame seems to be begging for a foam backrest!)
Bill P
The floor board is 4mm ply, it is hinged down the middle and rests on the keel and chine stringers, and is held in place with velcro glued to the stringers and the underside of the seat. It's supported at the back on cleats sticking out from the cross frame, and reinforced at the front by 3mmx40mm strips of WRC (venetian blind slats) glued above and below the ply. Yes, will put a closed cell foam backrest velcroed on to the rear cockpit frame when I get the chance.


Is your zip arrangement conventional Yost or did you manage to shave some grams there too? I 'm thinking about prefabricating the 5" zipper strip & velcro flap as one subassembly and sticking it on in one go.
Bill P
More or less conventional - but prefabricated much as you describe. If anything heavier than Toms with PVC flaps across the zip from both side then the velcro flap on top.

More pictures soon.

Ian

[IanHowick]

Erm, yes, Wood! Wood! Wood! Rhubarb... :wink:

Ian, what was the build up of your coaming? Two layers of 3mm marine ply with something inbetween? How do your coaming halves come together? Just screw to the ribs or do they interlock first? Are those T nuts under the top of your cockpit ribs?

I'm possibly looking at replacing my bent aluminium coaming (scientifically constructed btw - bow end bent around the top of a large blue plastic food barrel, stern end used two swipes of a tube bender). I definately need to implement some form of thigh bracing and might require the smaller ply coaming to provide a mount point for foam blocks. Would you have any ideas based on your current setup for adding thigh braces?

Regards,
Scott

Have added some more pictures of the cockpit coaming and associated construction to my flickr page:

Folding Sea Kayak - a set on Flickr (http://www.flickr.com/photos/50860028@N04/sets/72157624085895887/detail/?page=2)

Will tidy it up with a few more comments and order when I get the chance.

Thigh braces: perhaps just some pieces of closed cell foam mat with velcro to the PVC under the cockpit coaming and possibly the front cross frame?

Ian

[IanHowick]

My polypropylene is indeed too soft so I reckon I will be going marine ply frames with HDPE corners!
Bill P

Hi Bill, I've posted some pictures of a mock-up of the marine ply frame/HDPE corner concept on my Flickr photoset:

http://farm5.static.flickr.com/4027/4718622577_15e54ab673.jpg

http://farm5.static.flickr.com/4050/4719274426_7dda94e925.jpg

Rest of the photos with comments, higher resolution here:
Folding Sea Kayak - a set on Flickr (http://www.flickr.com/photos/50860028@N04/sets/72157624085895887/detail/?page=2)

I'm still curious to see how this concept will go if all the holes are cut square rather than angled to match the stringer-frame angle at that point. I've got a jig for the drill press that let me cut precise angles, also a system to calculate those angles, could make it do so off a table of offsets from another designers design. Can give you details if you like.

Am also curious to see the commercially produced connecters you have in mind and if you can make that work.

Ian

[scottz]

Thanks for the information. Nicely illustrative photos. Appreciate your effort! :)

A fixed coaming will definately be an improvement. My floating aluminium coaming doesn't provide sufficient rigidity to mount an effective fulcrum or to reduce the height with. There's simply too much movement in it. I may investigate some further alteration options. Besides, wood grain does look nicer.

Again on the initial shaping of the aluminium coaming, the foreward half was bent around the top of a 40 gallon plastic drum but you could probably knock something up easily. A jig made with three layers of inch think exterior ply, bench mounted and some bolts. Maybe use a thick beading of hard silicon gel or similar in the corners of the channel to help stop the flattening of the tube as you bend it. Or you can route the appropriate semicircular channel.

Regards,
Scott Zwanenbeek

[Bill P]

Thanks for the extra pics Ian. The coaming does seem a bit weighty but at this stage I intend to copy it. :U I might try and reduce the cover plate to say 40 mm wide and the spacer to say 20mm and maybe route out the middle of the spacer. That's a lot of Velcro on the coaming! She aint goin' nowhere!

Thanks for the corner mockup . Looks rather strong. Would you drill the 19mm hole in the HDPE, screw two of them to the ply & then sand the outer edges flush to the ply? Looks good.

I found these pole brackets today in a camping shop. The grip width looks OK at about 10mm but the other end might not be meaty enough to sustain a couple of screws after its sanded 1/2 flat. That end is about 16.5mm dia so maybe a tubular frame or some other idea could work.

I'm thinking of using 1/2 " ply for the four biggest frames (with centre ribs for the rear ones ) and conventional HDPE for the first & last frames as the weight savings would not be great as these 2 are so small.

Scot, What's the GP going to made of?

Bill P

[scottz]

Hi Bill,

I spoke quickly with one of the Trend Timber folks at the wood show on friday. They've had quite a few people come to them over time for GP wood. They recommend composites of Nuigini Red Cedar and Lauan (Phillipino Mahogany). I was also drooling over the purpleheart for the ends of paddles...

I'm going out to their new location at Mulgrave later this week after I get some roof racks. I may also have to have a chat with Mr Plywod about marine ply...

Regards,
Scott Zwanenbeek

[Chuck C]

I did see the article on the boat named Alice, I thought the construction out of lots of very thin tube made it very complicated and fragile, (but was dictated by a source of cheaper tubing?).



Ian[/QUOTE]

Ian,

I’ve just been made aware of what I’m guessing is called your thread. I’ve pored over a number of forums but never tried to contribute. So I’m not at all confident that I’m doing this right or that you will see what I want to say but think I should at least try.
I’m really impressed with your effort and the results. Great job.
I’m the designer of the Alice boat. I’d just like to do a little clarification that I hope is appropriate for your site.
Our boats are both folding kayaks with some carbon framing, but that’s about as far as the similarity goes. Mine is a 12 ft. (3.7 m), flat water, open cockpit, day boat. And it does only weigh 10 pounds (4.5 Kg.). It was designed to be back packed in to remote mountain lakes. The nearest ocean access is about 500 miles from where I live. The first three design goals were light weight. The use of small diameter tubes was pretty much dictated by the weight goal, not cost (currently around $850. US which includes plans, instructions and seat pads). My solution was laterally connected, discrete, curved, longitudinal trusses. The fact that the interior of the hull did not need to be kept open for storage made it possible to utilize trusses and the trusses pretty much made it possible to meet my weight goal.
Just two other of the points of dissimilarity: the aircraft polyester may not look it but it’s really tough and makes it possible for a “shrink to fit” skin which I like. And the extra longitudinals below the waterline makes it possible for greater control of the shape of the wetted surface.
My least favorite aspect of the design was assembly time: around 40 -45 minutes from bag to water. I have just completed an improvement to the design of the skin that gives me an honest (should never exceed) 30 minutes.
As for strength. I can assure you that it is plenty strong for its intended use. If I wanted to build a boat for an ocean environment and if the interior of the hull didn’t need to be left completely open, I’d go with the trusses. They can be made as strong as you would like with very little increase in weight.

Cheers,

Chuck Corwin

[IanHowick]

Hi Chuck, thanks for the comments.

I re -read my comment about your design and it came across as dismissive of your efforts, for which I apologise, it wasn't my intention at all. It's a very impressive effort to get the weight of a kayak down to 4.5kg and it seems ideal in terms of what you wanted to achieve. I meant perhaps to say that I had seen your article, but because our design aims were quite different, I didn't follow your methods.

I agree very much that trusses made of very light tubing can make a stiff structure for the least weight, so were the ideal way to go for the purposes you had in mind.

My perception would be that although such a light weight truss structure could be made very stiff for it's weight, it would be vulnerable to a shock load - i.e. in ocean surf, or to taking a hit at any one point as there may only be a single 6mm piece of tube at that point, and that damage at any one point would endanger the whole structure.

Again, no problem for the sort of use you are making, and I would be curious to hear you opinions in this regard and/or to have the above perception refuted.

I thought about truss structures, but further iterations of my design will involve using the tube I have - some refinements to components within the current design, then possibly a double using the same tube, possibly a hybrid inflatable - frame version using Tom Yost's Sonnet concept with a minimal amount of the carbon tube.

I'm interested in your polyester aircraft fabric skin with hyperlon waterproofing, and that it can be shrink fit before waterproofing. How does it stand up to repeated assembly and disassembly and storage?

PVC has some good properties, but the PVC with a polyester weave inside is not really stretchy enough - you end up with wrinkles, or putting large forces on the frame if you try to stretch it sufficiently to remove the wrinkles. I'd be curious to hear of others opinions/experience in this regard.

I find it remarkable that a half dozen people in the world with some of the same strange ideas can end up corresponding and sharing information about those ideas, and thanks again for sharing your experience and ideas in the Duckworks article and now here.

Ian

[Chuck C]

Ian,

Can’t thank you enough for your kind ,thoughtful reply.
I’m still trying to get the hang of this Forum, Thread thing, so a reply and in the right format is, as the lawyers say, problematic.
Yours is a good question about shock loading. I’m afraid I don’t have the absolute answer. My guess is that it wouldn’t be a problem but I certainly can’t prove it. Here’s my thinking : With the multiple trusses there is less unsupported areas of skin which I guess could be either good or bad depending on the loading. The bending strength of the 6mm tubes in my estimation is nothing short of phenomenal. I’m amazed at the inadvertent abuse these little tubes (pultruded) have withstood. Incidently my tubes are made in the US and considerably stronger (deflection) than some equal size samples I got from China.
As for impact strength I don’t have any personal experience or on hand test data. I believe resistance to impact would only be a problem where something hard hit a tube at say a joint where there was no give.
If the multiple trusses are joined “correctly”, the whole structure results in a “space frame”, inherently strong and with a lot of redundantcy. At this time I’m just not prepared to say what, if any, changes I would want to make, to an Alice to make it ocean ready. I’m going to go ahead and try to send a reply now but I confess I need to spend some more time looking at Tom Yost’s concepts. DIY hybrid inflatable frames sound interesting.
I’ve never seen any proof that SOF kayaks must have taut skins. However, If nothing else they look nicer. I’m now doing two things in the quest for tight : for almost ¾ the length of the boat, the skin is tightened with shock cord during assembly. As contrasted with a simpler (quicker) zipper closure. And even more basic than the tensioning the skin I start with a custom (shrink) fit skin. The aircraft polyester can shrink an amazing 10% with heat. Compound and even concave curves are not a problem.
And I am sold on the Hypalon – I have not detected any problem so far with repeated assembly/disassembly.
I’d love to go into more detail on these and several more topics. But I’m afraid that for a two finger typist this is about all the time I can spare for now.
And yes, for someone normally working in isolation, to be able to communicate with someone else of like interest, is really stimulating.

Best regards

Chuck

Tried to send pictures - no go

[IanHowick]

Hi Chuck, good to hear our thoughts. As far as posting pictures goes, there are two ways.

If the picture is already on the WWW somewhere (for example if you've put it up on Flickr or similar, or it's on you own or someone else's website already), then you click on the insert image icon (the little square one like a picture with mountains in it) at the top of the page and paste in that pictures URL.

Here is a picture of one of my corner connectors added that way.
http://farm5.static.flickr.com/4027/4718622577_15e54ab673.jpg

If you only have the picture stored locally on your own computer, then you use the paperclip (attachments) icon on the top line, then you can select the picture on your computer and it appears at the bottom of your post like the one below.

It's possible to sprinkle pictures through your text with the first method, pictures done the second way all appear at the bottom of your post.

Hope this helps, more on various things soon, probably tomorrow.

Ian

[Chuck C]

Ian,

This is a test.

Chuck













http://www.woodworkforums.com/attachment.php?attachmentid=140769&stc=1&d=1277847507

http://www.woodworkforums.com/attachment.php?attachmentid=140768&stc=1&d=1277846502

[IanHowick]

Hi Chuck - good to see the close up pictures of the skin on your kayak. I'm definitely interested in alternatives to the PVC, will have to look at a source of the hyperlon - problem down her is getting it freighted as dangerous goods and all that. Another skin possibility is an unsupported urethane such as the Firstlight people use. www.firstlightkayaks.com/ (http://www.woodworkforums.com/www.firstlightkayaks.com/)
Had a link to the people (Bayer, Germany?) that supply this to them, must follow it up.


The coaming does seem a bit weighty but at this stage I intend to copy it. I might try and reduce the cover plate to say 40 mm wide and the spacer to say 20mm and maybe route out the middle of the spacer. That's a lot of Velcro on the coaming! She aint goin' nowhere!

Hi Bill, you might want to be careful reducing the dimensions of the cockpit coaming - mine is strong enough, but not overly strong, there's some reliance on the foam hip pads providing support on either side. Good thing about alu is it just bends if you put too much force on it, bad thing about wood is it breaks which could be embarassing in the middle of a re-entry after capsize. I'd say go for the smaller dimensions, but be prepared to add a strip of wood lengthways along either side of the bottom of that 12mm ply after you've made it if you feel it is necessary. (You could also use some fibreglass tape).

Stronger/lighter than the 12mm ply under-lamination for the wooden cockpit coaming would be to make a 18mm or so MDF former the shape of the cockpit hole then wrap/laminate thin paulownia or similar wood strips around it, once it's glued up, take it off, clean it up then glue on the 3 or 4mm ply top piece. All the wood grain would be pointing the way it should if you got that to work.

By the way, yes, all that velcro plus the wrap over the top and bungee is overkill, easier would be just the velcro and velcro on the edge of the skin around the cockpit hole.

Wooden cockpit rim is of course made as one piece and then cut in half before inserting the hinges if you want to make it folding.



Thanks for the corner mockup . Looks rather strong. Would you drill the 19mm hole in the HDPE, screw two of them to the ply & then sand the outer edges flush to the ply? Looks good.

Yes, I think I'd do it that way. I have been thinking about the issue of angling the holes to match the stringer meets cross frame angle at each corner.

It would only be necessary at the chine and gunwale corners for the frames away from the two central ones, but I think it would be necessary/worth doing at those points. Good news is it wouldn't be hard to do - I had to do some tricky stuff with a jig and angles in 3D for my end frames but the intermediate frames only need angling in one direction and are more forgiving.

A ballpark figure for the angles at the chines and gunwales for the footrest frame and the one in the middle rear would be one in ten. Couldn't find offsets of the Sea Otter on Tom's website, could tell you more accurately if I had them but it probably doesn't need to be more accurate than that. A PDF drawing of a jig from 12mm ply for sorting out these angles is attached below.



I found these pole brackets today in a camping shop. The grip width looks OK at about 10mm but the other end might not be meaty enough to sustain a couple of screws after its sanded 1/2 flat. That end is about 16.5mm dia so maybe a tubular frame or some other idea could work.


As you say, the issue would be getting a secure attachment to the ply. I'd be curious as to how you go if you try this, but my impression is you might have more trouble making it work than going to my HDPE triangle idea. Especially if you had a bench saw, you could make up a jig for cutting the triangles and knock up 50 in no time. Then it's just drilling holes in the corners and screwing them on the ply corners and as you say sanding down the edges/opening so the tubes can snap in place.

You could cut the HDPP you have into breadboards and go around swapping them for HDPE bread boards - you'd get enough 10 or 12mm HDPE for these connectors from a couple of breadboards I would guess.

A good thing about doing the corners this way, if you stuff one up, you only have to make a new little triangle connector for that corner rather than starting again with a big piece of HDPE.



I'm thinking of using 1/2 " ply for the four biggest frames (with centre ribs for the rear ones ) and conventional HDPE for the first & last frames as the weight savings would not be great as these 2 are so small.

Or just see how you go with the other frames first - beauty of these take apart designs is you can replace any bit/change how you do any bit any time you like.

All the best,

Ian

[Chuck C]

Ian,

Since humor is good for your health it’s too bad I don’t feel I have the time to tell you all, or some, of the problems I’m having with “Forum”. You could have some good laughs.
Since I have now figured out how to read all the postings, I have to ask about your carbon tubes. I see words to the effect they are made on a mandrel. Does that also mean they are wound with some marvelous fiber. If you check the specifics for arrows you’ll see there are two ways to go carbon: the old cheap pultruded or high tech built up on a mandrel. I use the pultruded, they are significantly tougher. On my second boat I went hi-tech. I still use the boat but only after repairing/beefing up numerous times. There was a period there when it seemed every time I used it, some tube, some place, broke. They were easy to repair but a real pain. The hi-tech were a little lighter but larger diameter and overall a disaster. I have never had a problem with the pultruded. They are stronger, tougher and better performing for my use. Your question about shock loading now makes more sense to me.
Got time for one more item. The water proofing is spelled Hypalon. I’ve spent a lot of a limited life span trying to find a supplier that will sell reasonable amounts. In the US the one and only Gaco Western Retail (just google it). I know there is a European supplier but I don’t have a name handy. There is also a possibility that there is another product out there that would do the job. Some stuff called liquid rubber (EPDM) brand name Tuff Coat sounds promising. I’m personally reluctant to try them. On my first boat I put on a product called tool dip or something like that. It worked, sorta, it was prone to rub off. I ended up removing it all and putting on Hypalon.

Cheers,

Chuck

[IanHowick]

I have to ask about your carbon tubes. I see words to the effect they are made on a mandrel. Does that also mean they are wound with some marvelous fiber. If you check the specifics for arrows you’ll see there are two ways to go carbon: the old cheap pultruded or high tech built up on a mandrel. I use the pultruded, they are significantly tougher. On my second boat I went hi-tech. I still use the boat but only after repairing/beefing up numerous times. There was a period there when it seemed every time I used it, some tube, some place, broke. They were easy to repair but a real pain. The hi-tech were a little lighter but larger diameter and overall a disaster. I have never had a problem with the pultruded. They are stronger, tougher and better performing for my use.

Hi Chuck, interesting to read your comments. My carbon tubes were made by C-Tech in Auckland, New Zealand. They are mandrel wound pre-preg carbon with a Young's modulus of about 95GPa. I have been entirely happy with their quality.

My understanding of the mandrel wound manufacturing process is as follows: They wrap cellophane around a steel rod mandrell. They then wrap unidirectional pre-preg carbon tape around the mandrell using a special machine. The amount of ovelap as they wrap the tape in a spiral along the length of the mandrel controls the wall thickness. Next they wrap more cellophane shrinkwrap to compress the layup, then they bake it at quite high temperatures to cure it.

Information I have found on the web has been that the mandrel wound tube is superior - see Small Carbon Fiber Tubes (http://www.carbonfibertubeshop.com/small%20tubing.html) (at the bottom of a long page), so it is interesting that you have found the pultruded tube superior.

It may be that what you have found applies only to the small sizes of tube designed for arrows that you used for your trusses. My understanding is most larger tube is done mandrel wound and this is superior at larger diameters as they can build in some hoop strength so it is less vulnerable to splitting at the joins.

Pultruding results in all fibres running purely along the length so bigger sizes with thin walls can split quite easily. This wouldn't be a problem at smaller diameters as the wall thickness is a much bigger percentage of overall diameter, so hoop strength as a percentage of longitudinal strength will be plenty high enough for the small size pultruded tube.

The people who did my tubing do a lot of high tech boat masts, which are all made by this mandrel wound process. It's a reasonably hands on process, I was able to talk to them and discuss my application, and specify the OD of the ferrule tube to better than 0.1mm so it made a good slide fit in the joins between main tubes.



Your question about shock loading now makes more sense to me.

My question about shock loading was more around the properties of the trusses. I guess I was concerned that the carbon tube although very strong is hard to join reliably at the corners of the trusses.

Bicycle frame manufactures have wrestled with this for a long time and I think it has slowed/limited the use of carbon in bike frames when on paper it is far superior to aluminum in strength to weight. (Shock loading on bicycle frames being very high compared to static loads)

I'd be curious as to the failure mode for the tube that was breaking on you - was it splitting on you or breaking/buckling at the joins?

I've just had another thought regarding your experience of pultruded versus wound tube in your trusses, so perhaps cancel most of the above:

Pultruded is presumably a greater wall thickness relative to overall diameter. This is probably ideal for trusses where the main thing that determines overall stiffness is the overall dimension of the truss. The greater wall thickness/thin tube will take the stresses that concentrate in the truss corners much better, whereas a larger diameter thin wall tube will fail due to buckling forces in the relatively thinner tube at these corners.

In situations where the main structural element is the tube itself, then thin wall larger diameter will be much stiffer, and the wound mandrel process will be superior as the unidirectional carbon fibre can be angled to provide enough hoop strength to prevent splitting at the corners. The C-tech people were able to tell me that hoop strength of the layup was 30% of the longitudinal strength, and that with overlaps at ferrule joins of 3 times wall diameter, the joins wouldn't be significantly weakening the tube lengths.

I think that in the end, we probably both got lucky and settled on the correct product for our different applications!

Perhaps the message from all this for others looking at adapting some product to a new application is to discuss your application with the manufacturer/supplier and or to get samples before proceeding. Being able to discuss technical details of their product and it's suitability for my application with C-Tech was a big confidence booster when it came to shelling out $1000 on something untried.

Maybe I've caught the bug on this as I'm going to order the first carbon mast and yard for a Goat Island Skiff from those guys...

Cheers, Ian

[Chuck C]

Ian,

Thanks for your well thought out and presented response. As I wrote my case for pultruded, I had the thought that in larger diameters, pultruded may not be practical. The failures I had in the mandrel tubes were breaking of the chords any place with high moment (bending) stress. The specs for the mandrel tubes were (are) impressive but for my application the pultruded are absolutely tougher and superior.
I have had some splitting of the ends of the pultruded, which I think I have completely resolved. They were in the ends of the web pieces of the trusses. There is so much redundancy in my frame that it never was a safety issue. They weren’t discovered till disassembly. Repair was simply a glued (wet out) fabric wrap around the end.
Oh, and my ferrules are high strength, thin walled, aluminum arrow shafts. Besides naming my boat for a local lake, I also considered naming it Arrow.
As for joints, see the attached picture. There was a long (like everything else about my boat) idea , test, development time before I arrived at the final (I hope) arrangement. The picture shows a typical connection of a web (vertical) piece to the bottom chord (horizontal). The bottom wires are two separate hand made “music wire” brackets (I provide a simple jig with my plans to help make them). During construction two brackets are shoved into each end of the web piece. One of the advantages of this arrangement is the rigid web pieces (same as chord carbon) don’t have to be cut precisely to length. The web pieces and brackets are held temporarily with super glue, then fixed with a cloth wrap around the chord and epoxy in the web. The yellow fibers are Kevlar roving, which works but I have concluded that a simple strip of skin fabric is better.

Chuck

[IanHowick]

Here is the link to the skin material used by First Light Kayaks Folding Kayaks by FirstLight (http://www.firstlightkayaks.com/) if anyone wants to follow it up. Haven't seen many reviews of their kayaks, so not sure how good it is, if it's stood the test of time.

Ian

Foldable Kayak in Desmopan -TPU TechCenter (http://tpe-u.com/tpu/emea/en/markets/sport_leisure/docId-2399251/Faltbarer_Kajak.html)

[hellonwheelz]

I am interested it building this... I'm going to start with a sonnet 14, so I can get an idea about the pvc gluing and Yost style construction.

[scottz]

I've tried to make sponsons Tom's way, by hand. My first results were 'interesting'. I kept getting creases at the join which needed to be worked with heat gun and roller to get rid of potential (and realised) leaks.

I would recommend that you either use a pvc pipe or stringers to stretch out the mating edges (attached at multiple points) to assist bringing them together straight. I use two long flat stringers and tape them along the back of the join areas. Leave room for bulldog clips on the edge when the glue is drying. Paint the glue along the join and carefully position the edges together by means of the stringers. Clamp along the stringers and place bulldog clip along the edges. Wait for it to dry, then work along the edge with a heat gun and roller (nice solid flat surface underneath, of course), rolling from edge to inside, removing bulldog clips as you go. When you've gotten to the end, you can go back with the heatgun and roller, rolling along the edge.

If you use a PVC pipe you can fold over the join area, instead of matching along the longest edge. Just remember to protect the PVC pipe from the PVC glue. Remove the pipe before following up with the heat gun.

Use a pvc material for the sponsons without any extra 'solar protection' coating - or sand it down, judisciously. The sponsons require only the lightest weight PVC material. You can find

As per the australian management saying, "if at first you don't succeed, hide all evidence to the fact that you ever tried" :wink: Therefore practice making sponsons first, then you should be ready for the sponson holders and shell.

Of course, as this is a woodworking forum, your coaming will have once grown with the sun and rain :2tsup:

[hellonwheelz]

I believe that in 2011 Tom concluded that the folbot sponsons were cost/time efficient compared to the home built variation.

I do greatly appreciate your reply because it does make me visualize what one would need to get a great joint.


I've tried to make sponsons Tom's way, by hand. My first results were 'interesting'. I kept getting creases at the join which needed to be worked with heat gun and roller to get rid of potential (and realised) leaks.

I would recommend that you either use a pvc pipe or stringers to stretch out the mating edges (attached at multiple points) to assist bringing them together straight. I use two long flat stringers and tape them along the back of the join areas. Leave room for bulldog clips on the edge when the glue is drying. Paint the glue along the join and carefully position the edges together by means of the stringers. Clamp along the stringers and place bulldog clip along the edges. Wait for it to dry, then work along the edge with a heat gun and roller (nice solid flat surface underneath, of course), rolling from edge to inside, removing bulldog clips as you go. When you've gotten to the end, you can go back with the heatgun and roller, rolling along the edge.

If you use a PVC pipe you can fold over the join area, instead of matching along the longest edge. Just remember to protect the PVC pipe from the PVC glue. Remove the pipe before following up with the heat gun.

Use a pvc material for the sponsons without any extra 'solar protection' coating - or sand it down, judisciously. The sponsons require only the lightest weight PVC material. You can find

As per the australian management saying, "if at first you don't succeed, hide all evidence to the fact that you ever tried" :wink: Therefore practice making sponsons first, then you should be ready for the sponson holders and shell.

Of course, as this is a woodworking forum, your coaming will have once grown with the sun and rain :2tsup:

[scottz]

No worries. Try the process on a couple of inflatable dry bags then :)