Thread: 10 kg Folding Sea Kayak
14th Jun 2010, 05:15 PM #16
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?
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14th Jun 2010, 11:42 PM #17
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...). 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!
16th Jun 2010, 08:48 AM #18
C-Tech Carbon Tube - Round - www.carbon-tube.com
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.
16th Jun 2010, 09:29 AM #19
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
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
I always thought Herons, Cadets or Sabots would be the way to go for us. Let us know how your GIS goes.
16th Jun 2010, 10:03 AM #20
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.
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.
16th Jun 2010, 02:04 PM #21
Erm, yes, Wood! Wood! Wood! Rhubarb...
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?
17th Jun 2010, 10:22 PM #22
It is interesting that Wood is holding a worthy place in a field populated by high tensile alloys, carbon fibre tubes and assorted plastics. 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!.
19th Jun 2010, 08:37 AM #23
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.
More pictures soon.
19th Jun 2010, 09:59 AM #24
WOODEN Cockpit coaming
Folding Sea Kayak - a set on Flickr
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?
21st Jun 2010, 12:10 PM #25
Rest of the photos with comments, higher resolution here:
Folding Sea Kayak - a set on Flickr
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.
21st Jun 2010, 01:04 PM #26
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.
21st Jun 2010, 06:19 PM #27
Thanks for the extra pics Ian. 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!
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?
21st Jun 2010, 08:23 PM #28
GP wood selection
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...
26th Jun 2010, 08:42 AM #29
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?).
Iíve just been made aware of what Iím guessing is called your thread. Iíve pored over a number of forums but never tried to contribute. So Iím not at all confident that Iím doing this right or that you will see what I want to say but think I should at least try.
Iím really impressed with your effort and the results. Great job.
Iím the designer of the Alice boat. Iíd 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 thatís 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 itís really tough and makes it possible for a ďshrink to fitĒ 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 didnít need to be left completely open, Iíd go with the trusses. They can be made as strong as you would like with very little increase in weight.
27th Jun 2010, 10:14 AM #30
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.
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