10 kg Folding Sea Kayak

[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.


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













https://www.woodworkforums.com/attach...1&d=1277847507

https://www.woodworkforums.com/attach...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/
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 (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 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

[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" 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

[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" 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

[scottz]

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