Skin-on Frame Kayak Building Jig

[alan white]

The idea of building a skin-on-frame kayak has been on my mind for some time. I've been studying the many ways they can go together, the flexible Eskimo way, where U-shaped ribs of ash support the long stringers, and either nylon, canvas, PVC, or Dacron are stretched over and sewn.

A 35 lb boat, 15 ft x 24 1/2" with a gently arced bottom and two chines (rather than the Greenland kayak's single chine).
So far (and I'll keep photos coming), I have the mold for the widest beam, which is mounted atop a 3" x 3" square steel beam on legs. The idea is to adjust length easily by clamping molds to the beam at intervals corresponding to a particular paddler's weight. Then I can build from 12 ft to 18 ft kayaks and the mold relocation will take no time at all (each mold is 3/4" plywood with an angle iron screwed to it. The angle piece is what's clamped to the beam.

Now here's the part that I hope will speed the process: The boat is built rightside up. The mold is female, not male. There are notches in the mold to exactly place the stringers, which go in first along with the stems.
this by itself is a reversal of methods I've seen.
Once the keel (a 3/4" x 1" piece of ash) and it's attached stems are sprung down into the bottom of the mold, the four chine stringers are sprung into their respective pockets and attached to their lands on the stems.
Here's the benefit of using this process: The steamed ash ribs are pushed down into place, caged in already by the stringers.
This means the stringers have already defined the hull's shape, as if one might go on to build a plywood boat.
It would be difficult to go wrong setting up the ash ribs, since their shape is determined by the stringers, and simple spring clamps can be used to hold them until dry.

Note that the sheer (gunwales) pieces (3/4" x 2 1/2") are not yet attached.
The rib tops are first trimmed (if necessary, though I intend to pre-cut them to exact measurements, using steel banding for obtaining length).
With the rib tops all 3/4" above marks on the mold, the mortises in the underside of the gunwales should tap nicely over them and be pinned.
That's pretty much it. I'll use a total of five molds and two permanent triangular intenal bulkheads (with holes in them) at the ends, giving 24" spacing.

My hope is to streamline the building process and see if I can build frames very quickly. I would sell finished kayaks in any length, and also see if some folks would buy bare frames to oil and canvas/paint themselves, which it appears is the time-consuming part of the process, but perhaps needing the least skill.
I'd be interested in what others think about this idea.

[duluthboats]

I like the way you are thinking Alan, I also have been toying with using a female type building jig. A little more work to start but repeat frames would fast and easy.

[ned L]

I've built a number of canvas covered kayaks over the years. I really like your idea, quite creative. It sounds like it should end up being quite a time saver.

[alan white]

It's heartening to hear since I've already begun building the strongback. Usually, a seemingly good idea has already been tried and discarded due to some glitch.
I have been searching the web for some indication that a female mold has been or is being used, but nothing so far.
Like I said, I'll document the process.
The station molds aren't split to release the boat. Instead, the notches for the stringers and gunwales are shaped to let the boat slip out vertically when the time comes.
Because the amount of material in a skin boat is so cheap, I'm looking at what labor could be saved as well in order to produce a tremendous value for a buyer. Because of this, I'm searching for a quicker way to lash or attach frame parts, if anyone has any ideas.

[alan white]

Here's the cradle mold, 3/4" plywood, ready to be clamped to a 3" x 3" steel beam about 15 ft long. You can see how the stringers aren't trapped but will release easily. To make sure they don't tend to rise, I can mount swing-away wood fingers on the mold. The top of the mold is shaped to allow easy clamping of the gunwales.

[alan white]

Some progress. The strongback is heavy steel. The molds are screwed to the angle irons, which are at 24" spacing. We'll see how fast this goes.

[ned L]

Looks like your idea should really take time out of the process. Nice!

[alan white]

Yeah, though getting started is slow. The real time savings will come once the bugs are worked out. I want to be able to shorten or lengthen according to paddler size later, using the same molds (only the stems will be different). This boat will be a bit over 17 ft, but 20" mold spacing makes a 14 footer, etc.. So there will be a lot more angle irons welded to the beam eventually.
Changing molds should take about ten minutes.
Which designs have you built, Ned?

[ned L]

I'm not sure the ones I have were to any real design. As a a kid I built a 14 ft one from scratch with my dad back in 1974. It is still doing well, even has the original canvas. The two others I have I picked up as piles of broken sticks with a few shreds of rotted canvas hanging on. The one on the right is the 1974 build. You can see what I sort of started with in the second picture for the one on the left (12ft).
http://im1.shutterfly.com/media/47b8df10b3127ccec36bbff2007c00000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

http://im1.shutterfly.com/media/47b8df10b3127ccec36bd03ec12f00000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

They are fun little diversions to put back together,

[alan white]

Nice work. How are they to paddle?

[ned L]

They are very different from each other. The 14' on the right has a full length keel (parting strip 5/8"x3/4"), that and the hull shape make it track like a spear. You can point it at your destination and barely have to correct your track. Because of the narrow beam it is also fairly quick. It is also a bit like sitting on a tightrope & requires understanding the balancing routine. This is the one to use for distances in open water (growing up I used to take it out in the Atlanic off the Jersey shore). The other one is 'short & fat' with a perfectly flat bottom. It is like paddling a round bowl, not good for distance, but very manuverable. This one is so stable you can stand up in it.

[ned L]

This is my third one. Knowing a bit about where it came from I think it probably dates from the 1930's - 50's.
http://im1.shutterfly.com/media/47b9dd09b3127ccec6edfb4e5a4a00000040O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

http://im1.shutterfly.com/media/47b9dd09b3127ccec6ec6994fba500000040O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

http://im1.shutterfly.com/media/47b9dd09b3127ccec6eca0473aba00000040O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

http://im1.shutterfly.com/media/47b9dd09b3127ccec6ecb2d63a2200000040O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

[alan white]

I only see lashings used on virtually every SOF kayak on the web, but I have the feeling other methods of frame fastening have been used in the past. I am contemplating using clenched copper nails to fasten stringers to ribs and elsewhere. How are your kayaks fastened?

[alan white]

Progress. No drawn plans, boat is being modelled in true 3D, by eye. This is very tedious, fairing the hull without lofting. I like seeing it take shape this way though. Three out of five molds are done.
Tomorrow I'll tackle the two aft molds. Once all of the parts are fitted, the whole boat will be disassembled and patterns will be made. Everything will be sanded on the bench.
Then it should only take about a half hour to replace everything that was removed.

[Rick Willoughby]

Alan
I look forward to your tally of hours spent and what you believe would be the target with a honed procedure. My interest is for comparison purposes with flat panel construction.

Rick W

[ancient kayaker]

Wooden Boat Magazine numbers 205 & 206 (Nov/Dec 2008 & Jan/Fen 2009 issues) carry a 2-part article for the "Solo Carry", SOF canoe. It uses steam bent ribs installed inside previously assembled battens if I recall correctly (I lost #205). Hopefully this is not too late to be of use.

[alan white]

I appreciate the interest, Rick. The "cradle mold" as I call it, is obviously very time consuming. When both stems and all stringers are caged in by the five molds and two end supports I will remove everything from the strongback piece by piece and copy each item, and that process will be timed, along with reassembly on the strongback.
The steaming of ribs (about 14) is one big unknown, but I plan to do them fast, first cutting succesive ribs to exact length and then swinging them into place (they are tenoned into the gunwales and initially I'd thought I'd have to do ribs first and then gunwales, but I am fairly certain it will be much faster and easier to hook them into the mortises while at a 45 degree angle and then rotate them down. The fit should be good enough that no clamps should be needed.
Some CNC framed SOFkayak designs (Dudly Dix kayaks,e.g.) go together in two days (classes are offered where it takes that long to complete the boat except for so paint and finish).
The problem is, plywood is used, and compared to stringers sprung under ash ribs, I believe the boats cannot take the same punishment. Ther frame is too brittle and won't flex when bashed by waves. If you really look at the two types of construction methods, you'll see what I mean.
The CNC machine is a money maker where SOF kayaks are concerned, and I think those who build from precut frames (kits) ought to know it ain't the same thing as ash or oak ribbed, and the kitbuilders obviously are aware of this.
Precut frames are fine where plywood and strip built are concerned, but they are monocoque and SOF is entirely dependant on the frame for strength.

[alan white]

I'll check out the WB issues. Thanks!

[ned L]

Alan, the stringers on all three of my kayaks are fastened with small wood screws. For quite a few years (like 1930's - 1960's) there were all sorts of 'build it yourself' plans published in different magazines for kayaks similar to mine. The one that my dad & I built was from a purchased kit (if you want to call it that) that was advertised in I think Popular Science.

http://im1.shutterfly.com/media/47b8df10b3127ccec36bf6cbc1c900000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/
http://im1.shutterfly.com/media/47b8df10b3127ccec36b8292409a00000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

[ancient kayaker]

Alan: I located WB # 205 finally. It shows that the hull is assembled upside-down around male forms; stiff (temporary) ribbands are bent over the frames then the steamed ribs are installed under/inside the ribbands, which are then replaced one at a time by more flexible stringers which form part of the hull.

Getting the ribs in place inside the mold requires a second person to help, and seems clumsy. I can see how using the ribbands then replacing them with the stringers tends to assure a fair hull but that seems an unnecessary step, too.

I much prefer your method of building right-side-up inside female forms.

As a further comment, in my experience allowing the wood to bend naturally rather than forcing it around an arbitrary shape produces the best canoe shape and is more likely to a fair hull.

I think you are going to have a great boat, but I doubt that your method is going to be very quick. If speed is of the essence, a marine ply skinned boat is probably the way to go.

[alan white]

I agree that allowing the wood to "find its own way" is a good way to produce an easily driven hull. I did ery little to disturb the run of stringers, even raising them slightly to compensate for gravity. so far it looks just right, with no annoying inconsistancies of fairness. Of course, designing this way, I can't get a good view because of the female molds, so what sighting I am doing is taking hours and hours of time just to be sure.

I'm not looking for doing this in the blivk of an eye, but I'm pretty sure I could produce a finished frame in two days, and probably quicker. Marine ply is quick, though the epoxy/glassing processes slow things down if they are part of the process. Then again, I believe it was you who builds without epoxy, preferring stringers/caulk?

[alan white]

Alan, the stringers on all three of my kayaks are fastened with small wood screws. For quite a few years (like 1930's - 1960's) there were all sorts of 'build it yourself' plans published in different magazines for kayaks similar to mine. The one that my dad & I built was from a purchased kit (if you want to call it that) that was advertised in I think Popular Science.

http://im1.shutterfly.com/media/47b8df10b3127ccec36bf6cbc1c900000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/
http://im1.shutterfly.com/media/47b8df10b3127ccec36b8292409a00000010O02Bbs3DVuzZA9vPhI/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

I thought so. I see no other methods on the web except lashings. I am thinking of clench-nailing the ribs to the stringers, to speed things up.
I am thinking two clenched nails per joint. I think the lashings might be stronger though, so I'll have to do some tests.

[ancient kayaker]

QUOTE=alan white;265251] ... I believe it was you who builds without epoxy, preferring stringers/caulk? [/QUOTE]

Alan: guilty as charged! Worse, I try to eliminate as much as possible from the building process that doesn’t involve work on the hull itself. Not caulk though; if the joints fit properly so there are no gaps I use a quick-setting non-epoxy waterproof glue like Titebond III, but I use epoxy if I must. Lately I seem to spend far more time thinking about how to build than actually building, but I only have space for so many boats and I can’t bear to part with them...

... I'm not looking for doing this in the blivk of an eye, but I'm pretty sure I could produce a finished frame in two days, and probably quicker...

I was thinking the first one might take a fair amount of time to get everything right. However, since you plan to produce several hulls from the same set of molds and strong-back it makes sense to make up a proper jig, and I think the female mold idea is a good one. Repeat hulls should be much faster, especially if you buy the wood already milled to size or if you have the equipment for that type of work. I imagine steaming the ribs can be quite fast with practice and organization.

.
.
.

I think building the boat right side up is the way to go for SOF boats, especially if the joints are lashed, since that can easily be done from either side. I suspect the main reason to build a boat upside-down is cutting and bending large bits of wood around a form is easier and that step is usually followed by hours of sanding the outside. Neither is particularly relevant to a SOF. However, as you have discovered it’s harder to check for fairness from the inside: your mold must be very rigid to ensure that future hulls will be fair first time. Working inside a hull tends to be hard on the back - perhaps the mold can be tilted and raised for the lashing operation.

I also use ply forms with angle irons attached (shelf brackets are accurate and rigid) but I screw these to a table rather than clamping them to a strong-back. The table is handy for tools and there are never enough clamps.

The notches in the female molds may cause problems when it’s time to lift out the hull. Would it help if you make the notches wedge shaped and use turnbuckles or temporary lashing to hold the stringers? Electric cable ties are cheap and good for this, and there is a tool you can get that tightens them snugly.

I find using lots of spring clamps over a long period can be fiddly and hard on the hands; if the stringers and ribs are constant thickness, what about cutting out a bunch of ply "pegs" to do the job?

I worry about pre-cutting the ribs to exact measurements. Wood usually yields more in compression than in tension when it is bent and steaming may make it worse so they may end up too short which is worse than too long. You might be wise to make the first batch over-length by a fixed amount and note how much has to be cut off at each location. Then you can pre-cut for subsequent hulls. Personally, I would probably make up a simple jig to cut the rib tops to length in one operation: no worries.

I think the plan to build and sell frames is a good one, but I don’t think applying the skin is very time-consuming. HOwever, it is probably the step that would worry your customers. Selling the covered boat for the buyer to paint may work better from a marketing perspective.

Good luck whatever you decide to do!

[alan white]

I'm on the run right now, but a lot of what you said makes sense. I built the strongback to be at what I felt was an ideal height for me, but we'll see how that relates to each process.
As far as the release from the molds goes, each stringer notch has a vertical cut above its widest point from centerline. The boat will simply lift out. Holding stringers in place is done by clamps (25 of them, but swing-away wooden hooks with camming ends would be a better speed-building feature). The gunwales will be held by either clamps or short screws from outside that won't show in the finished boat.
It really appears that assembly of the stringers, keelson/stems assy., and gunwales, ready for ribs, will be a fifteen minute procedure. Streamlining the following procedures should be similar.

[ancient kayaker]

... As far as the release from the molds goes, each stringer notch has a vertical cut above its widest point from centerline. The boat will simply lift out ...

Sorry, you already stated that and it can be seen for the picture but somehow I missed it.

What cross-section are the stringers?

I'm wondering if they may flex between the forms under pressure from the ribs, resulting in an unfair hull. If this proves to be the case you can deepen the slots and use stiffer ribbands to support the stringers until the hull is complete.

Probably though, there'll be enough support already from the gunnels and keel to prevent stringer distortion.

[alan white]

The stringers are 3/4" square. The keelson is 3/4" x 1" wide.
Regarding unfairness due to differences in support between molds and stringers alone---- The mold centers are at 24" spacing. If I space the ribs at 12" centers, you would think half would fall on the molds. However, in fact I can have two ribs between the molds, spaced the same distance from those molds. Then all ribs are subject to the same relative condition. Of course, it is most probable that even if a small difference did occur due to spacing half, for example, on the molds and half between, my guess is the boat would self-fair, once out of the cradle.
I am concerned with the bottom rounding, and I'm thinking of blocking up the keelson in six places, halfway between the molds. Very easy to do. The length of the ribs will be critical. If the keelson is blocked up, the correct length will ensure the stringers couldn't be forced out.

[alan white]

Terry, what do you think about using a bisquit joiner to make rib pockets (MORTISES) IN THE GUNWALES? It would aid in swinging them into place and I should be able to get about 3/4" depth. They then get pinned with a couple of 1/8" dowels, glued. The machine would have to be reset once to get the full 1/4" width.
The slots may not look as elegant but there wouldn't be any wracking force to worry about and if anything the cuts in the wood are less abrupt than straight-sided mortises, which I like. I like the speed advantage in any case. Some use a router, but that takes a dedicated setup with plunging and hassling with a bit that wants to walk unless the rig is held very steadily.

[ancient kayaker]

3/4" sq stringers should be stiff enough to stay fair I would think if supported by molds at 2' centers. I haven't much experience with steaming and none on boats, but if the ribs are uniform and steamed sufficiently to the same degree, the boat should, as you suggest, self-fair.

I agree I would not like to cut lots of miters but I'm not sure I understand what you have in mind with the biscuit joiner, without a picture anyway. I assume you will drop the gunnels in place over the rib ends after all the ribs are in place, or did you plan to put in the gunnels before the ribs? Either way, biscuit slots seems like a lot of huge cavities for this.

I can imagine a couple of methods. One would be to simply drill holes in the underside of the gunnels for the rib ends and round off the ribs to fit, possibly using a plug cutter. That would work best if the ribs were not too wide, and the gunnel would go on last.

Another would be to cut a full-length groove in the underside of the gunnels for the ribs and insert short battens between the ribs, the way balusters are fitted into the groove underneath a wood handrail. I would think that would be fast and easy; the battens could be cut to length on a chop saw very quickly. That would allow the ribs to be put in after the gunnels, but I would still put the ribs in first so I could cut the tops off to length in one pass. there's some pics here http://www.hammerzone.com/archives/decks/handrail/traditional/assembly.htm

Don't forget the photos as you progress!

[alan white]

I thought of a full length groove. The biscuit joiner cuts a slot in a second, so since those pieces are nearly 18 ft long, I'd rather clamp the gunwales and then move along with the biscuit joiner, dipping where marked. The ribs are 1/4" x 1 1/2". I'll round off the ends before steaming and the gunwales will already be in place. I'll insert the ribs into the gunwale slots hot, skooching them in and swinging the bottom into place. That way no clamping (or little clamping) will be needed. At least that's the plan.
I finally finished the last mold today and am working on the cutwater (stem)shapes. The stringers will land on hardwood wedges screwed atop (two)steps in the stems.
That way the stringers can be cut square instead of being cut at compound angles and lashed or screwed to the cheeks of the stems. It's quicker and stronger.
I'll take some pictures soon, as soon as there's something significant to record.

[ancient kayaker]

I didn't realise the ribs are 1-1/2" wide, your plan makes sense now.

[alan white]

An update. Although I've replaced all the wood, modifying the ealier pieces, I still have to remove it all again for making measurements and templates. It would be far more gratifying if this were a one-off!
anyway, the design is coming together. It measures out to be a high capacity touring sea kayak. Dimensions are 17' 4" x 23 1/2", swede form hull. It looks like a West Greenland kayak but it's got a lot more cubic volume. I like the greenland kayak look, but this will have a longer waterline for its length and a larger (egg shaped) 30" coaming. Easier to get into and out of, and it will still take a spray skirt.

[ancient kayaker]

That's looking really good, Alan! How much rocker have you got there? With the deep forefoot it will track well but might be a bit hard to turn without some rocker.

[alan white]

Should be about three inches of rocker, very close to the depth, which will probably be about 3 1/2"-4". She's well rockered.

[alan white]

I'm getting down to the steamed ribs, which are now 1 1/8" at 8" centers. the trick is to carry a fair curve athwartship, ending with the upper end of each rib seated neatly in a mortise in the underside of the gunwales. Getting this fair curve at each point along the whole length is tedious.
So I'm using a piece of ash 1/16" thick to test each rib location. I'm pretty much ready to mortise the gunwales. I have no mortising bits so I'll use a drill and connect with a router fluting bit chucked into the drill press, running fast. With a fence and a vise grip clamp I should get pretty accurate mortises. I'll leave the rounded ends where I've drilled and just round off the rib ends to match. The only other thing left to do is to make two more gunwales (but these are for setting the ribs so the tops have something to rest against. Then I'll remove the temporary gunwales and tap the actual gunwales down over the rib ends.
This method will be accurate because the temp gunwales will allow placement of the ribs into open mortises (pockets) rather than closed ones as are in the actual gunwales. That solves the problem of doing the ribs first and then the gunwales. I'm certain it will work, since the pockets on the temporary gunwales will be positioned exactly where the actual gunwale mortises will be.

[ancient kayaker]

Steamed ribs sounds great, although we usually barbeque ours:D Seriously though -

:?: How is the steaming process itself? What thickness are the ribs, looks about 1/8. Is this still looking like a good production build method?:?:

[alan white]

Ribs are 1/4", maybe slightly less. Of course, rather than say "production", I'd rather say fast and repeatable while being an excellent boat.
I don't want to sacrifice any quality but I need to make money and so while many others are cutting CNC frames out of plywood, making non-flexible boats, I want something different, something with ribs that absorb shock well, allowing movement and eliminating point loading, and I can use that as a selling point.
The fastest way to build a SOF kayak right now is of course precutting sections using a computor-controlled router. Good for kits for beginners or someone who wants a fast build. If I can get close to that speed with steamed ribs, I'll be real happy.

[ancient kayaker]

How long did you steam the ribs? If they are 1/4" or less, using the 1 hour per inch rule of thumb, you wouldn't have to wait long to start fitting the first rib and after that you could work as fast as you like.

As an experiment I tried making a laminated rib this afternoon, using 3 layers 1/16" think. I just glued the layers together flat, clamped the ends only and bent it to shape: the laminations were kept together without clamps. It held its shape and there was very little spring-back. A bit messy but not as fiddly as I expected and with a bit of development it might be a viable technique. Cutting the strips would be a bear but I believe the material is sold precut for basketwork. I might try it out on a boat one day.

[rwatson]

Just a hint that might help somewhere.

Steaming ribs for a canoe is a tiresome business, but the wood will break if not steamed.

I found that if you plane good quailty wood down to say 3/16", and apply f/g and epoxy to the outside of the curve, that you can get some good bends in without steaming, and without the wood breaking.

Having the canvas resting against a waterprooof side of the frame isnt a bad thing either.

Might be worth trying a test piece to check the possibilities

[alan white]

Thanks for the tip. I will try that if for no better reason than it's easy to try and it is going to be useful on some project. Besides, my girlfriend's teeth are killing her from the chewing.
Currently, the ribs are in the bathtub sunk by a brick. I will give them three days underwater. I could have used green ash rather than this kiln dried stuff, but my sawyer didn't come through on time. I like one aspect of dried wood---- it is nicer to joint and rip.
I don't anticipate problems with the ash since no wood seems to steam as well. Ash is just very bendy wood, even not steamed.
Just glass-tape a wide piece and rip it after? I've got some 4" tape.

[ancient kayaker]

Neat idea, ensures wood is under compression instead of tension and is much less likely to break! Actually, I read somewhere that most of the distortion that occurs when wood is steamed and bent is on the inside of the bend.

I have some data on strength and elasticity of wood; for example southern longleaf pine with a modulus of elasticity of about 2,000,000 psi has a yield point about 8,400 psi suggesting that it will distort by up to 0.42% before breaking, at least on the inside. Assuming that it will stretch by, say half that on the outside gives a total distortion of 0.63% or 1 / 158. The data for all the woods that I have give very similar results, so a bending radius of about 200 x thickness should be OK without steaming, although steaming will enable the wood to bend much more and hold the new shape better.

I am looking at a new boat design which has a coaming bend radius of only 14 inches in one place, suggesting the wood will have to be steamed to allow a sensible thickness to be used; 3/8" lumber would be OK but that's is only 1 / 40 of the radius. To avoid steaming I may try ply with the outer grain running vertical: I might be able to get away with 1/4" which should be adequate in ply.

[alan white]

How long did you steam the ribs? If they are 1/4" or less, using the 1 hour per inch rule of thumb, you wouldn't have to wait long to start fitting the first rib and after that you could work as fast as you like.

As an experiment I tried making a laminated rib this afternoon, using 3 layers 1/16" think. I just glued the layers together flat, clamped the ends only and bent it to shape: the laminations were kept together without clamps. It held its shape and there was very little spring-back. A bit messy but not as fiddly as I expected and with a bit of development it might be a viable technique. Cutting the strips would be a bear but I believe the material is sold precut for basketwork. I might try it out on a boat one day.


I haven't steamed the ribs yet. i am ready now to do so, though. I had to fiddle around with the forms today. The next boat won't be but a few hours to build but the first one is a lot of work.
All you need is the right blade. An 80 tooth 10" will rip very smooth. My trying batten is 1/16" or so and it is nice and smooth. My blade was cheap too, about $30.00.

[rwatson]

Thanks for the tip. I will try that if for no better reason than it's easy to try and it is going to be useful on some project. Besides, my girlfriend's teeth are killing her from the chewing.
Just glass-tape a wide piece and rip it after? I've got some 4" tape.

If you have a girlfriend who will chew ribs for you - you dont really need a boat :-)

Yes, sawing a wider section will work fine.

I find that tape tends to pucker on the edges, so I tend to cut my own strips, but it will work fine.

http://au.blog.360.yahoo.com/blog-9Lzn38s2aaNjbox8Tf4JBaMLBFaBlmI-?cq=1&l=11&u=15&mx=46&lmt=5&list=

illustrates the bend I put in my own canoe using the technique after breaking 3 other pieces of timber.

I discovered the technqiue after having cheap exterior ply start to break when I was bending it while building a skateboard ramp. 1 layer of epoxy and 6oz cloth, and it was a breeze to curve afterwards

[alan white]

What model canoe are you building?

[alan white]

New twist. I will be dropping ribs into the upright hull cavity, as described, and tonight I figured out how to hold the rib tops exactly in place. I will raise the gunwales 3/4" using spacers under them. Then 38 individual "clips" (already made) will position the rib tops. The clips will be spring-clamped onto the gunwales (pictures to follow). One by one, I'll remove the clips and tap the gunwales down. This will be fast and accurate. It was work making the clips out of hard maple, but now I've solved another problem and if it goes like I think it will, I'll have the ribs and gunwales done in no time.

[alan white]

I steamed half of the ribs tonight. I had to build a steam box and set up the steam generator, which worked out well. It's a small steam box anyhow, about 6" x 6" x 40".
The ash had been soaking for a day in the tub. The foremost rib has a very small radius as you can see in the picture. Maybe a 3" radius. Of course, ash steams beautifully.
Note the clips m,entioned before. They are seen at the top of every rib and just below the gunwales. They get removed as the gunwale drops 3/4". Right now, the gunwale is raised exactly 3/4" to accomodate the clips.
Tomorrow I'll finish up the ribs.

[alan white]

The ribs are in, copper-nailed to stringers and gunwales. I lost three to breakage. I didn't realize the generator was disconnected and I didn't get a full steaming of one load. The frame will be done tomorrow.

[alan white]

Hull framed. Later I added the deck frames.
The copper nails were driven through and when the boat was removed from the molds the nails were bent over and while bucked from the inside the clipped (to 1/4") ends were driven back in with a punch, so each nail formed a J. This is because I am working alone and normal clenching isn't possible.
I used unskilled help to buck the nails when punching.

[duluthboats]

Very nice, Alan

[ancient kayaker]

Agree In spades. Less than a month from a cold start, too!

[ned L]

Agreed, Very Nice!

[alan white]

Thank you. Yeah, about three and a half weeks from the drawing of the midsection. I guess I now know how long it takes to do a new design (unless I loft, which I may do next time).
I'm now hesitant to build another until sea trials on the first. But I need to skin this one while the water warms up anyhow. Few good instructions on the web about skinning, so I will probably havr to buy a book.

[alan white]

Here's another photo showing the ribs. I still have to make three ribs but I have to laminate two 1/8" strips to get the tight radius. How necessary these ribs at the ends are is in question, but they are light and can't hurt.
AK, I need your advice on coaming design--- what shape is needed for a spray skirt to stay on, for example.

[Rick Willoughby]

Alan
What does it weigh at this stage?

Rick W

[alan white]

33 lbs is a rough guess now with all the framing done--- 31 as you see it in the outdoor photo, with the foredeck frames but not the afterdeck frames.
So the skin must weigh 5 lbs and the coaming maybe 2 lbs. A foot brace and knee braces, another two lbs. That makes 40 lbs and I will probably lose a pound of moisture from the spruce gunwales and stems, as the wood was outdoors at the yard and wet. That would be 39. Or am I off with the skin guestimate?

[ancient kayaker]

:) Alan: here's a net page I made a note of some time ago that has good info on the skinning process, and you can find definitions of the various stitch types specified in Wikipedia:-
http://capefalconkayak.com/howtoskinakayak.html

If you Google kayak coaming you will find several pages and sites with good information.

Here's one really good page with links to pages on coamings, skinning etc: http://www.guillemot-kayaks.com/Building/SkinOnFrame/index.html

I build canoes not kayaks (so far at least) so I am not an authority on coaming design and construction, but the following is about what I would do rather than what I've done. You have probably already researched these topics however, and may well know more than I at this stage. Good luck either way:!:

There are several styles of coaming construction that I know of: 1) steamed solid wood 2) horizontal laminated stack of thick ply (or solid wood cutouts arranged cross-grained) and 3) several vertical laminations of thin bent ply. Since you're already into steaming the steamed wood approach may be most attractive to you.

As far as design is concerned, based on the plastic ones I have there should be a rolled edge that the spray skirt fits over, the inside edge should be smooth to aid entry/exit, and give a lot of thought to getting in and out, also consider where your weight will rest during entry/exit so you can reinforce those locations.

BTW -and I don't want to sound patronizing - but if you haven't actually paddled a kayak before I strongly suggest you try out one before finalising the coaming design :)

Another suggestion: unless you are making the spray skirt it would be wise to buy one first so you can make sure the coaming fits it!

I have looked at the construction of several Inuit kayaks at the Canadian Canoe Museum and the coaming appears to be attached to the skin more than than the frame. However, that is likely to be a reflection of the limitations of their materials rather than recognition of some obscure design requirement. Here is a view of the kayak area of the museum you can scan around using the mouse:- http://www.canoemuseum.ca/docs/PANS/3ARCTIC.swf

[alan white]

Thanks for those links. I'll check them all.
Yes, I've seen that SOF kayaks have holes in the coaming and the skin is drawn up into the inside and sewn to the coaming. It appears that little else but the stretched fabric holds the coaming down and this is exactly what I don't want.
I prefer to have a coaming that's solidly mounted to the boat. To do this I will have to have a perfect fit between an inner and outer steamed set of ovals. One shows, and is ash, which would be 1/4" by maybe 2 1/2" high. It would have a lip on the outside at the top. I guess that lip has to be just big enough to accept a spray skirt. 1 1/2" of that coaming would stand above the deck, and one inch would be below the deck. Another 1/4" by 1" hoop would fit around the first coaming.
Now get this: The outer hidden hoop is not glued together (the coaming, however, shows is scarfed and glued, or has a decorative joining piece).
The other (unseen) hoop isn't glued but is adjustable by means of an all stainless hose clamp that's cut and simply screwed to the two joining parts.
Now this would be a problem if the shape isn't round or at least egg-shaped, since flat sides wouldn't allow tension against the outside, but I'm doing an egg shape. Attaching the unseen hoop to the boat makes most sense. That allows the fabric to be stapled to the inside of the hoop first. The fit can be checked against the coaming before the stapling to ensure that little tightening will need to be done (so no wrinkle appears at that point).
the adjustable hoop then is easily screwed to the frame at several points. Maybe forward, aft, and to each side to the knee braces. The adjuster can be anywhere there's space.
Now the coaming is held in with tension alone, and some sealant, which also keeps it from coming loose.
I had originally thought of a 3/8" coaming, but with the added support of a hoop, I can go with 1/4". A 1/2" x 1/2" spray skirt keeper, if that turns out to be the right thing, will be glued to the top of the ash coaming.

I've found that virtually everyone out there building steamed rib kayaks is copying the Eskimo boat and probably often the builders don't bother to ask how some of the methods of yore could be done away with in favor of a much better method using modern materials.
I see lashings being espoused as "very strong and resiliant" but frankly the lashings were a result of a thousand year old screw and nail shortage. While lashings are strong and resiliant the stringers have to be grooved unless the thread is so thin that a million turns have to be done to do one joint. That groove makes a weak spot.
I tested the clenched nail method to destruction and found that the wood breaks first. Dyed in the wool Greenland or Baidarka builders claim no metals means no problems with galvanic corrosion. I used brass and stainless screws and I doubt the kayak will ever have to deal with conditions that could eat metals.
I'm also using construction adhesive (new "THREE TIMES STRONGER" adhesive that costs five bucks). I like it for bedding and screw backup. it will prevent the wood from moving at important points like the gunwale/stem joints and the stringer/stem joints. Plus it will keep water out of the joints.

[ancient kayaker]

The coaming as you have described it makes a lot of sense.

There is usually some emphasis on the flexibility of the frame when reading about SOF boats of all kinds. Partly that's because the skin adds a great deal of stiffness. I think that flexible joints between thin members like ribs and stringers allows the joint to give slightly so the load is shared with adjacent members.

However, the use of glue for more robust frame members like gunnels is probably good as it would make for a boat that holds shape better.

[Petros]

Alan,

I just came to this thread (been off the forum for a while) and I have a few observations and ideas to share. I am an engineer, and have built 9 kayaks and 14 boats over the last 30+ years, and I have considered various ways to make a "production" SOF kayak. I have built using traditional "native" methods, modern methods and "production" methods (pre-production really with an eye towards production). I have used lashings, wood pegs, morticed joints, bronze and stainless screws, fiberglass, alumunim, plywood, and many types of grown lumber for any and all parts.

If I was going to make several exactly alike (no two of mine have been the same) as in a limited production I have considered the strong back and mold method you are using, which would likely save the most time on the next one (just make sure you have the hull shape you want first!). I have done it several times that way, but I find it is much faster just to do it the "native" way: build up the gunwales and deck beams using a few plywood jigs to "eye ball" the form, and than flip it over and build up the ribs/stringers from there. The assembly just sits loose on top of saw horses (only to bring it up to work height but can also be done on the floor). Though I do use a couple or three temp blocks to hold the keel in place to control rocker and depth (and indirectly the curve of the bilge). from there I test fit a strip of plastic to find the length of each rib (I number their location), cut to length and boil them, and hand fit to each location. This is a very fast way to size and install ribs. I use 3/4" x 0.2 inch ribs, if I want a flatter bottom I make them .25 thick and using a joiner plane off each end down to .2" think for 8 inches (so each end is .2" think, and center at .25").

I have found that lashing the stringers and keel with polyester "artificial sinew" cord the fastest and strongest joints to make, I put an 1/8" hole through the stringer at each rib and found it works best (no lump from the lashings in the skin). I have also considered the copper rivet at each rib location, a good idea, but I have never tried it. Lashing is lighter, faster to make, corrosion proof, and stronger I think.

I found using a router on a router table the fastest way to make clean mortises in the gunwales, I attach the ribs with wood dowels through the gunwales and glue them in place (some say the glue is unnecessary but I want them to stay in place). I have considered the copper rivets like you have used, it is an excellent idea, but they cost more and there is no advantage at this location to the addition strength.

I have used both Alaskan yellow cedar and white oak for ribs (and aluminum too, but I like the wood better), I have found boiling them works much better than steaming. I have much less breakage (almost none in fact) and it is far more tolerant to grain run-out and other defects, and since I use very dry salvaged lumber the moisture content is not an issue since the boiling puts the moisture back in.

Traditional coamings use just a steam bent hoop that is only about 1.25" tall with a 3 or 4 cleats to hold on the skirt. I have made a number of different styles, plywood ovals with the top one larger than the lower one to make a lip, steam bent oak, laminated spruce. Most of the fiberglass factory kayaks have coaming lips much bigger than necessary (sometimes making it difficult to remove the skirt quickly). I like mine steam bent oak of .2" think and about 7/8" tall, with a 3/8 x 1/4 strip glued to the upper edge to make a lip. I have an egg shaped particle board mold to warp the it around to get the shape I want. I have found that lightweight coaming that just "float" on the skin work the best, they are simple and light and have never been a problem. Though it is possible to simply size it so when it is all stitched (or clamped) into the skin, to lash it to the mastic or foward frame, aft frame and to the gunwales on either side to hold it solidly in place. I think once you try out a traditional one you will find making it "solid" is not necessary, it work just fine (you have to stop thinking scaled down big boat, that is the way "white-man" thinks, think like a native builder, light and simple is better).

Also your frame weight seems a bit high, most of mine have completed weights around 20 lbs (8 oz nylon with 4+ layers polyurethane finish) including seat and deck rigging. My daughter's Greenland type made of doug fir, 19" x15' lol weighs only 16 lbs. complete The heviest one I have built weight 35 lbs, and it had sealed bulkheads, deck hatches, foot pedals, heavy frame mounted coaming and other "white-man" accessories on it. Perhaps you could lighten up some of parts?

Before you skin it wrap it with plastic and duct tape and go paddle it around. If you want to make any changes there is no point in wasting a good skin, the "Saran Wrap test" is a good way to try it out before it is done. I have used 4-5 layers of commercial grade Saran wrap followed with several spiral wraps of clear packing tape. I have also used that heavy duty white shrink wrap they deliver on new boats, it is tough and self sticks once heated. I used a heat gun to soften and shrink it up, makes a good cheap test skin.

I am not sure you would gain anything by buying the books that shows you how to skin a kayak. I own 4 or 5 books and found none have complete enough information to be useful. When you get to that stage I can outline here what I do and you can give it a try. There are several options you can uses, some I have developed that use no hand stitching with the idea it would be used in a production SOF kayak that work great.

Good luck.

[alan white]

Thanks Petros. I will take it all into consideration. one reason my boat has a few extra pounds is that I built it with spruce rather than cedar gunwales, and spruce bow and stern as well. I used cedar for stringers.
Next boat will be about an inch shorter and that will save some weight. I use 5 stringers, and may go to 3. I can lighten up on the deck beams and save some weight. My ribs are .25 x 1 1/8" @ 8" centers. Ash. I can go down to 3/4" and save a bit I may laminate the gunwales for more consistant curves and size them 1 1/2" high and 1 1/4" thick. That way I can have open mortises for the ribs and I'll add the extra meat (1/2") to the inside--- I can do this because the gunwales don't need spreaders to hold their shape.
All in all, it's not hard to shave the weight down 20% I think. I do see that most SOF kayaks at 17 ft (and mine's nearly 24" wide) are about 35 lbs.
A 22" wide kayak a couple of inches lower with lighter scantlings would be a lot lighter, maybe 10 lbs. I do like a rugged boat though.

[alan white]

I weighed the boat tonight. 34 lbs fully framed. I wonder about the weight of the skin. Maybe you, Petros, know the answer to that.
i have done some research too, checking out scantlings of stringers, ribs, etc..
Turns out the ribs are spot on typical, and ash is very commonly used. The gunwales are spruce, as I mentioned. This particular part need not be spruce, which is heavier than my native cedar that grows here in Maine. I just had a tree cut from my sawywr's land, 18 ft lengths with few knots. Already very light a few days after cutting, these will make gunwales for future boats. I'm going to guess that the native white cedar comes in at about 22-23 lbs per cu. ft., and the spruce maybe 28. Maybe a 25% difference. This amounts to 2 lbs if my math is correct. Another pound could be saved by using cedar to do the stem and stern.
These are areas where I know I'm overbuilt. I don't believe it's worthwhile to thin or narrow the ribs because they account for such a small weight to begin with. I see smaller keelsons and chines being typical, such as a keelson of 5/8" by 3/4" while mine is 3/4" x 1". Ditto for the chines (and I've got two chines per side).
I'm using wrc for the stringers, since it's available clear and native cedar is not. You can have knots in the gunwales and stems but not in stringers.
Tonight I cut out a coaming form and so I'm ready to do the coaming.
I will take Petros word that the coaming can be strongly enough supported by a combination of fabric tension and minor framing support.

[Petros]

The weight difference between cedar and spruce is not much, so I would go with what ever is easier to get (less cost) and which ever I liked working with, surface finish, etc.

You might consider increasing the rip spacing to 12" aft and forward of the center, keeping the 8" spacing in the cockpit area only. That will save weight, reduce your part count and save labor too. I think 8" spacing is much closer than necessary for the areas away from the higher loaded center section. Consider both the forward and aft ends do not have large loads on them compared to the center section. Epically with your larger ribs.

24" wide is pretty large AFAIAC for a kayak, though common on factory hard shells. 24 inch wide hulls feels to me like I am pushing a large shoe box through the water, slow and clumbsy. Though from a marketing stand point when a newbie gets in a 19 or 20 inch wide kayak and flips over 4 feet from the beach, they would not buy it. So production kayaks makers are unfortunately stuck will selling very fat, very stable kayaks just to get them sold. They would consider a 21" wide kayak "high performance" and recommend them only for very skilled paddlers, that is pretty large and slow for a typical native kayak design. I think the hard chines of a SOF design also improve the secondary stablity of a heeled hull, so once used to the width most can relax with a kayak that is a bit tender on the keel.

With a thin padded seat right on the bottom, and a properly shaped hull, 21-22 wide is usually comfortable for most paddlers who are past rank beginner (and as wide as I would ever want for myself). I tell beginners it is like learning to ride a bike, once you develop your natural balance skills it becomes automatic and you do not have to think about it, and you would never go back to a three wheeler or training wheels. So just tough out your first few paddling trips in a sleeker, narrow hull, and you will not regret it. My daughter was happy paddling an 18" wide greenland hull at 15 years old, my wife wants something wide and comfortable, hers is 21" inches wide.:)

You should consider who your target market is and design the hull around their preferences. If you want to stay in business, you need to sell what your customers want, not what you think they should get (General Motors is a good recent example of that).

I think you will find the lighter coaming will work out fine. It is really a matter of how you view the function of the coaming. On most larger boats the coaming is an integral part of the structure, solidly attached to the primary hull frame. On a traditional kayak it just there to give something to attach a spray skirt and keep the water out.

As for skin, depending how heavy a fabric you use, the sealed finished skin would only weigh about 2 oz a square foot. So perhaps 50-60 sq ft of skin area, 6-7 lbs skin weight. I like using raw 8 oz/sq yard nylon, I see no reason to use heavier than about 10 oz, some have used as heavy as 16-20 oz/sq yard, much heavier for normal sea kayak conditions. The resilient fabric skin is tougher than fiberglass or most there skin materials as far a dent and tear resistance.
Good luck.

[rwatson]

Looks like a good effort, and I havn't read all the other comments in detail, but I would add my contribuition to the "mix".

The construction is quite "conservative"- up to way overbuilt.

Petros suggestion about a bigger gap between frames is right on. You could leave every second one out. The deck members really need a severe prune with a jigsaw, and maybe some "knotholes" cut in the gunnel as well to lighten it all up

You do not have enough stringers on the bottom, and the side ones you do have are too big.

The gunnel, could be just two of the chine stringer laminated together, with maybe some spacing blocks for extra rigidity. In fact, traditionally the ribs form the spacing blocks in many boats. The one you have is way oversize.

You need at least two more stringers the size of the chine stringer under you bum and feet. (they dont have to run full length) The keel is about right, but might have been better to laminate from two "chine size" bits.

I think you will find this one will run in a very straight line, and not want to turn easily, which is mostly good for an ocean going vessel but a bit scary if you want to make a steering correction in the front of a big wave. If you make the bottom stringers almost level with the bottom of the keel (not as thick though, use some spacers), so that you do not have such a pronounced keel line (up to a metre from the bow and half a metre from the stern), you will get better turning ability without losing the good "tracking" ability.

Hope that all makes sense, and proves usefull.

Keep up the good work - and it is quailty work you are doing there, have no doubt.

[alan white]

Thanks both. I was planning on two more semi-chines, and if you look at earlier photos, you'll see the support stringers I used to keep the ribs from oil-canning.
With seven stringers, the bottom is not veed anymore, but it has that classic "White guide canoe" shape.
Regarding rib spacing, I've seen all kinds of spacing used but certainly one per foot (at the same dimension) would be simpler.
Gunwales: The mortising was a quick job and it automatically spaced the ribs properly (I did the rib-to-keel spacing by eye to seat the rib-to-stringer faces at flatly as possible). I know I can lighten up the gunwales, maybe reducing their height to 1 3/4" from 2 1/2".
The deck beams are massive. iU know. I used screws, and into end grain, I used LONG screws. i wanted to make sure I had enough meat to prevent splitting. However, I have some real skinny long stainless screws now so I can go with 3/4" beams next time.
Stringers: All are 3/4" x 3/4" except keelson, which is 3/4" x 1". If I change those scantlings, I can see doing 5/8" x 3/4" for all but the keelson, which could be 3/4" x 3/4".
I made the pattern for the coaming today. 16" x 28", and I also ripped out the original cockpit-forward frame and laminated up a WRC curved arch (lighter and better looking, and most importantly, relocated to support the forward end of the coaming).
I wonder if the boat is too full forward, but realize it makes for outstanding bouyancy at the cost of top speed. It will reduce wetted surface anyway and raise the bow forefoot to make turning easier. Also will narrow the beam at the waterline.
I am tempted to make a forward hatch as there's a lot of room in there. I'd like to camp cruise some of these big lakes we have up here. i'm wondering how to make a simple hatch.

[ancient kayaker]

Don't worry, just paddle it and find out. The next boat can be a smaller/lighter/faster boat. The Darwin theory applies to boat design as much as anything else.

Regarding screws in end grain, you can prevent splitting by binding the end of the wood with thread. And/or you can drill a hole through the side near the end and epoxy in a dowel. Run the screw into the dowel and you have it running into hardwood across the grain so it will hold a tonne. However, don't put the dowel too close to the end.

[Petros]

FYI, I use 3/4 x 2 1/2" gunwales, and 5/8" square stringers. I also use a laminated WRC mastic, or deck frame at the front of the coaming.

Since this frame is used to brace my thighs against I make it wide, about 1-1/2", but at the top of the arch it is only about 1/2" thick. At each end I put a 4" long wedge between the laminations to give me enough material to put dowels into from the gunwales. Using (2) 3/8" dia dowels at each end through the gunwale, with epoxy or polyurethane glue, into the masktic ends solves the screw into the end grain problem. The dowel has more surface area to bond so it reduces the risk of splitting, it weighs less and with glue in the joint will not allow moisture intrusion into the end grain. I have not had one fail yet, despite a lot of abuse. I also use dowel and glue on all the deck beams.

Also I second ancient kayaker's suggestion, just get this one done enough to give it a paddle. Do not assume you will get all details correct on the first one, you will always find things you want to do differently and at this point it would be faster and better just to consider this a test build, and refine both the hull shape and construction details on the next one (or two or three).

I rebuilt my wife's kayak 3 times before I and she was happy with it. I was using a hybred design, using an Alaska Biadarka type bow and stern with the simpler and lighter Greenland type hull construction, so there was some experimenting. I changed the rocker in the keel, the cockpit location and a few other important items before we found something that worked well, easy to turn yet tracks well, balanced and comfortable at only 21" wide. The SOF construction allows such radical changes to the hull shape without having to do totally new hulls, a little trimming, some shimming, and the hull shape has changed. I am always experimenting like this so I just come to expect it, the only one I did not have to make adjustments to was my daughter's west Greenland type because it was the only one I built "per plan" (or rather according to traditional "native" sizing and construction methods). So when you deviate, expect to have to make a few adjustments before you are done.

Good luck.

[alan white]

Thanks for the advice. I am anxious to get it in the water (ice out was last week).
I worked on the coaming today. Found it would be a good idea to layer two hoops one over the other. They will add up to about 5/16" x 1 1/4". I figured out early on that prior to putting the two lams together I should scarf and glue the inner layer round and then boil water on the stove (in my long metal pan) and dip it in and hand shape it to my liking. Then I'll hand shape the outer layer without gluing it into a hoop, then glue the two together and scarf the outer one just before finishing the clampling of the two lams together. I realized that using a form would not guarantee the wood was relaxed into the correct shape. We'll see tomorrow when I add the second layer. Then I'll also add the lip, something about 3/8" x 3/8".

[nordvindcrew]

Alan, I am finishing a skin on frame rowing boat. It is much heavier than a kayak due to the tresses transmitted to the frame by the oars. Current weight is about 80 pounds for a 16' boat. Measure the keel all the way out to plumb at stem and stern, then measure the gunnels. you will find a difference of several inches. the fabric at the gunnel needs to be stretched to eliminate puckers. I did this by using vise grip welders pliers to grip the fabric and come-alongs attatched to trees to provide the stretching power. With care, the 10 ounce canvas conformed perfectly to the frame. Painting has been a shock, coat after coat to fill the weave. I must have done something wrong becauce I've used up 2 gallons of paint and still don't have a smooth hull. If you build multiple boats, your system should work out to save a ton of time. Good luck.

[alan white]

You must be using cotton canvas. Is that right?

[rwatson]

re skin stretching ... you might like to try the method that upholsterers use as well,

get a bit of wood say 12 inches by 2 inches by 1/2 inch, place it near to the gunell, resting against the cloth, then holding the cloth and the wood together, "roll" the wood. The cloth will wrap around the timber, and you will get a lot of leverage to pull the skin tight. You can then anchor it and move a bit further up the boat to tighten the next section.

Its a bit like using a "spanish windlass" but with cloth instead of rope.

I think it works better to do it than it sounds.

have fun :-)

[alan white]

And then, i guess I have to start looking for a source for some sort of fabric. Thanks for the tips. I'll be referencing this as I stagger blindly into the covering job.

[rwatson]

The cheapest method is to buy cotton "duck" or calico, if fabric shops still know what it is. Its the stuff you use for paint drop sheets, bought by the metre.

There are a number of great flexible waterproof paints around, some that end up with the texture and smoothness of rubber.

Knowing what I do now, I would use a strong nylon cloth, get it all stretched and tight, and fibreglass the lot the with 6 oz cloth and epoxy.

The cost will be at least double that of any waterproofing compound, but have 10 times the life, and 50 times the strength. yes, it will be a little heavier than cloth alone, but you are way overbuilt anyway, so it wont matter. If you choose a really snazzy colour for the nylon, you can varnish the epoxy and have a really wild looking boat.

The fg will tend to develop a bit of a "hollow" in the fabric as it cures, especially if you dont have the fabric super tight, but this is what the fabric will do when you are sitting in the boat on the water anyway.

You might like to try stuff on a small test frame to get the feel for it. That applies for the cotton or the nylon. Build a few throwaway test frames and get a feel for the method before doing the real boat.

[nordvindcrew]

Alan, Yes, I used 10 oz. cotton and it was a bear to stretch. I wanted to use nylon but couldn't seem to figure out what weight to use. It seems that the nylon would be both lighter and more puncture reaistance than nylon. If the boat rows well, I will eventually change to nylon. Look on the "designing a fast rowing boat" thread to see a couple of pictures.

[duluthboats]

Any news :D

[alan white]

Yes indeedy. I ordered the nylon and urethane coating tonight. I had to "save up" because i'm living in "Maine" which is a depressed area under the best of conditions. Nevermind the economy!
Otherwise, the coaming is mostly done and I'm ready to skin. I will post all developments and thanks to all interested parties.

[alan white]

Alan, Yes, I used 10 oz. cotton and it was a bear to stretch. I wanted to use nylon but couldn't seem to figure out what weight to use. It seems that the nylon would be both lighter and more puncture reaistance than nylon. If the boat rows well, I will eventually change to nylon. Look on the "designing a fast rowing boat" thread to see a couple of pictures.

I just now read your comment and I went to the rowboat thread. What a great thread! I will have to read all of it (it's more like a book) when I have time. So you are in Marshfield--- is that somewhere down 128? i used to live in Mass.

[alan white]

The weight difference between cedar and spruce is not much, so I would go with what ever is easier to get (less cost) and which ever I liked working with, surface finish, etc.

You might consider increasing the rip spacing to 12" aft and forward of the center, keeping the 8" spacing in the cockpit area only. That will save weight, reduce your part count and save labor too. I think 8" spacing is much closer than necessary for the areas away from the higher loaded center section. Consider both the forward and aft ends do not have large loads on them compared to the center section. Epically with your larger ribs.

24" wide is pretty large AFAIAC for a kayak, though common on factory hard shells. 24 inch wide hulls feels to me like I am pushing a large shoe box through the water, slow and clumbsy. Though from a marketing stand point when a newbie gets in a 19 or 20 inch wide kayak and flips over 4 feet from the beach, they would not buy it. So production kayaks makers are unfortunately stuck will selling very fat, very stable kayaks just to get them sold. They would consider a 21" wide kayak "high performance" and recommend them only for very skilled paddlers, that is pretty large and slow for a typical native kayak design. I think the hard chines of a SOF design also improve the secondary stablity of a heeled hull, so once used to the width most can relax with a kayak that is a bit tender on the keel.

With a thin padded seat right on the bottom, and a properly shaped hull, 21-22 wide is usually comfortable for most paddlers who are past rank beginner (and as wide as I would ever want for myself). I tell beginners it is like learning to ride a bike, once you develop your natural balance skills it becomes automatic and you do not have to think about it, and you would never go back to a three wheeler or training wheels. So just tough out your first few paddling trips in a sleeker, narrow hull, and you will not regret it. My daughter was happy paddling an 18" wide greenland hull at 15 years old, my wife wants something wide and comfortable, hers is 21" inches wide.:)

You should consider who your target market is and design the hull around their preferences. If you want to stay in business, you need to sell what your customers want, not what you think they should get (General Motors is a good recent example of that).

I think you will find the lighter coaming will work out fine. It is really a matter of how you view the function of the coaming. On most larger boats the coaming is an integral part of the structure, solidly attached to the primary hull frame. On a traditional kayak it just there to give something to attach a spray skirt and keep the water out.

As for skin, depending how heavy a fabric you use, the sealed finished skin would only weigh about 2 oz a square foot. So perhaps 50-60 sq ft of skin area, 6-7 lbs skin weight. I like using raw 8 oz/sq yard nylon, I see no reason to use heavier than about 10 oz, some have used as heavy as 16-20 oz/sq yard, much heavier for normal sea kayak conditions. The resilient fabric skin is tougher than fiberglass or most there skin materials as far a dent and tear resistance.
Good luck.

I'm getting back to the kayak after an interval of doing other things. The skin is draped and I am now facing the staple or sew question. I have Monel staples. I also have waxed dental floss.

Petros, your familiarity with the skinning process appears pretty well informed.
I can't, in any case, find anything useful on the web to guide me. Every site is extremely limited, often a teaser for an instruction manual you have to buy.
Not to say comments from anyone else aren't welcome. I can use all the help I can get. I am a carpenter, not a nylon technician.

I've painted the framje with two coats of interlux single part urethane, since I happen to have inherited 6 gallons from a friend.
Then I applied extreme waterproof medical tape to each of five stringers to (hopefully) prevent sand abrading the nylon.
The nylon I bought is 9 oz, shipped with a two-part urethane coating system.
I can just wrap the 60" x 18 ft nylon around the middle with a small overlap.
At this point I wonder if it would be easier to staple the skin to the gunwale (first the bottom and then the top) so that the process requires only sewing the ends. also, and importantly, the ridge down the middle of the deck will be eliminated. I would hope to set the staples below the surface enough to fill and simply urethane right over them--- and the overlap of nylon would be glued (what glue is best here?
Spreading the polyurethan two-part skin water-proofing comes next, and here I am again lost, as I haven't used such a system ever before, and I want to ensure I am well armed with the dos and don'ts before I start.
Then I'm essentially done. I've already installed a pair of light aluminum 10" adjustable foot braces (I got these froma buddy, so why not?).
The hoop is figured out. I will drill through every inch or so for sewing the nylon inside of it and lash it to several places including two stanchions attached to the sheer stringers at 3:00 and 9:00.
Then I'm done, except for strap eyes (Harken black plastic) for bungees, painter, and so forth.

[alan white]

FYI, I use 3/4 x 2 1/2" gunwales, and 5/8" square stringers. I also use a laminated WRC mastic, or deck frame at the front of the coaming.

Since this frame is used to brace my thighs against I make it wide, about 1-1/2", but at the top of the arch it is only about 1/2" thick. At each end I put a 4" long wedge between the laminations to give me enough material to put dowels into from the gunwales. Using (2) 3/8" dia dowels at each end through the gunwale, with epoxy or polyurethane glue, into the masktic ends solves the screw into the end grain problem. The dowel has more surface area to bond so it reduces the risk of splitting, it weighs less and with glue in the joint will not allow moisture intrusion into the end grain. I have not had one fail yet, despite a lot of abuse. I also use dowel and glue on all the deck beams.

Also I second ancient kayaker's suggestion, just get this one done enough to give it a paddle. Do not assume you will get all details correct on the first one, you will always find things you want to do differently and at this point it would be faster and better just to consider this a test build, and refine both the hull shape and construction details on the next one (or two or three).

I rebuilt my wife's kayak 3 times before I and she was happy with it. I was using a hybred design, using an Alaska Biadarka type bow and stern with the simpler and lighter Greenland type hull construction, so there was some experimenting. I changed the rocker in the keel, the cockpit location and a few other important items before we found something that worked well, easy to turn yet tracks well, balanced and comfortable at only 21" wide. The SOF construction allows such radical changes to the hull shape without having to do totally new hulls, a little trimming, some shimming, and the hull shape has changed. I am always experimenting like this so I just come to expect it, the only one I did not have to make adjustments to was my daughter's west Greenland type because it was the only one I built "per plan" (or rather according to traditional "native" sizing and construction methods). So when you deviate, expect to have to make a few adjustments before you are done.

Good luck.

Rereading, and now letting you know what I did to create the masik. I laminated (30" radius or so) a one inch high bunch of fir strips, then thinned the middle down to 3/4" tall. I didn't add anything to spread the strips (like a tree base looks--- your method) but instead ran two 6" long by 1" (tapering fore and aft to 1/2") shelves, screwed inside each sheer stringer. I positioned these to set the 1" tall masik on, and screwed the masik down into the shelves. I like this because it was the same material bulk but I think stronger and faster to build, with the shelf well glued to the stringers. I'll have to take some pictures if the rain ever stops (boating season here in Maine has been rain every day since Summer started).

[alan white]

Finally, I got the skin started. It took, finally, a synthesis of a lot of poor internet how-tos, and some common sense. So far, it's been easy. Dental floss was suggested by a lot of builders, so I got some. Way too weak! I switched to a heavier polyester thread I use normally for whipping rope. It is incredibly strong and allows really tightening the stitches.
The bottom is done. I stretched it on using staples and little cardboard squares at the sheer. One per every two inches. The deck will be stretched independantly.
Time-consuming but gratifying. After all. I am going from frame to finished boat in a short period of time, relatively speaking.
i don't know how others can sew a whole boat in a day. My hands are killing me and I'm half done.
I still have no idea how exactly to apply the two-part polyurethane. Anyone who knows, I'd love to hear how.

[ancient kayaker]

Lovely job: you are may be making too good a job of it and are suffering from the associated wear and tear! You can shrink the material to get rid of minor wrinkles and sags.

I believe in the value of experiment; in my case I would make up a wood frame and cover it so I could try out my proposed finishing method first before committing it to the boat.

[alan white]

Thanks, AK. The deck is going well. I will get back to it in a while.
once I had a feel for it, the calculation of how much gap would pull together was natural.
I slipped a temporary centerline wood backing in, attaching with brads (pulling them out just before covering). i drew two lines on it to indicate the place where the seam would be folded on each of the two sides that would come together. So far it's worked very well to aid in keeping the seam centered.
In a way, the process allows experimentation because stitched are easily taken out.

[rwatson]

i don't know how others can sew a whole boat in a day. My hands are killing me and I'm half done.
I still have no idea how exactly to apply the two-part polyurethane. Anyone who knows, I'd love to hear how.

Did you try the "wrapping the loose cloth in a small bit of timber" and tightening, like upholsterers do ?

Dont use two part epoxy paint on the fabric. It will crack and split. You have to use some kind of flexible, rubberised or tarry coating. Some of the rubber compounds dry really smooth, but stretch like .... rubber.

The other option is to use a silicon waterproofing compound like truck tarpaulins use, but most of them are for cotton based cloth.

Have fun.

[alan white]

Did you try the "wrapping the loose cloth in a small bit of timber" and tightening, like upholsterers do ?

Dont use two part epoxy paint on the fabric. It will crack and split. You have to use some kind of flexible, rubberised or tarry coating. Some of the rubber compounds dry really smooth, but stretch like .... rubber.

The other option is to use a silicon waterproofing compound like truck tarpaulins use, but most of them are for cotton based cloth.

Have fun.

Thanks--- this is a rubbery formula, specifically for ski8n-on-frame boats. It's squeegeed on. I've never used it before either! The outfit I bought it from had videos online for all their products, but the link doesn't work!
As far as tightening goes, I should be okay. I'm on the home "stretch" now(get it?).
It's the polyurethane I'm scared of now. Who's used it?

[alan white]

Except for final shrinking and the poly coating, the skinning is done.

[Rick Willoughby]

Alan
A see-through boat.

It is an elegant shape. If looks are any indication of performance it will be a winner.

Looking forward to the finished job and estimate of time with a honed procedure.

Rick W

[nordvindcrew]

The skin on frame rowing boat is working out very well. I've raced her twice and the boat is better than I am right now. I'm rowing at about 5.2 knots over a distance of up to 5 miles. By your kayak standards, she's very heavy, but seems to stand up to the stress of rowing quite well. It is almost a shame to cover up the translucent skin but in my case it was necessary to waterproof things. I'm told that varnish makes cotton canvas brittle and easy to rip. I'm very impressed by the speed of your build. I'm almost a year into mine and still have a few details to finish. Marshfield is on the coast, about 1/2 way between Boston and Plymouth. The local nick name for the area is the "Irish Riviera". Me, being mostly Norweigan, I'm a bit out of place, but it's a great place to live and be right near the water

[ancient kayaker]

Weight is crucial in a kayak or canoe if it has to be portaged. Not so in a rowing boat. Any human-powered boat may benefit from a bit of weight in a sea.

[alan white]

The skin on frame rowing boat is working out very well. I've raced her twice and the boat is better than I am right now. I'm rowing at about 5.2 knots over a distance of up to 5 miles. By your kayak standards, she's very heavy, but seems to stand up to the stress of rowing quite well. It is almost a shame to cover up the translucent skin but in my case it was necessary to waterproof things. I'm told that varnish makes cotton canvas brittle and easy to rip. I'm very impressed by the speed of your build. I'm almost a year into mine and still have a few details to finish. Marshfield is on the coast, about 1/2 way between Boston and Plymouth. The local nick name for the area is the "Irish Riviera". Me, being mostly Norweigan, I'm a bit out of place, but it's a great place to live and be right near the water

Sounds like a good shape you built. I'm about to waterproof, and finally I found some instructions. Grammatically horrible, but I muddled through and now I'm not too afraid to sling the goo.
I know the area of the Cape and Boston, I grew up near there.
I estimate the speed of the build to be a bit faster than the usual way of eye-balling ribs, but infinitely slower than using plywood frames (which can be built very quickly without much skill required).
I am not convinced the plywood frame method is resiliant enough, but I sure like the build speed.
Now that I'm done, I'd say, addressing Rick's comment, I am pretty sure it would take 10 relaxed days to completely build the boat once refined, and far less time if:
1) I stapled the nylon on and added a guard to the gunwale to cover the staples.
2) Made the cockpit ring out of a single steamed spiral-wound piece of ash or oak (the beginning of the piece would be tapered to a sharp point on a jig).
3) Pre-rounded the stringers prior to assembly
4) pre-painted the parts pior to assembly (linseed oil is very traditional, but two coats of marine enamal will last a long time).

[Gilbert]

I only now spotted this thread and haven't read it all yet. There are some pictures in my gallery of native skin on frame boats built by my niece and others at Corey Friedman's shop in Annacortes, Washington. The gunnels and deck beams and bow and stern pieces are lashed first and then it goes from there, adding the keel and the frames and the battens.

[ruediklein]

This seems like a good idea. I was wondering about putting in ribs inside of stringers ever since I saw that being done on the airolite boats by Mr. Platt (http://groups.yahoo.com/group/Airolite_Boats/)

I have not bent any ribs myself, but always thought it might be easier to put them over something, rather than inside.

Interesting thread though with nice information. The boat also seems to have come out nice.

BTW: I'm building a plywood frame SOF for my wife right now. I guess, I'm used to these kinds of frames from the many Klepper kayaks my family has owned over the years.

[boat fan]

Nice work Alan ! Have only just found this too.....I think I will get some tools out ......:D

[alan white]

Thanks. Glad you are inspired. I finished and paddled the kayak a few times on the pond across the way. Excellent comprimise of stability, speed, and cross-wind balance. Cockpit was too far back and so I'll be adjusting the cockpit position forward 8" or so.
The internal mold method is sound, nice to build right side up. I hope to try an improved boat when I have time.
Thanks for your interest.