Skin-on Frame Kayak Building Jig

[alan white]

Originally Posted by 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.

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]

Originally Posted by 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.

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]

Originally Posted by alan white

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]

Originally Posted by rwatson

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.

[Guest625101138]

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]

Originally Posted by 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

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 ......