Skin-on Frame Kayak Building Jig

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.

 

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.

 

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.

 

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.

 

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.

 

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".

 

skin problems

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.

 

You must be using cotton canvas. Is that right?

 

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

 

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.

 

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.

 

skin

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.

 

Any news

 

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.

 

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.