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How NOT to build a SOF Kayak


Mar 22, 2008
Or: How I Learned to Stop Worrying and Love the Steam Box

After following, with great interest, a number of other members SOF projects I got inspired to finally bite the bullet and start my own Skin-on-Frame kayak. I have access to a pretty well equipped workshop that my Father-in-law has assembled from decades of farming. I also have a good relationship with a local cedar mill so I am able to get really good quality, straight grain cedar quite easily. I also found myself with some free time over the Christmas holidays so I was confident that I could get something built over the course of a couple weeks. My goal was to build a Greenland style kayak that would be used almost exclusively for rolling. I have an excellent touring boat, so I was not overly concerned about speed, tracking and certainly not cargo volume. I am also somewhat “rough” with my toys, so I had planned to beef up certain parts of the boat for extra strength. Weight wasn’t a huge concern but I knew that working with Western red Cedar would make for a lightweight craft. What follows is not so much of a “How to”, but more of a “How Not To” and while it may not serve as much of an inspiration to anyone, it could perhaps serve as a warning. I’ve also tried to highlight some of the information that didn’t seem to have been addressed by the many build reports I read online.

Building Guide:

My reference guide for the most part was Christopher Cunnigham’s book “Building the Greenland Kayak - A Manual for Its Construction and Use”. I found the book to filled with a ton of information on building, but his instructions for specific parts of the build are sometimes scattered throughout the book. I’m used to Ikea style directions, where a picture of the part, a description of the part, the dimensions of the part and the assembly of the part are all on the same page. You won’t find that in this book. There are two incredibly comprehensive build threads on this forum that were far more useful than relying solely on Cunnigham’s book. I also refered back to the instructables.com website which has an interesting method for building SOF kayaks. It was every bit as crude as I expected my first build to be, so I knew I would be in good company, regardless of the eventual outcome.

Lumber Selection:

Having access to good quality lumber is usually considered a cornerstone of SOF construction. I’ve been dealing with a local cedar mill for ten years as part of my house construction business, so the owner is very accommodating about letting me pick out CVG (clear, vertical grain) Western Red Cedar. He will even pull aside boards for me that I have used for paddle building on several occasions. I really like working with WRC; it’s lightweight, easy to carve, naturally rot resistant and smells great while working with it. When I asked my supplier to start watching for some 16’ - 18’ lengths for building a full boat, he offered to cut the boards for me out of a few sizeable logs. After picking through the trees, I asked for the them to be cut to my rough lengths and dimensions and arranged to pick them up the following week. All told I spent $198 for three 17’ lengths of 2” x 4”, four 8 foot lengths of 2” x 6” and two 6’ lengths of 2” x 8” Western Red Cedar. While that may seem like a considerable amount to pay, I still have enough left over to build two more kayaks, so my lumber budget for the first one is probably in the $75 - $100 range.

One of the downsides to having wood cut to special order, is that you’re stuck with it once it’s cut. Upon inspection of the finished product I found that what appeared to be nearly perfect wood on three sides can have sizeable defects internally that don’t appear until the wood goes through a band saw. Of my three 17’ long 2 x 4’s all three had some sort of defect that would have to be coped with at some point. I picked the one with the smallest defect and it would serve as my gunwales. I began by taking about 6 inches off of the overall length to deal with the worst of the knots in that board. My first “compromise” of many.

Gunwale Construction:

My experience with boat or kayak construction up to this point is almost zero. I have built several Greenland Paddles over the past few years, but this was certainly more complex than spokeshaving a 2x4 into a somewhat symmetrical stick. The first several days of workshop time are spent making and re-making jigs and forms that “streamline” and “simplify” (yeah, right!) the repetitive parts of the build. All told, 11 pairs of deck beam mortices had to be cut at a 20 Degree angle into the sides of the gunwales and 24 pairs of rib mortices had to be routered into the bottom of the gunwales. If you don’t have a proper plunge router you can use a basic laminate trimmer with a flush cutting router bit, but it’s imperative that you find a way to cut each mortice to the same depth. You’ll thank yourself later. I found that you could “fix” a mis-located rib mortice by gluing in a plug, cut to the same size as the offending hole, and then re-drilling the rib mortice. Since the rib mortices all face down, you’ll likely never see the repair. This became my mantra; “If I can’t see the mistake, it really isn’t a mistake. It’s experience”.

Another important tip, though it may seem obvious to experience boat builders, is to make sure you turn the gunwales right side up BEFORE you saw the beveled ends off. However, if you decide to forge on anyways, (without re-cutting your gunwales, redrawing your deck beam and rib locations, routing out the rib mortices for a second time and re-drilling and filing all of your deck beam mortices again) there is an effective fix. If you haven’t sawn completely through the upsidedown gunwales install and glue a thin fillet of wood in the saw kerf. I’ll reiterate, “if i can’t see it, it may not have happened”. Some builders recommend cutting both pairs of rib mortices into a single 2” wide board which is then split down the middle, into the two matching gunwales. The big advantage to this method is that your rib mortices and deck beam locations should line up perfectly (if your router jig is any good) and that your boards will have an even amount of flex to them (as they come from the same part of the same tree). The big disadvantage to this method is that screwing up one part of a gunwale means that you now have to restart BOTH gunwales. Or not...

It was about this point that I reconciled with myself that I was now building a Greenland “Inspired” kayak, not a “Traditional” Greenland kayak. I was utterly justified using polyurethane Gorilla Glue to fix the odd wart because I was also relying on the most modern tools, and even materials, to build this thing. Ballistic nylon skin, Spirit Line Poly-urethane coating, electric planers, laser levels, Internet forums: No native builder ever had access to these, so how could I claim to be building a “traditional” kayak. It was time to go “all in” with technology and just get through it. After all, the NEXT one could be “traditional”

The knot hole in the stern gunwale was reinforced with a small plate, glued and clamped over the defect. I installed a matching plate on the opposite side gunwale so the flexibility of each board would match. I didn’t want the gunwales to have an un-even bend on one side, as this could affect the straightness of the frame. More on this later…


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Deck Beams:

Prior to laying out the deck beams the gunwales are placed into spreader forms that give the kayak it’s fish form or tapered shape. These simple plywood forms can be held tight with wedges so they don’t move during construction. Hint: Wedges don’t work! The gunwales can still shift, ever so slightly, and must be checked and re-checked constantly. Ultimately I decided to screw the forward and aft spreaders to my sawhorses. This allowed me to level the kayak (left to right) and reduced the chance of the gunwales slipping out of position. I was then able to check my centre line with both a string and a laser level to ensure the gunwales were perfectly aligned and then I clamped and wedged them firmly in place.

I also checked the ends of the gunwales to ensure they were perfectly matched up. I even used an 18 gauge finish nailer to temporarily pin the ends together. None of this worked either. They still slipped.

Cunningham suggests make the deck beams from 1” x ¾” stock and recommends beefing up deck beams #4 (the foot rest) and beams #7 & #8 (rear deck). He gives no clue as to how much wider or thicker they should be to take the greater strain required in those positions. I figure 2 ½ times larger should just about cover it. I also added ledges under those beams where they attached to the gunwales just for good measure. After laying out the deck beams, marking the tenon locations, sawing them out and test fitting 11 deck beams I was satisfied that I was going to be happy with the shape of the kayak. I did notice that the forward-most and aft-most beams seemed to be not quite perpendicular to the gunwales. In an effort to determine why this optical illusion had manifested itself now, I went back to my forms and again checked the ends of the gunwales to see if they were still lined up. They weren’t. An 1/8th inch slip on the ends of the gunwales had translated into a slight “s” shape bend to the frame of the kayak. Fortunately I had glued my deck beams in already and was saved the trouble of re-aligning (again), re-clamping (again), re-measuring deck beams (again) and re-cutting 22 tenons. The joinery was good though.

Ribs & Stem Bending:

In both the Cunningham book and in a previous forum build, Alaskan Yellow Cedar had been used for ribs. Some people have experienced “issues” steam bending cedar but I was hopeful that given excellent straight grained wood, and a well built steam box I could use the same material for my ribs as for the rest of the kayak. However, rather than test my theory in advance, I was confident that if I just put in the effort up front, I’d have success. It turns out that Western Red Cedar is nothing like Alaskan Yellow cedar when it comes to steam bending.

It’s important to note, at this point in the build, that not everything you read on the Internet is true. (I know what you’re thinking, but sadly, not everything is.) Case in point; when someone claims that their “wall-paper steamer” based steam box can reach a temperature of 212 degrees, they are mistaken. Simple physics dictates that steam cannot reach 212 degrees unless it is pressurized, and trying to get your steam box to 212 degrees is never going to happen. You can get close, 209 degrees is close, but you’ll never get 212 degree STEAM. You can get 212 degree water, but as soon as it turns into steam and leaves the pot, the temperature drops. So stop trying. All you’ll do is boil your pots dry, run through 4 or 5 canisters of propane, melt your way through several sheets of rigid foam insulation and put a lot of water vapour into the air. You’ll never get the temperature in your steam box to 212 degrees. If you think you did, you might need to re-calibrate your thermometer. The good news here is that you don’t actually need 212 degree water vapour (or steam) to successfully bend your ribs. You do however need the right wood. NOT Western Red Cedar.

I built my steam box from 2 ½ inch thick, foil backed, rigid styrofoam insulation. The inside frame was made of 2x4 lumber blocks that allowed me to screw the foam together using a large plastic washer on the end of the screw. This enabled me to make very tight fitting sides that were then sealed with foil tape and then red tuck tape to minimize heat loss. The front had a removable foam door with a wooden handle. A digital cooking thermometer with a range of up to 500 degrees F gave me accurate readings of the internal temperature of the box. A single electric induction burning produced ample steam to reach 209 degrees and hold it steady until the lid was opened.

All of my first batch of ribs were from WRC, thinned on a planer to force the bend into the right spot on the rib, soaked in water for seven days and then steamed for 15 - 30 minutes before being put in the bending jig. Every rib either snapped on the bend or sheared along it’s length. there was no combination of steam time, rib size or temperature that led to success. In short, don’t even try with WRC. Two days of cutting and milling ribs and then their replacements was wasted. After careful consideration I decide to try something radical and source my rib stock from somewhere else. A quick search through the (on-line) yellow pages I thought I would check some of the local flooring suppliers. Afterall they use hardwood for all sorts of things. A trip to Reimer Hardwoods on Monday got me a 10 foot long 2” x 5” of kiln dried ash for under $20. I was a bit concerned that the kiln dried wood might not bend so I did a test piece and it was frankly magical. 15 minutes in the steam box and the piece wrapped itself around my bending jig like a python on a rat. I was back in the boat building business.

I hurriedly set about re-cutting and milling a new batch of ribs, which I then set to soak for a few days before starting again. Of the 24 ribs that I steamed I had one failure that had to be discarded. One rib had the be re-done because the rib mortices had been cut too deep and the rib sat too low in the boat. (I didn’t want to fall back on fairing blocks as this might have taken away from the overall quality of the build… :lol: )

The two stern most ribs were their own special challenge. They are very short and not only have to bend very tightly to fit into the mortice, they also have to be twisted as the mortices are not parallel to each other (wider at the front, narrower at the rear). On my first attempt the rib wrenches that I made severely damaged the inside face of the ribs. It probably wasn’t a structural concern as they don’t take much weight, but I knew I could do a better job so I decide to start over on rib 23 and 24. To compound the difficulty, the extreme bend of the ribs caused the gunwales to split open along their length. A couple of clamps and some reinforcing plates ensured that the splits didn’t compromise the overall strength.

There were a few ribs that had a bit of grain lift, right on the bends, but a clamp on the lifted fibers held them until they cooled and dried. The next day I sanded down the rough spots and they looked perfect. What I thought was going to be the single biggest challenge turned out to be one of the easiest parts of the the build. It was also really satisfying to see the results.


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Keel, Chines & Stems:

With the ribs in place the shape of the kayak was now clear. It was also the time I discovered that having a slight “S” twist to the frame leaves you with a choice to make. A keelson that is centered, or a keelson that is straight, but not both. The slippage on the gunwales early on had now come back to haunt me. After some thought I was able to come up with a fix. Given that the top of the stern plate was clear of the water, it was a simple matter to tilt it slightly to compensate for the twist of the top deck. This left me with a stern that wasn’t centred at the top of the deck, but was centered below the water line. With this simple fix in place I set about lashing the keelson in place.

Another tip, obvious to some, but learned the hard way by me, when winding artificial sinew onto a serving stick, make sure you wrap the twine at overlapping angles. If you just wrap it up like kite string, as soon as you pull it tight the first time it will lock itself together.

It’s actually quite surprising how incredibly strong the artificial sinew is.
In fact, the “V-Y” lashing method is strong enough to break the chines, if you’re not careful. If you have a good clamping rig set up it's relatively easy to replace a broken chine.

It’s also very satisfying when you’ve put a nice sharp edge on a block plane and seeing that first clean shaving come off the new piece of wood. When lashing down the floor boards you can just hank some sinew across your thumb and finger to create a bundle that will fit between keelson and the floor board. the thread holds itself together quite well if you remember to pull on the right spot while tightening.

Skinning and Coating:

The last few steps can get rushed if you’re an impatient person. By this point on the calendar I had expected to be paddling my new kayak. With pool sessions booked for March 15th, I knew I was running short of time so I set about the final stage in earnest. I had decided to use Corey Freedman’s welting cord method to sew up the skin. He makes it look pretty easy on his Youtube video, so it must be pretty simple. One thing I discovered is that following a batten, placed under the skin while sewing is really effective if your batten doesn’t bend left and right every time you touch the boat. I guess a few extra clamps here wouldn’t have been a bad idea. Luckily I learned this lesson on the rear of the boat, so I won’t have to look at the wobbly line while I’m paddling. It does leave a really nice tight skin job. There were only a few very small wrinkles in the cockpit area once the stitching was done. These were easily removed with a hot iron and the skin was drum tight at that point.

While assembling the bending stock for my cockpit hoop I again had to make a decision with no actual measurements available, and only the benefit of my (non) experience to guide me. Cunningham’s book suggests making the riser for the cockpit coaming from 1 ½” stock, but then says to make it shorter for a “rolling kayak” if you want to avoid having the cockpit rim dig into your back. This seemed like a good idea so I reduced the height of the riser to 1” but when I had run it through the planer to smooth it out wound up closer to ⅞ “. With a coaming flange at 7/16” I had just under ½” of space between the top of the deck and the underside of the flange. Perfectly adequate for a spray skirt or a seasock. But not both! Doh! I did dress up the coaming quite nicely with some decorative brass screws though. Looks pretty good, if I can say so myself.

The most challenging part of the build was coating the skin with Spirit Line Poly Urethane. It had watched several of the Skin Boat Schools online videos prior to beginning. The instructions indicate that the poly will continue to flow for up to two hours after mixing. It’s actually much longer than that. The flow rate just get’s slower, but it will still leave sizeable drips if you’re not there to babysit the goop for hours and hours after coating it. Resist the temptation to use a paint brush on any area other than the seams at the end of the boat. Also, buy a jumbo box of latex gloves. You’ll need about 30 pairs.

Having used rare earth pigment to tint the material, I’m confident that I will never use it again. The finished colour is totally mottled and inconsistent. Adding more pigment to the second and third coating doesn’t seem to help. I might try acid dying next time or just leaving it white. On the upside, I’ve yet to see a modern SOF kayak that more closely resembles actual Seal Skin. Smells different though. Better, actually.

So now it’s done. It floats and there’s really nothing so satisfying as paddling your own, handmade kayak. I can’t wait to start the next one.

Feel free to comment. You certainly won't hurt my feelings, no matter how blunt you are.


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Nice job, and excellent description! Thanks!
Ash and yellow cedar are both great bending woods. WRC is plentiful and pretty and light, but it can be quite brittle, IME. So it was a 'wood selection problem' not a technique problem that you encountered! :D
If you build another SOF I would not recommend using acid dyes. For fly tying, I dye some materials myself. I had one fly that was black when it I gave it to a friend. He placed the fly in his hat band and wore it all summer. The black faded to cerise before fading to white. Don't know of any material that you could place over the dyed material to UV stabilize it so it won't bleach out.
The kayak looks fantastic and I really enjoyed the story. Relived a whole bunch of moments from my first one. The ribs were an especially not so memorable moment for me too, until, like you, I tried ash and then really enjoyed it. Turned into one of the nicest parts of the build. I like the mottled look of the skin coloring, more natural looking to me. Have fun with the next one, it's hard to stop after the first.
Congratulations and thanks for posting the build.

:clap: It looks absolutely stunning! I am so happy for you... I know exactly how you feel. I really enjoyed the story of your build. Thanks so much for sharing with us.

Jill said:
It turned out great! Hows the rolling?

The lake was a bit chilly yesterday (2.2 Degrees C) for anything more than a quick sculling brace. I've got a pool session booked through the club for this weekend so I'll let you know on Saturday. I expect it to roll like a barrel.