floating

curing

waterproofing

Tuesday 4 May 2010: I've been slathering coats of Target 9300 water-based polyurethane coating on the skin to waterproof it. First doing the hull, then an hour-and-a-half or two later flipping it and doing the deck. This coating has been used by David Mills, aka "stumpy" who posts regularly on the Blue Heron Kayaks' Kayak Builders' bulletin board for some years. David has been using this on nylon fabric. I was surprised to hear that because everything I have heard about nylon is that most things won't stick to it, or will be too inelastic and subject to failure when the nylon stretches beyond the limits of the coating.

By the way, if it seems like I am growing less enthusiastic about updating this blog, it is mainly because the editing interface is terrible, and especially the process of inserting these images, and linking them back to my website is an enormous pain-in-the-ass. I find it so frustrating to manage that I am ready to consider that finding myself in a situation where it might be necessary to resort to cannibalism to in order to survive, would be preferable to finding myself in a situation where it is necessary to create or edit posts using this crappy web interface!  That's all I'll say about this right now because it has worn me down and I am tired of fighting with it....

Anyway, where was I?  A nice long thread was started on Blue Heron's Kayak building forum about fabric for skin-on-frame kayaks. This thread rambled along for awhile and contains a lot of interesting information about fabric choice for skinning. But eventually David gives a nice explanation of the specific water-based polyurethane sealer he has been using for a few years; and how he applies it. Did I mention that there are many who would advise against use of water-based poly? The experience of some who have tried is that it would get soft and turn whitish when it gets wet; or that it might even just peel off in sheets. The only two references I have for positive results using water-based poly come from Robert Morris, in his book, "Building Skin-on-Frame Boats", and from posts on the Qayaq USA bulletin board by Turner Wilson. Robert Morris mentions that an interesting characteristic of water-based poly when used as a sealant, is that it does not stick to wax. So that by waxing the frame, it is possible to prevent the skin from becoming glued to the frame by the sealant. Probably I am crazy, but this idea appealed to me. Just noticing, how springy and alive the lashed frame is when it is bare, made me interested in trying to preserve that feel in the boat after it has been skinned. So the frame had been oiled with tung oil and then waxed with some Meguires paste wax before skinning. 

Another strong motivation for my interest in water-based polyurethane is a desire to find a boat building technique that is less toxic, and that generates less waste. This was a big part of what motivated my interest in skin-on-frame boats.

The Target water-based polyurethane was very easy to use. Since it is water-based, it is very low on volatile organic compounds. Everything can be cleaned up with water. There are no volatile thinners or solvents required. The same brush can be used throughout so there is much less waste. It is very much like working with acrylic paint. In fact, ordinary acrylic paints can be used to tint the Target coating. David Mills has some very nice examples of whimsically painted boats colored in this manner. In fact, I mixed a little titanium dioxide into the layers that I put on the deck. I did that to make it a little more reflective in hopes that would help to keep it cooler in hot weather.

There is a specific technique for using the Target coating successfully that was developed by David in consultation with Target. The technique is to use coating that has been thinned with water to a concentration of 50%. Special care is taken with the first two coats using the thinned sealer, to work the coating into the weave of the fabric as thoroughly as possible. Since David has been using this coating on nylon, that instruction is likely especially important in that case. With the rather loosely woven polyester fabric I am using, it is quite easy to work the coating into the weave. I followed the same procedure, using two initial coats of coating thinned 50%. After that I just slathered on 6 or 7 coats and used the good part of a gallon! I laid down the rice-paper ensos onto the bow with the first coat of full-strength coating.

The second instruction to be observed, is to allow the coating to cure for 72 hours before exposing it to water.

In the picture below, you can see some of the pull-holes that opened up while I was sewing this very loosely-woven, 8 oz. polyester cloth. Over many coats (6 or 7) the Target coating eventually filled these holes right up. You can see how the boat is leaning to one side on the starboard bottom panel and so I can apply a very thick coat of polyurethane and allow it to run up against the center seam which traps it where it can fill in the holes. Neat. I'd like to type some more stuff after this picture, but this crappy editor makes it impossible to get a cursor down there without deleting the image and reloading it. This makes me sad.

shrinkage

Sunday 5 May 2010: The afternoon was sultry. I spent an hour or two out on the deck in the hot sun with a hot heat gun shrinking the fabric nice and tight. Perhaps I should have used an iron, but I have a heat gun that has pretty good temperature controls and decided to try that. I was quite conservative with it at first, not wanting to burn a hole or catch the house on fire or anything. So it took me a little while to get the proper temperature, and acquire a feel for the skin tightening under one hand, while I was aiming the gun at it using the other hand. I was concerned about opening up the pull holes again while tightening. And my concerns were justified. I also wasn't sure how tight I should make things. So I did enough to take out the wrinkles but didn't get carried away. It is tight, but not drum tight. Set it out in the yard to take some pictures of how things are before I start waterproofing.

skins

Sunday 17 April 2010: Following the method shown in the skinboats school videos,  I roll out the cloth -- 8 oz. polyester from George Dyson -- and sew a small pocket on the bow. Then I unhook this pocket from the bow, walk to the stern and pull the cloth back about 3 inches and sew a pocket there. This is where the trouble starts. I should note that skinboats school uses nylon rather than polyester in the very helpful videos they provide. I'm guessing that their nylon is a little more stretchy than the polyester that I am using. Also this polyester is very loosely-woven. It doesn't take much to open up large pull-holes in the cloth if stitches are subjected to any tension. So I pulled and pulled and opened up ugly holes and backed off and restitched and pulled and there may have been some foul language involved. In fact, I'm certain there was substantial amount of foul language involved. But so far, no cannibalism -- that was right out. Throughout this frustrating beginning, I was coming to understand the nature of this cloth that I have, and decided that a better approach would be to only make things as tight as can be pulled without opening substantial holes. I managed to get the cloth tight enough end-to-end that there are no obvious wrinkles across the hull.

So Monday I rolled the boat right-side up, and started the center seam from the cockpit, forward to the bow. Again, where the skinboat videos demonstrate better ability to pull transverse tension in the center seam to make it nice and tight, too much tension in this fabric opens holes. I manage to find a compromise where enough tension is pulled to result in a reasonably wrinkle-free skin, while keeping the pull-holes manageable. So the skin goes on with little-to-no obvious wrinkles, but it is not as tight as might be possible with a more tightly woven fabric. An advantage to polyester, is that it can be permanently shrunk in the end using an iron or heat gun. So hopefully, it is not necessary to worry so much about getting it quite as tight during the initial stitching. I'll have a better feel for how that works when this is finished:)

Over the next few evenings, I stitch up the stern and then use a blind stitch to roll the excess cloth at the seam over into a tube:

Basic stitching is mostly done. I also steam bent one last thin strip of ash around the cockpit coaming lip to build it up to be wide enough to provide a good hold for a spray skirt. I've put some last little smoodges of wood-flour thickened epoxy into some gaps here and there between the various strips that make up the cockpit coaming lip. It only needs to cure overnight, some finish sanding and stitch holes drilled before it will be ready to sew into the skin.

I've also accumulated the materials to make float bags and ordered 2 gallons of water-based exterior polyurethane coating to waterproof the skin. That will be a bit of an experiment about which more later.

bones

Sunday 4 April 2010: I only just summoned the will to proceed a bit further this weekend after picking up a cold weekend before last. But the time has come to get this one done. Last week I received 40 feet of 8 oz. polyester fabric from George Dyson. He shipped the day after I had emailed the order on the basis of my word that the check was in the mail. It arrived USPS Priority Mail from Bellingham, WA, 2 days later. Outstanding service. I was expecting that to take a week or two. I unpacked the cloth and rolled it onto a section of 4 inch diameter PVC tubing to let the creases resulting from being folded, to relax.
 
Today is a beautiful day, I took the frame out on the deck and cleaned up the deck stringers. I also cut a small piece of cedar gunwale stock to place on top of the masik to lift the forward deck stringers a bit higher. I put a couple of oak pegs in the the top of the masik to lock it in place and glued it to the top of the masik with some Titebond III waterproof glue.

I lashed all the stringers down and then brushed tung oil on the frame. I may add a lashing here and there to the bow and stern plates, and redo one or two lashings. But I think this is more or less ready to be skinned.

Time to review the videos at skinboat skool:
http://www.skinboats.org/skinboats/sewing_your_west_greenland_kayak.html

Instructions at Cape Falcon Kayak:
http://capefalconkayak.com/howtoskinakayak.html

And the relevant sections of Robert Morris's, Chris Cunningham's, Mark Starr's books on building skin-on-frame boats.

The bones are exhaling tung oil vapors this week and should be about ready for skin this coming weekend.

i torture the timbers

Sunday 14 March 2010: Over the last couple of weeks I have been experimenting with various ways to fail at steam bending a cockpit coaming from red oak. The process began in the last week of February when I sketched a coaming outline, 23 inches long by 16 inches wide out of poster board. I transferred this pattern to MDF and cut it out on the bandsaw. After drilling holes to allow for clamping, and hammering it all together I had a jig for steam-bending the cockpit coaming.

This jig is taken mostly from Chris Cunningham's book, Building the Greenland Kayak and uses a strip of aluminum flashing that wraps around the outside of the piece being bent to help support the wood and prevent splits from developing.

Though it is not the ideal material, I so far have nothing better to try than some kiln-dried red oak 2x4 from Home Despot. I ripped it down into strips about 1-1/4 inch tall, 3/8 inch thick. The strips were then cut to length -- the circumference of the form, plus 12 inches -- and then the 12 inches at each end are planed to make a long scarf joint where the ends overlap when wrapped around the jig. My first try almost worked. But I was too slow getting it clamped down, and it was a rather cool windy day, so that it came out somewhat asymmetric. The section near one end where I started the bend held close to the form. The other side and far end of the strip had cooled too much by the time I got it clamped and so didn't bend as easily. This resulted in a somewhat lopsided coaming. I may try to fix it with a heat gun. This is a general problem with the approach of bending by starting at one end of the strip and wrapping it around. You have to work very fast. It seems easier to get symmetry by marking the spot where the strip crosses the center of the cockpit at the front, clamp there first and work both sides back together. But that would make it more difficult to use the aluminum flashing to contain the strip. I'm still pondering whether the ability to brace the outside of the bend with the flashing is worth the potential for asymmetry induced by uneven cooling when wrapping around from one end to the other. I used the end-to-end approach with the aluminum flashing for 3 coaming attempts. But when I later tried to bend the coaming lips, I tried bending them from the front of the coaming symmetric around to the sides.

My second try at a coaming cracked right at the front of the cockpit, where the radius is the tightest due to some grain runout there. By the third try, I finally got a reasonable coaming.

This strip was just under 3/8 inches thick and was steamed for about 30 minutes before bending. I glued with epoxy thickened with wood flour and it looks good enough:

I have since failed on three attempts to bend a coaming lip from strips 3/8 inch by 3/8 inch. Two tries lost to grain runout; the third try today almost worked. The strip came out of the steamer very pliable and went around the form quite nicely. But it insisted on twisting so that the top of the coaming lip wanted to twist to the inside by the time it was wrapped all the way around. I was not able to fix the twisting before the strip cooled off too much and I snapped it while trying to get it to lie flat. Probably it would be better to bend the coaming lip around the bottom of the form where it can be braced against the base. I tried to bend it around near the top of the coaming where it would be in actual use but this made it easier for the strip to develop twist as I was bending it.

I finally was able to contact someone at Garman Brothers lumberyard near Annapolis to inquire about obtaining green, white oak. White oak or ash would be preferable for this purpose, especially if it was still green. I guess I'll try to get out there sometime this week to take a look. This is rough-cut lumber used for exterior fencing and construction so it sounds like a job to pick through and find some suitable boards. I may need to buy a planer, or find someone to surface it for me. Guess I'll take a look first to see if I can even find some suitable boards. This stuff is cheap at least. Exotic Hardwoods in Gaithersburg claims to have quartersawn white oak, but it is all kiln dried and expensive.

I also got in touch with George Dyson to inquire about material for skinning. He sent these PDF files describing the various weights and weaves of nylon and polyester fabrics available. I'm thinking about going with an 8 oz polyester skin and water-based polyurethane coating. I'll order the fabric this week. I also need to order vinyl material to make float bags. Float bags are necessary because this kayak will not have any watertight compartments. Inflatable bags maintain positive buoyancy in the event the frame is flooded.

The frame can be finished and oiled at any time and will then be ready to be skinned. If I can just get a reasonable cockpit coaming, everything will fall into place to finish this off.