SOF - mixing fabric weights

Submitted by traveler on Wed, 03/18/2020 - 07:45

About to start skinning a 16 foot fuselage frame, touring style skin on frame kayak, primarily for light duty overnight tripping. Trying a few things to keep the weight down while ensuring respectable durability, and was thinking that I might shave a couple of pounds off by using a heavier fabric only on the bottom up to the gunnel (e.g. 9 ounce poly or 12 ounce nylon), and a light fabric (3 ounce Dacron) for the  deck, where presumably there wouldn't be much stress/abrasion risk. Would staple both top and bottom halves along the gunnel and cover with a lightweight cedar rub strip. Anyone done this? Any reason why it would be a bad idea from a structural (or other)  point of view? Thanks all

I have built six skin on frame kayaks, haven't tried mixing fabrics. I think I would sew the fabric together not mixing nylon and polyester or Dacron   I don't know what kind of abuse yours will see but my in my experience nylon with Cory's goop is the toughest finish I tried. After ten years of abuse on 15' Sea Tour EXP it's still water tight. It shows some loosening on cool humid days but tightens when humidity drops. Polyester with other finishes has proven to require more care to avoid damage. I brushed a oyster shell with my traditional framed Greenland skinned in 8 oz polyester putting 6" slit in the skin by my foot. Even with float bags made to fit this kayak it was un-paddlable.

George

Thanks George - I am perhaps too fixated on keeping weight down, and looking for ounces where I can find them. I am at about 21 pounds with the frame only, excluding the coaming, and hoping to end up with something under 35 pounds overall, but not at the expense of a durable kayak. Do you have a ballpark idea as to how much weight a 12 ounce nylon skin would add? Thanks again.

What length kayak? 15'-16' I would guess 12lb. Total guess. My 15' EXP came in below 27lb with 8oz nylon and Corey's goop, very durable. My 17' Greenland with 8oz polyester around 25lb, not so durable.

Thomas Duncan

Thu, 03/19/2020 - 13:48

Some years back a fellow Robert Morris devised a method of skinning w/o sewing. It involves burying a spline in the gunwale. 

You can read old forum posts: http://www.kayakforum.com/cgi-bin/Building/index.cgi/md/read/id/218490/…

And the issue of the Masik newsletter mentioned is here: https://s3.amazonaws.com/ClubExpressClubFiles/349669/documents/Masik_Su…

The article is on page 14. 

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I've never done that method, but have made several 17ish foot SOF, with big box store wood (selected for availability and cost not nice weight) skinned with 9ish ounce nylon and others with equivalent polyester. They all come out about 35#, whether it's Corey's Goop or just varnish paint. Skins seem to add about 8lbs if I recall. 

The reason you want polyester -- it doesn't stretch near as much, and won't go slack when it's wet. I've run over oysters with polyester and varnish paint skin w/o damage, but it was a light graze. I've seen gooped nylon skins be cut on barnacles on cypress knees. So... Polyester can be more difficult to sew, but if you get the kind you can shrink with a heat gun, then you can sew it on comfortably tight and shrink it up after. It'll stay like that, unlike nylon, that you have to sew on soaking wet and stretched, then it loosens up anyway when it gets wet enough again. Less so perhaps if it is encased in urethane. I think I'd only mix the two if they were unattached from each other, and the spline method might be the trick. If I was going to sew them together I'd want to maybe get an awning shop or something to do it, or get my own thread injector and learn to run it. 

 

Hope that helps! Or confuses! Or maybe even start an argument! ; ) 

Thanks Thomas. Good information, and not confusing - just confirms that within certain boundaries there is no single "absolutely correct" way to do things for SOF builds (just like building with cedar strips, and most other things in life too I guess).  While I am anxious to make sure I have a serviceable boat, this is more liberating than confusing.  I have read a fair bit about the grand polyester vs nylon skin debate, plus I have seen a bit of chatter on various forums about successful application of a thin, flexible layer of fibreglass cloth and epoxy over Dacron as a third alternative.  I have the material on hand for any of these techniques - looks like I have a decision to make.  Thanks again.

Just FYI, went with 12 ounce nylon all around, with center stitch. Getting the skin on actually went fine, despite a couple of weeks of angst and second-guessing beforehand. Now hope I don't ruin it with the coating (again, too many options to mull over).

Photo of nearly completed SOF, drying in the sun