Boat skin - Polytarp?

[mike160304]

My coracle has a calico skin, 200 gsm (grammes per square metre), with 6 coats of bituminous roof paint on the outside only.

I am wondering whether Polytarp would make a good skin for a canoe or small boat. Polytarp is cheap and easily sourced, e.g. there's a 186 gsm, 16' x 12' Polytarp on Ebay for £19.95 delivered.

http://www.ebay.co.uk/itm/260900312485?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I can imagine myself and a helper or two warming it up with hand-held fan heaters and then stretching it onto the frame and round the gunwale and stapling it down with type 53 staples, then fixing an inwale and outwale with screws only, so that the skin can easily be replaced later.

I already use 90 gsm Polytarp for sails and I like it a lot.

Any advice on boat skin please?

Mike

[mike160304]

No skin boat buffs here, then?

Mike

[AdrianG]

Hi Mike

I suspect we're all wondering if Polytarp would make a good skin, too. How pioneering do you feel? Sounds like a worthwhile experiment to me.

Good luck and kind regards
Adrian

[mike160304]

Thanks Adrian,

Yes, right now Paul Fisher has designed for me a pram/scow called the Surf 8', kind of Skylark 8 Mk 2 on steroids, for serious sail-carrying.

With ultralight 5mm (5.0mm measured) 3-ply Okoume marine plywood, the stitch-and-tape hull, plywood only, excluding frames, tape, epoxy, etc, will weigh about 9.33kg/20.5lb - it's about 4.29 sq metres.
 
I could reduce the weight by using "3mm" (3.15mm measured) Robbins Elite for the whole hull (7.43kg/16.4lb) or the 5mm 3-ply for the "bottom " and 3.15mm for the "sides"(ca 8.38kg/18.4lb) but I doubt it is worth it, more stiffening might be required.
 
The whole skin using the 185gsm Polytarp would weigh about 832 grammes/1.83lb . . . errr, plus the spruce frame. Hmmmmm. I would probably go to the next thickness Polytarp up, whatever that is. Seductive figures though.

As I have a lot of spruce here I bought in 1955 (!!!) for a mast, I have a tempting opportunity for some ultralight framing.

I suspect Surf 8 will be made of the 5mm plywood, as my wife is then more likely to get into the boat, but I have some ideas for the spruce-and-Polytarp for the future, if I have one.

Mike
 

[mike160304]

My current project is not skin-on-frame, so any conclusions about skin for skin-on-frame are for future consideration. Anyway:

1.  My inspiration would be "coracle/working boat", not "kayaks/canoes" where greater cosmetic perfection is usually striven for. Function not form. As in 800 AD.

2.  I might try, at my own risk, heavier polytarp/polyethylene tarpaulin, or vinyl tarpaulin, both of which are used on trucks etc and need no sealing or coating. I would discuss this with tarpaulin makers here in the UK.
The tarp would be stapled to the gunwale only, exactly as done on coracles, with "folds" sewn where needed on "corners". I would not be aiming for cosmetic perfection and it would be quick and easy to remove the skin if I did not like it.

3.  If looking for best function, I would phone George Dyson in USA and discuss ballistic nylon, and find out what urethane (polyurethane in UK?) coatings are best, and whether they could be opaque paint, not clear, as I would not want a translucent hull.

Mike