Is 9oz. fiberglass cloth too heavy for my Rob Roy?

[David James]

Hi folks,

I am currently building a little 13' RobRoy and it's just about ready for 'glassing.

I'm considering using 9oz. fiberglass cloth. Typically 6oz. is recommended, sometimes with an added extra layer over the football region.
I happen to have some 9oz. cloth ("e" weave, 44" wide) and wonder if it would be too heavy to use, and what sort of problems I might have with it.
My thinking: for my first canoe (Freedom 17) I used 6oz. inside and
out for an overall weight of 12oz. Now for the Rob Roy I would use the
9oz. on the outside and then go with 4oz. on the inside, for a total
fiberglass weight of 13oz.

I'm thinking an initial seal coat of epoxy might not be a bad idea for
the outside 9oz. wet out. I suppose I should really put together a
test panel (maybe 1 ft by 2 ft?) of redwood strips and see how well
the 9oz. wets out.
Also, I've decided to go with MAS epoxy with the slow hardener this
time around. I used West Systems for my first canoe.

I would sure appreciate some feedback on this.

Thanks very much, Dave

[vann evans]

Hello Dave,
I think the 4 oz cloth is perfect for the inside. I also used the 6 oz cloth on the outside along with an extra layer of 4 oz on the outside football for my Freedom 15. This seems to be a great combination.

I have not used 9 oz cloth. I would be afraid that the 9 oz cloth would have several basic downsides-1)-it would be stiffer, and thus harder to conform to the curves, 2) it would take more epoxy resin to wet out, making the entire boat more expensive and heavier than necessary,3)it would take more epoxy coats to fill a thicker weave, again adding more weight and expense for epoxy.

I would certainly recommend using a precoat of epoxy before applying the glass layer of any weight. I think it would be particularly important if you use the heavier cloth because that 9 oz material would be harder to wet out and would soak up more resin. Without the precoat, it could leave the wood resin starved and create bubbles.

my opinion only-if you go to the expense and trouble to build a beautiful boat, go the extra mile and buy the right cloth, don't use something that may not work just because you already have it on hand.

Vann Evans

[Juneaudave]

My experience with 9 oz is that it is very hard to wet out even if you warm the epoxy. The test panel is a good idea...but a small panel might not give a a good "feel" for how difficult it is going to wet out.

I do like MAS slow though...working alone, you have plenty of time to get things right and work at a more leisurely pace. I typically wetout in the evening, wake up early for the fill coat in the morning and build coat in the afternoon. It has been a very reliable and predictable epoxy for me....Dave

[AlanWS]

The test panel will answer the biggest question, of how well the 9 oz cloth wets out. You might want to do part with a seal coat of epoxy to see how much difference there is in the amount of epoxy you need to get to soak in. Slow setting low viscosity epoxy seems like the right approach.

Extra glass on the outside will help with abrasion, but keep in mind that if you hit a rock in the canoe, it's the cloth on the inside that provides hull strength. For that reason, the combination of 4 oz and 9 oz glass sounds odd to me, though 4 oz may be strong enough.

[David James]

Thanks for your feedback guys.

I'm beginning to lean towards a 4oz. inside / 6oz. outside combination. The fact is, I have a whole roll of 9oz. 44" wide and thought, well, why not use it. One reason why is the Rob Roy hull has turned out better than expected; feature strips, no staples, etc. Why be cheap with a canoe I've worked on for two years? Another reason is maybe I should worry less about wear and tear and concentrate more on keeping overall weight down. Afterall, this canoe will likely see only light duty.

Anybody ever go with 4oz. inside and out?

Dave

[Glen Smith]

I have glassed a few boats (canoes & kayaks) with a single layer of 4 oz cloth inside and out. It suits my light-duty use and reduces the weight. My 12 foot self-designed canoe weighs 29 pounds.

[Rick]

Anybody ever go with 4oz. inside and out?

Other builders of small and light pack canoes have done this, so they can be portaged long distances more easily.

[doe4rae]

I heard that generally you should use the same weight of cloth on the inside as the outside... or if you feel you want to add strength to the boat then the extra layer should go inside where it will protect better from impact that happens to the outside of the hull. If your primary concern is abrasion resistance, then, a little extra in the football region would be helpful maybe. However, having had my canoe out a few times now, I see the little scratches and abrasions that have happened and I know an extra layer of cloth would not have prevented those.... they would have happened to the outer most layer anyway and still have to be repaired or dealt with at the end of the season. So... in my opinion - and with my limited experience-- the "tried and true" of 6 oz. inside and out is going to suffice for most purposes. Of course I'm from the Midwest and my canoe has never seen whitewater. The biggest threat to my boat is probably mud and driving to and from the lake!

[Moonman]

re 4 oz cloth, this article is very interesting. Might be pushing it on such a big boat as mentioned in the article but should be no probs for a Rob Roy.

Regards,

Moonman.

http://www.smallboatforum.com/PDFfiles/ ... Canoes.pdf

[sedges]

I once used a 9 ounce satin weave cloth on the outside of a 15 foot solo canoe. The inside had two piece of 4 ounce that overlapped below the waterline. The 9 ounce satin weave is really tough, but the canoe is heavy for its size. It takes a lot of resin to fill the cloth. If I was building a whitewater boat or a woodstrip power boat I would use it again. The Rob Roy is designed to by light and easily carried, why put extra weight if it is not necessary.

[Sherm]

O.K. my "two-cents". 6 oz. on the outside 4 oz on the inside. Used it on two 15ft canoes.
Plenty strong, With the Rob-Roy; should-be even stronger.

[David James]

Thanks everybody for your thoughts on this.

I've decided to go with 4oz. inside and out, with maybe a bit of extra cloth for the football area. I stripped the hull with thinner srtips to begin with, so I'll go with the lighter cloth / philosophy. I'll be wetting out with MAS epoxy with slow hardener.

Thanks again for all your thoughtful replies.

Dave