Fiberglass question(s).

[Wing Zero]

I've been looking at making a fiberglass hull of about 6 feet in length. No real internal supports other then a few bulkheads, but I have concerns. I've heard that fiberglass (epoxy) hulls in heat, will sag. Especially ones that are heavier in the center, such as destroyers and battleships. As I understand it, I've heard they say you have to "Cure" the fiberglass using almost like a heat treat to prevent it from sagging, using U.V. lamps. Does anyone know about this? I read a while back, about a small battleship made with a fiberglass hull that was left in the back of a jeep wrangler during warm weather, in which the model had just the bow an stern supported as it stretched the width of the vehicle, resting on the fender wells. The top was left up, during 90 degree weather, with the model in a direct position of the sun. The owner said the model bubbled, sagged, and the paint softened. Can someone please tell me more about fiberglass when it comes to heat, and sunlight? How to best protect it, and paints on it. I made a few hulls, but this one would be very unsupported inside, using the fiberglass shell as a strong stiff hull. Thank you. -James

[P. Tritle]

James, I used to have problems with fiberglass cowls on airplanes turning to "rubber" when they got hot, but the problem went away when I abandoned "hobby quality" resins for the "full scale" grade, my favorite being West Systems. Or, you could go with a "full scale" marine grade polyester. If in doubt, it would be easy enough to lay carbon fiber into the basic lay-up down the length of the hull in several places. If the lay-up is adequately thick, and using good quality materials, I can't imagine a 6' hull being any problem at all.
PAT

[Wing Zero]

Thanks for the reply. Is the difference between hobby quality and full scale quality a matter of U.V. or heat stable formulas? I'm just not understanding exactly, why one epoxy made for a hobby would differ so much from a larger type of hobby or recreational use. If full scale systems are fine dealing with heat, what about U.V.? Sunlight have any effects on it? Is there a paint, that would be better suited to U.V. protection than others? Thanks again.

[martin richards]

I don't know the rules in America, but here in Spain, if you want to register a boat over a certain size, you have to be able to prove it was built to professional standards using industry recognised materials. I'd guess most polyester or epoxy resins sold by the hobby trade are not up to the strict boat building standards and, judging by my attempts to glass, the lay-up standards are probably as equally dubious:rolleyes:

[LtDoc]

Speaking of fibreglass... I just did my first 'glassing' of a boat. It is a disaster, to put it mildly. The first 'half' of the lay up went pretty well, but the longer it took, the worse it got. Guess it was a combination of not working fast enough and probably an incorrect mix. [Did this outside, the neighbors must'a thought I'd hurt my self from the screaming.] Ended up with bubbles, floppy edges, and other goofs I don't even know what to call. The sandpaper industry had better put another plant on line, I'm gonna need some.
- 'Doc

PS - Anyone know of any 'miracle' product or procedures to help?

[P. Tritle]

Wing, In my experience, you can usually spot the "cheap" resin by the way it sands. High quality resins cure hard and sands to dust, where the cheap stuff usually rolls off in little rubbery globules and clogs the sandpaper rather quickly. Most of the time its stays relatively plyable, where the good stuffs remains firm.
Another thing that is common with low end resins is that the pot life can be radiaclly inconsistant. Sometimes a "30 minute" epoxy will fire of in as little as 15 minutes, or as long as an hour. The trouble is, you never know which one you have until it kicks! With the good stuff, you can just about set your watch by it.
Funny thing is, the good stuff is actually no more expensive to use then the hobby stuff. I buy West Systems for around $85 per gallon. If I bought the same quantity of the other stuff, by weight, at $9.95 for 9 oz, the 150 oz of good stuff I get for $85.00 would cost $165.00, but I could do it $10.00 at a time, where with the good stuff, you have to buy it all at once. West Systems can also be bought in smaller quantities, but the cost goes up accordingly.

Doc, I know hind sight is always 20/20, but the best bet is to mix realatively small quantities of material until you get a feel for the pot life. Also, the larger the mix, the more heat it will generate in the pot, and the faster it will fire off. Unfortunately, the only secret weapons you have now are sandpaper, and elbow grease!!!!
PAT

[LtDoc]

Spent 4 hours sanding, lost count of the number of sheets of sand paper. Used a 'Mouse' sander to save my strength for work (hmmm). Got things smooth sort of, at least much better than to start with. Mixed something like a 1/4 of what I did to start with (all advice gratefully accepted, and thanks). Thinned it down quite a bit. Brushed on a second coat. Wait a few hours and my that shines nice! Except for the itty-bitty dimples(?). Huh, wonder what that's from. More sanding...

The resin I'm using is from an auto paint store, they claim it's very good. I think I don't want to mix different kinds of resin, so the next boat is going to be with the 'WestSystem' stuff. Ought to be much easier to mix (no tubes of hardener and S.W.A.G.'ing at the number of drops). I did say the 'next' boat, so I'm not as discouraged as I was. It's gonna be a while though! [Doubt if the neighbors could take the excitement.]
- 'Doc

[P. Tritle]

Doc, Based on your comment about "counting drops" it sounds like you're using Polyester Resin. I used that stuff for years -- and loved the smell, even though my wife DIDN"T -- but gave up on it do to it's extremely short pot life. Seems like no matter how hard I tried, I could never get the mix quite right. The good news, if you do switch to West, you'll get the same results every time! That will give you a chance to work on your technique without having to worry about waht the resin is going to pull next.
PAT

[LtDoc]

Pat,
Yep, you guessed right. Oh well. I seem to learn best by making mistakes (not recommended, by the way), so I'm at least getting an education.

Now I've got one of 'those' questions. I'm sure you've seen the plastic/rubber/vynol or whatever coated picnic tables/benches. There's a company here that does that, and I've been wondering if it would be useful/possible to do the same thing for boat hulls. Seems like having a built-in, full coverage 'bumper' on a boat would be a nice thing to have. Not much for strength, I would imagine, but...?
- 'Doc