Epoxy glass laminate- how thin should you go?

[Guest]

I'm aware of the thickness of many commercial epoxy glass submarine hulls. I've laid up a very small epoxy glass hull, but until now have only moulded larger hulls in polyester. However I wish to mould a larger boat in epoxy glass. It has a high freeboard, so I want to minimise displacement as much as is feasible. The boat is about four feet long, but is split into four discrete sections, also the boat will only have radial splits, so the main body will be a stiff homogeneous monocoque. The hull will be wet hulled, so only handling and the ability to take the odd bounce will be required.

Looking at model aeroplane builders, specifically lay-up's for pylon racers, they tend to use very thin lay-ups consisting of three to four layers of 2 oz cloth. I was thinking something a little thicker, maybe an extra layer or two of 4 oz.

Opinions?

[KevinMC]

Re: Epoxy glass laminate- how thin should you go?

Hi Andy,

When I was laying up OSCAR hulls I had similar concerns, but I took different approaches above and below the waterline. Everything below was a layed up with a "typical thickness" to maintain rash resistance. Everything above was layed up with "aircraft thickness" (or should I say "thin-ness") to minimize the required ballast tank size to get her to sit at the waterline. If I recall correctly I was down to a 2 oz layer and a 6 oz layer with 1" wide chopped fiber mat "ribs" layed in at 12" intervals between the two cloth layers. All my hulls were epoxy.

I think you're on the right track planning to use only a couple of layers of 4 oz. Of course hull shape will also have much to do with how well this works out - if your hull is essentially tear drop shaped you'll do well, but if it's got lots of corners and flat sides you may need to bulk up a little more in places. Experimentation is necessary, but I don't need to tell you that. (I suspect there's probably also value in using similar cloth weight across the layers as well, so four layers of 2 oz would be better than a 2 oz and a 6 oz set, but I never proved that out.)

Cheers!

[Guest]

Re: Epoxy glass laminate- how thin should you go?

Okay, good feedback, thanks.

The boat I'm moulding is the one shown in my avatar. Not exactly a teardrop shaped, but plenty of curves.

[thor]

Re: Epoxy glass laminate- how thin should you go?

On boats of length under 48" and less than 6" beam I use a single 2 oz surface cloth, followed by 2 x 4 oz structural layers. In between the 2-4 oz layers I run a stringer of 1" wide carbon fiber tape within 1" of the edge of the part for rigidity. If you choose to eliminate the carbon tape I would suggest an additional laminate of 4 oz glass or a 2" wide tape all around the perimeter of the part.

Matt

[Guest]

Re: Epoxy glass laminate- how thin should you go?

I thought of running a bit of carbon reinforcement here and there.

The boat is exactly four feet long, but owing to it's rather unorthodox design, it's really like a much smaller boat with bits tacked on. The main hull is 28" long, with a 6.5" barb on the front, the rear end accounts for about 9", with the props making up the rest. The props I plan to cast from PU resin, reinforced with carbon. There will be a central tube running down the middle, which will also be a composite item. That will link the stern with the forward part.

There will be no breaks in the main part of the hull, the module will slide in radially from the back, so it should be a lot stiffer than hulls which are split equatorially.