Cord

iTrader: (2)

I need some edukatin on boat layups. I hear a lot of talk about different types of resins, coring and stringer systems. Which systems are better than others? Why?

Ok, to get this started I'm going to repost a layup that sharkey posted:

Bottom: 3/4oz mat, 2 layers of 1708 bi-directional cloth, 3/4oz mat, 1/2" Blatek balsa coring, 2 layers of 1708 bi-directional cloth.
Side: 3/4oz mat, 1 layer of 1708 bi-directional cloth.
The layup was not vacuum bagged, vinyl-ester resin was used.

Ok, now his friend suggested a different layup:

3/4 oz mat, 1 layer of 1708 bi-directional cloth, Airex coring, 1 layer of 1708 bi-directional cloth
The layup was vacuum bagged, but I don't know what resin was used.

So which layup is the superior one? Lighter? Stronger? Is one layer of cloth really enough? Why do some mfr's use 1/4" coring in the sides and deck? I was thinking of using fir stringers, but should it be Douglas Fir? Does it need to be clear wood? If not what grade? Why do some boats run 3/4 length stringers? When are full stringers not needed? Then what about bulk heads? I've seen some boats with plywood and other boats with balsa bulkheads. It seems as if balsa would have some really terrible shear properties. Can you spray gel coat with a regular paint gun or does it take a special one? Do I need to go on?

CigDaze

Lots of questions here, Good topic!

Balsa is superior to foam coring in virtually all applications and strength modes. It can be a little trickier working with, though. See here:
http://www.baltek.com/data/graphs/allcore.html
and here:
http://www.netcomposites.com/education.asp?sequence=53
The only problem is that it is a natural wood and can create special problems in a marine environment is not properly encapsulated...rot!

Core thickness is determined wholely by the strength and stiffness requirements of the application. A cored panel is preferred to flat laminate when rigidity and bending strength is required. You are essentially increasing the moment of inertia of the cross-section by thickening the panel with core. The shear strength of core material is typically an order of magnitude less than the skin plies(glass/carbon/kevler) so it doesn't do a whole lot in that department, however it does provide some noticible benefit.

Resins are another story altogether. Two part epoxies are generally the best commercially available matrixes for composites, but can be prohibitive due to cost and working difficulties, ie gel times and set times. Your vinylesters and polyesters and not quite as good strength-wise but cost a whole lot less.

Another variety not common in boating are phenolic resins. These resins are in between epoxy and your vinylesters in terms of cost and strength.

CigDaze

BTW, here's another good thread on a comparisson between some different fiber materials.

http://www.offshoreonly.com/forums/s...threadid=64213

Cord

iTrader: (2)

I was seriously considering the foam coring because of the rot issue. I'm not interested in making this a wood free boat, I'm just not certain about using wood coring. I have a rather negative first hand experience and really don't want to be on the receiving end of a lawsuit.

Epoxies have different set times don't they? I can't see why an epoxy would be any harder to work with than any other product. Guess I'm just relating to those little tubes of epoxy from the hardware store.

Cord

iTrader: (2)

Of the foam cores, which is the better one to go with and why? In fact, what the heck are these?

Areix, Klegecell, Divinycell, or Termanto

Gary Anderson

Before using foam coring, read the articles on the following link reagarding coring. Very good info.
http://www.yachtsurvey.com/structuralissues.htm

CigDaze

Pascoe's site is awesome. Definately spend a bit of time reading his material.

CigDaze

Epoxy curing is a highly exothermic reaction. You have to be very careful with temperature. Mixing large quantities can often be difficult because of this reason. It also typically has quicker set times and once it begins kicking off, there's no stopping it.

Cord

iTrader: (2)

Yes, I've read his material before. To say that he's a bit biased would be an understatement.

Reed Jensen

If you are using an epoxy system like West system... they work great... but if you mix a large amount and pour a big puddle... you will get too much heat and the stuff begins to smoke and foam up... There are different curing rate catalyzers.... the best part about epoxy compared to polyester resin is the epoxy will not allow moisture to pass through. Polyester resins will allow water to pass through by capillary action and will eventually penetrate any wood in the hull....