Fiberglass Core Material - What to use?

[Benz]

For this I would use Coosa, since there's a lot of torque load. Build the shape out of coosa, leaving enough space to have at least 3/8" of lamination thickness on the water side. On the other side, where space isn't an issue, you can build it up as thick as you like.
Use biaxial cloth, with a final layer of 10 oz woven E-glass. You can use 1708 biax, which might be easier to find than plain biax, with epoxy, as long as you pre-soak the fabric pretty good on a wet-out table (piece of cardboard) before laying it into the piece.
You can measure the thickness a laminate will be by stacking dry layers and squeezing them with a micrometer or caliper: it will give you the approximate thickness that the product will be when finished.

[Pete7]

Originally Posted by CaptainShack

I'm new to fiberglass work, but I figured it be easier to get the shape I need to make the "pocket" with a foam material. Then cover that in fiberglass vs just laying sheet after sheet of glass to build up the 4-5 inches of material?

Go down the supermarket and buy a couple of none stick loaf tins. If it needs to be deeper then use an old 5L oil can upside down as the male mould and lay on top of that. Final option is a bucket, lay up inside and then cut down to size.

Pete

[s/v Jedi]

For matching to the hull shape…. if the boat is on the hard and level, you can pour epoxy and create a flat base to further build on, cut the hole through etc.

I am using West System terminology here: use 205 resin and slow hardener. Mix well, then add high density filler until syrup consistency. Pour slowly, try to prevent bubbles forming (also during mixing).

Use a kebab stick to stir and agitate the pour. Stir all along the sides to eliminate any air bubbles.

After cure, this base will be crush proof, but you can still wrap the sides with fiberglass together with what you build on top.

[CarlF]

I’d just use oak. Laminate it from some 1” board. Very strong. Takes fasteners. Much easier to shape and work than any foam. Oak isn’t going to rot in that location. Will far outlast those electric drives in the water.

You could put a couple of layers of cloth on it but I’d just coat it with a penetrating epoxy, fair it to the hull with a good epoxy filler and then paint it.

[Madehn]

Jedi had it right IMHO-- if i was doing that project i think i would just use a wood core of oak-- if i wanted something that was bulletproof and would last longer than the boat, i might be tempted to use GP03 layers with fiberglass over it-- stuff is a beast to work with in terms of dulling tools but is stronger that anything else i can think of-- i did use composite foam for a deck are (decking over a well at the aft end of my boat- 4 feet by 8 feet- i was expensive but i put 5 layers of cloth over the top and three over the bottom- i tend to overbuild everything- the plus side is that a little water intrusion from fittings etc can do no rot damage. best of luck.

[Chotu]

As you can see, there are 1,000,001 ways to do this. All you have to do is make sure whatever you are going to use for a core, if any, can take a lot of compression. It Has to be something that doesn’t crush. Coosa board is very good for that actually. And probably more available than high density corecell.

The laminate schedule Benz described is perfect.

Luckily, you don’t really have to worry much about epoxy brands. As much as the companies wouldn’t like to agree, they are all basically the same. Just make sure you get one that is thin enough. A laminating resin. Even more so if you are using the 1708 fiberglass cloth.

[smacksman]

Being below or slightly above your keel is the least of your problems. What about catching your anchor rode, somebodys mooring line or even a strong lobster pot line round your outdrive. Potentially a lot more force than the torque of your motor. And if you run aground you can't assume the bottom is flat.
Maybe a strong skeg in front of it?

[CaptainShack]

It being lower than my Foot skegs for the entire boat is kind of a big deal. As beaching the boat, or running aground would for sure hit the pods making it the most important issue.

If they are higher they would at least be behind those same foot / skeg keels for protection Even if the bottom isn't flat I'd have to have come down on something thats inside those same twin keels or drifted sideways into it to hit said object. Basically the same worries as any sail drive or any drive that isn't sitting right behind a full kheel? or built into a rudder/ directly?

At that point any boat could have the issues listed happen to them. But it have to dodge my full rudders and the keels to hit the drives. Unless I'm missing something. Picture attached.

[Chotu]

You’re good. If you keep it shorter than those keels and the rudder skeg, you have the exact same set up as a Catalac Catamaran has. Just like all of the rest of them that have sail drives.

just keep them short enough.

[smacksman]

Very true. My comment was to steer you beyond just designing for torque but for catching ropes. Outdrives take a lot more clout than just torque.

[thinwater]

Or you could make the keels 4" deeper. She would probably go to weather better.

[CaptainShack]

Was chatting with a fella at the boatyard suggested the same thing. Though that's a project I'm really unsure how to start. Would I remove the boot? Just build up fiberglass? Make the boot bigger?