GRP floors

I am drawing a light 35' wl. sloop. It can either be strip planked round bottom or plywood multi-chine. I see that I can design the floors to be silicon bronze or galvanized steel. I don't weld or have a foundry at my disposal. I have in the past made plate fiberglass floors for solid glass boats. they were say 3/8 to 1/2" glass flat plate of mat and roving glassed into the hull.
I'd like to make floors of s-glass and carbon or kevlar vacuum bagged in epoxy on a mica table. I'd put a flange on the top to support the sole and one on the bottom to fay on the "garboard". my question, is how to size them? The boat is 38' x 10' x 5.25' deep at the midsection. it's about 10,000 lbs.

Any ideas
John

 

Hi John,

I would love to see more about this project. Any good-looking boat will draw a crowd on here.

Kevlar's main attributes are tensile strength and abrasion resistance. It is terrible in compression and a real pain to work with; carbon is awfully expensive, and weight this low in the boat is generally not a problem, so S-glass gets my thumbs-up out of the fibres you suggest.

Do you have a copy of Dave Gerr's Elements of Boat Strength? Using his rule, your boat would have scantling number Sn=2.0, thus standard steam-bent frames would have siding and molding dimensions both equal to 1.8 inches. Under the guidelines in that book, the floor siding is equal to the frame siding (1.8 inches), and the floor molding 9 inches for sawn or 6 inches for laminated/grown floors. It's a rough estimate, but his rule is good and conservative, and seems fairly popular.

To convert to a composite floor, what I'd do is to try to come up with a laminate with similar overall properties- stiffness, ultimate strength, etc.- to the wooden one above.

But if you're talking carbon, you're probably also talking high-performance sailing and a serious drive towards minimal weight. And that complicates things a great deal, since the very rough estimate I just discussed is based on a very conservative rule and very little knowledge of the boat being discussed.

 

Thanks Matt,Thank you for your response.
I think that S-glass is probably the best for the reasons you mentioned.
I do have Dave Gerr's book and use it for scantlings in general. Being unreasonable, I want to "have it all" (or at least I want to have headroom and low topsides in a shallow bodied hull form without a deckhouse that looks like a house). metal floors provide strength with a low profile. using the laminated floor molding as an initial guide I'll make the glass floors with superior properties to the wood floors. Can I post a drawing on the forum?
thanks again
John