CONTINUOUSWAVE

Q1: Is [using an aluminum sheet to reinforce the fiberglass deck that covers the fuel tank cavity on a Boston Whaler OUTRAGE of unknown length] good method of repair?

Q2: Does aluminum hold screws well?

Note: I want to add aT-top.

Q3: Do you need to use aluminum screws instead of [stainless steel] screws (screwing into the floor) to avoid additional corrosion mixing metals?

Q4: Does an aluminum sheet provide suitable rigidity for a strong floor?

BACKSTORY. Speaking with a nice guy (about buying his boat) who, when replacing his fuel tank on an [OUTRAGE] and removing the floor deck plate, repaired the deck plate with an aluminum sheet panel. I believe I am correct in saying he laminated a sheet of aluminum in place of the plywood on the underside of the fiberglass deck cover.

I haven't heard of this before.

Boston Whaler uses aluminum plates as a backing material for holding fasteners in many applications in their boats, both in recreational models and commercial models.

A1: I don't think using a thin aluminum sheet as a backing material for a large area like the fuel tank cavity deck cover is a good idea. Wood is really a great material for this application. Wood is very nicely bonded to the fiberglass using a resin like epoxy. Aluminum may be much harder to bond to fiberglass.

Note: I am not a mechanical engineer, a boat builder, or a materials expert, but I have built many structures from aluminum. The strength of aluminum varies with the alloy.

A typical high-strength alloy is 6061-T6. It is quite strong, fairly hard, and has good corrosion resistance. To learn more about the strength of aluminum research the various alloys. I built many large antenna arrays from 6061-T6 and 6061-T832 aluminum alloy tubing and plate that survived 70-MPH winds. There are stronger alloys but they are more expensive and harder to find.

Also aluminum sheet of sufficient size to be used as reinforcement for a big fiberglass panel like the fuel tan cavity deck cover would be heavy, expensive, and probably not particularly rigid unless quite thick.

A2: aluminum holds screw fasteners very well. It can be tapped and accept machine screws. Usually a machine screw is used in aluminum if the material thickness is sufficient.

A3: I suppose somewhere you can find aluminum screws--maybe on a storm door. But for any sort of structural integrity and strength, steel fasteners are used, and in marine applications stainless steel fasteners. Use an anti-seize compound. See the FAQ for advice on this at http://continuouswave.com/whaler/reference/FAQ/#Q9.

A4: The rigidity of sheet aluminum is related to its thickness. Aluminum foil is very flexible. A 2-inch thick aluminum plate is not very flexible. If you used aluminum sheet as thick as the wood, say 1-inch, it would be very rigid, very much too heavy, and very ridiculously expensive.

Ltwhaler wrote:I want to add aT-top.

I advise against this unless you are located very close to the equator.

To be clear I wasn't thinking of using it.A fellow who I'm considering buying his boat did. Never really thought about using it myself. I think I'd using marine plywood or coosa board.

Just thought I'd ask the experts if it's ok.

Q5: would I need to plan on replacing it?

To be clear, I tried to answer your questions.

A5: to know if a prior repair needs to be redone is difficult to judge without knowing much about the state of the repair. Walking on the deck and not experiencing softness or flexing would be the base criterion.

Q6: how thick is the aluminum sheet and what are its dimensions?

Q7: what alloy was used?