Over plating an aluminum boat

I would avoid over strain hardend and go with O or H111 temper.

Welding 6000 series below the waterline is generally not accepted anymore; corrosion issues owing to copper content.

You will also need to know what grade and temper the alloy is, to ensure you select the correct filler wire. Most aluminium material, in the US, was/is focused upon the aircraft industry (thanks to Boeing et al). Their grades and tempers are different. As such your boat may have been built with an alloy spec for that industry and as such would not be accepted today in the marine enviornment.

 

Welding new plate over old frames, my concern would be the compatibility of the two alloys, so far as the weld taking properly to both. I guess you need an accurate fix on what the original material is, precisely, and what best to match it with in new plate.

 

Wow theres a project not impossible but alot of work. Where would i start and believe me as a niche market builder working alot in hull conversions i've had to make or recommend decisions on similar presentations over the years. My first concern would be why did the hull corrode. There has been some problems in the past re factory errors on processing and labeling marine alum. I recall a thread on this forum discussing such. I have worked with 1950's era marine alum. hulls and saw little to no corrision problems so i am suspicious of your orig. hull plating, which also could include some of your framing in gussets, knees and maybe bulkheads to hull attachments. It's important you do some research and get to the bottom of this first. If it is a case of corrosion due to lack of proper zinc protection, internal/external stray electrical currents, then a rebuild is more feasible. Are the above waterline sections in good to excellent condition? If so just do spot repairs and re plate below the waterline. If you just want to get say 10 yrs or so out of her then maybe sandblast and plate over the old but only up to the waterline. To compensate for the extra weight reduce your above waterline weights in areas that will keep her on the designed lines. Some examples, extra un necessary super structure,reduce water and fuel tankage, some frivilious extra gear or rigging, every pound counts down to the books in her library. We did this on a friends boat and removed 800lbs of non attached un necessary carried aboard items. I would NOT swap the engines to outboards, you're just getting into to much structural design change plus upsetting her lonitudional balance points which depending on the weight shift involved you might never be able to correct. Better to locate used or rebuilts even with less power. The present setup was expensive designwise to begin with and is the best system for your boat. I don't like outboards they are too high maintenance and almost impossible to repair at sea. There is a standard list of spares i carry for my inboard diesel. filters, belts, impeller, hoses, clamps, alternator, starter, and so on. I can get at these parts on the engine to make repairs. What would one carry as spares for outboards? If you did carry spares how could you get at the engine to make repairs even in a moderate sea state. No thankyou not for me. Engine life comparison between inboard and outboard engines, inboard usually wins every time.The last item which no one has addressed, "Welding Aluminium" of which i have experience being self taught. not easy,not a short learning curve( months to years verses weeks) You need the best in gear unlike steel welding where the gear is half the battle, in alum. the gear is 75% of the battle. Alum. welding gear is expensive, 10 times the cost of steel welding. Surface prep work and ongoing welding gear TIG(low production) electrode sharpening and replacement, gas shielding cup cleaning and replacement, MIG.(high production) You should have a special wire feed/holding gun (Cobra style)and these are only 2 lb. wire reel units requiring constant re fills, If not you have to constantly move the heavy welding unit close to the work location, install a special teflon liner for your whip, and still the constant regular hourly to daily cleaning or replacement of the welding wire cleaning pad, the tip and the gas nozzle. jammed feed wire, and on and on. You'd be money in to get a few plates cut and tacked in place say with a cheap tig unit and bring in an pro. welder with his own gear. Hope this gives you insight and maybe some of the guys here can add to it. Been there done that, want to save others from the same -Geo.

A yacht is not defined by the vessel but by the care and love of her owner.