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Question:

how long do aluminum hulls last in saltwater?

If I were to purchase a large aluminum boat from, say 1989 that was not taken care of, and has been in the water the whole time, and has stuff growing off of it 6 out from the hull, does that mean that it is on its way out with a rust hole soon? Or will it last a long time because aluminum doesn't rust? I think aluminum does rust doesn't it?

Answer:

Having been around marinas for quite a while, I've seen up close what happens if you neglect an Aluminum Hull boat. I can see this as a Disaster in waiting. In my area there where a pretty good number of 32' Marinette Aluminum hull boats, Each year we would pull and repair and bottom paint several of these boats. None had 6 of growth on them. The welder would work a day or so, repairing or replacing bottom plates.
Aluminum does not rust, but does corrode and is vulnerable to galvanic corrosion. If taken care of they can last a long time. The USCG is now phasing out their 41' UTBs which were built from 1973-78. Many of them are still operational. The good thing about aluminum or steel is a good shipyard can crop out and bad hull plating and weld in new.
as Mark points out COAST GUARD maintained boats will last a long time. What you have seems like a proverbial can of worms........stuff growing out 6 from the side? Shudder. What kills aluminum boats is galvanic corrosion, the tendency for every other metal any where near aluminum in salt water to eat it. I knew a famous aluminum ocean racer where people had to empty their pockets of loose change before going aboard, because stray pennies in the bilge would eat a hole thru the boat. No fairy tale. And if there is stray electrical current on or near the dock, the problem is ten fold. I would very very carefully scrape some growth off and hope you don't scape thru the plating. You very well might, so be prepared for an emergency haulout. You didn't mention how large the large boat is, but up to 45 feet or so, the plating probably wasn't much over 1/4 or 5/16th to start, so there's not a lot of room for galvanic action to make it literally paper thin. Depending on how much you are planning on sending, you should probably get a marine surveyor with an audio gauge...a portable Magic Thinghy that Measures Hull Thickness.....

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