Pin holes in aluminum bottom

7mm

Seaman
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I have been confident in my 1987 221 islander restoration so far. I have removed the transom, decks, and all of the flotation foam. The foam was water logged in the bow, near the gas tank, and the transom area. I pressure washed and acid etched the inside of the hull. While I was under the boat drilling out a few rivets I noticed some small blistering in the bottom paint. After scraping off the blistered paint I discovered 6 pin holes. About 1/16 to 1/8 in diameter. From the inside of the boat these pin holes were undetectable. Now I am not so confident. What caused this? Will it continue if so how do I stop it? What is the best way to make a repair? Help Please.
 

Scott Danforth

Grumpy old guy who plays with boats
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below are a number of reasons for pin-holes. they are caused by galvanic corrosion

someone replaced bunk boards on the trailer with treated lumber
someone boats in salt water and the carpet on bunks retains salt-water against the hull
someone used the boat as a ground for something electrical.

if it is just the 6, clean the area, drill out to a larger size, install a rivet with some 5200
 

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Thanks again Cheesehead, you have been a great help in my project. The holes are in the area of the gas tank filler hose, below water line. As far as I know the boat has never been in salt water. The PO had a make shift 120 volt power inverter system with 4 home style outlets and a string of rope lights. The anode was painted over. Hopefully drilling them out will get into some solid metal.
 

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After I cleaned it better with an abrasive wheel, it’s worse than it looked. 2 sections (between 2 ribs) are deeply pitted and several more holes have showed up. Some around rivets and under ribs. I am thinking about patching in two large pieces of aluminum from the inside. Will this work. Or gas welding the pitted areas. Or maybe glassing the inside.
 

Scott Danforth

Grumpy old guy who plays with boats
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with a riveted boat, there is a sealant material between the outer hull sections that are riveted together that makes welding difficult.

my guess something was wired wrong with the power inverter, etc. and you have a lot more galvanic corrosion elsewhere.
 

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Do you think glassing or riveting in sandwich type patches will work?
 

Scott Danforth

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glassing wont work

post pics of the corrosion so we can see what you are working with
 

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[No message]
 

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7mm

Seaman
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I have circled the worst of the corroded areas. Note how the corrosion May be under rib #7. The problem area is in between rib #6 and #8 worst in the port side and progressively better as it goes down to center line and up the starboard side. Note I numbered the ribs from the transom forward. #6-#8 are about midship under the gas tank. Oh. I have also found some minor pitting inside the gas tank directly under the sending unit.
 

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Seaman
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Thanks for that suggestion. It looks like I should remove the #7 rib to make repairs underneath and then re rivet it back in place.
 

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Back to square one. Those products are cost prohibitive. Smallest amount shipped is over $700.
 

jbcurt00

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This question belonged here, not where you asked it

What do you think about drilling out a pin hole to the proper size and using a solid rivet to stop the leak in an aluminum hull
 
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