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 Vintage Moderator still playing 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

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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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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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