tips for diagnosing boat leaks (welded hull)

I’ve got a ~~25 year old all welded 1450 alumacraft mod v jon. It’s leaked water for most of the time I’ve owned it (10 years). It’s not a lot of water, and it depends on the load in the boat. Fishing by myself a few hours it’s 20-30 ounces, fishing with a buddy and gear it’s around 2-3 litres. It never seems to get more than this. I could tie the boat up on a dock for 2 days and it won’t fill with water and sink. I just crawled under it today to inspect the underside of the hull. All the welds look in good shape, all I saw as far as a compromised hull was a small pinhole on the starboard side weld on the bottom edge of the boat. I’m going to inspect more with a flashlight and a very thin awl to see if the hole is all the way through. It is the size of a pencil point. My other big question is whether water could be coming in through the bolts/screws in the transom. There’s 11 I counted and on one of the larger bolt heads it appeared whatever gasket was made around it is coming loose. Any trouble shooting tips appreciated! Also good recommendations on a good marine sealant/silicone product I could use on the transom screws/bolts.

Anything thats under water while loaded can leak. I would start with all your transom bolts. Hit everything with silicone or I’ve used aerosol Flex Steel…yes it works.

Have you filled it with water on the trailer to see where it leaks?

Fill the boat with water and see where it leads out from under the boat.

suzuki wrote:

Have you filled it with water on the trailer to see where it leaks?

This is great advice. Just be cautious with trailer weight. Water weighs roughly 8.34lbs/gallon.

I’ve fixed 2 leaky aluminum boats up north with J-B weld.

Plug your livewell intakes in the transom and go fishing. See if the problem goes away.

Flood boat. See where it leaks. Circle with sharpie and diagnose

A lot of attention is given to the transom and rightfully so due to all the penetrations. However, I once had a leak at the bow eye because it was bolted on and loose. Other leaks that I have experienced in a welded boat include transducer screws.

munchy wrote:

Plug your livewell intakes in the transom and go fishing. See if the problem goes away.

^^^^^

This

9 out of 10 boat leaks aren’t from the hull itself. It’s usually a bad fitting, loose fitting, cracked plumbing, etc.