so we bought a '92 Sea Nymph 17.5' - aluminum transom rot?

[old_school]

quick specs - 1992 Sea Nymph - 1999 75hp Merc OB
water driven/tested before buying - transom seems solid

so I was taking off some old screws/hardware from the transom of the boat, saw what looked like a rust hole/pit hole about 1/4" in diameter, so I poke/dig around and there is lots of water and rotten wood in that immediate area (this post is more about the transom than the wood rot)

took a closer look at transom and there were about 4 other 1/8" holes in the same area (10" starboard of the motor - three quarters the way up the transom - scattered about in a 8" diameter area) - so I poke/dig around and water actually dribbled out of one hole and was able to easily pull out rotten wood out the others

QUESTIONS
1. what would cause the pitting/holes in the aluminum? (they are not from old mounts or hardware) - the Merc has anodes
2. when the motor is running and under power the transom does not move/bend - how do you know HOW SERIOUS the transom problem is? In the yard I can pull/push on the motor hard and not see the transom move.
3. I know aluminum welding is best for these holes/pits but if I am concerned about integrity of the aluminum sheet can I use Marine-Tex OR JB Weld OR stainless steel screws with rubber washers/sealant for these small holes? (we are taking off the 2.5" wide top aluminum transom cap/cover today to have a look down inside
4. when reinstalling the transom cap/cover what caulk do you recommend? Home Depot or West Marine stuff? It does not look like it was sealed before and I am sure water has been getting in under it.

Our Sea Nymph and transom is almost identical to the following repair post (an excellent post I must add)

https://www.tinboats.net/forum/viewtopic.php?f=3&t=13354

 

[crkdltr]

quick specs - 1992 Sea Nymph - 1999 75hp Merc OB
water driven/tested before buying - transom seems solid

so I was taking off some old screws/hardware from the transom of the boat, saw what looked like a rust hole/pit hole about 1/4" in diameter, so I poke/dig around and there is lots of water and rotten wood in that immediate area (this post is more about the transom than the wood rot)

took a closer look at transom and there were about 4 other 1/8" holes in the same area (10" starboard of the motor - three quarters the way up the transom - scattered about in a 8" diameter area) - so I poke/dig around and water actually dribbled out of one hole and was able to easily pull out rotten wood out the others

QUESTIONS
1. what would cause the pitting/holes in the aluminum? (they are not from old mounts or hardware) - the Merc has anodes
2. when the motor is running and under power the transom does not move/bend - how do you know HOW SERIOUS the transom problem is? In the yard I can pull/push on the motor hard and not see the transom move.
3. I know aluminum welding is best for these holes/pits but if I am concerned about integrity of the aluminum sheet can I use Marine-Tex OR JB Weld OR stainless steel screws with rubber washers/sealant for these small holes? (we are taking off the 2.5" wide top aluminum transom cap/cover today to have a look down inside
4. when reinstalling the transom cap/cover what caulk do you recommend? Home Depot or West Marine stuff? It does not look like it was sealed before and I am sure water has been getting in under it.

Our Sea Nymph and transom is almost identical to the following repair post (an excellent post I must add)

https://www.tinboats.net/forum/viewtopic.php?f=3&t=13354

1: Aluminum will corrode as any other metal. It just doesn't show up as the rust red/orange/brown we're familiar with when we see steel rust. So bare aluminum plus moisture plus any sediment, salt or what have you could have attached and lead to these holes. I have a similar issue with the floor of my aluminum boat due to sediment/salt getting stuck under the foam padding. Sometimes those holes can be caused by a bad ground or wiring short.

2: You can drill small holes in and around the suspected problem areas to see if the wood is rotten all the way through or just near the holes. You will want to refill these holes after you've drilled with some kind or sealer or even an epoxy/wood flour mix. . Hopefully your transom rot is isolated to those small holes.

3: I'm not an expert but if you can't get the holes welded for a less than a small fortune then that area may not flex enough to cause a problem if you seal them with a marine silicone/sealer and/or screws with rubber washers.

4: If you use 3M 5200 Marine Sealer (or anything labled as marine caulk/sealer), it doesn't matter if you buy it fro West or Home Depot. It's the same product. It's probably more expensive from West.

*disclaimer* I'm new to the site and inexperienced so I'm answering your questions using common sense, my personal experiences and from other individuals experiences I have read about.

Good luck. 8)

 

[old_school]

thanks for the comments - I am big on posting what I find in hopes it helps others ...

1st off, you were right, there was LOTS of moisture (salt water) and LOTS of rotten wood in the transom - 2/3 rotten - and lots of small holes and SUPER THIN aluminum on the transom

Luckily I have a friend who is very experienced in making surfboards, kiteboards (both wood and foam) and has repaired transoms before - he found a local place that sold this "liquid transom repair" - I opened up the transom, repeatedly dug out rotten wood and dried it over the course of 8 days (with 2 huge fans) and then we poured in this stuff that looked like a plastic gray cement - wow, worked great - just put masking tape over any holes an when the tape came off the holes were filled flat

Here are a couple pics for everyone

Now I must post something in the outboard motor section! lol It is always something!