Sealing external transom

[BrayD]

Sorry for the newb question. I'm rebuilding an 82 Sea Nymph 14k and I'm looking to install the transom tonight. It's 3/4" ply that sandwiches the hull, so it will be fully exposed to the water.

The transom boards are thoroughly coated in spar urethane, I was just curious how excessive I should be with the 3m 5200. Should I coat the entire back of the board so it's 'glued' to the hull or should I just apply it locally to the bolts to seal it up?

My concern is getting the transom boards off of the hull if/when it needs replaced in the future. Is this an issue or should I just go to town with the 5200?

 

[sonny1]

I would just use it on the bolts.

 

[airshot]

How " waterproof" is the urethane coating ? If you have any thought of replacing it in the not to distant future then bolt holes only. If this is to be the last repair, mabey a complete cover ? Not sure how easy that stuff would come off if totally covered. On my jon, the wood is easy to replace, I don't go overboard sealing it up other than bolt holes, to make replacement as quick and easy as possible.

 

[BrayD]

That's the answer I was looking for. Thanks guys. This is my first boat build and I'm sure I'll be doing some of this stuff again. It's sealed up pretty well, but I'll be OK with replacing it in a few years if necessary. I'll apply liberally around the bolts and call it good.

 

[ripdmup]

I would use 3m 4200 on the bolts. 3m 5200 is tough if you ever have to go back in. This statement was told to me years ago. "The stupidest question is the one that is not asked" Good Luck to you.

 

[BrayD]

Good intel. I didn't even think of that. Thank you!

 

[jethro]

I agree with the others, just the bolts.

 

[LDUBS]

X5 (or 6). Just the bolts. I think a good rule of thumb for a lot things we do to our boats is to always consider future removal/access.

 

[mbullen]

Sorry for the newb question. I'm rebuilding an 82 Sea Nymph 14k and I'm looking to install the transom tonight. It's 3/4" ply that sandwiches the hull, so it will be fully exposed to the water.

The transom boards are thoroughly coated in spar urethane, I was just curious how excessive I should be with the 3m 5200. Should I coat the entire back of the board so it's 'glued' to the hull or should I just apply it locally to the bolts to seal it up?

My concern is getting the transom boards off of the hull if/when it needs replaced in the future. Is this an issue or should I just go to town with the 5200?

There is a lively debate on whether adhesive is needed at all in the transom installation.
Folks can make pretty persuasive arguments for either.
Personally, If I were to use an adhesive (I don't), I would favor 3M's 4200 over the 5200. Semi-permanent vs. Very permanent.

 

[DaleH]

Just the bolts but for ANOTHER reason that none of you posted ... those goops will etch and corrode the aluminum!

 

[ripdmup]

Since I am one of those who posted I will say that I just do the bolts in 4200 and have never had that type of horror exposed afterwards..................................Good to know!

 

[BrayD]

Just to follow up, I decided against the 5200 and picked up some Goop Marine. I'm sure there's debate around that choice, but it dries quick and I just did the holes. Got it out on the water Sunday and it's dry as a bone!

 

[airshot]

Over a number of years of using goop, I have had great sucess with the stuff in a variety of uses..

 

[thill]

Just the bolts but for ANOTHER reason that none of you posted ... those goops will etch and corrode the aluminum!

View attachment 116755

I think the above images are worst-case scenarios, and are not what you should expect IF the aluminum is properly painted before the sealant is applied.

I need a lot more information before believing this is typical.

 

[LDUBS]

I think the above images are worst-case scenarios, and are not what you should expect IF the aluminum is properly painted before the sealant is applied.

I need a lot more information before believing this is typical.

I think what you say after "IF" is the important part of avoiding this issue.

 

[thill]

Aluminum primer under the paint really helps protect the metal.

Even so, I would still like to know more about those pictures, because I have used straight silicon, probably GE, on numerous projects with raw, unpainted aluminum, and have NEVER had any corrosion.

In fact, I used silicone just today, while mounting an engine. I had used silicone previously, and the old stuff was very solid and had to be cut off. I put in fresh donuts of silicone inside and out, tightened the bolts and wiped the excess. I’m 100% confident that the bond is good.

I recently pulled some aluminum stuff apart to reuse the metal, and where the silicone had sealed, the metal was still shiny and new underneath, despite the rest looking darker and weathered.

My Princecraft is a completely unpainted boat, and I use/used clear silicone to seal a number of areas, and it’s still tight and clear, with no corrosion issues.

With silicone, cleaning the area carefully before applying is very important. If the bond is broken, and salt water wicks underneath the sealant and sits there, it probably could cause pitting. So just take a minute and clean it first!

There has to be more to the story behind those pictures.

 

[thill]

And for what it’s worth, I had to use a thin pry bar to get the motor off, because it didn’t come loose when unbolted. The bond and seal was excellent

 

[Shootstraight]

Over a number of years of using goop, I have had great sucess with the stuff in a variety of uses..

I also have used Goop for many years on all types of surfaces, it’s worked flawlessly!

 

[LDUBS]

According to a little research, not all silicon sealer is the same. The problem is not the silicon but the acetic acid contained in silicon products. A silicon sealer that does not contain acetic acid or other corrosives would be fine to use. It should be easy enough to check if something is compatible with aluminum. And of course trapping salt water is always going to be something to avoid. There are better products and best practices apply. I won't be using any bathtub sealer/caulk on my boat. My two cents.

 

[ripdmup]