Sealing transom to hull

Hi all new to Tin boats and I got a question. I took my Sylvan Aluminum 14 foot apart this week to tackle the 'sinking' issue I've been having. I found a bunch of rivets missing and leaking in the front and fixed those. In the back water enters from under the transom where the two pieces of aluminum join. I've removed the entire transom and now i'm ready to put it back together. What I would like to know is can I use Butyl tape to form a gasket between the two pieces of aluminum prior to riveting? If not butyl can i just use 3m 5200?? I would like to do this only once as the neighbors are getting mad at all the banging and cursing. Thanks and a great site you have here.

Welcome to the confusion and fun of tin boat ownership and also WELCOME to the site.

As they say pictures are worth a 1000 words. It might be easier for someone to give the best advise if they can see the area in question.

Fishfreek said:

Welcome to the confusion and fun of tin boat ownership and also WELCOME to the site.

As they say pictures are worth a 1000 words. It might be easier for someone to give the best advise if they can see the area in question.

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+1

I have never replaced a transom so take this with a bit of salt.

3M5200 is the ONLY glue/mastic/caulk, that I know of, that is rated for below-water-line use.

However, there are tons of transom replacement pictures and detailed work on this site. You might want to do a search and get some input. That being said, some of the far more knowledgeable guys will soon pipe in.

richg99

Here is a pic of the boat all apart. I want to reattach the transom to the boat. It takes 115 rivets and some kind of gasket or caulking between the two metal parts.

https://i123.photobucket.com/albums/o316/sterios/IMG_20160312_174312_zpsduvyg75a.jpg

Rivet it back together then coat the seams and rivets with Gluvit.
Seal the rivets with 3M5200 when installing them.

When I removed the transom there was a black substance between the two metals and I'm just trying to replace that stuff.

IMHO you MUST zinc chromate prime any aluminum before sealing, regardless of what you use to seal. See here for graphic :shock: pictures Johnny just posted of "untreated" aluminum, see:

https://www.tinboats.net/forum/viewtopic.php?f=3&t=40251

That said, take a look below:



For those who need details, that sealing tape is a 3M closed-cell vinyl foam that Starcraft recommended. Before riveting together, I also wiped a bead of 5200 onto the tape, then a nice bead where my transom met the hull.

FWIW I just went through a TOTAL transom replacement and there's lots of pictures and tips in my posts about it - see my signature.

That is exactly the kind of info i'm looking for. I will go through all your posts tomorrow and get this job done right. Thanks for all the tips and great site!

Is there a reason why tig welding it back together isn't an option? With all the work you've done I would think that you'd want it better than new rather than like new. Just my opinion but I'd never get involved with all those rivets and sealers. Unless you're looking for a restoration instead of an upgrade/fix...

momule said:

Is there a reason why tig welding it back together isn't an option? With all the work you've done I would think that you'd want it better than new rather than like new. Just my opinion but I'd never get involved with all those rivets and sealers. Unless you're looking for a restoration instead of an upgrade/fix...

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Don't be so sure welding makes a stronger final product... welding introduces heat to the material which can weaken it. And if the hull was sized to be assembled with rivets then most likely that is how you should reassemble. Plus if someone wasn't planning to strip and repaint, then rivets are the way to go.

jethro said:

momule said:

Is there a reason why tig welding it back together isn't an option? With all the work you've done I would think that you'd want it better than new rather than like new. Just my opinion but I'd never get involved with all those rivets and sealers. Unless you're looking for a restoration instead of an upgrade/fix...

Click to expand...

Don't be so sure welding makes a stronger final product... welding introduces heat to the material which can weaken it. And if the hull was sized to be assembled with rivets then most likely that is how you should reassemble. Plus if someone wasn't planning to strip and repaint, then rivets are the way to go.

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Here's a GREAT read on welding 5052, which is the predominant aluminum alloy used for our tin boats:

https://www.thefabricator.com/article/aluminumwelding/aluminum-workshop-where-in-the-world-is-the-5052-filler-alloy-

And here's that UGLY picture :shock: of what can happen to UN-primed aluminum if not prepped and sealed correctly ...

Welding is not an option for me because I've never done it nor own any welding equipment. Future goal to learn though.

DaleH said:

And here's that UGLY picture :shock: of what can happen to UN-primed aluminum if not prepped and sealed correctly ...

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I keep seeing this picture pop up on here from time to time. I do NOT believe the 5200 is what caused the corrosion. I have to think it was some sort of galvanic corrosion caused by whatever was glued/sealed to the hull with the 5200. I have several spots on my boat with 5200 on bare aluminum with zero issues in nearly 3 years. I sealed between rivet and hull with every solid rivet I used when redoing my transom, as well as other modifications I made to my boat using solid rivets. But the biggest spot was where I had a 1" hole welded shut from a previous livewell drain hole. After the welding I slobbed both sides with 5200 for extra measure. Zero issues thus far. I would also think that as much as 5200 is used in the boating world a quick google search would find the same issue if prevalent. Yet I have yet to find another issue as in the pictures.

BigTerp said:

DaleH said:

And here's that UGLY picture :shock: of what can happen to UN-primed aluminum if not prepped and sealed correctly ...

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I keep seeing this picture pop up on here from time to time. I do NOT believe the 5200 is what caused the corrosion.

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I believe you're quite right IMHO too! I don't thinnk it is the bonding agent or sealant per se.

But I think the main point is ... if 2 pieces of aluminum are not primed properly before affixing the pieces together - regardless of how done (rivet, weld, glue, bolts, etc.) .... then one may experience destructive corrosion ...

You raise a good point (thank you!) though - one should not shy away from using 3M 5200 - just prime the material properly beforehand!

Can I use etching primer on the aluminum before riveting the pieces together? if not is there another primer I should use? I'm up in Ontario and I looked for ferric chloride and couldn't find any for sale to the public.

Zinc chromate. Boat stores sell it in spray cans. Electrical supply, fabrication houses and good industrial supply stores not only may have it - it may be cheaper than the boat chandleries!

floater said:

Can I use etching primer on the aluminum before riveting the pieces together? if not is there another primer I should use? I'm up in Ontario and I looked for ferric chloride and couldn't find any for sale to the public.

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DaleH said:

Zinc chromate. Boat stores sell it in spray cans. Electrical supply, fabrication houses and good industrial supply stores not only may have it - it may be cheaper than the boat chandleries!

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You can find Zinc Chromate Primer (Spray Can) in the Automotive paint section of any Canadian Tire/PartSource store. Same probably goes for HD/Lowes or any other auto parts store. I have yet to see it sold by the quart/gallon but really haven't looked YET!!

Ok I will hit up the local CT tomorrow and get this transom back on! Thanks