Replacing Transom on Aluminum Boat

Epoxy working time is based on temperature and humidity, so I'd be guessing without this information, though you'll have more time in colder weather, but viscosity also goes up. The bolt holes can be filled before hand. I'm still guessing about how much epoxy you'll need. A lot depends on how much the plywood drinks up on the first coat. Some pictures of the transom would be helpful.

 

Once again, Thanks!

As for pictures, I tried to put some up but could figure out how to.

 

Sorry, click on "Go Advanced" or the blue post reply button, then click on "manage attachments." A small window will popup where you select and upload the photo(s). When they have uploaded, close the small window and post the message. It's not the most user-friendly, but once you do it, it makes sense. Have a quick look at
http://www.boatdesign.net/forums/faq.php?faq=vb_read_and_post#faq_vb_attachment_explain

 

Here are a couple pics of the old transom before I removed the pressure treated core. You can see in the first pic how it has to slide in between the aluminum transom skin and those 2 brackets which are connected to the stringers. The second picture just shows a little of how the core is bolted in. Most of the bolts had been removed at that point. Also there are 2 additional transom pieces that sit on top of this piece, one on either side. They don't appear to contribute to the strength of the transom. They are just held in by a couple bolts. The floor has also been taken up now, as I'm going to replace the vinyl flooring at the same time.

 

Got a chance to work on the transom replacement project again this week. Got the new core cut out and screwed together. Put it in and drilled all the holes, then took it back out and drilled all the holes 1/4" inch oversized. I guess its time to pull the screws back out and start mixing epoxy. So I want to coat the surfaces to be laminated with unthicked epoxy, then glue them together with epoxy thickened with equal amounts of West 403 and 404, then make sure the whole thing has 3 coats of unthickened epoxy on the outside and edges...correct? And I will fill the all wholes with the same thickened mixture?

 

The amount 404 you'll need will depend on how thick you need it. Generally, you mix it as thick as you need. If you'll be doing the gluing together part laying flat on a bench, then it doesn't need to be very thick at all, about the consistency of ketchup. On the other hand if you're installing it in the boat and gluing it together at the same time, then it should be the consistency of peanut butter and applied with a notched trowel.

 

OK thanks. You mentioned 404, but I will also be adding the 403 into the mixture for the glueing process, correct?

 

West 404 (calcium metacilicate) is their version of "cab-o-sil", which is a thickening agent, used to control viscosity and improve hardness. It's part of most "mixtures" to improve adhesion, hardness and viscosity. 403 (cotton flock) improves bonding and toughness, 406 (silica) does the same though is better at bonding.

I know you're looking for a specific mixture and ratios, but there really aren't any. I'd start with a soupy mix of 403 then add 404 as needed to control viscosity.

 

I also Have a 22' Holiday (1990)

I was wondering how your transom replacement job went. How did you get all of the aluminum that makes up the motor well out (drill out rivets). I'm debating whether to have this big job done or do it myself. I didn't call for a price yet as I just discovered a 10" long crack running along the 90 degree bend just in front of the motor between the two drain holes that drain the water from the motor well. I'm sure the crack developed due to a weak transom. I did see some dry rot when I replaced the floor last year. I have a 110 Johonson outboard, did you make a sling to hoist the motor off the boat or do they sell some type of sling for that?

 

use something like Aluthane (an aluminum filled moisture cured urethane) as a primer on the pitted aluminum. You can then use thickened epoxy to fill in the pits, but 'epoxy cream' is a thickened epoxy for minor flaws that flows off a putty knife much better than regular thickened epoxy - which drags behind the putty knife like taffy...

2 or 3 coats of the Aluthane will also seal the wood about as good as epoxy...

left by itself the aluthane will give the surfaceds a galvanized metal look. Folks have used it to restore old unpainted aluminum boats to 'new aluminum' look.

PAR is 100% correct about those penetrating epoxies - they don't drive the water out or away. At best they harden around the damp wood. - essentially forming an epoxy crust around the bad stuff. They will not penetrate any more than the solvents in them would penetrate if you just poured the solvents on the surface. Note that all the ads use dry balsa, end grain etc. which any liquid will 'soak into deeply'.

paul