Setting transom with epoxy

[Drivewayboater2]

Okay… question regarding setting the transom in with the west system epoxy. This is for a small transom section on a 1990 Bayliner 2651. It’s not a the entire transom that’s being refitted. Just the middle section. Approx 24 “ x 27”. Here’s what being replaced.

after reviewing all options I’ve come to the conclusion that the west expoy is the best way to go. considering adhesion and strength properties.
question is…. Looking at the clamping scenarios ( west systems ) encourages not to over tighten the clamping when adhering new wood to the hull. There is a bit of unevenness to the existing transom. There fore i don’t want to starve the bonding while clamping in the new transom. I get that you mix the resin with cabosil but what’s the best way to not over tighten the clamping. Yes there’s the old all thread with 2x4’s on end but is this really the way to go? saw some vids on putting pressure boards against the new transom to hold in place till cured. Any help would be appreciated.

 

[Woodonglass]

 

[Drivewayboater2]

Thanks woodonglass… I’ve see this before. However I’ve got an I/0. Was hoping to get insight on how much clamping is needed. All west system stuff recommends minimal clamping as to not push epoxy out too much out creating voids. I’ve got some irregularities on the transom due to wonderful craftsmanship on this Bayliner and need to account for that. And obviously I don’t want it to shift during the curing process. I plan on using thickened epoxy for the bond. should I set a layer of 1.5 mat in between the wood and transom?

 

[Baylinerchuck]

Here’s some pics from my I/O transom install.

 

[Baylinerchuck]

Thanks woodonglass… I’ve see this before. However I’ve got an I/0. Was hoping to get insight on how much clamping is needed. All west system stuff recommends minimal clamping as to not push epoxy out too much out creating voids. I’ve got some irregularities on the transom due to wonderful craftsmanship on this Bayliner and need to account for that. And obviously I don’t want it to shift during the curing process. I plan on using thickened epoxy for the bond. should I set a layer of 1.5 mat in between the wood and transom?

I wrapped all of the transom wood to build thickness. Not necessary on the side that goes up against the boat, but I added it to help meet the thickness spec for my outdrive. I drilled several holes in the wood as vents for air to escape as I tightened the clamps. I also drilled these holes because it helps to show even clamping as the resin will begin to push out the holes. Once glued in place, the entire transom gets thickened resin fillets and wrapped with 1708.

 

[JASinIL2006]

Thanks woodonglass… I’ve see this before. However I’ve got an I/0. Was hoping to get insight on how much clamping is needed. All west system stuff recommends minimal clamping as to not push epoxy out too much out creating voids. I’ve got some irregularities on the transom due to wonderful craftsmanship on this Bayliner and need to account for that. And obviously I don’t want it to shift during the curing process. I plan on using thickened epoxy for the bond. should I set a layer of 1.5 mat in between the wood and transom?

I didn't use epoxy, but I think the idea is the same whether using epoxy or polyester. I don't think you need a layer of glass between the transom core and the hull if you have thickened your epoxy sufficiently. I clamped mine similar to what @Baylinerchuck depicts above, slathering on the thickened resin over the parts to be joined. That way, the clamps only need to be tight enough to insure good contact over the transom area. It's easy to tell when you've tightened the clamps enough because you'll see resin oozing out of the relief holes.

One other tip you might consider: since the hull itself can be a bit flexible (especially when clamped), and since the tolerances for flatness of the transom are pretty tight (if you want your gimbal housing to seal up against the boat), it makes sense to try to avoid causing any ripples or uneveness in transom around the keyhole. I made a clamping shield for the outside of the boat so the clamps would mess up the flatness. (You can see a picture of it in post #55 of my resto thread: https://forums.iboats.com/threads/t...6-sei-i-o-bowrider.552555/page-3#post-3970626 .)

It is much easier to prevent problems with unevenness around the keyhole than it is to fix them after the fact.

 

[Baylinerchuck]

I didn't use epoxy, but I think the idea is the same whether using epoxy or polyester. I don't think you need a layer of glass between the transom core and the hull if you have thickened your epoxy sufficiently. I clamped mine similar to what @Baylinerchuck depicts above, slathering on the thickened resin over the parts to be joined. That way, the clamps only need to be tight enough to insure good contact over the transom area. It's easy to tell when you've tightened the clamps enough because you'll see resin oozing out of the relief holes.

One other tip you might consider: since the hull itself can be a bit flexible (especially when clamped), and since the tolerances for flatness of the transom are pretty tight (if you want your gimbal housing to seal up against the boat), it makes sense to try to avoid causing any ripples or uneveness in transom around the keyhole. I made a clamping shield for the outside of the boat so the clamps would mess up the flatness. (You can see a picture of it in post #55 of my resto thread: https://forums.iboats.com/threads/t...6-sei-i-o-bowrider.552555/page-3#post-3970626 .)

It is much easier to prevent problems with unevenness around the keyhole than it is to fix them after the fact.

This advice!!! I learned the hard way. I think my transom was already out of spec, but I didn’t know enough at the time to ensure it was perfectly straight around the keyhole before I clamped. This lead to me having to fare out the exterior of the transom to get it within spec. Mercruiser wants no more than 1/16” deviation around the keyhole where the gimbal housing mounts. It pretty much has to be perfectly flat. You can certainly pull it back into spec when clamping and ensure it’s in spec. It’s a lot easier to do it now than to fare it later.

 

[froggy1150]

For your keyhole if you have material..... either thick wood or steel plate.... make something that sandwiches keyhole like 2 big washers. Use like 4 or so pieces of allthread. As long as whatever you use dont flex.
Also when I did my transom I mixed in a little 1/4 chopped glass to give the resin some added strenght.
I will tell you this. Practice Installing several times so you know when you do for real you are prepared. I did mine by myself and knowing how things were going to fit and where to set clamps and tools helped because it setup faster than I expected. If I would have had to stop to address anything i probably would have been screwed.

 

[Chris1956]

OK, probably too little too late. General stuff for transom replacement. Replace transom with like materials, say plywood and cloth. Use Polyester resin, as was used in original construction. If you want to tighten clamps, use thin resin, and give it a long time to cure. Put cloth/mat between layers of plywood. Make sure you have a way to clamp transom on all sides. I used 2X2 to line the perimeter of the transom. It allows screws to replace clamps. Use only stainless screws.

 

[Drivewayboater2]

Thanks All! Great information and advise as usual from everyone. Here is my dilemma… And I know this has been discussed and is probably going to create a ton adversity. Epoxy vs polyester to bond the transom. Pros and cons.
epoxy- better bonding strength. So say all the research ive done. But doesn’t bond well with polyester? True or false?
( that is what the boat was made originally with) and it’s more expensive.

polyester - less than half the bonding strength than epoxy. That alone makes me nervous on such an important part of the transom. Will bond better to existing structure? Hmmm. Yes less expensive but what’s the tradeoff?
I’ve got both epoxy and polyester in my possession.
Any advise? I’m perplexed here.

 

[kcassells]

I used 100% EEEppoooxxyy for my build. There are many discussions pro and con regarding one over the other or a combination of both. You will need to make your own decision based on your research and others input.
Ultimately, it's your call. My opinion is what you start with is what you finish with.

 

[Chris1956]

Epoxy will bond well to polyester, and vice versa, provided the existing glass is sanded and clean. Always wipe existing glass with acetone, prior to adding any resin+glass. Epoxy bonds are stronger.

I use epoxy for high-strength repairs. That would be structural repairs like punctures in hulls, especially where you cannot spread the patch out.

Transoms are real strong due to the two layers of 3/4" plywood typically used. The plywood simply needs to be sealed and bonded to the hull. If replacing transom from the inside, the bonding is pretty easy. You just need to waterproof the interior of the plywood. If installing the transom from the outside, you need to find a way to clamp the edges of the plywood to the hull, then you can glass it to the hull inside and outside. Much harder repair from the outside, but easier to gain access to the transom, versus pulling the cap of the boat.

 

[froggy1150]

Epoxy is also a little more flexible too. General debatable rule is epoxy sticks to everything and poly dont. If your prep is perfect poly will stick to epoxy. Also same with gel coat. It dont stick to epoxy well. With my build I had to do some stuff with epoxy due to prior repairs in the engine area ( dude thinks he hit a whale ) so I planned my transitions from epoxy to poly. I pre wrapped wood in poly/csm. Then I did all the epoxy stuff leaving a poly transition around the perimeter of the repair / transom stuff and did deck In poly so I could gelcoat

 

[kcassells]

See... what I said. lol

 

[Drivewayboater2]

Again thanks all for the input. Im leaning toward epoxy.

 

[Baylinerchuck]

Your boat was originally built with poly and it lasted how long? Probably would have lasted longer had attention been paid to quality and the previous owner(s) treated it well. Poly makes a fine glue, epoxy is better. Strength in a transom doesn’t come from the bond of the plywood to the boat, it comes from the layers of plywood and glass that make up the structure. I personally don’t see much benefit in epoxy with the exception it’s cure time is more forgiving and it doesn’t stink as bad. But it’s your boat use whatever makes you happy.

 

[JASinIL2006]

Your boat was originally built with poly and it lasted how long? Probably would have lasted longer had attention been paid to quality and the previous owner(s) treated it well. Poly makes a fine glue, epoxy is better. Strength in a transom doesn’t come from the bond of the plywood to the boat, it comes from the layers of plywood and glass that make up the structure. I personally don’t see much benefit in epoxy with the exception it’s cure time is more forgiving and it doesn’t stink as bad. But it’s your boat use whatever makes you happy.

This is a really good point. In almost all these restorations, it's the transom wood that fails, not the bond supplied by the poly resin.

Use whatever you want. Both epoxy and poly will get the job done, and if cared for properly, the boat will outlast you.