TOPIC: 1964 Crestliner Del Rio transom question.

I have run into a question on my boat restoration. The Del Rio had an 80hp motor on it and the hull tag says it is rated for 90hp. When I opened up the rotten transom, it is only 1" thick. The recess on the deck won't allow it to be thicker. It's hard to tell because it was so waterlogged, but it actually looked like it may have been made up of 3 layers of 3/8". That would be 1-1/8" thick. Either way, everything I've read says that it should be 1-1/2" thick for an 80hp. Am I going to run into trouble if I replace it with two layers of 1/2" marine plywood? I was thinking of possibly adding some vertical stiffeners to the inside of the transom at both sides of the bilge, but they could only be as tall as the deck recess would allow. Any advice would be much appreciated. Jim

jimdelrio,

1st, WELCOME ABOARD.

IF it was my boat and I was "limited to" one inch thickness, I think that I would use as many layers of 5MM plywood as I could get into the transom & "butter" them all with thickened epoxy.
(Epoxy by weight is stronger than steel.)

In any case, a 1" thick transom with an OB motor that big/heavy would make me "nervous".

yours, satx

How thick is the glass on the outer skin? If the cap of the boat will allow you to increase the thickness of the transom without interfering with it going back on then I'd for sure go back with a 1.5" transom. Pics of the back of your boat will help us to help you.

Make it as thick as the cap will allow then keep adding what you need to make it thick enough but make it as tall as the inside of the cap.

If your transom is that rotted your stringers are most likely goon as well

Scott

FWIW every transom I've replaced was two layers of 3/4" ply.

Thank you all for your input. After thinking it over for a while, let me run this by you: The only thing that's limiting me to 1" is the recess in the deck where the motor will clamp. It comes down about 5". The actual motor bolts through the transom are down about 9". I'm thinking two layers of 1/2" marine plywood the full height and then a third inner layer to the bottom of the recess to provide a full 1-1/2" thick at the bolts. (I may even make that third layer from 3/4" ply) I would also add a block at the clamps when I finally install the motor to spread the pressure across the width of the transom. I'm not sure if most of the reaction from the motor occurs at the bolts or at the clamps, but I assume at the bolts if they are securely tightened.

MyFlamingo: The outer skin is about 3/32" thick. I plan on adding a couple layers of fiberglass on the inside to make a backing for the holes that need patched before I add the wood transom.

Woodglass: The stringers are long gone.

Thank you again everybody. Jim

Jim, I've been thinking about your problem and thought that maybe your transom could be reinforced like the factory did the older models of Del Rio. The piece of Marine grade plywood on the outside of the transom might have been their way of strengthening it. Here's some pics of the plywood on mine when I repainted it a few years ago. I hope (if you go this route) maybe these pics will help out. Jim L

That's interesting Jim L. Is that just through-bolted?

I'm also giving serious consideration to just grinding out the back wall of the deck recess and re-fiberglassing it back in 1/2" forward. Drastic I know, but it seems like maybe that is how it should have been in the first place. The original aluminum cap is pretty trashed so I have to remake that anyway. I'd just have to make it 1/2" wider.

The top 4 bolt through the cap and the rest just screw into the transom. Most of your stress is at the top of the transom anyway when you throw the juice to it.

In the late 1950s, many boats had transoms made up from three layers of 3/8" plywood - Glasspar being on of them.

By far, the best way to add strength is to build thickness across and up the entire transom. If you have to, cut the back out of the motor splashwell and trim the sides of the well to allow for the additional thickness. You can glass the splashwell pan to the new transom face so it's water-tight again. Bolting up sandwiches of plywood on the outside of the boat will invite rot, and not add much strength. If you have a motor with clamp screws, the depth of the clamp opening is the maximum thickness (finished) that the transom can be. If you are using a bolt - on motor without clamp screws, you can make the transom as thick as you want.

I agree Bruce. The more I think about it, the more I think that is the way to go. Thank you.

I'm back at it and have another quick question. The inside of the outer skin has that green coating on it which I assume is epoxy. The holes that were filled have the same green epoxy filling them. As you can see from the photo above, it chipped out in some spots when I removed the wood. Do I need to get all that green off before installing the new wood, or is it sufficient to just rough it up and smooth out the harsh edges? Thanks Jim.

Doing a quick test is a good idea when dealing with unknowns like this. Glue on a small test block maybe a inch square. After it sets up knock it off with a hammer. If stuck enough to rip the wood off the block, then just rough it up (60-80 grit) and go. If it just popped off leaving little behind.... Sorry you got a lot of work to do.

Great tip! Thank you. Would it make a difference if I was planning on putting two layers of matting on the inner face of the outer skin before I add the wood?