Modify transom for twins to single conversion?

Does anyone have a link to a good DIY on closing in and re-glassing the transom; I'm doing away with my twin gas sterndrive setup and will be repowering with a single diesel sterndrive. Any help would be greatly appreciated!

 

I've done exactly that 2 years ago.
I had to close both the transom and bottom holes when I removed 2 Berkeley jet pumps. The bottom holes were easy because gravity helped and the bottom was 3/4" laminate without core.
The 2" transom I closed from the inside with numerous layers of glass that kept sagging. When the bottom was 2" thick, the top was only half that, so I used smaller strips of glass to fill the upper half. And when the boat was back in the water there were 2 small leaks in the corners that were impossible to close with grp, so I used Sikaflex 292 in the outside.

Should I ever do it again - and a doubt that very much - I would first make a wooden or styrofoam core, glue that in the hole with Sikaflex or silicone, then build up grp from both sides. I would keep the outer side a fraction deeper than the surrounding surface, add a filler to the resin, liberally cover the grp with it and use a disc sander to obtain a smooth surface. Finally I would spray paint the whole transom with 2 component polyurethane gel gloss.

 

Piperca

When I pluged the hole from an old Omc drive (very large circuilar hole)
I made a simple square jig (of 1x2"s screwed in place) double the size of the cut out and then used a router to cut an inset suitable for a piece of 3/4 in ply wood.

The ply wood was screwed in place then bedded in with a viscous Cabosil & milled fibers slurry. Then with some healthy overlaps glassed on the inside with the outside wall glassed to minimize faring out.

With yours there will be no real load on the transom wall at your repaired areas, so it would seem that you could reduce the distance outward of your actuall plugs, then just do a nice glassing job with the repairs tied into the bottom and sides from the inside.

This approch has worked well for me, but there are many here that are more knowledgable than my self.

 

Thanks for the replies!

Do you guys have any pictures of the process?

I know I have to fill the holes with plywood, but how tight does the plug need to be and should it be tapered to one side of the other? What would be the best compound to fix the plug in position? Is mechanical fastening necessary? Should the plug be sealed with resin prior to fixing it into the hole?

I know, a lot of questions, but this will be my first glass/repair project and, since it's an important one, I want to get it right the first time!

 

Piperca, sorry no digital pictures of my repair.

PM me with your phone # and I can explain.


Mark

 

I am still tossing around the idea of the single setup and inquired on a price from a professional to do the job. I was quoted $4500 to close the two holes in and add a couple of short lengths of stringer (< 5' each) to support the single ... does this sound right? Sounded expensive to me!

 

Closing up holes in a transom is no fun to do, but you must have found a guy who really hates it. Is it a dentist?
I didn't write down how much time is took me, but I estimate it to be 10 hours, so your guy asks $450 an hour, minus a piece of wood, some glass fiber and one Coke bottle of polyester resin...

 

I actually got the estimate from Crystaliner in Costa Mesa, California. They specialize in gelcoat/fiberglass repair and also build boats. I was sort of shocked when he gave me the estimate. I know there is a certain amount of skill involved to make it look just right, but, come on, don't fleece me for it!

I'm still hoping my twins idea will pay off, but in the event it doesn't, I'll be doing the bulk of the repair myself.

 

I justs saw this post. I am currently doing the same thing on a Bertram 25.

I pull the entire core out as you can see here.

http://www.boatdesign.net/forums/fiberglass-composite-boat-building/transom-dual-single-28015.html

I never got a quote, but if it would have been $4500, I'm happy I did it myself.

I have not completely wrapped things up, but I am in for just under $700 which includes:

4X8 3/4" Meranti BS1088 marine ply
5 gallons of Vinlyester resin
10 yds of 1708
Various mixing pots, etc.

Ian.

 

Thanks for the info, Ian, I sent you an email.

Can someone take a look at this and tell me if it is feasible?



The red area would be material removed from inside of the transom, 3/4" thickness, and would be replaced with new 3/4" plywood. The blue area represents the outdrive holes that would be 1-1/2" total thickness. In essence, I would be making one large plug (red area) that would be 1-1/2" at the outdrive holes ... does this make sense? Would this have adequate strength to support a single drive? If so, now all I need is the education to lay up the fiberglass. Are there any books that would show me how to best accomplish this task? Is anyone willing to mentor me?

Here's a picture of the actual transom, so you can get a better idea:

 

That looks good piperca, but make sure the corners have a radius of 1-2 inches. I made them too sharp and had lots of problems with water coming in because the fiberglass didn't want to bend that sharp.
Place a piece of plywood (painted, waxed etc) on the outside and fix it with small screws. Apply gelcoat and laminate from the inside, then remove the plywood after the resin has cured and meticulously inspect your work.
Only when you are absolutely sure that it is watertight, place the plywood core and laminate until the thickness is the same as the existing transom.

 

Your problem is not filling the holes ,thats easy. Your prob is removing the center keel strengthener enough to lower the engines sump low enough so that the leg is low enough in the water to work.

Your original holes look to be about 6 inches from the planing water line. now if you put one of them 6 inches above the planing water line on the keel then you will see that is very low. I don't know if you will be able to mate up the motor but its difficult to judge from here.

You will need to glass in some new engine beds too, rip out the wiring and replace it for a single. Not such a little job.

Then fil in the two holes fare and paint

 

Frosty, I know it can be done. This particular boat attracts a lot of interest to this type of conversion. Here is a photograph of one that has already been done:



My follow up questions were going to be related to the engine beds and moving of, what you refer to as, the keel strengthener. In the above photograph, it appears that they removed it and left it without any added strengthening; however, the entire length of the keel, forward of the engine bay, is strengthened. Here is a photo:



Should I remove the existing keel strengthener first, repair the transom, then install the new engine beds and smaller keel strengthener, as in photo number two or ?????

As for the wiring; I assume you are referring to the engine harness. I have taken that into consideration. As you can see by the photograph of the empty engine compartment, there was a recent rewire done to the boat. As far as the primary wire is concerned, a little reconfiguring will need to be done, but not too much.

Please keep the comments flowing! Any input will greatly assist me and is most welcome!

 

Where is the water intake for that motor? not that piddly little thing over on the stb side is it.

I take it there is no gear box on that Yanmar 6LP as the 6LP needs the rear mounts on the gearbox.

But nice installation

Don't tell you are using the Yanmar 300HP?

 

Yes, I'm considering the 6LP or the 6LY, both 315hp. This engine, as will mine, butts up to a Mercruiser Bravo IIIx outdrive. To be honest, I have no idea where the water intake is for that engine. I believe through the outdrive and (if it were mine) from a through-hull fitting.

Frosty, now that you see what I am trying to accomplish, do you have any advice for me? How should I go about tackling this project ... I am a complete novice!