TOPIC: Transom Prep

I am replacing a transom on my boat and I am preparing the fiberglass on the stern. It looks like the original plywood transom was attached to the fiberglass with a putty. Is it necessary to completly remove this putty or will the new fiberglass bond to it? I am asking because if I sand until the putty is completly removed the fiberglass will be quite thin. This is my first time using fiberglass and any help would be appreciated.

Jason

If you are putting a new transom on, the general practice I believe is to use a layer of fg cloth between the outer layer and the new transom. I use epoxy when "gluing" so I'd sand the area enough to get a rough texture and then use epoxy then fiberglass cloth then the new transom. You can mix epoxy with microballons to get it thicker to help fill in all voids.

Jason,

I don't understand why anyone would bond the glass to the plywood transom with a putty, could it be a layer of epoxy? In any case, if it were my project, I would get rid of it so you have a good surface for a solid bond to your new wood... I would sandwich a layer of thick mat, saturated with laminating resing beween the original fiberglass shell and the new plywood, clamped very well.

Remember that your transom takes the most abuse (needs to transfer all kinds of forces from the engine) of any point on the hull.

Welcome to the forum and good luck on your project. Please keep us posted with your progress and photos. By the way... what kind of boat are you working on?

Dean

Dean

I picked up Runabout Renovation by Jim Anderson...very informative and very well written.
If I was you I'd hold off buy this book and read it.

He explains the steps for this particular part of your rebuild, and when done stronger than factory..i believe his description was using two 3/4"plywood..mat against hull, one pieces sandwiched the the outer piece..course using resin and all...he does explain different types of mat and applying methods of the glass and resins.....
..other option is to use SeaCast.haven't used it myself but have talked with a few people that have and were very happy w/ outcome...

Thank you everyone for the responses.

My boat is registered as a 14' 1970 Star. I am not sure about this because there is no plate on the boat anywhere. I would post a picture but the deck is off of it now. It has a closed bow and sits low in the water. It looks like a small speedboat. I have a 1975 70hp Johnson outboard for it.

The stuff I thought was putty could be epoxy. It is grey in color where the fiberglass is pink. I have posted a picture of it below.



I think I will try to sand more of it off and add a thicker mat or two before the plywood goes on.

I too have been using the "Runabout Renovation" book. The book mentioned to use ACX construction plywood instead of marine plywood but I was thinking of using the marine plywood because I would like it to last longer. Beside my transom is only 5'-9" x 1'-8".

I have found this site very informative and am leaarning alot. Thanks again for the responses.

Jason

Jason ............

I am pretty much at the same stage of transom wood replacement as are you. I made a new transom lamination using two pieces of really nice waterproof 3/4" plywood from Home Depot. One side is clear and the back side has some inserts.

After laminating it, cutting it to final size and rounding over the edges with a router, I slipped it in it's slot. Ha! It only went in about half way. I used the crowbar to get it out and it was easy to see where the tight spots were, with the scratching, color marks and denting on the wood.

I started using my belt sander to grind down the high areas. That was yesterday. After several hours of work (using a too-fine belt), I wrapped it up for the day and hit the shower.

Today, my neighbor came over and brought me a bigger belt sander with a 120 grit belt. He didn't have anything coarser. After a couple of hours of sanding and trial fitting, I had the wood going in about halfway.

Enough of the gentle treatment! I moved a bunch of stuff in the shop and slid out my 6" jointer. I have a 12" thickness planer, but the transom wood is about 16" wide. For the first time, I got out the dial calipers and measured the one piece of the old transom wood. It came up to 1.3", at least 0.15" thinner than the new wood.

I ran each edge of the forward side of the new wood through the jointer several times, trying to get it down to 1.3" I had a hard time trying to get an even cut. It was taking a lot more off the center than the edge. I stopped when the center was down to size, but the edges were still close to 1.4". There was a stripe down the middle a couple of inches wide where the jointer wouldn't reach. I took care of that with the belt sander.

When 4:00 rolled around, I was pooped and wrapped things up for the day. The wood is still 2" shy of going in the slot all the way. Perhaps I'll have time and energy next week to finish the fitting and epoxy the wood in place. I do not plan to use any mat because it will just slip off when I drive the wood into the slot. I'll use West System epoxy with some microballoons to thicken it up.

Looking at the thrust vectors for the transom, I don't believe the epoxy is under much strain. I think I will add some triangular wood gussets to transfer the engine thrust to the floorboards and perhaps the sides of the boat. In my wood homebuilt airplane, the engine mount attachment points on the firewall are tied into the fuselage longerons with similar gussets. The gussets on the boat will be under the outboard well and won't constitute a tripping hazard. I'll make them with an edge glued to the transom about 5" long and an edge glued to the floor and sides about 12" long. (I erred on the sketch. The gusset measurement should be 5" x 12".)

Something like this . . .

Stick with the marine grade. Fewer voids, better quality wood layers and much better glue. I prefer more layers with epoxy and microbaloons between. You can "Clamp" by driving screws in from outside and then from inside. You can then just fill the holes with epoxy paste. Good filets around the edges are important as well. Tie the bottom in behind the floor stringers. In the attached pics, I added an extra 5/16" and just let it sit above the stringers. I hung a 373 pound four stroke on it and it is rock solid and has been in service for 7 years.

Different strokes for different folks or, as me pappy used to say, "Each Cobbler to his own last".