Transom Plans-Fiberglass Mat Questions

[jmwj03]

I have read every transom repair thread here, and most of the general fiberglass questions and I still need a bit of help. All of the wood is out, the glass is prepped, but I have some generic fiberglassing concerns. Here are my plans<br /><br />Cut a piece of 3/4 ply and a piece of 5/8" ply to the proper shape, epoxy togethere with thickened epoxy and screw with stainless screws. Let dry.<br /><br />Wet the rear transom existing fiberglass hull and one side of wood (from above)with a thin epoxy but do not let dry. Lay a piece of mat against the existing fiberglass, then using a layer of thickened epoxy, "glue" the wood against the rear of the transom.<br /><br />Wet the front side of the new transom with thin epoxy (don't dry), then install mat with thickened epoxy, then install the original inner fiberglass from the transom and let dry.<br /><br />Use tape around the seams from where I originally cut the inner transom. I left about a 3" border all the way around so I could reattach. I will feather the edges of this cut so that when I had the tape, it will result in the same thickness as the original.<br /><br />Then, seal the top with new glass cloth (using epoxy) and install another piece of mat across the front of the new transom (over the tape and seams that I did previously). I will cut this mat 8-10" (4-5 on each side) oversized so it will wrap into the sides of the boat.<br /><br />Sound OK? Here are my questions...pretty generic. The transom needs to be 1.5", which is why I am using a piece of 3/4 and a piece of 5/8. The difference I assume will be made up by the mat I install between teh new wood and the original rear of the transom. <br /><br />First of all, what weight mat should I use here and again on the front? What are the normal thicknesses for different weights of mat? IOW, what weight mat will give me that 1/8"? Remeber, there is going to be a piece of mat at the rear and on the front, so each will need to add only 1/16" to the mess. Is this enough?<br /><br />Lastly, it is an I/O (3.0 OMC) that will be in the boat. If I can, should I add braces between the transom and stringers? They weren't there originally, but I have space if it would help and make a difference as to the thickness of mat.<br /><br />Is that a detailed enough description?

 

[mutron77]

Re: Transom Plans-Fiberglass Mat Questions

Jay,<br />Imo<br />The best thing to use would be Biaxial cloth instead of mat. Expensive, but much, much stronger. Would put some thickened epoxy fillets in the corners where the transom meets the hull on the inside. Your taped corners should be curved and not right angles.<br />I would suggest calling West System and asking them for advice. They have a tech assistance number to call on their website. They are all into boat building over there and will share their expertise about that and about the correct West system products and methods. I talked to them several times and they are always glad to help. Alot of great free epoxy work info on their site too.<br /><br />Good Luck <br /><br />H90

 

[record hunter]

Re: Transom Plans-Fiberglass Mat Questions

I see you are getting closer I don,t think you should use the mat or any cloth with the thickened apoxy though You will not be able to saturate the cloth with that kind of filler once you mix it up you will see that When you use cloth any type you have to saturate anyone who reads this thread and that has done glass work will tell you this is right. keep going getting closer

 

[JasonB]

Re: Transom Plans-Fiberglass Mat Questions

When I did the transom for my 85hp outboard, I used two pieced of 5/8 ply with two layers of heavy roven woven between them, the encapsulated the entire transom board in cloth/resin. My guestimate is that my transom is strong enough to throw about anything at, so an 85hp should be no problem.

 

[jmwj03]

Re: Transom Plans-Fiberglass Mat Questions

Recordhunter, reread my 1st post...I plan to saturate the mat with a thinned epoxy, and then use thickened to make the bond. I talked to a local fiberglass place and they said this is what to do for the strongest transom. Since 99% of the folks here were doing the same thing, I decided to keep with the mat.<br /><br />I do understand what you mean about the thickened not wetting out the mat...that's why I was going to use thin stuff 1st. <br /><br />I may get a start this weekend on at least encapsulating the wood. I'm going to try and find additional information about the thicknesses of the mat today/tomorrow.

 

[Winger Ed.]

Re: Transom Plans-Fiberglass Mat Questions

Sounds like you're doing OK. You might keep a little resin handy for mopping around inside any holes that penetrate the transom. Often water will get inside a bolt hole, can't get out, and will begin to rot the wood around the hole a few years sooner than you'd think it should.<br /><br /><br />If its a I/O, I'd check the engine mounts real, real well. They're at least as important as the transom as far as taking the engine's weight, and the stresses of thrust.<br /><br />For example: I did a big project on a 75 Starcraft 23' fiberglass hull with a small block Ford 351 Mercruiser in it back around 2001. The engine mounts looked like they came from a railroad tressle and were tied into the hull from the transom forward for about 5 feet.<br /><br />But;<br />The transom looked normal inside & out. I found it was almost completely made of 2" thick fiberglass covered cardboard--- <br /><br />CARDBOARD: <br />as in a real thick corragated cardboard box---- <br /><br />Imagine my surprise,<br />once you got a few inches away toward the sides from where the outdrive unit actually penetrated the back end and tied onto the bottom of the hull, no more plywood, just cardboard with a layer of mat on it to look normal. <br /><br />In this application, the transom bore almost no force, or even very much weight from the engine or I/O unit. It was carried by the engine mounts and the bottom of the transom under the outdrive unit as they tied into the bottom of the hull. <br /><br />Not saying that is how your OMC I/O bears its weight & forces, but don't forget to check your engine mounts while everything is apart.<br /><br />Ed.

 

[jmwj03]

Re: Transom Plans-Fiberglass Mat Questions

Well recordhunter,<br />I took your advice. I went to the local West Marine the day before the store manager moved to another city! He used to own a fiberglass repair shop.<br /><br />What he said was that he's heard of people doing teh mat, and that it coundn't hurt anything, but that he wouldn't take the time. So I didn't.<br /><br />I soaked all edges of the exterior grade plywood with thin epoxy, glued the two pieces together with thickened epoxy, than parked my van on it overnight!<br /><br />I then put a pretty good coat of the thickened on both sides of the wood and fit it down between the fiberglass shell. I did drill quite a few additional (maybe 15-20) holes through the transom into the wood to help clamp it. Should be no problem to fill...just have to remeber to not get excited and forget about them before I take it on the water the 1st time! <br /><br />Came out great! Then I rebuilt the stringers. One more piece of wood to go across the top of the stringers and I'm done (except for touch up fiberglass and mending where I cut the top of the boat off)...I hope to get the motor back in this weekend!