Need some advice on transom materials

[matt88]

I have spent the last 2 weeks gutting out the rotten transom on my new used boat and I took the advice of a local boat builder and bought some pressure treated 3/4 in plywood at lowes today. According to the builder he told me I could used the pressure treated as long as I let it sit out in the sun and dry out for a few days. He even gave me a scrap piece that he was about to throw out that made the first layer of my transom. I got the first piece cut and fitted and noticed it was a little twisted so it is sitting in the bed of my truck with cinder blocks all around it. I started reading some transom rebuilding threads here on iboats and it seems that lowes/home depot pt ply is not the best choice. I also bought another can of resin which I think is the polyester type and it seems that more people prefer the epoxy. If I build it with the materials I have will it be strong enough and last several years? Not sure how long I will keep this boat but I would think this would last ten years or more. Does this sound accurate? thanks

 

[Woodonglass]

Re: Need some advice on transom materials

Is this a tin or fiberglass boat?

 

[Mark42]

Re: Need some advice on transom materials

If the ply is warped, be sure to cut the two pieces so they each have the warp the opposite orientation. That way, when glued together, they cancel each other out. Believe me, this works. Its what I had to do to get a removable section of my deck to be flat. Even the non-pressure treated CDX I used for that piece was warped. Darn near imposable to find really flat ply, even from real lumber yards.

BTW, I used water proof carpenters wood glue to attach the two pieces of ply together. Used regular sheet rock screws to hold them together until dry, then removed the screws. Bingo! Pool table flat ply. Using carpenters glue will make a better bond than poly resin, even with chopped mat between. And its less messy, and less expensive.

I noticed that the transoms I dug into were not laminated using resin and glass. They were laminated using glue. Just something to think about.

Here is the section of deck (about 22" wide by 48" long). It needed to be strong enough to walk on without flexing, lay flat, and was only supported by the edges. It was covered in resin/glass and works very well.

 

[matt88]

Re: Need some advice on transom materials

15ft fiberglass imperial ski boat with an 85hp mercury. I have some pics on another thread here. Mark, I do remember reading some posts about using gorilla glue and the like. If I get back to the hardware store before I set it in I will pick up some. If not I will probably go with what I have now. I appreciate the advice. The builder I mentioned before also told me that he would sometimes cut the back of the hull off to get to the transom. Then he told me he was selling out and he hasnt owned the place for a year so I figured I would be better off taking the word of the iboats guys instead of his,lol.

 

[Woodonglass]

Re: Need some advice on transom materials

DO NOT Cut the Back skin of the transom!!!!! You will Never get the boat to align properly again. Bite the bullet and do this the right way. Make Certain the PT plywood is Dry. the Chemicals used can inhibit the bonding characteristics of the resin.

 

[matt88]

Re: Need some advice on transom materials

I have taken the cap off the boat. When the builder told me that he was cutting the back off that was when I decided to get a second opinion from you guys. I have the first piece glassed in now and I am hoping it will be solid. I mixed approx. 120 drops of hardner to 16oz of resin. (I screwed up was thinking of 8 oz mixture) The can said 14 drops to one ounce. Used a roller to heavily apply resin to the ply then rolled a coat to the hull cut a piece of mat for in between and used scrap pieces of ply and wood screws to pull it tight to the hull. The screws will come out once the resin cures. Am I screwed royally on the mixture being off or is it possible for the resin to cure properly with a longer curing time?

 

[Woodonglass]

Re: Need some advice on transom materials

With that amount of Hardener I doubt it will harden. You should probably go ahead and remove it and start from the beginning. You're not the first to make that mistake.

I'm just sayin...

 

[matt88]

Re: Need some advice on transom materials

Im done for the day now. Been working on it since this morning. I had to raise the transom a few inches and the first batch of resin is exposed at the top with some mat. If I go back tomorrow and it has hardened do you think it might be ok? I was reading somewhere on the net and it stated that during hot temps you could get by with a 1/2 the amount of hardener that would normally be used. That might be true and it might not I really have no idea? When I left it this evening it had hardened some but not fully yet. I fitted the second piece and glassed it before I quit so it will really be a pain to get it off now. The high today was 89 degrees. Would that make a difference? thanks

 

[Mark42]

Re: Need some advice on transom materials

As far as cutting the back of the transom, there were maybe 3 members here that did it that way rather than remove a complicated cap. If done well it should be strong, but the real issue I see is getting it to look nice. Most people have the skill to replace the transom core, but not all have the tools and/or skill to do good finish work with gel coat, etc.

The down side is if its not done right, it can cause catastrophic failure.

 

[oops!]

Re: Need some advice on transom materials

it will take much more than "a few days in the sun" to dry the pt ply.

try 2 weeks in a hot sun with a fan on it. if the humidity in the air is high.....it will take a lot longer, and you are better off to dry it in a humidity controlled area. (the drying wood will tend to soak up the humidity in the air)

while the resin may seem to soak in....the bond is still weak as the moisture from the wood will come to the surface during the cure of the glass.

 

[matt88]

Re: Need some advice on transom materials

I wouldnt risk cutting the back off unless I was attempting a project like the hull extension but I probably wouldnt attempt that either unless I really really loved the boat. That looked like a whole lot of work. Good job on that oops.

 

[Gypsystar17]

Re: Need some advice on transom materials

Just finished transom on my MFG,used exterior 3/4 ply,glued layers together with epoxy and bonded to hull with epoxy,then polyed the whole thing over with matt and roving.would not use pressure treated.just made sure no epoxy on outer edges of transom cause poly won't stick to epoxy.

 

[Bob_VT]

Re: Need some advice on transom materials

Exterior ply would have worked unless you are concerned about bugs infesting the wood........

 

[eavega]

Re: Need some advice on transom materials

With that amount of Hardener I doubt it will harden.

Wouldn't it depend on air temp? I was doing some fiberglass work outdoors. Here in GA the temps have been in the mid 90's during the day, and even in the evenings when I have been working on the boat the temps are still in the upper 80's. I used the recommended 10 drops per ounce using poly resin, and found that my resin had a pot life of less than 5 min, and a working time of less than 10 min before it totally gelled. I cut it to 8 drops per ounce and found that I now had closer to 10 min pot life, and almost 20 min of working time. The resulting work was sandable within a couple of hours.

-E

 

[Woodonglass]

Re: Need some advice on transom materials

Cutting the amount of hardener by 1/2 could be a problem. 25% is the max I would ever recommend to compensate for temperature issues.

I'm just sayin...

 

[matt88]

Re: Need some advice on transom materials

It has hardened but it did take several hours instead of the 10-15 min it took the second batch with the correct amount of resin to harden. Think I will give it another day or so to cure take the screws out and if I cant separate it by moving it back and forth I will probably leave it. Probably will add some stainless screws for piece of mind though. i have a big piece of diamond plate aluminum that would look good on the back of the boat. What would be the best way to seal the screws to keep water from getting in? Or would adding the aluminum plating and screws cause more problems in the long run than they would fix now?

 

[Woodonglass]

Re: Need some advice on transom materials

I really see no need for the plating. You should have adquate strength with what you have. If you use the screws predirll the holes fill the holes with resin, coat the screws with resin and drive em home.

 

[matt88]

Re: Need some advice on transom materials

This is where I am so far. Took the screws off this evening shook it with all I had and it seems pretty solid. Even though it doesnt look like it in the pic there were many many many hours of sanding around the circumference of the transom. Also,Im far from done. Ran out of jelly tonight. I plan to sand some more and go all the way around again with jelly and hit the spots I missed. I also plan to sand some more after that and put a couple layers of woven glass on it before I put the cap back on. My hats off to some of you guys that made this look easy because although this is officially my first fiberglass transom rebuild. It was anything but easy. Lot of blood and sweat in this one. I remember the good ole days with my aluminum jon boat. The transom replacement consisted of one 2x8 some cutting and some bolts. Took me all of half of a saturday,lol.

 

[redfury]

Re: Need some advice on transom materials

My supplier of resin completely recommends working faster and not going below the minimum hardener to resin ratio. You can get MCP hardener instead of MEKP if you need longer gel times ( about 2x )

Polyester is recommended at 1.25% ratio, so a 500ml batch of resin is going to need approximately 6ml of MEKP. Really, it's so that the resin hardens properly and bonds to the surface it's being applied to. This is chemistry, and the wrong ratios screw up the chemical reaction.

 

[matt88]

Re: Need some advice on transom materials

Well,living in minnesota probably helps too,lol...Im sure you have a nice big climate controlled garage so Im just messing with you. The resin to hardner ratio was more of a brain fart than strategy. Thanks for the reply though.