transom material

going to replace the transom in my boat sometime after this summer, the lower part has some rot from being 20+ years old and being stored outside most of its life before i purchaced it.seems to be a fairly easy one to replace after removing the engine,outdrive and a few other things mouted to it.very easy to get to without having to cut to much glass out to remove. so i wanted to see if anyone had an opinion on or experience with using plastic plywood in the transom? my transom is basically nothing more than 5 sheets of 3/8 inch plywood on top of each other with fiberglass on either side. does'nt look to even be as much as pressure treated, but i'm unsure of the strength of the plastic plywood? it does come in the same standard sizes as wood does so fitting would'nt be a problem. i'm just don't know alot about the plastic, but it sure seems that if it was usuable it would eliminate the rotting issues in the future. any comments helpful, thanks

This is some interesting reading

http://www.rotdoctor.com/glass/GLrotrepair.html#transom

Bill

DO NOT use pressure treated material for this. Resins DO NOT adhere to PT material, and will release shortly after installation!

Also, you should not be cutting into any fiberglass material other than the laminating layers and final top layer.
The Original Hull material should remain un-disturbed.

A router w/ a straight flute bit, set to the correct depth, will allow you to section the original "Core Material" into smaller sections that will make removal much easier.
A pneumatic chipping tool works great for this.

Cover yourself with Baby Powder to help keep the glass from entering your skin.

No need to use layers of 3/8" material, IMO.
I'd use two (2) layers of Fir plywood that will make up the thickness required (maybe one layer of 3/4"... another layer of 1", for example).
You will be creating a "Box Beam" effect when all pieces are completed.
(I.E., original hull/matting/plywood layer/matting/plywood layer/matting/ finished with Roving.)

This plywood need not be Marine Grade. Many factory installations did not use Marine Grade..... they opted for construction grade CDX. It will work just fine! Make sure that the core is also Fir!
(Fir is one of the best that offers both strength, and resistance to moisture deterioration and lends itself to resins very well)
Oak, Maple, Birch, Oily woods, are all inferior to Fir, IMO.

Layout, more layout and layout.... accompanied with many dry fits!
It may take you as many as ten/twelve dry fits to get all pieces to fit well. This is KEY to having a good job!

Use every available hole in the transom to pull the resin wet first layer into position. You may even need to make a few new holes, as hard as that is to bring yourself to do!

A straight edge, or "stiffener" can be used on the exterior to prevent the original hull material from distorting while the original core material is absent! A hull/transom without the core material may flex.... the new core will stiffen the Un-Straight transom causing issues when the Volvo transom shield is installed later!


Second layer can be screwed to the first layer from inside!

Cut your transom unit opening last!

While this may seem like a fairly easy and straightforward repair, I must put in a strong recommendation for having this work done professionally. It probably won't be as expensive a job as you think it will be especially if you only have them do the actual wood replacement and reglassing and do the final finish work yourself.
The number one reason to farm this out is that it will require a significant expenditure in resin, glass and wood as well as the consumables that go along with glassing operations. There will also be the woodworking tools and sandpaper, primer, paint , gloves, tyvek coveralls, respirators, vacuum cleaner...quite a long list of stuff. If you already have most of this stuff on hand it's not so bad, but if you have to get it all just for one job, it gets pricey. Add to this your labor for doing the demolition, making the new parts and glassing it all in. Count on it taking three times longer than you think. At the end you will have an amatuer job, a big mess and a bunch of leftover materials.
Another factor is weather. Once you open up the transom it must stay dry until you have finished the job. Do you have an indoor work space?
Not least is the itch factor. Even with the coveralls, you will have that nasty fiberglass itch. I hate that.
I consider myself a fairly good fiberglass person and a transom repair is a job I wouldn't take on. Last time I had one done it was $1400 for an 8 foot transom. Best money I ever spent on hull repair. I did all the prime and paint so it was easy. Drop it off, and pick it up two weeks later; write a check and boom it's done. If there are any issues, you can always take it back. I used Composite Yacht in Trappe MD. Tell Martin that Bill with the Allmand sent you.

eastcoastitalian said:

don't know alot about the plastic, but it sure seems that if it was usuable it would eliminate the rotting issues in the future. any comments helpful, thanks

Click to expand...

What eliminates rotting is full encapsulation of the wood. Plastics like Coosa are great for making forms to wrap with glass, but have very little structural strength on their own. If you do the repair use good old fashioned wood. Just don't poke holes in it after the fact. In many cases the transom is made of wood laminates but gets drilled into, has a stern drive poking thru it and other assaults which leave pathways for water. If only the holes were made the right way (drill out oversize, fill with thickened resin, drill for fit) there would be far fewer repairs needed.

I've only done five transom core replacements. Evey one has been much better than the factory had done! This will become apparent as you remove the factory core material.... particularly if this was a "Chopper Gun" built hull!

It is nothing more than carpentry work and common sense..... mixed in with teaching yourself how to work with glass and resin.

I rebuilt my transom, stringers and deck last spring. Took the complete boat down to the bare hull. It's not rocket science but it does take time, patience, and ability to follow directions. I'd say it's as much art as science. As far as material choice, opinions are all over the board. I happened to use marine ply since it's made locally, is readily available, carries a limited lifetime warranty, and the price is reasonable here. Your mileage may vary.

It may be just the transom that's rotted but you'll need to carefully check the stringers as well. Would be rare to find just the transom affected. There are other forums that get into restoration in great detail with a considerable amount of expertise to lean on.

Some of us go to those other forums as well . Come on now, it's not illegal to be a member of other forums. It's like being a member of the Elks and the VFW at the same time!

appreciate all the input, i'm sure once i get into it its gonna be a bitch,i have most of the tools needed and indoor space to work on it, so weather won't be a factor.i'd love to have someone repair it for me, but there are'nt many trustworthy places around my area that want anything less than around $2000.00 for it, and that kind of money into a $1500.00 boat just is'nt gonna be a wise investment on a tight budget, so i've either gotta do it myself of part the engine out and to the landfill with the boat. glad to know the plastic plywood will not work, will stay clear of it, quite a few lumber yards around so the wood should be easy to come by.will not be cutting any of the original hull its self. i can remove it very easily with out damaging the hull, its actually very accesable to get to, will post pics. when i get to it.i think the original problem was water leaking through holes on the transom when i purchased the boat there was at least 20 random screws or bolts throught the back of the transom all striped out with no signs of ever having gone to anything?"the guy i bought the boat from was a 1st class idiot!" i've learned this from many other things he attempted to repair on the boat that i've had to go through and fix the correct way, after trying to figure out exactly what he had done.i reglassed in all the transom holes he had made before i ever took the boat out, but who knows how long they were there?? i'm sure the damage was already done.once again i appreciate all the input, i'll post back on how it goes in a few months. gonna start after the summer, we don't really have winter here in fl so the boat gets used year round but much less in the winter so i figure that will be the best time to start on it. just will have a loger time waiting for the glass/resin to cure in the colder weather, but i'm in no rush as long as i get it done sometime before summer 2011