TRANSOM REPAIR... Experienced advice needed

Hi to all members,
I have just joined this forum and I am hoping someone with experience will be able to offer some sound advice for me so I can complete my transom repair. I hope I am posting this in the correct section. I apologize if I'm not.

Condensed version of my questions:
1) Will epoxy adhere to and created a strong bond to plywood for transom that has been treated with timber preserver?
2) Will polyester resin adhere to and create a strong bond to plywood for transom that has been treated with timber preserver?
3) How deep do timber preservers penetrate the timber?
4) Can timber that has been treated with timber preserver be successfully encapsulated in fibregass (as in the transom) without delaminating or having moisture build up inside the fibreglass?
5) Am I better off using epoxy resin on the fibreglass bi-axiel cloth instead of using polyester resin?
6) Will epoxy resin give a better and stronger bond than polyester resin on the transom?

I wanted to use timber preserver because I bought A grade exterior plywood instead of marine grade ply because I was on a budget.

I appreciate any advice on offer and thank you all in advance for your help.
Cheers
Dick.

Boat: Savage brand.
Age: 1970's
Material: Fibreglass
Hull shape: slightly rounded but is almost flat.
Transom: Origionally designed for a short shaft motor but because I am putting in a new transom, I will be adding another 5 inches of height to the transom wood to make the transom capable of taking a long shaft motor becasue my boat motor is a long shaft motor.
LOA: 12' feet.
Beam: (at widest part) 5'3" inches (five foot and three inches)
Power: Mariner 30 HP long shaft outboard motor.
Motor weight: Approx 65 kilogrammes (2.2 pound = i kilogramme)

HISTORY:
In June 2008, I was given this boat - an old fibreglass 'Savage' 12' foot runabout manufactured sometime in the 1970's (I imagine). It had no details on the consignment plate. A friend gave me the boat as a project to fix up for fishing trips and he told me it would be really easy for me to get it back in good condition and would not cost much to do this. I have never had a boat before this one and I soon realized there is no such thing as a 'cheap' boat. So far it has cost me an arm and a leg and I feel I am almost getting nowhere with it because I just can't seem to find someone with experience to answer my questions. Once I am armed with good sound knowledge from someone who has rebuilt a transom like mine then I will be better prepared to complete my transon fix using the right method and materials.

I had to remove the old transom wood because it was rotted. This was a nightmare of a job but I think I did it right. I cut through the fibreglass skin from inside the back of the boat and removed the rotted wood. I left the outer fibreglass shell on the outside of the transom, so all I needed to do was to then cut the new transon plywood to shape and epoxy it in and then encapsulate this in fibreglass. NOTE: I have used polyester resin with chopped strand fibreglass mat as well as fibreglass woven cloth on other parts of the boat, however, I will be using bi-axial fibreglass cloth to encapsulate the transom.

My problem however is this: I could not afford to buy marine grade ply for the transom wood so I bought a half sheet of 'A Grade' of 3/4" inch (18 mm) exterior ply with the idea of treating this with an epoxy based timber preserver. I have been in touch with the company's technical support team at Wattyl - the company who manufactures the timber preserver - and I was given different information to the information I was given by the company's sales rep. I simply wanted to treat the timber using the timber preserver before I put it in the transom. However, now I don't know what to do because even the tech support guy from the company that manufacturers the timber preserver isn't sure if timber treated with this product can be successfully encapsulated in fibreglass without delamination and/or weakening of the transom timber under the weight of the outboard motor and the stresses placed on the transom. And he is not sure if the timber preserver will react in a negative way with the epoxy resin.

I wanted to use epoxy to install the new transom plywood. This would entail me smearing a thin paste of epoxy over the surface of the old inner surface of the fibreglass shell of the transom and also applying a thin paste over one side of the new transom plywood and then clamping these together. Once cured, I then wanted to encapsulate the new transom wood in bi-axial fibreglass cloth using epoxy resin. The sad thing is that no one can tell me if either polyester resin or even epoxy resin will make a strong lasting bond with the surface of transom plywood that will be treated with the timber preserver and then encapsulated in fibreglass. Another irony is that the tech support from Wattyl can't tell me how deep the timber preserver actually penetrates into the surface of the timber. I had the opportunity of buying the West Systems timber preserver but I went for the Wattyl brand instead because it was half the price of West Systems. I was told the Wattyl product was just as good. I should have bought the West Systems product because I'm sure they probably know more about their own products than Wattyl does!

Many thanks for reading my post and I look forward to hearing from someone who can advise me. Sorry this post is so long.

Cheers
Dick

 

This is a difficult question to answer because I don't know what type of wood preserver you've used. In most cases yes, unless it's waxed based or one of the newer CA types of treatments.

Ditto the above answer. You'll have to tell us what you used.

Who cares (frankly) so long as it does it's job, right? Each type of preserver handles protection differently. Some seal the wood fibers, others apply a repelling material, others a pesticide, etc. Penetration is irrelevant so long as it works.

Again, we need the type of preservative used.

These questions appear to be the same. Epoxy is far superior to polyester resin in strength, water proofness, it's ability to stay stuck to a substrate, etc. It's so much better that you don't even need to use mat, unlike polyester, which requires mat to bulk it up.

Simply put, you don't need timber preservative if you fully encapsulate the plywood with epoxy. An encapsulated wooden part is far more protected from rot with epoxy then than any wood preservative, assuming the coating remains intact.

You are miss using the term "encapsulate" as we use it. You are thinking you'll "encapsulate" with 'glass cloth (biax) but this isn't how we use the term, even though from a technical view point you're correct. When we say encapsulate, we mean coat every inch, notch, cutout, end grain and fastener hole with unthickened epoxy, at least 3 coats. This forms a water proof barrier and seals the wood into a dimensionally stable piece. In this state it's immune to rot, no preservative required.

For the best job of your transom core rebuild, coat (encapsulate) the transom core (plywood) with at least 3 coats of epoxy. Then bond this to the inside of the hull shell with thickened epoxy. Fillet the edges to the hull shell with thickened epoxy and add biax in over lapping layers around the perimeter, "tabbing" the new core to the hull shell. 6" or more should be the over lap onto the hull shell. This is the basic version of what you need to do.

So, to recap:
- Skip the wood preservative, epoxy will do a better job anyway.
- Epoxy will stick to well prepared surfaces and is preferred over polyester
- If you've already used some sort of wood preservative, tell us what it is so we can determine if it's going to cause an issue.
- Use the search tool on this site. We have literally hundreds of previous threads about your very set of issues. Transom core replacement is a commonly encountered problem. You'll learn a lot, though you will have to wade through a lot of previous stuff too.

 

Epoxy is a superior product. However, polyester will last twenty years or so. I would not use any preservative. The resin, whichever type you use, should penetrate the wood as much as possible.

 

Hi Par,
Many thanks for your reply. I was laid up in bed yesterday with back problems so I wasn't able to reply to your response sooner.

I have read your reply, and what you said makes a lot of sense. On your advice, I have decided NOT to use the timber preserver which is "Wattyl SeaPro TP 80" - a two part epoxy system. It has a it's own specific thinner that the company said must be used to thin the SeaPro TP 80 by thinning it 50% for the first coat and then thinning it again by 25% for the second coat. It is simply called "L760 Thinner". Sad though, because I already have enough of the product to do the transom. I may think about using this product instead on my own coffin so that it preserves it longer!

I will now just be using fibreglass bi-axiel cloth with epoxy resin to cover the transom in the method you described. And I will be making up a bog (paste) of epoxy and filler to fillet the transom wood in. Any holes that I have to make in the transom after it is installed will be the holes near the top of the transom to hold the engine and a hole for the bung in the lower part of the transom. I will be sealing these holes with SIKAFLEX Marine compound prior to fitting the bung etc.

Par, I apologize if I used the term "encapsulate" incorrectly. I will now be reading as many of the threads on this site as I can regarding transom repair.

Par, many thanks again for your help in answering my questions.

Also for gonzo...many thanks for your advice. I will now be using epoxy from now on, even if it is a little more expensive than polyester. This old boat I am fixing up may be that only boat I will ever own (because of finances) so I want it to last a very long time.

Thanks guys!
d_e_dick

 

Another simple trick that will make your transom live a lot longer is to "bond" the engine mount holes. To do this, mount the engine about where it should live, then mark the hole locations. Remove the engine then drill the holes 30% over size. Fill these over size holes with thickened epoxy (silica/milled fibers/wood flour, etc.) and let cure. Then drill the epoxy plugs for the actual bolt diameter. Any moisture that gets past the bedding caulk will not be able to get at the plywood, because of the epoxy ring around each bolt hole.

 

You can combine the last boat you will ever own and your coffin. Viking lords did it.

 

Par, many thanks for your advice on the method you described when installing the engine mount holes. I will definitely be doing this on your good advice.

I alreay have the epoxy paste for fixing in the transom and yesterday I bought some epoxy resin and hardener for when it comes time to cover all areas of the transom in bi-ax cloth. I wanted to get some wood fiber for mixinng with the epoxy resin when I fillet in the areas around the transom but the place where I bought the epoxy appeared not to have heard of it and he suggested another man-made fibre product at a ridiculous price. I may even decide in the next few days to see if I can get the wood fibre from a supplier via the Internet. I would like to have my boat in the water by Christmas. The weather will be warmer here then (Australian weather) and the fishing can be really good.

Thanks again for your advice Par.
Cheers
d_e_dick

 

Hi gonzo. Your sense of humour is good. My finances being the way they are (bad) I doubt if I will even be able to afford a coffin when the time comes. So, your suggestion of combining my boat as a coffin really got me laughing. In my mind, I can see them pushing my boat (coffin boat) out to see with my body covered in dried tinder and the flaming arrows being shot from afar into the boat and igniting the tinder and everyone weeping onshore as the smoke gets higher. I hope they just push me out to sea without the flaming arrows because I hate the smell of smoke!

Have a good one gonzo.
Cheers
d_e_d

 

Your luck, none of your friends can barely hit your floating funeral barge with the flaming arrows. When they do the harbor patrol sees the fire, calls the fire boat and it's quickly put out, off course the water sinks the boat. They raise the boat as a hazard to navigation and find your partly toasted, slightly enjoyed by the locals as a "dropped from the sky" entree and the investigation begins. Eventually, they decide to press charges against one of your arrow wielding friends and wife, for possibly expediting your demise, certainly responsible for the navigation hazard..

 

Will polyester resin adhere to and create a strong bond to plywood for transom that has been treated with timber preserver?

ANSWER TO USING POLYESTER ON ANY SORT OF WOOD IS NO!!! NOT NEVER!!!!! , DONT THINK ABOUT IT!!!! YOU WILL BE WASTING YOU TIME AND EFFORT !!!!:?:

 

I would suggest pre-drilling the core with 1/8th (3mm) holes 2" (50mm) apart to allow the primary core bonding adhesive to squeeze through when you clamp it, bringing any excess mix and trapped air out with it.
Allow to cure and grind flat before laminating the new inside skin.

 

Hey Par,
If I was to make a comedy movie about boating, then I would (with your permission and a share of the royalties) like to incorporate your VERY humourous ideas about my 'funeral barge' as aprt of the main story line. I'm still laughing about what you wrote. My luck doesn't run too good these days, and in a way, with my almost lack of experience with boats of any kind - be it owning one or refurbishing one - I feel a bit like Charlie Chaplin at the moment. I do however really hope I can complete my boat by mid December (at least) so I can have it out on the water on Christmas Day. The damn thing will probably sink as soon as I take off from the pier!

Par, I'm beginning to become a little concerned about one matter though: I'm getting the feeling that "POLYESTER" seems to be a dirty word in the boating community. I have (perhaps regrettably but due to financial restraints at the time) already used polyester resin on every other part of the boat. I used it to re-build and re-shape some of the chines using polyester resin and chopped strand mat as well as thin layers of woven cloth (the woven cloth being a pain in the a## to work with) over angles etc. I also used chopped mat and woven cloth and Polyester resin to re-pair a 60 cm (2' foot long gash near the upper chine at port - side near water level and then had to re-shape this area because of a very bad repair it obviously had well before I got the boat. So, almost the entire bottm of the boat that will be below the water line is covered in either choped stand mat and poly resin or a covering of chopped stand mat and poly resin and woven cloth, or both. I did however use about three layers of woven cloth on all the chines simply because chopped strand mat was too bulky and I was led to believe the woven cloth would be stonger than the chopped strand mat. I re-skinned almost the entire inside of the hull using just chopped strand mat and poly resin. The only part of the inside of the boat that will have EPOXY will be when I use it to lay the biax cloth over the transom and also for fixing in the transm wood.

I have also painted the bottom of the boat with POLYESTER FlowCoat. I used this FlowCoat on the underwater part of the hull instead of painting it with marine paint because there may be times when I may need to drag the boat up onto the sand etc. and I wante dthe boat to be a little abrasion resistant in thes area. I intend using marine paint for all the above water parts of the boat and the outside of the transom. I'm sorry now that I didn't use epoxy resin from the very start of my project. I will however consider applying two coats of epoxy resin to the above water line parts of the baot as well as on the inside of the boat. If I hadn't already applied the FlowCoat to the bottom of the boat, then I would conside applying two coats of epoxy resin to this area so as to water-proof it better and make it a bit tougher.

Okay, I'm off now to begin writing the script for the movie. Have a good one Par. I hope the day is nice for you.
d_e_dick

 

Hi Astute Boats,
Thanks for your reply. I have never done this kind of a repair before and never worked with epoxy or polyester either, so please forgive me if the following question sounds stupid: Would pre-drilling the core of the plywood with 3 mm holes every 50 cm apart weaken the overall strength of the plywood. Your method of drilling these holes makes a lot of sense. I know epoxy is a very srong adhesive and becomes rigid when cured. I can see how by drilling the holes you suggest will allow any excess mix and trapped air out, making a better bond between both surfaces (plywood and inner transom skin), but I was just wondering about the overall strength of the plywood transom doing it the way you suggest as opposed to not drilling the holes.

Are you saying to pre-drill these small holes over the entire transom wood? Would I come in from every edge of the plywood 50 mm and then drill the holes or would I drill close to the edges? I'm just curious about the method you suggest because I may do what you say.

I look forward to hearing from you.
Cheers,
dead_eye_dick

 

I'm not sure what Astute is talking about, though it sounds like he's describing one rather tedious method of repairing delaminated plywood. This isn't the case in your boat Dead Eye, so you can discount that post.

There are ways to improve the bond of polyester resin to wood and there are ways to improve the waterproofness of polyester resin over wood. Unfortunately, judging by your descriptions, you've not employed these techniques in your repairs. This means they will be tenuous at best.

Keeping the boat covered, clean and dry will prolong the life of the boat, so keep this in mind for the future.

If considering epoxy over coating on your boat, rather then the topsides, I'd coat the bottom first and all of the outside is the budget permits. This will barrier coat the hull, which of course needs to be painted, but it will waterproof what you have.

This isn't the end all of things for your boat. It'll survive depending on the care you give it. If you stay after (quickly repair) nicks, dings and divots in the plastic sheathings, then you're boat can last a generation, maybe longer. On the other hand, if you let the care get away from you, those marginal polyester coatings will come back and bite you in the butt (a place to aim at during the funeral march?). Again, keep it clean, dry and covered and she'll serve you well, much like a good woman.

 

Exactly and correct,that also makes for a consistent bond line.