More Transom Questions

[TripleBBB]

New to all this and maybe taking on more then I can chew here but I been reading what I can on the subject and have a few questions.


1. Is Epoxy and Fiberglass Resin the same thing? .... What i Picked up at the store is "3M bondo brand" Fiberglass Resin with hardener. Is this suitable for the job or not?

2. The lumber yard dealer here in Canada (Windsor Plywood) is telling me that the good one side Fir plywood they have, is made with the same glue as the marine grade plywood only difference is its good both sides, and of course the price $122 for marine. $42 for good one side Fir. This project needs to last only about 5 years. Is the one side good Fir suitable, and if so should I put good good sides of plywood to the inside or outside.

3. The old Transom I ripped out had a sandwich of fiberglass mat between them (factory). this is the way I planned to do it also. Please correct me if I'm wrong ... Two coats of epoxy to both layers of my cut out Plywood a layer of soaked fiberglass mat between the two and screw together using 1 and a 1/4 inch screws. (should I remove the screws after it drys and fill in the holes with another coat of epoxy?)

4. What is Tabbing? "tab the plywood into the hull"

I will see if I can get this far ok with out asking the next batch of questions ....

Thanks for all replys

[ondarvr]

1. The resin you're looking at is a polyester, not an epoxy, but it will work. The problem with this particular brand is that it gets hard very fast and can be difficult for a rookie to work with, especially in the summer.

2. Marine plywood is a better product and there are various grades of marine ply for different applications. But if all you want is 5 years out the repair, most any exterior product will last that long. Are you sure you only want it to last 5 years?

3. Yes you can bond them together in this fashion.

4. When the transom is in place it needs to be tied into the rest of the structure, the tabbing typically just refers to the laminate used to do this.

[apex1]

Do´nt know why repeatedly people are talked into polyester on wood? Leave the crap where it is and use the cheapest "real" Epoxy resin instead. It is not that much a difference in price. Polyester has severe bonding issues on almost every material, including polyester. Epoxy sticks to almost every material, polyester included.

Your plywood dealer is a liar! It is not only the glue what makes a marine grade ply, it is the quality of the single veneer layers too! Especially the inner layers of almost all ext. ply sold in North America can hardly be named wood, it is (well you know).

The inner layer of chopped strand mat you´ve found in your transom was a cheap trick the manufacturer used to have no gaps between the wooden surfaces. If you have a reason to fear gaps you can go the same way. If the shape of your transom is simple and you do´nt have a issue with uneven surface and possible gaps, you can just thicken the resin with sawdust (finest grain, almost no grain), and you have a very nice and strong glue.
Yes you should get rid of the screws and either drill holes for dowels which you glue in with Ep, or just fill the holes with thickened resin (a bit tricky).

That will last much longer than 5 years, but a insufficient repair might last just one, and then? Then you know the poor man pays twice.

Regards
Richard

[ondarvr]

As you can see by Apex1's response he does not like polyester, this is a common opinion on this site and for good reason. Most here are into building larger craft of far more value and for what they do epoxy is the product to use.

On small boats of little value and a budget even lower, you need to evaluate the need for some of the higher end products. If you planned to pass this boat onto your grand kids, then yes, you should use marine ply and epoxy, if you want this boat to last five years its not going to make a difference which product you use.

[CTMD]

Originally Posted by ondarvr

As you can see by Apex1's response he does not like polyester, this is a common opinion on this site and for good reason. Most here are into building larger craft of far more value and for what they do epoxy is the product to use.

On small boats of little value and a budget even lower, you need to evaluate the need for some of the higher end products. If you planned to pass this boat onto your grand kids, then yes, you should use marine ply and epoxy, if you want this boat to last five years its not going to make a difference which product you use.

Your missing the point a little here. Polyester is a fine product on a straight fibreglass boat. However it does not bond well to marine ply. Hense the advise in this case to go expoy.

[Stumble]

Lets consider...

Polyester is hard to work with, doesn't stick to anything well, and wood even worse, absorbs water, is mechanically weaker, chemically active, and causes all sorts of problems if you want to paint it with compatability.

Epoxy is aesy to work with, adheres to almost anything, makes a stronger bond to wood than the wood fibers themselves, is effectively waterproof, is mechanically very strong, chemically inert, can be painted with almost anything, and costs about 30% more than Polyester.

For my money there is no competition. Particularly when you remember that a polyester boat has to have an EPOXY barrier coat on it to keep the hull from absorbing water.

For the size of the repair you are talking about there probably isn't more than $10 difference in the material cost of the two.


As for Marine grade ply vs exterior ply:

The definition of marine grade ply is that the veneer must be B-grade or better on both sides, may have knots but no knot holes, and may contain wood or synthetic patches. Internally the maximum void size is 1/8 of an inch, and must be made entirely from Douglas fir or Western Larch.

Standard exterior ply may contain any other permissible species of wood, may have core gaps up to 1 inch, and knots or knot holes up to 1.5" across and only has to be finished on one side.

They both do use the same waterproof contruction adhesive however.

Again this comes down to cost vs reward, but in five years a lot of things could happen, and it might be nice to know that if you decide to keep the boat you won't have to rip the transom out again and replace it.

[Frosty]

If you get half way through the job and things dont go perfectly and the polyester starts to go off before its clamped up or screwed, then the whole thing, Ply and all is scrap.

You will have to chisel it all out and grind back. A bigger job than fitting the transom in the first place.

Does this transom hold a motor?

[Ilan Voyager]

Using a polyester over wood it's a waste of time and materials. I'm almost sure that the stuff Bondo is more expensive per pound than an epoxy. On a transom, if the required thickness is enough you can use a strip-plank of one or two layers of a light wood and a good fiberglass. All bonded with epoxy. That will be less expensive and of better quality that a scrappy plywood bonded with some polyester stuff.

[fasteddy106]

For advice on how to go to this site................

http://www.fiberglasssite.com/servlet/StoreFront

there are lots of tips there plus all the products you might need and they will resond to emailed questions, or you can go to this site for products as well, both offer pricing well below that of retailers..............

http://www.uscomposites.com/

Seeing as how you are new to this you might want to heed conventional wisdom and stay with epoxy resin.

[ondarvr]

I still say I'm always amazed at these responses.

"Most" everything said about epoxy is true, and "some" of what's been said about polyester is true, or at least has some truth in it, but most of it is an exaggeration of both the benefits of one and the negatives of the other.

A repair like this can be done very well with polyester and will last a very long time, the typical DIY repair (done with a little care and some guidance) will far out last the desire for the boat.

I’m not concerned (biased) about which product is used on most repairs and there definitely are situations where epoxy is the product that should be used, but this type of repair isn’t one.

[mark775]

"Marine plywood" was made by Simpson in one plant in Oregon and does not exist annymore. Please research Shelmarine product when thinking "marine plywood". The okume is void-less and put together with a rot and water resistant glue. The meranti is denser, stiiffer, stronger. I know of a scrap of Shelmarine okume (In itself, an unremarkable light-weight wood) that has been sitting in a rotting dory in a temperate rainforest for decades. It has moss growing around it until the dory partially fills up with water and the piece floats. Summer comes and dries out everything, making mud of the detritus leaves, etc.. The boat is literally turning to earth. The sample in the boat - with it one could make a violin.

[SamSam]

Polyester will work, rough grind it first, and yes, you take the screws out and fill the holes with resin worked around with a toothpick to get the air out. You can also drive rot resistant wood pegs into the resined holes. If you drill any holes through the new transom for drains, engine bolts, screws etc, you should also resin those holes before proceeding.

[Ilan Voyager]

The main interest of epoxy, specially for a beginner, is a part the precaution of a very good mixing, is practically fool proof. You have time to work, it glues with no problem, it's intrinsically waterproof.

Take an excel sheet of this small project: calculate the cost of a light wood, some yards of fiberglass cloth and a few pounds of epoxy, plus an estimation of the work and compare with the same in good plywood and polyester resin. The difference is small.

But there is a huge difference; the epoxy version will be easier to make and WILL LAST, being lighter. There is no comparison in quality and duration.

Unless you use the plywood as "lost mold" and use a lot of fiber and polyester to make the transom. That becomes heavy and finally expensive.

FastEddy gave some good links, I'll add one http://www.raka.com There is a small and useful manual.

[ondarvr]

Back to the old E vs P.

Yes epoxy is a better product for many applications, the problem is in the small boat world it just doesn't make that big of a difference either way. Cost saved with polyester is minimal in many cases, but not always, weight saved with epoxy in minimal in most cases, it comes to a few pounds at best.

The better bonding with epoxy is a plus, but for the most part polyester is up to the job, the main reason for failure in these older boats if from rot due to poor workmanship during construction, not an inherent flaw in polyester.

For transoms the bond between the wood and polyester is rarely tested, the forces applied and the numerous bolts clamping the two skins together result in few bonding issues. Its the bolt holes and poor workmanship that result in leaks and rotten wood, it would be the same with either resin.

As for ease of use, one of the main reasons polyester is used in mass production is precisely because of how easy it to use when compared to epoxy. It can be tailored to do just about anything you need it to do and be used by a relatively low skilled work force, this is one of the main problems.

Craftsman building and/or modifying larger wooden craft should never use polyester. But those rebuilding a $200.00, thirty year old polyester boat will see little or no difference in the finished product. These rebuilt small boats get used for a few years and then either sold or scrapped, they aren't high quality items of value that get handed down to the next generation like what many on this site work on.

[apex1]

Unbelievable that this crazy dispute comes up every single time a novice mentiones Poly.

A amateur builder has two choices:

leave it

or use Epoxy



Et basta!

There is no IF, or WHEN, or SOMETIMES ONE CAN and such nonsense!


EPOXY RESIN ON WOOD, OR GOLD PLATED CORTEN STEEL! and even that is only second best.

Was that clear now? And loud enough for the alltimes deaf?

Originally Posted by ondarvr

The better bonding with epoxy is a plus, but for the most part polyester is up to the job, the main reason for failure in these older boats if from rot due to poor workmanship during construction, not an inherent flaw in polyester.

For transoms the bond between the wood and polyester is rarely tested,

As for ease of use, one of the main reasons polyester is used in mass production is precisely because of how easy it to use when compared to epoxy. It can be tailored to do just about anything you need it to do and be used by a relatively low skilled work force, this is one of the main problems.

Craftsman building and/or modifying larger wooden craft should never use polyester. But those rebuilding a $200.00, thirty year old polyester boat will see little or no difference in the finished product.

And , sorry mate that was the sheer nonsense too! You may ask PAR about the "rarely tested" issue for example, he did and as a result he has a very straight opinion on that subject!

Regards
Richard