More Transom Questions

Apex said it loudly, I'll use a softer voice:

Polyester is inherently not waterproof nor a good glue. Polyester is a product for laminating nothing more. Whatever the level of craftsmanship the wood and polyester will delaminate and rot, I have a long experience of this fact. None of the trials of wood polyester I have seen since 35 years, whatever the precautions taken (polyurethane primary, phenol inhibition by cobalt naphtenate, mechanical "keying", and others) has been successful. Delamination appears within the first year.

Wood and polyester are simply incompatible like oil paint and galvanized steel.

Transoms on small boats using outboards have a lot of stresses. And truly I do not understand the rage of using polyester with an exterior plywood while you get easily better and more durable results with some cedar or pine and epoxy/glass for a very little difference of price.

I'll add that the shell life of epoxy is very long (I have an epoxy 10 years old that I use for fixing doors and small items) and shell life of pre-accelerated polyester very short. A matter of weeks in tropical climat. If the reseller gives you an old polyester you are "F....d". And I won't talk of the problems induced by paraffined polyester, which is the most common.

Using polyester is far more technical and ask for higher skills than a common 2/1 marine non blushing epoxy. Besides polyester, because of the styrene, is far more toxic than epoxy (and smelly).

 

It looks as if you may not have understood what I said or meant by "rarely tested", it has nothing to do with actually testing the bond with each resin, epoxy does it much better.

What I meant was transoms don't typically delaminate at the bond with either resin. When you take apart an old transom (small ski boat), even when the wood is almost pulp, the polyester laminate is typically still bonded to what little wood is left, it may pull off very easily, but was still stuck in place. I meant the bond doesn't get stressed to the point of failure.

The other factor is that in production these boats were built with poor practices, rarely was the wood pre coated with resin, it was put in place and then chopped over, resulting in an even poorer bond.

Many people get very emotional about this subject, mostly on the “hate polyester” side.

Like I said before polyester is not the product to use on wood boats and when engineered correctly epoxy can be far superior polyester, its just that on these small old ski boats it doesn’t make much of a difference.

 

Depending on the type of epoxy and the hardener used, it can be far more toxic than polyester, this one of the other reasons for it not being used in mass production. Styrene does have a very strong odor, but the actual toxicity and health issues are less.

This has nothing to with aged product, or using the wrong type of polyester.

Polyester can also be purchased in an unpromoted state, this extends the shelf life dramatically.

The waterproofness of polyester has little to do with the failures on small ski boats, they sit on trailers for 99.9% of their life. They need to be leaf and weed proof. They get used for a few years and then sit in the side yard under a tree for the next 6 or 7 years and fill with debris, many times the plug was never even removed, so it turns into a frog pond. The poor methods of production now come into play, with thin laminates and unsealed wood, there’s little hope for survival.

 

Mexico is the cemetery of the old American motorcycles, trucks and boats. A lot of used items are sold to the Mexican who are too "poor" to buy the new item.

So I'm continuously asked about how to fix a surprising array of polyester boats since the 12 feet to the 45 feet. Almost all (let's say from the smaller to 36 feet, about 98%) have a structural web, decks and transoms of plywood and polyester and 100% are delaminated everywhere and most rotten at least at the web and transom.

My general advice is "if you are not ready to a total rebuilding of the boat, just keeping the outer fiberglass hull, use one or two gallons of gas and matches to burn it"

At five years old, all these hulls I have examined show structure damage at different extent. At 15 years old it's generally junk: the hulls are "soft", needing a general rebuilding. It's cheaper to go to Tampas or Corpus Christi and to make the bet of buying another used boat.

It's incredible to see the amount of work, and material (crappy plywood and lot, but lot and lot of fiber and polyester) used in those ill fated structures when a simple 1/2 inch marine plywood, some 1*1 and 2*1 inch pine and good epoxy resin would have done the job for less work and money.

 

"polyester, because of the styrene, is far more toxic" but dead is dead. Don't take epoxy lightly because it smells pleasant.

 

Nice and practical idea, I must say.

Just calculated a theoretical layup using my (yard internal) data, but should be valid in general. Based on 4m² two strips of WRC 18mm slightly offset, glassed with 240 gsm multidir., 3 layers Ep both sides is a tad cheaper than the same layup in marine ply, isophtal poly. Pennies only.. but quality sure worth it.

Regards
Richard

 

I V

(Qoute) At five years old, all these hulls I have examined show structure damage at different extent. At 15 years old it's generally junk: the hulls are "soft", needing a general rebuilding. It's cheaper to go to Tampas or Corpus Christi and to make the bet of buying another used boat.

It's incredible to see the amount of work, and material (crappy plywood and lot, but lot and lot of fiber and polyester) used in those ill fated structures when a simple 1/2 inch marine plywood, some 1*1 and 2*1 inch pine and good epoxy resin would have done the job for less work and money.


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I agree, the construction is poor and these boats were built to a price point, not to last. Had they been made from epoxy they would still be failing due to the poor methods and workmanship though, poorly done epoxy laminates and cheap ply still add up to failure.

Remember, the polyester resin used to build many of these boats was purchased for its price, not for its strength and water resistance. Every time a cheaper resin was formulated it went right into production, as long as it got hard it was approved for use.

It may have been a blessing that epoxy was tougher to work with, had it been easier and used in production more often, the product would have been degraded and sold on price like polyester was. This would have destroyed its reputation also

 

No chemical product is innocent. A smell is not a criterion of toxicity. Prussic Acid has a pleasant smell of almonds... But epoxy is mainly a contact (skin) toxic with almost no vapor and it's rather easy to avoid its contact with gloves, creams etc... Styrene is a vapor you breathe, a toxic for the brain and the liver, directly by the lungs, straight into the blood stream. it's far more difficult in a DIY shop to have active carbon filter special respirators, or outside breathable air than to put gloves and cream, that you have also to use with polyester.

Just search the security sheets of epoxy resins and styrene. With epoxy you'll use little solvent, with polyester you'll use lots of delicate products like peroxide, cobalt naphtenate or octoate (good explosives mixed together, highly corrosive), and solvents in high quantity, from acetone to some chlorated stuff.

Polyester is highly flammable and uses a lot of dangerous adjuvants. Epoxy is hardly flammable and apart a few drops of xylene as solvent won't use dangerous products.

Besides I find easier to mix 2 parts of resin/one part of hardener with a tolerance of 10% (better to go a bit on the side of the resin), than 1 part of polyester with 2% of cobalt and eventually paraffin diluted with styrene, and after catalyse with 1 to 3 % of peroxide following the ambient temperature and the "jellification" time wanted .

And I hate this horrible smell that can last years in a boat. A I precise again; the short shell life of polyester makes if you have bought an "old" polyester resin you're "F....d" even if the resin looks good. I do not see an amateur making the mix of accelerator for small quantities.

A last thing, no often you can finish a work in a day. A cured polyester resin needs sanding until exposing the fibers to insure a mechanical key.

A lot of non blushing epoxies have until 2 days of tolerance. Generally a cleaning with hot water and soap plus a light sanding insures a good bonding. Better you can use delaminating cloth; a bit expensive but fast and effective.

 

Thanks for the compliment. Here I use Chiapas cypress, a kind of light white cedar, very durable, rather cheap I can find locally. With 2 layers (0-90 and 45/45) of about 240 gr cloth each side is more than strong as I use a resin with good resilience. I make even the floors and decks this way now, the scantlings being adapted. I do not bother anymore to import plywood here in Mexico.

 

I agree with you.

 

Well thanks to all for the reply's and information you all have provided.

After weighing all that has been said, the polyester resin went back and I picked up West system 105 epoxy resin and 206 hardener. After looking at there chart I also selected the 403 microfiber adhesive filler. I hope this was the right selection to laminate the 2 (also heeded advice and went with the marine grade plywood) together and then secure them to the the transom shell?

BTW this is a smaller boat, 15 1/2 foot open bow with a 60 HP on it.

BBB

 

You're welcome and I'm very happy of being of any help. Do not hesitate to send a message if you have a problem or a doubt. Best wishes for your project. (yes you have bought the right products, a bit expensive but good ones. Buy a few ounces of colloidal silical or cabosil to control the thixotropy of the resin)

 

and i fully agree
finally epoxy works out cheap anyway

 

Welcome 9B
and I would like to backup Ilans statement.
Thanks Manie.

 

Well after a nice vacation I'm back at my little project and chugging along slowly, right now I have my 2, 3/4" sheets of marine grade plywood cut out and coated twice with un-thickened epoxy. I am about to bond the 2 together and am not 100% sure so looking for advice ... Do I have to wet them out before applying the thickened epoxy? and I plan on applying the thickened epoxy with a 1/8 notched trowel, will this be a thick enough layer to bond the 2 sheets?