Baltic Birch for transom recore ?

Checked out sheet for for a transom recore on a 26' twin I/O boat. This stuff is marketed as premium underlayment material. Says all plys Baltic Birch, no voids and exterior glue. Looks like good stuff, flat & smooth and 9 plys I think.
This is about $55 for a 4x8 sheet of 1/2" nominal thickness, will be laminating 3 sheets one at a time in the boat.
Is it worth using this or would plain old cheap ext ply work just as well for core material?

 

A transom on an otherwise cheap old boat might not warrant top shelf materials, but an otherwise high value boat deserves better stuff.
The wood you should be investigating for a transom replacement for a reasonably nice boat would probably be Douglas fir, two layers in your case,3/4" marine plywood. The transom is subject to a lot of issues--- it sits in water with a drain hole below the waterline, has motor mount or outdrive bolts passing through, a great force pushing on it, in short, you want the best materials and methodology when you build it.
The 3/4" marine ply would require only one gluing, half as much. The three 1/2" layers will eat more glue and time.
As important is that you encapsulate the whole panel in epoxy (three coats usually) before you attach it to the boat. The holes for bolts, fittings and drain and other holes all need to be given a lot of attention since they are just about always the source of water ingress, and no doubt the cause of the original transom problem.
Those holes all need to be oversized to begin with and jacketed by epoxy rings (prior to glassing is best).
Any case, the bottom line is use the materials that contribute to a boat that is made up of parts that have similar longevity and value. If it's an old work skiff you want to get another five years out of (because the whole rest of the boat is nearly played out, go quick and dirty and cheap. But if it's a gold plater, don't chase that with materials that would detract from its value.

 

Baltic birch has rather high sugar content which makes it a good ground for mildew etc. So if used monoethyleneglycol before epoxy..

 

Baltic birch is not waterproof but water resistant. If you take a square of it and boil it you will see the plies separate. I did this before using on my boat rebuild. I do use it where water is not an issue - for interior joinery where it is either painted or epoxied and kept out of the bilge in any case. For structural and possibly wet areas I use Joubert ply which I believe is the best available. Not only are there no voids but every ply is void free to start with and not pieced whatsoever. It is Lloyds approved. I think a piece of exterior grade fir is more waterproof than the baltic birch and the boil test would prove it to be so or not. The problem I had is that good quality marine grade fir is almost unattainable locally (Victoria B.C.) and exterior while probably as waterproof as most is full of patches and lousy looking surface veneers but if it will be encapsulated in epoxy and biaxial cloth or similar then it would be ok in this regard. It will have voids though and you have to watch out for these. Here is a link to Joubert: http://www.westwindhardwood.com/PDF/Jourbert/JOUBERT-SalesBrochure-ENG.pdf
Brian

 

Do´nt use birch ply for marine applications! Although the material of choice in aviation, it does not do well on the water.
Use a hardwood marine ply instead. All the "Mahogany" substitutes, like Okume, Sapeli and so on.

Regards
Richard

 

If you plan to use it you want to get more specific information about the mfg country. If it is Finland the glue used will stand the boil test and you only have the rot/mold to worry about.

If it was made in Russia or Estonia you don´t want to touch it with a two meter pole.

 

Well, the best quality actually is made in Russia! (and the highest quantity too) it is completely DIN EN ISO standard and stands every common test as the best.
And Estonia btw. is the number one country in terms of efficiency in the whole EU. The Baltic Suisse.......

sorry to contradict you completely
Richard

 

How come they sell us only the cheap and non-waterproof stuff?

All the cheap no-good plywood in Finland seems to come from former Soviet states, wheras all the domestic production has been glued with waterproof stuff for decades.

 

I have heard that there is very crappy stuff around the Baltic, but do´nt know where it comes from. It may be (just a wild guess) that they export mainly to central Europe (the good quality).
The Finnish was (and is) known for being first quality thats true, but the Russian at present is better.

No offense meant.

 

I'd try Baltic Birch if it were cheap AND it passed a boil test (I bought a booty-load of 1/4" once for very cheap, but did the boil test).
However, other plywood doesn't need to be tested every time. It's also going to be a wood species that holds up well in the marine environment even if it does get wet. That's why I'd use fir in a transom. It isn't best for many applications due to the surface changes it can go through, but otherwise it is reasonably light and ultra-strong.

 

DO NOT GO FOR BIRCH PLY IN MARINE ENVIRONMENT

That was clearly stated (and backed by arguments) above.

 

Apex, Im curious as to why are you so adament about not using baltic birch plywood in a marine enviroment? if you are concerned with resistance to rot it is rated as "non durable",the same rating as Okume which you seem to approve of so obviously either panel will require epoxy protection, as someone suggested,one should do a comparative boil test of the birch before using it to test the glue line but throw in some known BS1088 Okume samples as a baseline. Ive been seeing the Baltic Birch in the lumber yards and have been very impressed by the construction as pointed out by the OP but have not yet done the boil test myself. As Alan has pointed out Doug fir is very strong and "Moderatly durable" but unfortunatly the construction of every panel i have ever seen is woeful,we make the worst plywood in the world here in the US, a good reasonably priced panel with the same duability rating as fir is BS1088 meranti which i find offers good value for the money where weight is not an issue,unfortunatly you cant just walk in to the lumber yard and pick up a sheet so its worth exploring the Birch option.
Steve.

 

Well, if your coice is between devil and satan, of course it is worth to try birch ply too. I do´nt know the quality of US ply from own experience, have just heard (mainly here) that it is almost all crap.
As I stated above it is a perfect material in aircraft building (a top quality Birch) but a weak one when wet. And Teddy brought another point up, the sugar content. It rots much faster than, for example, the Mahogany substitutes. The boil test is a obligation, no matter which ply you buy, but thats common knowledge I think.

Richard

 

Absolutely right!