Plywood for Transoms, Decks, and Stringers

[Ned L]

:encouragement: Its all good!

 

[GoldDuster360]

I paid $94 plus tax for a 4 x 8 sheet of marine 3/4 fir. It was 7 plies, good stuff. Compared to the labor the cost of the wood is almost insignificant.

 

[Woodonglass]

I paid $94 plus tax for a 4 x 8 sheet of marine 3/4 fir. It was 7 plies, good stuff. Compared to the labor the cost of the wood is almost insignificant.

Well, a full restoration on a typical 20ft boat will usually require about 6 sheets of plywood. At that price That would be a little over $500 bucks for the wood. If you bought the cheaper Ext. Grade at $35 bucks a sheet and used Polyester resin, the savings on the wood would pay for approx. 10 gallons of resin. Some guys need to budget for their boats in such a manner, others want the "BEST" of everything. To each his own. I think it's important that we try to show everyone ALL the options so they can make the best choices for their situation.

 

[DeepBlue2010]

Well, a full restoration on a typical 20ft boat will usually require about 6 sheets of plywood. At that price That would be a little over $500 bucks for the wood. If you bought the cheaper Ext. Grade at $35 bucks a sheet and used Polyester resin, the savings on the wood would pay for approx. 10 gallons of resin. Some guys need to budget for their boats in such a manner, others want the "BEST" of everything. To each his own. I think it's important that we try to show everyone ALL the options so they can make the best choices for their situation.

As long as we make it clear that these options are not equivalent and they DO NOT accomplish the same results. The extra money for marine grade is not for the word "marine" like some other product out there, it is for the quality and characteristics of the plies and glue manufacturing process. CDX, Arauco or whatever else is just not the same and I did work with all of them.

Personally, I would advise against cutting corners or be pennywise when it comes to structural elements like wood that will form the backbone of the vessel and will be buried deep under the deck with no way to get to it and upgrade without a complete teardown and another restoration efforts.

If anyone is really that short on cash, they should sacrifice going out on the boat the number of times that will make the extra cost of rebuilding the boat. This will be wiser choice in the long run. JMO

 

[bonz_d]

As long as we make it clear that these options are not equivalent and they DO NOT accomplish the same results.

I may be mistaken but I think that is just what WOG was stating in his last sentence. At least that's the way I took it.

 

[Decker83]

All of the real strength comes from the glass and resin.. You can, if you chose to, build your stringers out of cardboard..

 

[Arawak]

All of the real strength comes from the glass and resin.. You can, if you chose to, build your stringers out of cardboard..

That's a bit misleading. You can certainly build stringers that do not require any core, but most of the boats people are repairing here rely on the core for some portion of the load bearing. It's a cheaper way to achieve the same net strength.

 

[Arawak]

On the topic of baltic/russian birch..... I built a daggerboard for a 12' sailboat out of it several years ago. Did well enough over the 3-4 years of occasional use it got. It did not stand up to the boil test, which is supposed to simulate behaviour over time, but it's hard to say how different manufacturers will behave.

It's certainly strong and fairly stiff, but really really heavy. I might consider it for a small transom, but definitely not for stringers.

Also, if it's in any location where it might eventually absorb moisture, it will rot quicker than exterior fir plywood.

 

[Decker83]

That's a bit misleading. You can certainly build stringers that do not require any core, but most of the boats people are repairing here rely on the core for some portion of the load bearing. It's a cheaper way to achieve the same net strength.

What I meant was you can use cardboard for the form to lay the glass over instead of wood.. It has been done that way.. The boat manufactures use wood
because it's cheap and will not last the way they build them in days past.. There are boat manufactures that don't use wood at all now days..

Not trying to mislead anyone here.. Just a comment..​

 

[Arawak]

Not trying to mislead anyone here.. Just a comment...

I know, and of course you're not wrong, but some folks might read that and think they can use the same lamination schedule most of us use here with any or no core material at all.

I'm all for innovation, but unless people really know what they are doing (or are willing to do the research), it's safest and most cost effective to stick with the methods people have been successful with here.

But the kinds of construction you are mentioning are often discussed (often by professionals) at boatdesign.net and Joel Shine at bateau.com had an article on foam core stringers, for those who are interested (and can afford those methods).

 

[Woodonglass]

Well I mentioned the cardboard stringers back in Post#10 and they were in a 1950's runabout and trust me they were not constructed with any better methods than what we use here on the forum. In fact probably far worse. One layer of what was probably 24oz woven roving and even then it was poorly done and resin starved in many places. They counted on the hardened rounded 1/2 pipe glass structure to carry the load and it had done it's job for over 15 years with no noticeable failure in the hull. Every discussion of cardboard stringers in any detail on this forum, has always mentioned the need for the glass to be built up to an adequate thickness(usually around 1/4") to carry the load since the cardboard would only be the "Mold" and not carry any of the load. This post was not a detailed discussion of building cardboard stringers, only a passing mention of them. The risk of a newb reading this one dissertation on cardboard stingers and then taking off and doing his entire build based on this one post is minimal IMHO. And if he did...and is not willing to do enough research, then the error would be on him not on iBoats!!!

 

[Frey0357]

Thanks WOG for mentioning this product! I for one got an incredible deal on a 3/4" sheet of the product ($10.00 on the discount rack!!), and I intend to use it. I will coat it with epoxy for moisture resistance and just go for it. 13 ply, birch is a heck of a lot better than the wood chips (pulp) that was my transom when I started my project!

Frey

 

[61mysteryboat]

Check the glue lines on it. Waterproof glue will generally be dark in color. I will post a picture of mine when I get to a PC. Although, It does look like baltic birch from the number of plys and the void free core. The other difference I see is that my plys are all parallel and of even thickness. No overlaps in the same ply. Then again does it matter if it is sealed in epoxy. I am going to seal mine in penetrating epoxy first.. Others have said it wasn't necessary but since I already own the epoxy I figure it wouldn't hurt. Best of luck.

 

[Woodonglass]

Uhmmm Frey, I'm pretty sure that's NOT Baltic Birch plywood. It's probably Interior Cabinet Grade Birch Plywood and uses interior grade glue. As stated not the best choice for Marine grade but structurally prolly better than you had and as long as you do a good job of glassing and then take good care and do good maintenance to ensure no water penetrates the encapsulation, it should last a good long time. Make sure to pre-coat the wood with a good soaking coat of resin prior to laying any glass.

 

[bonz_d]

As a tin builder all I can say is that I'm glad I don't have to deal with this issue. I'll stick with decking and transoms. Thanks!

 

[61mysteryboat]

Here is the photo of the Baltic birch I had spoken of earlier.


notice the dark glue lines and uniform ply

 

[Watermann]

That is some nice looking ply. Someone needs a new plywood saw blade for xmas though, :lol:

 

[61mysteryboat]

I knew someone was going to comment on the fuzzy cut. That was a cut off piece using a cordless circular saw. I just use that to get pieces more manageable. Actually, I have a Forrest blade in my cabinet saw that will almost leave the cut shiny. Sorry.... my insecurity made me explain that.

 

[61mysteryboat]

Ahh.... now I can sleep. lol

 

[pro-crastinator]

No Title

Heres what I did.
3 pieces of 1/2 inch plywood, glued together with epoxy
12 layers. good to go.

I'm not sayin 13 layers is unlucky........