Excellent Article In Bass And Walleye About The Comparisons Of Wood To Composites In

I have a 1960 Norris Craft with almost no rot in the transom even with a few holes through the glass cap. A little get rot and away I go.

On my Formula V race boat it was an Allison 1983. The bottom broke. The bottom used thin plywood from the transon to the seat area in rectangles of appox 4" X 10". They were all rotted. from the seat area forward was balsa in small squares. Appox 60% of this was bad.

I re did the bottom with foam inbedded in epoxy cut into small 1 1/2" squares. I used the foam for the weight. The epoxy mixture formed minature I beams and made the bottom very strong.

However after being involved with capsules and accident investigations as an inspector and referee I chose balsa core for the capsule I put in. It is 3/4 balsa, end grain. I would put my capsule aganist any built. When we put it in we cut the nose section off and glassed the capsule into the boat. We then ran a 18 wheel tractor over the nose section without even a deflection. A foam cored section could not hold up to this. It did weight more, but hell it is my butt in it.

We kept the transom of wood core.

So it depends on what you are trying to achieve, and how you do it that will determine the material used.

One interesting part of the article is some manufacturers use pressure treated wood for their boats. All the resin manufacturers I have worked with always said it was a no-no. Something to check out.

Klegecell is a PVC-based, rigid, closed-cell foam with high thermal stability and structural integrity similar to Divinycell.

In addition, Klegecell foam is impervious to moisture and unaffected by rot causing fungus and mold.


Klegecell is resistant to oil, fuel, and cleaning solvents and completely compatible with polyester, vinylester and epoxy resin systems.

It will not support combustion and is self-extinguishing.

Also, since Klegecell is a closed cell foam it will not absorb water.

Klegecell has a high strength-to-weight ratio like Divinycell. Therefore, it is ideal in applications such as boat transoms, LNG storage tanks and many others


Foam vs. Balsa Wood and Honeycomb

Balsa wood and more commonly plywood have been used extensively in boat construction for many years.

While these materials provide excellent compression and stiffness properties for a relatively low cost, they can be heavy, susceptible to water absorption, and will eventually rot.


Foam cores can be much lighter, fungi resistant, and do not absorb water or any other fluids encountered in a marine environment.


There is also evidence that foam cores have better fatigue resistance than balsa wood. Laminates made with foam cores can last longer and weigh less than wood cored laminates, while producing adequate physical properties. Wood is still a viable material to be used in areas where highly localized compression loads or through fittings are present (such as engine mounts and around cleats), where the appropriate high-density foam core may be too expensive.

Balsa's drawbacks are that it is at least twice as heavy as foam, and can become heavier still by absorbing large quantities of resin (sometimes called wicking) along its grain during lamination - and water too if the skin should later be punctured, whereas PVC foam with its closed cells is virtually non-absorbent. Balsa is also vulnerable to impact, so it should not be used under a thin skin in areas where it might get dented, with consequent delamination.


As stated, NO ROT, NO ABSORBTION AND no FUNGUS and self exstinguishing...

I think the website your talking about that surveys boats is called yacht survey…here is the link.

Yacht Survey

When I started my own project I looked at all the alternatives; epoxy, marine ply, kevlar, vinylester, foam etc, etc, etc.

One big advantage to plain ol’ polyester resin is that you can reduce it by 10-15% with styrene monomer…it really becomes quite thin and really soaks into the ply. After it sets you can come back and lay down an un-thinned coat for glass or as a final seal coat.

Bottom line is that you don’t have to get too exotic to have a perfectly sealed and strong wood design that will in most cases out perform other materials.

The entire back half of my boat was designed with cheap CDX ply and poly resin…nothing fancy, very strong and light.

You could see in my Bayliner how the rot started at the motor bolts and went out. Then again, it was on there since 1983, and sealant only lasts so long. So I drilled the holes big and epoxied in there twice, then pumped 5200 everywhere around/under the clamps. I might have tried the pipe method had I known, but I am sure the boat will die before this transom if it lasts as long as the stock one. I did 5200 the inside nuts, and even forced it down the bolts. I did this in case it ever flooded on the inside for some reason as the bolts are not that high from the floor. I would guess you should reseal it every so long.

I also found since then, that at the local Menards you can buy small peices of oak plywood, like 2x2'x3/4". Supposedly better wood I would have used, even though the oak is only the outside the plys are high quality. Cost would have been ok for small chunk.

I just painted the wood with epoxy and it seemed to soak in pretty good, not knowing how far. Had to use two coats as the first soaked away. After second it had a shine, and a couple spots took three. Did floor panels that way too, and carpeted.

Several people interviewed mentioned the problem of the engine mount bolts not being sealed durring re-power as common problems.

I too was shocked to read of the use of pressure treated plywood with glass, and have read it is taboo!
Very much rot resistant but, can't glue it, can't glass it, can't paint it, humh?

Hehehe, ya the Force has a nice bright aluminum block in it, and the rest of the motor is painted, bolts all scratched up!!! Wonder what dealer did that?? I was done before I got it, but I found no sealant at all on the bolts when I pulled that big anchor off the rotten transom.

Does anybody use cyprus for anything? I know thats what they build water-wheels out of, like for grist mills , and they last for 50 or more years. However they stay wet. I think it makes a difference, getting wet and drying out over and over.

we were building the race boats. Spruce for all stringers and any kind of blocks. One of the strongest woods there is for its weight.
Lighter even than pine.
On low budget boats I have used (with good succes)clear white pine in place of the Spruce due to cost and availability (actually close in weight and strength).
For plywood we used Okume which is an African Mahogany and is still in popular use today.
I found out the hard way long ago that there is a big difference in "Marine" plywoods also.
On one of the budget builds I found what I thought was a great deal on 1/4". (They actually go by metric sizes)
Once it was deliver'd I found out why it was so cheap.
It was 3 ply (normally 5 ply in that size) luan which is the same stuff they sell as "under layment" in the local DIY centers.
It was crap!
Another time I ended up with 3 ply 1/4" fir (with the football plugs in it) instead of Okume.
The real deal was 5 ply with no voids, but was around $90. for a 4' X 8" sheet back in the '80's and I think has more than doubled since then.
We used to use 3 ply 1/8" (3mm) for decks, the stuff was amazingly strong for how thin it was.
Built one "A" Stock Hydro w/a 1/8" bottom and doubled the last 2' to make it a 1/4" thick. I think that boat was about 9' 3 or 4" and weighed 57 lbs un-rigged.
Try that with glass:D

I had a guy who does house trim make me a sub box once. It is 1/2" and looks like 9 plys. They use it for the sides of drawers in kitchen cabinets. How would that work in a transom?

Wood is the classic boat-building material. That's why you can find boats approaching 100 years old still in regular use that are made from wood. Pound-for-pound it is stronger than steel and far stronger than glass fiber (much lighter too). It has many, many good points going for it, and if used correctly, works better than just about any other material.

As astutely pointed out previously, it is itself a composite material. However each species of wood has its own "performance," and, therefore, the correct wood must be chosen for the appropriate usage. Decks on WWII (and previous) naval boats were teak which is nearly impervious to rot and deterioration. However, teak would not be the wood of choice for something like engine stringers or frames for a variety of reasons.

The problem with most wood used in boats is that it is not treated correctly. It needs to be epoxy encapsulated whether using Smith's CPES or a hard epoxy like those from West Systems, System 3, or MAS. The encapsulation barrier gets broken down when someone drills a hole through the wood and then forgets to encapsulate the edges of the hole - and that's where rot will start if the wood is exposed to water. Encapsulate the hole's edges, and you again have a totally rot resistant material.

An epoxy sealant like Smith's CPES makes a perfect "prime coat" for any type of paint or varnish. Hard epoxies can also be painted or varnished with most marine materials. In most glass fiber boats using balsa, the wood rots because the glass fiber materials have failed first and allowed water to get to the wood. The wood then has the task of hold the boat together while the glass fiber continues to fail further (think about that one). If the balsa was CPES treated prior to its use within the boat, it is probable that the balsa would not rot at all and the boat would be intact until the final total failure of the glass fiber material surrounding the balsa.

As far as gluing encapsulated wood, there are two methods. You can use the hard epoxy as a glue, or you can use 3M 5200. Regular glues such as PVA types (like Elmer's), or urethanes (Gorilla glue) won't work because they cannot penetrate the wood surface pores because the wood is sealed.

It all comes down to knowing and understanding the material, choosing the correct material for the expected performance/use, and treating the material to ensure longevity.

That did it, I'm dumpin my Allison (that I thought was tough as nails) & buyin a 20 footer built with a WHOLE ****LOAD of WOOD ! I've seen the light !! Scott :D

No wood has got to be the Hottest selling point on Recreational boat now...So many people will buy a boat solely on that even though its a piece of crap..The only thing they know is wood rots and composite doesnt..So many people are buying boats and getting loans for 10yrs or more, when it doesnt matter if its wood or not it is still going to be a piece of crap after 5yrs regardless!!
Wood has its place and composites have there place each just needs to used correctly..

Hey Scott Gilmore just buy a Allison drag boat / to my knowledge they STILL use WOOD in those. Lets hear it folks am I wrong!

Well if I did buy an Allison Drag boat (2001) , I sure as hell wouldn't POUND it for 100's of hours up & down the lake , tearing up powerheads & lower units running it on the ragged edge, through HUGE water & expect it not break into little pieces !! Scott :D

Franki- Hmm. Just how well does that 5200 bond? I glued my whole motor on with it, hope it will come off if I need it to. Never thought about it, but I was thinking it seemed like urethane....the stuff they glue car windshields in with.