Materials

Hello
Do all wood types after moisture barrier epoxy coating have the same moisture and rot resistance ?
Thanks

 

They have the same rot resistance as before. However, if they were epoxied in a low humidity content state, there won't have the conditions for rot to start. Epoxy is a moisture barrier, so the wood will absorb less humidity than left bare.

 

as epoxy ages it gets more brittle, and eventually gets tiny cracks that can allow moisture into the core. Normally regular stripping and repainting the hull keeps it water tight, but eventually moisture gets in. you will also risk moisture intrusion from minor impact areas (which will also crack the epoxy), such as the keel, or along the gunwales a long the dock. The more rot resistant core will allow you longer time between strip down and repair before serious or extensive damage occurs.

So in theory, if you can maintain a perfect water tight seal on all parts of the boat, all of the time, than it should not matter. Personally if you have a choice of more rot resistant wood, that is what I would use. Eventually moisture will reach the core. Rot resistant core wood can greatly reduce the extent of the repair you have to do when that time comes.

 

The time for a repair should never come with proper maintenance. Unfortunately, routine service is not always followed. Most boat owners wait until a core rots instead of re-bedding hardware every ten years or so.

 

So selecting wood itself has a big importance?

 

Yes, but not necessarily for what you are asking. For example, balsa can be the best because of its low density.

 

Actuall I have a general question about wood selection. What ıf I do complete boat just by using okoume plywood?

 

Plywood used in frames both side and bottom frames is not a good idea. To make them
stiff enough to equal solid timber they would have to be laminated quite thick. That is a weight penalty. The Glen-L Marine site has answered this question for over 50 years. ALSO A BAD idea to make the keel, engine stringers, all stringers and lifting strakes out of ply. On and On and On.........

 

You can design a boat with many different cores. Plywood cores are structurally much different than an end-grain balsa or foam is. Structures are designed as a whole, so there isn't a direct comparison between elements out of context.

 

There's no substitute for studying the physical properties of the various materials you'll use to engineer a structure.

Given the very basic nature of your questions, you are in no position to consider material substitutions without professional assistance.

What specific questions do you have about material substitutions and what are the applications of these materials?

 

Exactly, they don't do it until water is dripping on their bunk, and by then it has been leaking into the core for years.

Steve.

 

Usually the flat and developable surfaces are made by plywood. In my question I am asking other than developable surfaces, such as stringers or any component which is made of timber, can we make them with plywood?

 

Again, these decisions need to be taken in context, so the answer is no, unless you've evaluated the properties of the substitution.

For example, you suggestion of a plywood stringer, instead of a solid timber version (per the plans). Do you know the differences with such a change? Plywood, cut to the same dimensions of a solid wood stringer, will be 1/3 weaker longitudinally, though a bit fair bit better in cross grain stiffness. Of course, this depends on the species used in the panel and the type of plywood panel too. This same size plywood stinger, would also be heavier than the solid wood version. This is engineering basics, studying the variables and making the informed choices. If you don't know the realities of these types of wholesale substitutions, you'll likely not be successful.

 

Do you suggest that Okoume marine grade plywood has modulus of elasticiy 3 times lower than a solid timber? Or yield strength?

 

The ability of a stringer to support the stresses to which it is subjected depend, of course, on its mechanical properties, but also, and much, of the cross-sectional geometry. Therefore, without knowing the existing stringer and what you want to place, it is very risky to make a diagnosis.