Scantlings equivalence

I would like to calculate the scantlings equivalence between 2 type of woods for stripplanking building.
Did anyone can give me a formula with the explanation of the differnent terms ?

Thanks

Trim

 

I'm interresting too !!!

I only know the Gerr's rules based on wood density vs Sn

 

http://www.macnaughtongroup.com/publishingown.htm

look at the Scantlings Rule for Sheathed Strip Construction

 

MacNaughton writes:
"The longitudinal strength comes from the strip planked shell. The transverse strength comes from glass cloth or carbon fiber laid with the long fibers running around the hull crosswise to the run of the planking strips."

So according to him you can first adjust the thickness of the core proportional to the strength along the fibres, then if this gives you a thinner core you need to add more to glass to get the same transverse strength.

Theoretically you could use less glass if you have a lighter core that is thicker, but the you have to remember that you need a minimum glass thickness to resist puncture or very local stresses.

 

I believe (E)(I) of the original material should equal (E)(I) of the replacement material. Yes? No? Maybe?

 

MacNaughton's Scantlings Rules are the best resource for you. You don't mention whether the hull is going to be sheathed strip construction or strip planked over frames. Regardless, you can get good scantlings for either. As to the sheathed strip method, though I would not presume to speak for Mr. MacNaughton, it is my understanding that changing the thickness of the strip core should not affect the weight of the glass used in sheathing, as it is the glass that is giving all the transverse strength. You would not necessarily want to use less glass given a thicker core unless that core was giving you some additional transverse strength.

 

Here's how I remember it:

Old Macnaughton had a farm, (E)(I)(E)(I)(O)

 

My goal would be to do a sheated strip planked hull. The aim is find a costless alternative between a real stripplanked hull in WRC and a a sandwich hull with a balsa core.
The cost is not the only goal, it's also due to our difficulties to import at a good price and reasonable quantities WRC or balsa core ! But if we succeed in doing that we might be able to propose our new way to build. But for the moment, we are trying to make comparisons and are working by similarities.

If a naval designer is agree to perform some calculations for us it would be great because we don't have good software like FEM software !

 

For a start, as an estimate, you can regard the hull as a large beam. Then EA, modulus of elasticy x area of a section of the skin, must be equal when you change from one type of wood to another. If you look at EI (e-modulus x inertia) of a small part of the hull you may end up with a hull that is locally stiff enough, but that is too weak globally.

A agree with thos that recommend MacNaughton's rules, they cost about 10USd + shipping

 

The various ABS scantling rules are free at www.eagle.org.

The offshore racing yacht rules include strip plank. The required scntling depends on frame spacing which you can change if you need too, as well