Foam Sandwhich equavalent to 3/4in ply

I could use a rough estimate of what would replace 3/4in Fir plywood
with a glass/foam core. For example, I have a 16ft catamaran, the hulls are made out of 3/4in plywood. What is the equivalent using polyester resin and Airex foam?

 

It depends on the structure arrangement and the intended use. For example, a sandwich panel may have the same stiffness as plywood, but the puncture resistance may be much lower.

 

There are several factors to consider, cost being one often let out, but a big consideration for most.

 

...I have 16ft catamaran hulls. built using 3/4 douglas fir plywood.
The properties of 3/4in (18mm) douglass fir plywood are easily found.
http://www.worldpanel.com/plywoodcomparison.htm

Is there such a thing comparing plywood to foam cored panels with different layup schedules, thickness, etc. I couldn't find it.

 

Sweet God, 3/4" cat hulls? It's got to be the most over built 16' cat ever.

 

Yes 3/4 seems way too thick but just google for 'hexcel honeycomb design guide'. The calcs are simple.

Of course there is a lot more to consider than just the bulk panel properties.

 

There is also this simple calculator which could in the past be found on the Airex website.
After some fiddling you will find out how it works. Metric however.

 

http://multihullblog.com/2010/11/plywoodglass-strength-comparison/

 

Thanks! Exactly what I was looking for a simple rough comparison.
No 18mm ply, but that is ok.

Ply thickness Triaxial thickness Core
3mm ply equals (12 oz) 400 gsm w/12 mm core
4mm ply equals (17 oz) 600 gsm w/12 mm core
6mm ply equals (22 oz ) 750 gsm w/12 mm core
9mm ply equals (34 oz) 1150 gsm w/19 mm core
12mm ply equals (2) (22 oz ) 1500 gsm w/19 mm core

 

Not really. It depends on the design and application. There is no direct comparison since they are very different materials. You can compare modulus of elasticity, or puncture resistance, or stiffness, etc. However, each will give you different results.

 

147 foot mega yacht with 4 deck levels 6000 hp from twin 3000hp V16 cats and the skin thickness was just 15 mms of solid glass . and you want 18 mm!!! the last 25 metre lake boat we just finished had 15 mm solid glass and its made to sit on and hit on rocks!! . 3/4 wood is nothing !!