Originally Posted by nautdesign1

Uncle Dave –Every couple of months when I need a diversion from work, I browse this site for amusement. You seem to be getting a tough time here which isn’t really fair as you haven’t had a technical answer to your inquiry. Therefore let me have a go. You can’t look at the raw data of the core material in isolation when you are dealing with the dynamic loading of a panel for which the core’s is only a component part. Peter at Skater “get’s away” with balsa in his boats due to his proper bonding technique and epoxy resins which together permit the construction of very light and strong boats. Therefore it will be a very rare instance where the forces exceed the ultimate strength of his balsa panel. However if they do the result is an instant catastrophic failure. With Linear or (to a slightly lesser extent) san foam core, whilst the panel will have a greater deflection than a balsa panel for a given impact, such defection absorbs the energy of this force. As the linear/san foam will maintain its structural properties throughout this deflection (subject of course to the panel’s elastic limit), the total amount of energy absorbed from an impact prior to de-lamination (subject to the resin) will exceed that of the stiffer balsa panel. In high impact dynamic loading structures you need to look at the area under the stress strain curve. Whilst the balsa panel will have a very step curve with very high stress capability, the area under this curve will not match that of the lower stress linear/san foam core panel and thus is not capable of surviving the same magnitude of impact. Again in force calculations mass is a key component so Peter’s light and extremely well built boats will generally never exceed the energy absorption limit under his panel’s stress/strain curve-even though this area is less than that of the equivalent linear/san foam panel.

Hope this helps

Originally Posted by Uncle Dave

BTW Thanks for the recognition of the tough time.

I've never had an easy run in any site yet- never expected this one to be different.

Superb explanation.

Interesting how according to what you say technique affects the overall materials worthiness and applicability to this application.

Implication being unless you can really do it right, just use foam.

Are there any other material issues to consider in the choice of Balsa over Foam?


UD

Originally Posted by Uncle Dave

Any thoughts on T2's comment about how greater flexibility can lead to core shrinkage?



UD

Originally Posted by Steve 1

The Better cores cause Wallet shrinkage.

Originally Posted by tommymonza

The helm damage you see Dave is simply the hinged instrument console floating freely above the helm. That is a lightly connected area and most likely just broke free as the boat was sinking.
The only way that transom has that damage is because somebody was trying to tow it stern 1st. Boat ripped cleanly at the hawsepipes passing thru the coaming.

Your theory of water blowing out the transom does not work because the water would have to shoot up the companionway and thru the salon. and than back down the cockpit steps to the transom . As the Capture of the Princess Bride would say.
INCONTHEVIABLE

Originally Posted by Uncle Dave

Funny! and often a motivation......

I actually misquoted all due respect - "constrict" the core was the actual term.

This another downside I hear quoted in regards to foam, but I have never been able to verify..

Since we do have the a boatload of guys that are here - Id love to hear the thoughts on this.

UD

Originally Posted by Steve 1

Uncle I Apologize for not bringing this up sooner.


Here is a simple graph of what Nauti was referring to.

http://www.fram.nl/faq/how/SP_CoreCell_comp.pdf