Re: deck leak


James Alton
 

A mid range  Divinycell (H80) has a compressive strength of about 174 PSI (http://www.fiberglasssupply.com/pdf/core/hmanm.pdf)

End grain balsa core has a compressive strength of around 1,837 PSI according to this site.(http://www.cstsales.com/end_grain_balsa.html)  Balsa does vary in density but this is a huge increase over any foam that I am aware of.  (http://www.cstsales.com/end_grain_balsa.html)

In general, polyester resins  create a fairly low secondary bond.  The balsa soaks up the resin so that the bond penetrates deep into the balsa and and this can create an exceptional bond, even with polyester if the layup is done properly.  It is best to float the balsa in resin before installing to keep the wood from sucking up too much resin leaving a dry joint.  With a foam like Dinvinycell the resin does not soak into the product, it pretty much sits on the surface.  If a core fails in it’s bond to the fibreglass layers or crushes from an applied load it is a structural integrity is compromised even if the foam itself is ok.  Divinycell seems to bond quite well to epoxies used in aircraft construction but most boats are built with Polyester resins.

So yes, one has got to take care in keeping water out of a balsa core but there are some really good reasons to use this material as a core material in my experience so I do not fault Amel at all for using it.  In fact so far I have not seen anything that I like better for core.

Best,

James
 

On Sep 21, 2020, at 6:29 PM, Arno Luijten <arno.luijten@...> wrote:

Hi Bill,

Thanks for your wise words of advice. This is actually hitting on one my least favorite aspects of an Amel, the usage of balsa-wood in the deck core. This should have been abandoned in favor of Divinycell 30 years ago in my opinion.
For 54's a special word of advice: have a look at the point when the central stanchion sits in the rear railing/lifeline. It sits in this sort of cup that is bolted in the deck (it actually goes right through it). Amel fit this in with some caulking but (in my case) did not bother to protect the core material after drilling the hole.
In my case I had to remove the rotting core for about 10 cm diameter and fill the void with thickened epoxy. This also resolved a leak into the rear lazarette. Even great boat builders can drop a ball occasionally.

Regards,

Arno Luijten
SV Luna,
A54-121

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