Re: deck leak


James Alton
 

Arno,. You are correct, the Divinycell won't rot if water gets in. For a boat with a teak deck that has fastener holes I would prefer the Divinycell since with that many holes water is going to get in.  I have been in the boat repair business for more than 40 years and I have dug out a lot of rotten plywood and balsa core and you are correct it is a huge nasty job to do right.  The Amel design thankfully has very few deck and cabin penetrations so it is not that big of a job to decore each and every hole, fill with epoxy, redrill and seal.  From that point forward if a fastener leaks the water cannot get into the core.  The increase in compressive strength of the balsa will create a more Ridgid structure and the increase in the bonding to the fiberglass skins (assuming the layup was done correctly) also adds strength.  So this means that with a weaker core you probably need to to build the boat a bit heavier to have the same strength.  Are the HR's heavier than a comparable Amel?  I have worked with the Divinycell on sailplanes and I will say that it the the best foam type core that I have worked with.  Some of the planes were 20 plus years old and the core was still healthy.  I have seen many other types of foam used for core material break down.   So to distill yes on a boat where I feel that I can keep the core dry, I would much prefer to have balsa core such as my Amel.  On a boat where there is a high probability of water intrusion such as a deck or cabin with a lot of screw holes, a non organic core such as Divinycell would be preferable.  Best to you.  

James Alton
SV Sueno
Maramu #220

On Sep 21, 2020 11:49 PM, Arno Luijten <arno.luijten@...> wrote:
Hi James,

I'm aware of the differences between balsa and Divinycell, particularly the difference in adhesion to polyester. However Hallberg Rassy and many others have been using Divinycell since the eighties and correct me if I'm wrong, I've never heard of a soggy deck on a Halberg-Rassy. I used to own a 1992 model and the deck was solid, even with the gazillion holes because of the teak deck. Not that I would ever want a teak laid boat anymore, but that is another story. My previous boat had no teak deck but did carry a Divinycell cored deck and hull (above the waterline). Not a single problem manifested itself. I sold her when she was 16 years old.
The compression strength is something you can take into account when doing the structural calculations on the boat and should not be a problem.

So although there are some advantages to balsa I find it a poor choice for cored decks simply because water-ingress can be very hard to spot/monitor until it's at an advances state. There is a YouTube channel (Sail Life) that can illustrate the crazy amount of work it can be to rectify the problem once the balsa starts rotting.

Regards,

Arno Luijten
SV Luna,
A54-121

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