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Why does a wet balsa matter

 
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1Wiley



Joined: 30 Jun 2018
Posts: 14
City/Region: Bay area
State or Province: CA
C-Dory Year: 1986
C-Dory Model: 22 Classic
Vessel Name: Fidelio
PostPosted: Mon Aug 06, 2018 7:47 pm    Post subject: Why does a wet balsa matter Reply with quote

So I was looking at prairie boys pictures and seeing the core surrounded in fiberglass. I canít help but wonder with all that glass why would a wet core matter. I think a lot of new boats without a core are chopper gun glass and not even as thick as whatís in his pictures, and it looks like thereís two layers still. ?
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thataway



Joined: 02 Nov 2003
Posts: 16023
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Mon Aug 06, 2018 9:24 pm    Post subject: Reply with quote

The strength of the bottom of the boat is the "I" beam construction--and the integral part of the " I" beam is the the "Balsa core" Dry balsa is a high shear load resistance. The wet core has virtually none. The wet has delaminated from the glass, and there is no real support--you might as well fill the core with "mush". Think of the horizontal part of an "I" beam as the fiberglass on bottom and top--and the balsa as the vertical component--basic mechanics.

In areas with freeze and thaw cycle, the moisture in the core, freezes, and then thaws --and breaks up even faster.

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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
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Home port: Pensacola FL
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1Wiley



Joined: 30 Jun 2018
Posts: 14
City/Region: Bay area
State or Province: CA
C-Dory Year: 1986
C-Dory Model: 22 Classic
Vessel Name: Fidelio
PostPosted: Mon Aug 06, 2018 9:36 pm    Post subject: Reply with quote

Yup, I get that itís stronger and better with core but givin thereís two layers of glass isnít that still better than most boats ?
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thataway



Joined: 02 Nov 2003
Posts: 16023
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Mon Aug 06, 2018 9:55 pm    Post subject: Reply with quote

1Wiley wrote:
Yup, I get that itís stronger and better with core but givin thereís two layers of glass isnít that still better than most boats ?


Au contraire, the two skins of glass are both combined thinner and weaker than the single skin in a non cored boat. The idea of a cored hull is to add stiffness without adding weight. There are some boat builders who make the outer layer too thin, which makes it easy to puncture. Or the inner too thin, which makes the "I" beam too weak. C Dory fortunately balances these well. Too thin a skin is what balsa core has a bad wrap--as well as the allowance of water intrusion--which unfortunately C Dory has only recently gotten it right. The introduction of the fiberglass interior, and the molding in of the batten for the hold down of the fuel tanks. I recently went thru my "new" 25, and found that all of the screws into core had been properly sealed by the previous owners. Also I had used a moisture meter on the hull when I bought the boat, as part of my own survey. Where possible I prefer to glue or use fiberglass tabs instead of screws. I moved the water pump off the bottom of the boat, and put it on 3/4" thick starboard, which I "glued" to the inner hull with G flex, and I made "Y" cuts into the starboard to assure the epoxy adherence, as well a "flame treating" the starboard before gluing.

In some places the builder uses solid glass--such as where the bilge pumps are located. (But some of the sumps are still cored--so don't assume that they are solid glass unless confirmed. I prefer to glue pump bases in place over screwing them in place. Hot glue, will hold wood or plastic place until the epoxy has set.
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