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Why does a wet balsa matter

 
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1Wiley



Joined: 30 Jun 2018
Posts: 23
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: 16279
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
KA6PKB
Home port: Pensacola FL
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1Wiley



Joined: 30 Jun 2018
Posts: 23
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: 16279
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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dgeorges



Joined: 04 Sep 2013
Posts: 91
City/Region: Springfield
State or Province: IL
C-Dory Year: 1985
C-Dory Model: 16 Angler
Vessel Name: OPA!
Photos: OPA!
PostPosted: Mon Aug 27, 2018 10:48 pm    Post subject: Why does a wet balsa matter Reply with quote

Check out my photo's under boat name: OPA herein. You'll see what wet balsa looks like under fiberglass.

What a mess. I discussed the repair in the photo album.

Cheers.

Dimitri

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CD 16 Angler: OPA! 2013 to present (now available for purchase).
CD22 Cruiser: name TBA. 2018 to present.
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South of Heaven



Joined: 15 Aug 2015
Posts: 1246
City/Region: Stoughton
State or Province: MA
Photos: Blue Water
PostPosted: Tue Aug 28, 2018 1:29 pm    Post subject: Reply with quote

Dmitri: You had a mess on your hands! Good job on the repair sir.
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https://www.yachtworld.com/boats/2000/Camano-Troll-3246166/Boston/MA/United-States?refSource=standard%20listing#.W5EZuCRKij4

2007 C Dory 25' Cruiser (200 hp Suzuki, sold 7/17)

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dgeorges



Joined: 04 Sep 2013
Posts: 91
City/Region: Springfield
State or Province: IL
C-Dory Year: 1985
C-Dory Model: 16 Angler
Vessel Name: OPA!
Photos: OPA!
PostPosted: Tue Aug 28, 2018 4:41 pm    Post subject: Reply with quote

Thanks. I'm in the market for a CD22. Please let me know if you see any for sale up in yer neck of the woods.

Your CD25 is a jewel.
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pcg



Joined: 31 Aug 2018
Posts: 26
City/Region: Sherwood
State or Province: OR
C-Dory Year: 1999
C-Dory Model: 22 Cruiser
PostPosted: Sat Sep 01, 2018 12:14 pm    Post subject: Reply with quote

[quote="thataway"]
1Wiley wrote:
... 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... 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. ...

What model year did C-Dory get this "right"?

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capt. meares



Joined: 04 Jul 2013
Posts: 135
City/Region: Tillamook
State or Province: OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
Vessel Name: Vianey
Photos: Vianey
PostPosted: Sat Sep 01, 2018 12:46 pm    Post subject: Reply with quote

Why do bones matter?
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journey on



Joined: 03 Mar 2005
Posts: 3191
City/Region: Valley Centre
State or Province: CA
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: journey on
Photos: Journey On
PostPosted: Sun Sep 02, 2018 5:34 pm    Post subject: Reply with quote

Well, the reason for the balsa is to keep the two layers of skin apart. As in a I-beam, vertical loading puts the flanges in bending, with the web in compression. So, when you soak the balsa (the web), it loses the capability to resist compression, the two skins move together and the hull loses its ability to withstand loads.

As to the allusion to "getting it right", I can only speak to the 2005 C-Dory 25. We had several issues where the boat wasn't caulked correctly and the factory fixed it. Those issues were primarily in the anchor locker and the sump drain where the plug goes in. I also believe that Bob was referring to the practice of putting screws in the interior hull without sealing them, either by sealant or epoxy. This includes the bilge pump as well as the interior cabinetry. Until they went to a one piece interior cabinetry, which is tabbed in, the dry screws were common in all C-Dorys.

That said, we've owned Journey On for 12 years, which is a testament to the soundness of C-Dory construction. They're a very dependable boat. Sealing the screws is up to you. Testament to that is that this is Bob's second 25, for the same reason we have: simplicity, dependability, room and of course, the head.

Boris
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