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Potting screws - gauging balsa thickness?

 
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Ctarmigan



Joined: 14 Nov 2019
Posts: 21
City/Region: Whitehorse
State or Province: YT
C-Dory Year: 2004
C-Dory Model: 22 Cruiser
Vessel Name: Ptarmigan
Photos: Ptarmigan
PostPosted: Fri May 21, 2021 2:49 pm    Post subject: Potting screws - gauging balsa thickness? Reply with quote

Hello all,

22 Cruiser preventative maintenance. I'm beginning the process of removing a number of items screwed into the hull and epoxy potting screws to avert dreaded water intrusion. I'm starting with brackets holding up the rear seat (containing the water tank) and under the sink/stove counter and holding the foot pump in place - the current brackets (galvanized?) are quite corroded, and I'll replace with stainless steel hardware. All goes well, I'll progress over time to other fasteners in the hull (e.g. screws in the retaining strip in front of the fuel tanks).

Putting Dremel to hull, though, is a daunting prospect. My question to others who have done this before: how do I gauge the depth of the balsa, and avoid chewing into (or through!) the fibreglass of the outer hull surface?

Thanks!

Oliver
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ssobol



Joined: 27 Oct 2012
Posts: 3362
City/Region: SW Michigan
State or Province: MI
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: SoBELLE
Photos: SoBelle
PostPosted: Fri May 21, 2021 4:01 pm    Post subject: Reply with quote

When drilling you can feel the change in force required when the drill gets through the first side of the fiberglass and enters the balsa. You can also feel when it hits the FG on the other face of the panel you are drilling. Once you get through the first panel, just drill at slow speed until you hit the other side.

One trick is to use a bent nail. Drill the hole in the face panel, then put the bent finish nail through the drilled hole and use the drill to spin the nail. This will under cut the balsa under the FG pretty well. Use a vacuum to suck out the chewed up balsa and refill with epoxy. The bent nail will not penetrate the FG on the other side of the hole.
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localboy



Joined: 30 Sep 2006
Posts: 4656
City/Region: Lake Stevens via Honolulu
State or Province: WA
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: 'Au Kai (Ocean Traveler)
Photos: 'AU KAI
PostPosted: Fri May 21, 2021 5:14 pm    Post subject: Reply with quote

Old Allen wrenches work the same. Chews thru the balsa easily, but not the glass layer on the other side.
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clayhubler



Joined: 03 Aug 2019
Posts: 280
City/Region: La Center
State or Province: WA
C-Dory Year: 2003
C-Dory Model: 22 Cruiser
Vessel Name: Hammerhead
Photos: Hammerhead
PostPosted: Fri May 21, 2021 9:03 pm    Post subject: Reply with quote

Both of the suggestions above are good. It is easy to feel the bottom skin with the drill bit after drilling into the balsa. I prefer the allen wrench for core removal in holes. Since it has a hex shank it wont slip in the chuck.

My boat is a 2003, so maybe the same as yours. The hull balsa is 1.5" thick. Transom is 1". V-berth and v-berth floor is 1/4". The gunnels are 1/2" and the roof is 3/8". Only the two lower 'steps' on each side of the roof are cored, the top is not.

For large areas like the lazarettes, fuel fills, windlass, ect you can make a simple tool from 1/4" alum and a 1/4" bolt and chuck it up in a drill.


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localboy



Joined: 30 Sep 2006
Posts: 4656
City/Region: Lake Stevens via Honolulu
State or Province: WA
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: 'Au Kai (Ocean Traveler)
Photos: 'AU KAI
PostPosted: Sat May 22, 2021 1:45 pm    Post subject: Reply with quote

I’ve used router bits too. Put on a drill and start chewing.
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Yakmandu



Joined: 03 Nov 2017
Posts: 70
City/Region: Lake Lanier
State or Province: GA
C-Dory Year: 2005
C-Dory Model: 19 Angler
Vessel Name: Miss April
Photos: Pops GO!
PostPosted: Sat May 22, 2021 4:05 pm    Post subject: Reply with quote

I drilled out all the screw holes around the gas tank retaining strips in my 2005 Angler 19. I drilled one inch holes in the deck and then cleaned out any damaged balsa around the holes. It was very easy to tell when my one inch bit hit the hull under the balsa. I ordered three quarter inch round fiberglass rod and cut it into plugs that would fill the holes. I filled the holes with a generous amount of 5200 and then set the plugs flush with the deck. I replaced the tank retraining strips and set the screws into the fiberglass plugs.

You can’t see the plugs under the retaining strips and he strips are very solid. I am confident that water will not be an issue with this solution.

Good luck!

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Miss April
Lake Lanier, GA
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Ctarmigan



Joined: 14 Nov 2019
Posts: 21
City/Region: Whitehorse
State or Province: YT
C-Dory Year: 2004
C-Dory Model: 22 Cruiser
Vessel Name: Ptarmigan
Photos: Ptarmigan
PostPosted: Tue May 25, 2021 2:22 pm    Post subject: Reply with quote

Super useful information (and great to know I may be dealing with up to 1.5" of balsa, though I'll proceed carefully nonetheless). Thanks all!
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thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Tue May 25, 2021 9:37 pm    Post subject: Reply with quote

I would recommend removing any wet core material--or at least 3/16 undercut of the inner glass. Paint the balsa with unthickened and un diluted epoxy. You want the fibers of the balsa to have the epoxy to seal them. 5200 will not co it.

Then fill with the thickened epoxy. This gives your something which has a "bite" under the inner layer of the floor, and seals the balsa.

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Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
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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