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Water intrusion into balsa core
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Hugh and Jennifer



Joined: 03 May 2011
Posts: 11
City/Region: Denver
State or Province: NC
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Speckled Pup
Photos: Speckled Pup
PostPosted: Mon Nov 28, 2011 1:58 pm    Post subject: Water intrusion into balsa core Reply with quote

Over time the plastic gas tanks on my 2002 22' C Dory have buldged on the sides, causing the screws holding the tank anchors to the bottom of the hull to pull loose. When I removed them for inspection I found the balsa to be completely rotten underneath. There are twelve holes with varying degrees of intrusion.
By tapping and probing, it appears the moisture has only permeated to a radius of a couple of inches, but it will take a good moisture meter test and probably a hole saw to know for sure. I plan to disconnect the tanks and batteries and slide them forward.
I know it itsn't rocket science, but any helpful tips would be appreciated, including whether I should replace the balsa with something else.
My big question is that if the tanks tend to bulge like this over time why the heck did they put so many screw holes in the bottom anyway?
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Matt Gurnsey
Dealer


Joined: 11 Nov 2008
Posts: 1532
City/Region: Port Orchard
State or Province: WA
Photos: Kitsap Marina
PostPosted: Mon Nov 28, 2011 2:18 pm    Post subject: Reply with quote

Because the balsa is end grain- meaning the grain goes up/down instead of parallel to the boat hull, damage will be localised to a very small area surrounding the deck penetration.
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Matt Gurnsey
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Hugh and Jennifer



Joined: 03 May 2011
Posts: 11
City/Region: Denver
State or Province: NC
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Speckled Pup
Photos: Speckled Pup
PostPosted: Mon Nov 28, 2011 2:21 pm    Post subject: Reply with quote

Thanks Matt, I'm really hoping so. My boat sat unused for years before I purchased, so I really don't know how long it's been wet.
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tomherrick
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PostPosted: Mon Nov 28, 2011 5:36 pm    Post subject: Reply with quote

H & J,

My boat sat for about 10 years before I acquired it. Two-thirds of the balsa core in the transom was rotten. When balsa cores are made, they glue up end-grain square blocks to form a sheet. The glue helps to keep water from migrating between the blocks, but that didn't work in my case. I don't know if a freeze-thaw cycle delaminated the fiberglass from the core and allowed the water access to a larger area or not, but that's not uncommon; particularly over the course of several years.

I already had a pinless moisture meter (PMM) in my wood shop and used it to detect the extent of moisture intrusion in my boat. My sole is cored with plywood; that core material didn't rot and I was able to dry it thoroughly by removing the inner cockpit fiberglass. I don't recommend you do that unless you find that the whole core is soggy toast and you're willing to take on a real project. If you use a PMM on your boat the percentage readings won't necessarily be accurate values of core moisture; just use it to see where the most moisture is located. Having been a cartographer in a previous life, I drew a six-inch grid pattern on the transom and sole, then I moved the PMM along those lines and marked where the readings were 10%, 20% and 30%, then I drew 'contours' connecting those points. It was a very valuable illustration for me. PMMs aren't cheap (I own a Wagner), but after about three or four hours worth of a good marine surveyor you're gonna break even. That said, a good marine surveyor might be quite valuable in determining the extent of the moisture and structural integrity of the core if you're over you head. There are good articles online about how to use a PMM on a cored fiberglass boat. There are also good articles elsewhere online as well as in this forum on how to use a fastener through the fiberglass skin so that water can't penetrate the core.

If you could post some pics of your boat in the Speckled Pup photo album here showing what you're finding, those of us who've been through these projects may be able to provide more focused recommendations. It'll all depend on what you find below the fiberglass. Do be cautious though, because you don't wanna tear out lots of fiberglass just to dry an otherwise structurally OK core.
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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 Nov 29, 2011 12:05 am    Post subject: Reply with quote

Good suggestions--and definitely the freeze thaw cycle does accelerate damage, as does any water standing in the cockpit. Any large area is unusual in these boats, and I would start by just sounding out the area around the screws. It is very likely that the damage is only an inch or less--and you can probe the balsa by drilling out the top glass by about 1/2" and then using a right angle pick to check for the integrity of the balsa. If the Balsa is OK beyond an inch or so, then you can just route it out, fill with epoxy and in this case, I probably would use Cabosil and micro ballons--at least for the larger area--then a higher density filler where you are going to put the screws back in.

I note on my "new"--2006 C Dory 22, there are longitudinals glassed in to support the bottom of the tanks. So far we have not found any water intrusion.

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Bob Austin
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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CAVU



Joined: 02 Nov 2003
Posts: 665
City/Region: Spokane
State or Province: WA
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: CAVU
Photos: CAVU
PostPosted: Tue Nov 29, 2011 7:31 pm    Post subject: Reply with quote

I think everyone with a 22' around your time frame has had issues with the fuel tank mounting system. There have been several different fixes over the years. I eventually epoxied wooden strips under the tanks and used the wooden strips to hold the anchor screws for the tank hold-down fittings. I epoxy filled and sealed all the old screw holes. While you have the tanks loose it would be a good idea to check the bottom of the tanks carefully. I have a 2002 also and one of my tanks eventually cracked on the bottom. I have no idea why. I was working on the floor project when I noticed it and luckily the tank only had a few gallons in it.
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22 CD Cruiser, CAVU
Twin 40HP Hondas
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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 Nov 29, 2011 10:45 pm    Post subject: Reply with quote

Ken,
Did you have to route out any of the balsa core,--if so how far out was it involved. Why do you think that these year boats had more problems? I noted one photo of snow on what I think was your boat--do you think that the freeze thaw cycle made things worse?

A few fuel tanks of this era in some 25's and even some Tom Cat 24's did develop leaks. How many of the 22's had leaks in the tanks--and was it only one or both tanks?

Thanks.
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CAVU



Joined: 02 Nov 2003
Posts: 665
City/Region: Spokane
State or Province: WA
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: CAVU
Photos: CAVU
PostPosted: Tue Nov 29, 2011 11:45 pm    Post subject: Reply with quote

On my boat the area affected was very small. I just drilled out 1/2in holes centered on each screw hole and that revealed dry balsa in every hole. I then filled each hole with thickened epoxy. I made three approximately 1" x 1" wooden strips which I epoxy coated to seal them. I epoxied these to the floor and then mounted the tanks atop these. This raises the tanks about 1" but on my boat there was plenty of headroom under the splashwell for the tanks.

The cause of the problem, which involved several year models, was how the tanks were secured in the boat. The tanks were sitting directly on the floor. The piece of starboard which covered the front of the tanks was screwed to the floor with four SS woodscrews. A nylon strap was attached to the back side of the cover board and ran over the top of the tank. The screws only had about 3/16" of laminate to bite into on the floor. When the tank expanded and contracted this put a vertical pull on the screws. Check the first few photos in CAVU's album and you can see what I am alluding to. There was no way those screws could hold any load at all.

Why the tanks cracked I have no idea. Both tanks had a random pattern of cracks on the bottom, although only one was actually leaking. I felt the other one would leak soon so I replaced both tanks.
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rogerbum



Joined: 21 Nov 2004
Posts: 5922
City/Region: Kenmore
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 255 Tomcat
Vessel Name: Meant to be
Photos: SeaDNA
PostPosted: Tue Nov 29, 2011 11:49 pm    Post subject: Reply with quote

Bob, after about 2003 C-Dory began to install the tanks with the glassed in runners that you have. My old 22 was a 2003 model and originally came with the tanks installed as Ken describes. The factory had enough problems with that installation that they decided to fix/upgrade many of the 2003's at no cost. Mine was fixed when I brought it back to the factory (3 owners ago at the Kent shop) for other minor issues.
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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: Wed Nov 30, 2011 3:42 pm    Post subject: Reply with quote

Thanks for the reply. The 1992 C Dory 22 I owned before did not have any problems with the screws or tank. I suspect that the 2002 boats had a thinner inner glass layer. That boat also had the tanks sitting on the floor. What you have done is far better and should last well into the next century!
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Hugh and Jennifer



Joined: 03 May 2011
Posts: 11
City/Region: Denver
State or Province: NC
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Speckled Pup
Photos: Speckled Pup
PostPosted: Wed Dec 07, 2011 11:16 am    Post subject: Thanks for all the comments Reply with quote

I've had problems logging on. I took my boat in to my marina and consulted with the "experts". Although the holes around most all of the old screws look bad, the intrusion is only a couple of inches around the hole, at most. Simple fix to that. As far as fastening the tank down we decided to glass in a 1X1 and screw into that. Based on what I see now, I'm also going to inspect the tanks for cracking.
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Snider



Joined: 21 Jun 2013
Posts: 204
City/Region: Charleston
State or Province: SC
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Kestrel Dawn
Photos: Kestrel Dawn
PostPosted: Fri Jun 15, 2018 9:20 pm    Post subject: Same problem Reply with quote

My 2002 I just bought has the same issue. The outer ends of each piece of starboard forward of the tanks have pulled the screws out. I ran almost all of the fuel out over the last 3 days. We put about 16 hrs on the boat and did a lot of exploring, anyway before I digress, I plan to pull the tanks and inspect the core around the holes. I also have screws through the cockpit that hold the batteries down which sit between the tanks. Initially I thought about burying stainless anchors in epoxy, then using machine screws through the starboard to hold down the tanks. After reading this thread though I'm considering glassing in starboard or some other hardwood and using that to mount the starboard strip that holds the forward bulkhead and strap over the top of the tank. I just need to make sure I have enough clearance over the top of the tanks to lift them out and over whatever I glass in. Should I lay strips of something under the tank also to raise it up off the floor? Or just set it back on the cockpit floor? I can't really see a reason to raise the tank, unless I'm missing something. Is that the way they build them now? Once I fix the tank problem and glass something in to hold the battery boxes I won't have any other possible intrusion into the core, except the cockpit drain, trim tabs and depth transducer. Probably just let them be I guess. Plan on keeping this boat a while, trying to ensure it lasts a long time for me and the next owner.
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22ft Cruiser
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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: Fri Jun 15, 2018 9:32 pm    Post subject: Reply with quote

I would place the tanks on the floor, or on a neoprene pad, if you wish. If it was an aluminum tank, then I would suggest coating with coal tar epoxy, and using 5200 to glue plastic or fiberglass battens to the bottom of the tank, and then the tank to the floor--straps to hold in place into the strips you glass in place.

Often I have found that the trim tab screws are below the cored material--, so may be into solid glass.

The transducer should be removed, the holes filled in with under cut if necessary. Then a Starboard block fixed to the transom. In the 25 I just bought. I pulled the transducer, and it was properly installed with epoxy plugs. So I used those holes to put in the 2 SS Screws which hold the Starboard (HDPE) that I put both new transducers into. I also used "G Flex" epoxy with the Starboard. On the back of the Starboard, I made a number of channels, with a Fein (Osculating saw) which undercut the interface, to give the Gflex channels to flow into, and grip the Starboard.
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Snider



Joined: 21 Jun 2013
Posts: 204
City/Region: Charleston
State or Province: SC
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Vessel Name: Kestrel Dawn
Photos: Kestrel Dawn
PostPosted: Fri Jun 15, 2018 9:59 pm    Post subject: In that case Reply with quote

That's reassuring if the trim tabs are in solid glass. In that case I will add a piece of starboard for the transducer. Thanks
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Chester



Joined: 04 Sep 2006
Posts: 1176
City/Region: home
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sold to lovely couple
Photos: Chester
PostPosted: Sat Jun 16, 2018 4:11 pm    Post subject: Reply with quote

I found a bit of water intrusion in the screw holes under the cleats that locate the fuel tanks.
I pulled the tanks, drilled exploration holes and fished out the wet balsa. Next step was to use aquarium air pumps to blow air into the core. I did this for a month under the sun in the summer. Then used epoxy and filler to fill the void.
I sanded the cockpit sole where the tanks sit to reduce chances of abrasion.
Good to go.
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