Cockpit deck replacement

D

Design Dawg

New member
Hi all,

I have a 2005 25' C-Dory. It had a somewhat spongy cockpit deck when I bought her seven years ago, and it has amazingly enough gotten worse over time. Who could know that something like that could happen here in the PNW?

Anyway, I've finally worked up the courage to do a re-build of the cockpit deck. Plan is to cut away the existing cockpit deck in small sections, starting from the three in deck bilge accesses. I'll insert 1" rigid foam as I work between the underside of the balsa core and top of fuel tank and gas line so that I don't cut those. I'll work aft to where the engine well overhangs the deck. Would prefer not to go under there, and the balsa core seems in reasonable shape back there.

I'll cut out the deck to within 3" or so of the hull and cabin bulkhead. Deck seems sound in those areas. Once the deck is out, I plan to do a LOT of bilge cleaning (have a NIOSH approved respirator). I haven't been able to get any good pictures of how the existing deck is joined up to the hull. Feels like there is a molded ledger in there, but I won't know for certain until I work my way up to it. Depending on what I find, I'll either adhere a marine ply ledger to the underside of the remaining deck with 5200, or build a ledger off of the hull (hoping what I find allows me to do the former) Grind down and sand remaining fiberglass at deck and about 3" up the hull in preparation for bedding down new fiberglass.

I'll dry fit 3/4" marine grade plywood over the deck. Remove that, and glass over the underside of it for rigidity. Then I'll set the plywood down and glass over with a couple of layers. Cut in bilge access hatches and epoxy the exposed edges. Maybe one more layer of glass going into openings. Finish with Gelcoat.

Has anyone of the Forum had experience with something similar on their C-Dory? Would love to get suggestions from those who have been thru this.

Thanks!!
 
The search engine is your friend here. I believe you are making a number of mistakes doing what you propose.

First you should remove the entire deck and do it all at once. While. you have the cockpit deck off, you need to check the fuel tank--advisable to pull the tank and check the bottom for corrosion. IF sound then clean and coal tar epoxy the bottom and low sides of the tank. Be sure that the tank is set on some inert material, such as plastic or fiberglass batens (No material containing carbon, including neoprene). The tank must be raised off the bottom of the boat, and any water free to drain out from under the tank.

There is a fair chance that the fuel tank should be replaced at 18 years of age. Average age of failure of aluminum boat fuel tanks is less than 20 years!

You can make a decision at that time if you want to make the "new" cockpit floor removable or not. I advise to make it renewable as the 2006 on boats have done.
That way when the tank has to be replaced, you just unbolt some screws and take the tank off, after cutting the sealants.

The core of plywood will be excessively heavy at 75#. We made the new floor of NiaCore(hex cell 4# 4x7 sheet). You can also use Balsa as originally, or one of several foams. The Balsa has excellent characteristics, and if sealed will not give any problems--actually better than many other core materials. It is the I beam construction effect giving the stiffness, not the rigidity of core material such as plywood. The original balsa is bendable if not laminated on both sides.

In the 2005 C Dory 25, the deck is tabbed in after the fuel tank is placed or may be part of the original molded deck/cabin sides. On the 2003 C Dory 25, I owned the gel coat was rolled on.

We found that the inner layer of glass in the cockpit deck was poorly adherent to the balsa core. The "I" Beam strength of the cored laminate is defective if both upper and lower skins are not well adherent.

I would use a polyester/cabosil slurry if putting the new core material into the previous underside of the cockpit deck. Use a notched trowel to spread the slurry. Epoxy would be a bit stronger. Saturation and water proofing of the edge of plywood is difficult with polyester. Epoxy is far superior, and should be mixed with a filler, with the core material cut back slightly.

2007_05_16_001.jpg.

You can find other photos of our rebuild of the cockpit floor on page 5 of my album.
 
Bob and Colby-

Thank you VERY much for the input! Looked thru both of your albums, which were extremely helpful. As both of you advised, I will pull the tank. Only issue there is that I topped it off with fuel prior to taking her out of the water in October. Not a lot of options here on Orcas Island to transfer fuel. I'll ponder that some; may put this project off until the fall when I can start with a nearly empty tank. Many other projects to keep me occupied, (un)fortunately!

Bob - here's the link I found for the Nida-Core panels: https://www.merrittsupply.com/product/n ... lain-h8pp/ Is this the material that you used? I'll also evaluate using balsa core again. Marine ply is now out of the picture - thanks for the input on that!
 
My CD25 vintage 2005 had to have its fuel tank replaced due to leakage. Apparently it depends on what technique was used in the factory to support the tank off the hull.
 
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