1981 CD 25 - Seacock replacement - Looking for some advice

[Steve Bryant]

Hi Everyone,

I am in the process of finally replacing in-line ball valves on the sink and cockpit drains with proper flanged seacocks. On my 1981 CD 25, the hull liner down in the cockpit lockers have round recesses molded into the liner where the thru hulls are located, which look to be glassed directly to the hull. The diameter of the backing plates for the seacocks are larger than these recessed areas by 1¼” to 1¾”.

I seem to have two options:

1. Cut out the hull liner in a diameter large enough to install the backing plate directly to the hull and then seal around the backing plate and hull liner.

2. Fill the recess with either epoxy or polyester resin to make the hull liner flush and install the backing plate directly on the hull liner.

With option 1, I’m not sure what I am going to run into trying to remove the hull liner if the entire recessed area is glassed to the hull. If the hull liner is glassed to the hull over the whole area of the recess, option 2 would seem to be a solid enough foundation and the most practical and least destructive.

I have removed the thru hull and verified that there is 1 inch of solid fiberglass from the exterior of the hull to the opening in the recess. I just not sure if the entire flat area of the recess is in fact glassed to the hull.

The backing plates I am using are a new product from Groco (see the link below to the Groco website) that have threaded inserts in the plate to bolt the seacock flange, so I am not going to be drilling holes through the hull to secure the flanges. The backing plate will be installed with Sikaflex 291.

If anyone has dealt with this situation before, any advice or words of wisdom would be appreciated.

http://www.groco.net/

Thanks,

[joemerchant]

I can't picture your exact setup, but I can say you do not want to back against a liner. I would cut out enough liner to get to the hull and leave enough room around the seacock to be able to pry out the starboard if you ever have to re-bed.

[hilbert]

The backing plates I am using are a new product from Groco (see the link below to the Groco website) that have threaded inserts in the plate to bolt the seacock flange, so I am not going to be drilling holes through the hull to secure the flanges. The backing plate will be installed with Sikaflex 291.

Whether you make your own backing plates or use Groco's seacock backing blocks, they should be permanently attached with resin (either polyester or better yet epoxy). Sikaflex 291 is appropriate for bedding the flange and thru-hull, but not the backing plate.

http://www.pbase.com/mainecruising/backing_blocks

[hilbert]

The head of my 28 had flanged Spartan valves mounted on the liner, bolted from outside the hull. After removing the thru hulls, I could not detect any separation between the liner and the hull.

Since you are not planning to thru bolt the flange from the outside, grinding away the liner and epoxying the backing plates to the hull would be optimal.
On the other hand, filling in the recess would save a lot of mess. You will be adding a flange to what was an inline valve at the same location, which will be superior to the what was there before.
I think that the thickness of the liner would influence my decision. Can you determine the thickness of the liner by looking into the hole?

I didn't have to make this decision, since I fiberglassed over the holes on the outside and then filled them in.

[Steve Bryant]

Hi hilbert,

I've included a couple of photos to help clarify what I'm looking at:

I've removed the valve and thru hull from my sink drain and you can see the recess in the hull liner and also the current valve installation for the port cockpit drain. The recess is approximately 3" in diameter and liner appears to be bonded to the hull. The new backing plate is 4 1/4" in diameter and 1/2" thick, so it will overlap the recess by about 5/8" all around.

Hull Liner Recess 1.jpg

The depth of the hole for the thru hull is approximately 1". In this close up photo it appears that you can see the definition of the hull and the liner with the appearance that the hull is around 3/4" thick and the liner around 1/4" thick.

Hull Liner Recess 2.jpg

My thoughts are to grind or sand off the gelcoat in and around the recessed area and fill the entire recess with either thickened epoxy or a polyester resin with kitty hair, then from below use a hole saw to drill through the new material. I would have a level surface to mount the backing plate with no void underneath other than the 5/8" overlap. This would seem to give me a much thicker and stronger base for the flanged seacock than if I removed the hull liner and installed the backing plate directly to the hull.

Something else I wanted to mention which was very surprising. Removing the thru hull nut did not take a great deal of effort, and I was able to just push the thru hull out with my hand. There was no evidence of any type of adhesive/sealant used for the installation other than what appeared to be pipe dope on the threads. Not at all what I was expecting.

If you see anything that I might be overlooking, I would appreciate your feedback.

Thanks very much for responding to my post,

[hilbert]

My thoughts are to grind or sand off the gelcoat in and around the recessed area and fill the entire recess with either thickened epoxy or a polyester resin with kitty hair, then from below use a hole saw to drill through the new material. I would have a level surface to mount the backing plate with no void underneath other than the 5/8" overlap

I think your plan is sound, except for the part about leaving a 5/8" overlap. When you fill in the old 3" diameter recess, can't you create a solid 4 1/4" base for the new backing plate with thickened resin?

There is a lot of good and relevant information in these Compass Marine How To Articles about thru-hulls. Like "You'll need to do a dry fit before mounting the backing plate. The two planes must be parallel under both the backing block and the thru-hull head for a proper fit and this may take some sanding." As a group they cover most everything:
http://www.pbase.com/mainecruising/backing_blocks
http://www.pbase.com/mainecruising/replacing_thruhulls
http://www.pbase.com/mainecruising/inst ... a_thruhull

Something else I wanted to mention which was very surprising. Removing the thru hull nut did not take a great deal of effort, and I was able to just push the thru hull out with my hand. There was no evidence of any type of adhesive/sealant used for the installation other than what appeared to be pipe dope on the threads. Not at all what I was expecting.

And yet it was in service for over 30 years! It should give you confidence that you can do at least as well and probably a lot better than the factory. On my boat, I found a lot of black adhesive/sealant, but only a few threads of the thru-hull were screwed into the sea-cock. It was cut way short.

[Steve Bryant]

Thanks hilbert,

Your observations and comments are much appreciated and very valid.

Believe me, I have been worshiping at the "Church of Maine Sail" for quite sometime now, and have read and reread the articles you mentioned, along with everything else on his site. I have learned more about significant boat systems there than any other resource I have found. We all owe him a great deal of thanks for the advice he puts out there.

Thanks again,