Thruhull repair on CD270

[TomFogarty]

Two of the seven thruhulls on my CD270 are weeping water a bit when the boat is first put in the water for the season but stops within a week or so. I'm thinking of replacing the woodblocks between the hull and the seacock with some type of plastic material and reinstalling the original seacocks. if anyone has done this project or has any info on this type of repair it would be greatly appreciated. Thanks in advance. Impatiently awaiting the spring thaw.
Tom Fogarty CD270 "Lucky Star II"

[Jim Walsh]

It's almost inconceivable that you have a leak eminating from the through hull. Have the backing plates/blocks begun to rot away? Are you positive you traced the source of the leak to the seal of the through hull where it attaches to the hull and not where the Seacock screws onto the through hull (similarly almost inconceivable) ? Are you positive your seacocks are not weeping a little due to being a little loose after being disassembled for service? Have your seacocks become wasp waisted allowing a little water to seep? Have your seacocks ever been lapped to ensure a tight fit?
If your backing plates are compromised they need to be replaced and that will allow you to disassemble everything and find the root cause of your problem. People seem to be fond of G-10 as a backing plate material.
You may find this helpful.
http://www.pbase.com/mainecruising/backing_blocks

[barfwinkle]

Good morning Tom

In 2004 I discovered the backing plate for the galley sink was completely rotten. I inspected the others and found that one more was also rotten and two were questionable so since I was out of the water anyway, the decision was made to replace all backing plates.

After seeking the combined wisdom of this board and talking with a friend I decided to use fiberglass backing plates. I ordered a 12" x 24" 3/8" sheet of Premium Fiberglass (FRP) Sheet (Product # 8494-K64 from McMaster-Carr.com) for the project. It is some tuff stuff! While it can be cut with a hand drill, if the hole saw (that's what I used) binds it can seriously hurt, so I found a friend with a good drill press and cut 6 new plates. I dont recall the exact size but 5 1/2" or so, just measure the existing ones. That was the easy part.

The FRP WILL NOT BEND NOR CONFORM TO THE HULL SHAPE! The side next to the hull must be shaped to conform to the contours of the hull, leaving the inner surface flat for the seacock. We used a hand grinder with the FRP secured in a vice. It took some work and at least on the 25D, the scupper plates were the hardest.

Once this was done, we simply re-installed the seacocks. Those puppies (backing plates) are bullet proof, I promise! And they will never rot. Not the easiest project but you'll sleep better knowing the packing plates will not be the cause of any grief in the future.

Just to restate, two of mine were rotted out and had to be replaced. The others were more like "while I'm at it" type thing.

Fair Winds and good luck.

I didn't see the link to Maine Sails article. Excellent article. I did mine differently, but basically the same process. And it has been my experience, you can't go wrong with a MaineSail Process!

[TomFogarty]

Thanks for all the info on remounting seacocks and the link. This should make my project much more manageable.
Tom Fogarty

[Sea Hunt Video]

Good morning Tom

In 2004 I discovered the backing plate for the galley sink was completely rotten. I inspected the others and found that one more was also rotten and two were questionable so since I was out of the water anyway, the decision was made to replace all backing plates.

After seeking the combined wisdom of this board and talking with a friend I decided to use fiberglass backing plates. I ordered a 12" x 24" 3/8" sheet of Premium Fiberglass (FRP) Sheet (Product # 8494-K64 from McMaster-Carr.com) for the project. It is some tuff stuff! While it can be cut with a hand drill, if the hole saw (that's what I used) binds it can seriously hurt, so I found a friend with a good drill press and cut 6 new plates. I dont recall the exact size but 5 1/2" or so, just measure the existing ones. That was the easy part.

The FRP WILL NOT BEND NOR CONFORM TO THE HULL SHAPE! The side next to the hull must be shaped to conform to the contours of the hull, leaving the inner surface flat for the seacock. We used a hand grinder with the FRP secured in a vice. It took some work and at least on the 25D, the scupper plates were the hardest.

Once this was done, we simply re-installed the seacocks. Those puppies (backing plates) are bullet proof, I promise! And they will never rot. Not the easiest project but you'll sleep better knowing the packing plates will not be the cause of any grief in the future.

Just to restate, two of mine were rotted out and had to be replaced. The others were more like "while I'm at it" type thing.

Fair Winds and good luck.

I didn't see the link to Maine Sails article. Excellent article. I did mine differently, but basically the same process. And it has been my experience, you can't go wrong with a MaineSail Process!

Bill and all:

I am going to have to replace all of the backing plates on my seacocks when I remove the seacocks for cleaning, etc. I had thought of teak backing plates but am now considering FRP backing plates.

My concern is that I have a limited number of tools to work with - mostly they are "wood working" tools and not designed to deal with FRP material.

I would appreciate guidance on what tools, drill bits, etc., I would need to buy in order to work with the FRP material. Bill, as you know well, the backing plates for the scupper drains have to be "sanded" down to conform to the curvature of the hull on both port and starboard.

1. Can FRP material be "sanded" in the same way as wood or does it require special tools, etc. Bill, your post said you used a "hand grinder". Was this a special metal grinder or a standard grinder with a special sanding material or something else altogether

2. What caulking material do you use to secure the FRP backing plates to the hull I assume that there are certain caulking materials that do not react well with FRP.

Thanks in advance for any suggestions, etc.

[Ron M.]

I also replaced seacock backing plates with FRP a few years ago. It is tuff stuff, it can be worked with woodworking tools. It will dull carbide quickly but a sharp blade should get you through the project.
A grinder with aggressive abrasive discs and cut off wheels work pretty well.
Once fitted to the hull bed/caulk with your preferred product, 3M 5200/4200, Boatlife, Sika, or other.

[Sea Hunt Video]

After talking with a few folks about the benefits of using FRP material (and the downsides) I have decided not to use FRP. From all that I have learned, while this material is excellent for backing plates, to properly prepare and fit FRP material as backing plates is beyond my skill level and current equipment inventory.

While I remain open to other suggestions, my tentative plan is to use precut teak discs (1/2" thickness) as backing plates. They will be much easier to sand and prep and fit the curvature of the interior hull within the engine compartment.

I used a teak disc for a backing plate in the forward head compartment and it was reasonably easy to work with and fit to the curvature of the hull forward. Because of their locations, I anticipate that forming the shape of the four (4) backing plates for the engine compartment seacocks will be MUCH MORE difficult.

If anyone has any suggestions for other material that can used as backing plates AND can be worked with (sanding, forming, shaping, etc.), please post. In late August I will probably be ordering backing plates in various diameters (6", 5" and/or 4").

[Ron M.]

If your 25D has a heavy fiberglass, gel coated engine bed liner and your engine intake thru hull goes thru it a backing plate isn't needed in my opinion there. My liner is at least a 1/2" thick inside the hull.
I replaced the engine intake sea cock a few years ago with a bronze ball valve. Be sure to solvent clean the hull opening thoroughly and put a slight bevel on the hole edge before caulking.

[Sea Hunt Video]

Ron:

2 questions:

What solvent do you recommend

Dumb question - is the bevel on the outside or inside hole edge

[Ron M.]

3m 5200
Anytime I caulk a fitting to the hull/deck I bevel the top of the hole slightly. Same for bolt holes for fasteners on the exterior. Example, for a 1/4-20 screw the bevel would be 1/16 of an inch.

[Sea Hunt Video]

Ron:

If I use 3M5200 won't the guy who is the caretaker of S/V Bali Ha'i in the year 2036 be cursing my name for making it impossible (almost) to ever remove the seacock/thru hull without damaging the hull

I'll be long gone of course, but still, won't he be cursing me

When I replaced the seacock and thru hull in the forward marine head last year I used Sikaflex 291 LOT. What are the thoughts about this sealant

[Ron M.]

5200 can be removed but it takes some effort and solvent to do it cleanly.
I use it when I want a permanent bond. I've not used sikaflex but heard it's a good choice.
4200 would work as well.
I reinstalled the original transducer with 5200 after barrier coating the hull maybe 10 years ago.
The transducer crapped out 2 years ago and I got it out using the solvent and considerable leverage, it wasn't that big a deal.

[tjr818]

After talking with a few folks about the benefits of using FRP material (and the downsides) I have decided not to use FRP. From all that I have learned, while this material is excellent for backing plates, to properly prepare and fit FRP material as backing plates is beyond my skill level and current equipment inventory.

While I remain open to other suggestions, my tentative plan is to use precut teak discs (1/2" thickness) as backing plates. They will be much easier to sand and prep and fit the curvature of the interior hull within the engine compartment.

I used a teak disc for a backing plate in the forward head compartment and it was reasonably easy to work with and fit to the curvature of the hull forward. Because of their locations, I anticipate that forming the shape of the four (4) backing plates for the engine compartment seacocks will be MUCH MORE difficult.

If anyone has any suggestions for other material that can used as backing plates AND can be worked with (sanding, forming, shaping, etc.), please post. In late August I will probably be ordering backing plates in various diameters (6", 5" and/or 4").

Roberto,
I have looked at this "improvement" several times over the years and I still cannot bring myself to do it. Slainte is now 36 years old and has never had backing plates. I do think they might help in some way from damage that might occur from the inside. I do not see what could happen from outside that could cause damage that would be minimized by the addition of backing plates. That being said, IF I ever have to remove the through hulls I would probably add backing plates, but not until then. Has anyone ever though of using HDPE for backing plates? It is impervious and easy to form with hand tools.