Backing plate material

[PhilPB]

In the near future I need to do a haul and replace a few seacocks. The backing on them now looks original, appears to be wood and not in great shape. I could get some teak dimensional scraps but I'm sure someone here has a better idea of what I can use. Suggestions?

Also suggestions on seacock replacements would be helpful.

 

[jleonard]

I always used plywood. I like that it can absorb some shock if need be. And lots of 5200.

 

[luna]

Having just started down the same path I chose Groco’s FBV Flanged Ball Valves. The only difference that I could see between the FBV and their full blown Seacock was that the latter are serviceable with replacement parts and that they cost twice that of the FBV.
The existing are Groco ball valves now 27 years old. They look just OK, but for preventative reasons will be replaced. If these new ones last 27 years, at 93 years old I hope to be chasing women, not boats!

For the backing blocks, through eBay Merimarine sells Fiberglas units sized, drilled and tapped to fit the FBVs at about half the price of Groco’s foamed PVC malleable backing blocks.

Removal and installation stars in a month, wish me luck!

 

[mvweebles]

If bolt pattern is similar, the Groco backing plates are an excellent choice.

If starting from scratch, I'd go with GPO3 sheet fiberglass like this from McMaster.

McMaster-Carr Page:
https://www.mcmaster.com/fiberglass...c-resistant-gpo3-fiberglass-sheets-and-strips

Peter

 

[Comodave]

G10 fiberglass from Jamestown Distributers. Very strong stuff.

 

[mvweebles]

G10 fiberglass from Jamestown Distributers. Very strong stuff.

I love McMaster. Great value given the availability, quality, selection, and rapid delivery. Low price is not the reason I shop there. But for some reason, the sheet fiberglass is the cheapest I've found (though never priced Jamestown)

 

[Bmarler]

I love McMaster. Great value given the availability, quality, selection, and rapid delivery. Low price is not the reason I shop there. But for some reason, the sheet fiberglass is the cheapest I've found (though never priced Jamestown)

I’ve been buying that gpo3 from McMaster for years. So many dimensions available at a reasonable price.
For backing on seacocks it’s pretty tough to beat.

 

[mvweebles]

I’ve been buying that gpo3 from McMaster for years. So many dimensions available at a reasonable price.
For backing on seacocks it’s pretty tough to beat.

I love the stuff. Fast, easy to work with, paints well, delivers very quickly, and extremely durable. Even the frame on the flybridge cabinet is GPO3 (1" thick with rabbets cut to inset into cowling, and another for the panel).

Peter

 

[PhilPB]

I love the stuff. Fast, easy to work with, paints well, delivers very quickly, and extremely durable. Even the frame on the flybridge cabinet is GPO3 (1" thick with rabbets cut to inset into cowling, and another for the panel).

Peter

Very nice work!

 

[Bmarler]

I love the stuff. Fast, easy to work with, paints well, delivers very quickly, and extremely durable. Even the frame on the flybridge cabinet is GPO3 (1" thick with rabbets cut to inset into cowling, and another for the panel).

Peter

Plus, dimensionally stable and no rot.
The only downside is the itchy dust when you cut it.

 

[mvweebles]

Very nice work!

La Costa Boatworks in Ensenada. Fiberglass and paint work in Mexico is generally very good. Some of the other trades are a bit mixed. But the guys are artists with fiberglass.

Peter

 

[kapnd]

I’m all about using G-10 for backing plates.
Why would you core your hull at a thru hull with a material that will rot?

 

[Mac G]

If you completely remove a seacock then yes going with new fiberglass or some rot proof synthetic backer is an excellent choice.
But if you simply want to service existing seacocks without taking them out and the wood backing looks sketchy I have had luck simply saturating the existing wood backing with West System epoxy on all sides, everywhere visible and accessible and turning it into petrified wood in its existing location.
If the wood is thirsty it will suck that epoxy in and turn rock hard.

 

[Bacchus]

Take a look at Rod Collins Compass Marine How To website.
He is a commercial member here on TF (CMS) and has a wealth of knowledge he has shared with boaters for many years. He does have one for sea cock backing plates that is very comprehensive.

https://marinehowto.com/seacock-backing-plates/

 

[PhilPB]

Having just started down the same path I chose Groco’s FBV Flanged Ball Valves. The only difference that I could see between the FBV and their full blown Seacock was that the latter are serviceable with replacement parts and that they cost twice that of the FBV.
The existing are Groco ball valves now 27 years old. They look just OK, but for preventative reasons will be replaced. If these new ones last 27 years, at 93 years old I hope to be chasing women, not boats!

For the backing blocks, through eBay Merimarine sells Fiberglas units sized, drilled and tapped to fit the FBVs at about half the price of Groco’s foamed PVC malleable backing blocks.

Removal and installation stars in a month, wish me luck!

Looked at Merimarine blocks and the Groco's FBV's. I like the choices. Need to figure out the sizes . I will be replacing all seacocks, hopefully I won't realize after I am out of the water that I also need to replace the thru-hulls. The Boatyard I use is like a hotel at $65 per day so it kills me if the boat sits there idle while I wait on a person or delivery of parts.

 

[High Wire]

I use 1/2” G10 from McMaster Carr. I bought a 24”x 24” square to store onboard to use as needed.

 

[luna]

PhilPB

I looked around quite a lot and could not find a better deal on the Groco stuff than at Go2Marine, which is 30 min. away from me, albeit in another country. Started an account and they gave me $20 of my first order and two $10 off codes as well. Likely more to come.

For those advocating the use of GP-03 or G10, by the time you buy the sheet goods, 2 hole saws (at least), a couple of drills and likely 2 taps (FRP sheet is a killer on cutting tools) in order to spend a day of your labour to make them yourselves, you can buy them from Merimarine for about the same price.
I would have no problem making them as I have a mill, lathe, drillpress, and good quality cutting tools. But I won't subject them to FRP.

 

[PhilPB]

Now my next challenge is to try and figure out the thru-hull/seacock sizes so I can order before hauling. I have 5 holes: 1 engine, 1 a/c, 1 generator, 1 raw water for head, 1 for macerator/ black tank

 

[Circumnavigator]

I'm with the crowd here -- glass sheet from McMaster.


Jim

 

[luna]

Are the existing Seacocks not marked with some kind of indication of manufacturer and/or size?

Failing that, and I don't know this for sure, but it's unlikely that the Seacock has a different size of thread on the Thru Hull side compared to the hose barb side. NPS and NPT yes, but size I doubt. Anybody ever seen a reducing or enlarging Seacock?

You may be able to get a pair of calipers onto the small portion of male threads on the hose barb, just as it enters the Seacock. The outside diameter of NPT threads (at the large end of the taper) is the same O.D. as the NPS threads of the Seacock/Thru Hull connection. From there you likely can determine the size of the Seacock.

Not to tell you what to do, but I would plan on replacing the Thru Hull fitting as well, as how do you know that the seal between the Thru Hull and the boat's hull is not leaking causing the existing wood blocking to degrade?

 

[luna]

I'm with the crowd here -- glass sheet from McMaster.


Jim

The backing blocks from Merimarine (no affiliation) are made from Strongwell's Extren 525, a structural FRP plate with similar properties to G-10 and can be had for about the cost (in my case) of the sheet goods plus the cutting tools that I'm going to destroy doing the fabrication.

Perhaps I made a mistake in buying the Merimarine blocks.

Help me out here, tell me why you would put yourself through the exercise of making the backing blocks from some unspecified "glass sheet from McMaster"

 

[PhilPB]

Are the existing Seacocks not marked with some kind of indication of manufacturer and/or size?

Failing that, and I don't know this for sure, but it's unlikely that the Seacock has a different size of thread on the Thru Hull side compared to the hose barb side. NPS and NPT yes, but size I doubt. Anybody ever seen a reducing or enlarging Seacock?



You may be able to get a pair of calipers onto the small portion of male threads on the hose barb, just as it enters the Seacock. The outside diameter of NPT threads (at the large end of the taper) is the same O.D. as the NPS threads of the Seacock/Thru Hull connection. From there you likely can determine the size of the Seacock.

Not to tell you what to do, but I would plan on replacing the Thru Hull fitting as well, as how do you know that the seal between the Thru Hull and the boat's hull is not leaking causing the existing wood blocking to degrade?

I'm going to get a closer eye on the seacocks to see if there are any markings on them. The diver/bottom cleaner will be there in a week or so and I will ask him if he can take my calipers and check the id of the thru-hulls.
Definitely will change the thru-hulls as well which will make the replacement easier and everything new is a good thing.

 

[Nepidae]

Backing Plate Material

You asked about backing plate material so I'll avoid what you might use for new valves.

I have a cousin who for years prepared boats for the Annapolis to Newport & Newport to Bermuda races.

When I needed to make a backing plate for our LoFrans Tigres windlass on our bow pulpit I asked him what to use.

This (https://www.mcmaster.com/products/f...ss-sheets-bars-and-strips/?s=fiberglass-(frp)) is what he used and what I used for our windlass and also for our davits on our swim platform.

Has worked great. No additional coating needed. Put it in & forget about it.

Hope this helps.

 

[Capt Dan]

Phenolic plastic. You can get it by the sheets, probably from McMaster it glues well. You can epoxy it right to the inside of your hull. It drills. It machines well, It won't absorb water. You can make a nice wide backing plate and make it any thickness you want. Just stack them up

 

[HeadedToTexas]

Since the experts are assembled here for backing plate materials, what about decking material? My Mariner 37 has removable deck plates creating flat and usable space in the engine room between the stringers and other structures. It is lighter and less dense than the G10 I've used for backing plates, but some sort of fiberglass material. I don't find anything on McMaster-Carr. Any ideas?

 

[Noforad]

I used G10 material for the 27 seacocks I replaced. This project took most of the winter to complete. Cutting of this material is not easy. I cut all the blanks out destroying three carbide hole saws and two drills. I then had a machine shop bore center holes for different size thru hulls, and drill and tap the 3 flange mounting holes for the valve. The 3 holes do not go thru the hull. All new parts including all hoses. Valves varied between 1/2-to-1-inch sizes. Found rotten plywood backers and much oversized holes in the hull that I cannot believe did not leak. If moved it would have failed. Someone replaced a valve with the incorrect size, my guess. In my opinion this is much better than any other design I have seen, although a lot of extra work.

 

[Circumnavigator]

I used G10 material for the 27 seacocks I replaced. This project took most of the winter to complete. Cutting of this material is not easy. I cut all the blanks out destroying three carbide hole saws and two drills. I then had a machine shop bore center holes for different size thru hulls, and drill and tap the 3 flange mounting holes for the valve. The 3 holes do not go thru the hull. All new parts including all hoses. Valves varied between 1/2-to-1-inch sizes. Found rotten plywood backers and much oversized holes in the hull that I cannot believe did not leak. If moved it would have failed. Someone replaced a valve with the incorrect size, my guess. In my opinion this is much better than any other design I have seen, although a lot of extra work.

This would not be my choice. Unless they happen to be on a perfectly flat section of the hull, the 3/4" glass will not pull into the hull and will leave a gap which would have to be filled by whatever adhesive is used between it and the hull. I also don't like depending on threads in G10. I would use much thinner glass, probably 1/8" and bolt through the hull with silicon bronze bolts. The thin glass will bend to conform to the hull shape, leaving no gap for leaks to develop over time.


Jim

 

[rslifkin]

This would not be my choice. Unless they happen to be on a perfectly flat section of the hull, the 3/4" glass will not pull into the hull and will leave a gap which would have to be filled by whatever adhesive is used between it and the hull. I also don't like depending on threads in G10. I would use much thinner glass, probably 1/8" and bolt through the hull with silicon bronze bolts. The thin glass will bend to conform to the hull shape, leaving no gap for leaks to develop over time.


Jim

When something like the thick G10 backing plates gets used, it's typically bedded to the hull with thickened epoxy to take up any gaps and make it fit.

The threads to hold the bolts aren't holding the thru hull in place, they're to keep the valve from rotating and the flange firmly seated. Groco sells a similar setup with threaded inserts in a fiberglass backing plate to avoid needing to bolt through the hull itself (which doesn't really add much useful strength in my opinion).

Basically the idea of these plates is that you make the G10 block a part of the hull by glassing / epoxying it in, then the thru hull goes through the whole assembly with the valve flange bolted into the backing block.

 

[Bmarler]

The backing blocks from Merimarine (no affiliation) are made from Strongwell's Extren 525, a structural FRP plate with similar properties to G-10 and can be had for about the cost (in my case) of the sheet goods plus the cutting tools that I'm going to destroy doing the fabrication.

Perhaps I made a mistake in buying the Merimarine blocks.

Help me out here, tell me why you would put yourself through the exercise of making the backing blocks from some unspecified "glass sheet from McMaster"

I can’t speak for others, but I use the frp sheets for many things, and usually in some custom size. It’s a great electrical insulating material for buss bar mounting, or stand offs, compression plates, deck hardware backing, plus many other uses in my line of work. I have an abundance of tooling to cut, drill and shape, so keep certain tools aside for only that task.
If I was retired, and didn’t have other projects, I probably wouldn’t keep much stock of it, buying the project specific pieces would make sense.

 

[lwarden]

If you are looking to not have the bolts penetrate the hull, go with a thicker G10 plate material and counterbore from the backside and epoxy in 316 stainless inserts made by Seachoice. Apply PVA or heavy grease on the threads of a bolt when installing to prevent epoxy getting into the threads. The thickness of the G-10 on the screw diameter portion of the hole (not the insert OD hole) only needs to be 1/8-3/16" and there is no way you will pull the insert through. I'm not a fan of tapping the G-10 since it wipes out taps and the threads aren't near as strong as an insert would be.

For a thru-hull I would only use 316, but for other locations which aren't subjected to constant salt water I've used 303 from McMaster.
https://www.mcmaster.com/products/i...set-inserts-for-plastic-7/?s=stainless+insert