Groco BB-1 Seacock Backing Blocks

[ramoore]

The original plywood backing blocks for all of my thru hulls are rotting, so I'm trying to replace them, mostly following Maine Sails recommendations using the Groco IBVF adapters. But ...

I decided to trade some dollars for time and buy the Groco backing blocks rather than making my own. I've read several other threads here where people have successfully used them.

When I got them, I noticed that the little threaded inserts are Brass instead of Bronze. Isn't this a really big deal? (or am I overthinking here?) Will the zinc not leach out of the brass in just a few years leaving just crumbling copper?

I really hope I'm wrong here.

Thanks !

 

[dlochner]

Hopefully some of our metallurgists and chemists will way in for a more authoritative opinion.

With that said, I don't think the brass will be much of a problem for 2 reasons, 1) Groco is a very reputable company would not knowingly build something that was going to fall apart quickly; and 2) for the brass inserts will be well sealed and not subject to exposure to a saltwater environment, there really isn't anyplace for the zinc to go.

 

[sail sfbay]

Suggest confirming if the brass is De-Zincification Resistant (DZR) Plastics & Metals: Choosing The Right Material For Seacocks and Fittings - Boaterrific.

 

[DeniseO30]

Making my own out of the same material, going to use regular nuts, 3/4 inch bronze countersink machine screws seem to be unavailable everywhere,so I'll just heat set them into the epoxy and fiberglass board & use pieces of bronze threaded rod as bolts

 

[ramoore]

Dave, I agree with your point #1. For point #2, I'm hoping for confirmation. I'll try contacting Groco support and see if the Brass they use is DZR as suggested by sail sfbay.

But, if I can't confirm that, maybe I can use a variation on Denise's idea (if I understood correctly). It looks like I can get bronze hex bolts, washers, and nuts from McMaster-Carr (and probably other places). So I can leave out the brass inserts completely and heat set the hex head end of the bronze bolts into the Groco PVC, then epoxy that to the hull with the bolt threads up and drop the flange adapter down onto them and add lock washer and nut from the top. The holes in the PVC backer are just under 1/2", so maybe a 3/8" or 7/16" by 1.25" long bolt.

Or, is the threaded rod with hex nuts on both ends better?

 

[THECUSCUS]

If you are using G10 as the backing, just drill and tap it. Use bronze bolts to hold the base in place. The mounting bolts are only to keep the base from turning when you screw the thru hull and the ball valve onto it. The thru hull provides the squeeze force to the hull.

 

[DeniseO30]

My heart of hearts wants to drill through the hull but I understand the mushroom with the straight pipe thread works like a large bolt (need to cut it to length) and it pulls the flange against the inside hull giving it a clamping effect with the hull between the mushroom and the flange of the valve, the bolts are essentially just to keep the valve from spinning can you put pipe fitting on. with the use of g10 and epox it should be a very permanent and nearly indestructible

 

[RoyS]

I use these and like them. I would not use epoxy to bond them to the hull. If you set them in epoxy and they are not exactly on the correct plane your mushroom will be cocked against the outer hull. Better to just use an underwater sealant when you install the thru hull, seacock, and backing plate assembly and it will self align. Hard to imagine it ever leaking with a quality sealant sandwiched in there. The threaded inserts only serve to keep the seacock from rotating IMHO. Consider your old rotting plywood ones with just sealant probably never leaked either.