Are Bronze machine screws for Seacocks ok?

[Stirling Hasen]

Hello All,In preparing for my seacock installation, I was wondering if Bronze machine screws are ok for thru-bolting the seacock. I can't imagine that using anything else would be a wise move (Copper, Stainless, etc), since galvanic corrosion of dissimilar metals would ensue.Checking the Galvanic Series of Metals in Seawater (ABYC)I see that Stainless Steel (~-.46v) is far less noble than Bronze (~-.26v) and would corrode (If I understand it correctly). The possibly creating three unexpected sources of water intrusion into my boat for each seacock is not very appealing.Any thoughts?

 

[Scott]

Is it really necessary?

I just installed real Conbraco seacocks on my 85 H-34. They are sitting on new, 1" backing plates, but I hesitate to drill more holes through the hull to bolt the flanges down. I'm tempted to bolt them instead to the 1" backing plates inside only. the backing plates are bonded to the inside of the hull with copious amounts of 3M 5200...What am I risking? What is the downside of not drilling more than a dozen new holes (3 per unit) through the hull below the water line just to hold these in place?

 

[Ed Schenck]

Question.

Do the through bolts just hold the outside strainer in position? Or are there holes on the inside seacock that have to line up with those bolts?On mine the bolts(2) are just to keep the strainer from turning I think. The seacock bottom is smaller in diameter than the bolt circle. Probably not necessary to bolt so long as it stays in place while tightening the seacock down on the pad.

 

[Scott]

Most true "Seacocks" are flanged

I did a ton of reading and research on this before replacing my old H-34 factory gate valves. The only seacocks (characterized by NPS threads that complement the through-hull fittings) that I found without at flange are a Marelon model made by Forespar. I chose the Bronze Conbraco which have a flange base that snugs down to the backing plate. This base flange is triangular, and features three through-bolt holes. Several books including Don Casey's and Nigel Calder show these with the flange through-bolted to the hull. Screws are tapered heads countersunk on the exterior, gelcoat side. I hate to put more holes in boat than neccesary.To answer the original question, Don Casey recommends that only Bronze bolts be used with Bronze seacock flanges -disimilar metals galvanic issues.

 

[Scott]

Careful torking bronze through-bolts

again, according to Casey, bronze stretches. He recommends not overtightening them...no specific tork in ft/pounds mentioned though...

 

[Ed Schenck]

Bolt thru would be ideal.

If possible I think bolting the seacock flange to the strainer would be the best. But in limited space what are the odds that the seacock will be tight against the pad, the holes will line up, and the handle will be where it has clearance to open/close? Odds are slim in my bilge.

 

[Scott]

Stainer and flange holes not aligned

On my boat only one thru-hull is a strainer and the seacock flange holes do not line up with any holes on the strainer.Here again, in the interest of not drilling more holes in my hull vs. the lack of a downside logic, I chose not to bolt the strainer/throug-hull to the hull. As the strainer is integral to the threaded through-hull and since the through-hull is screwed tightly to the seacock, I see no obvious need for more screws.