Seacocks and mushroom thru-hull fittings

We noted electrolisis on all the mushroom thru-hull fittings, significant enought to warrant removing all seacocks and thru-hull fitting for close inspection. I was curious to find that none of the thru-hull fittings had been bonded. Experts seem to be divided regarding whether to bond or not to bond thru-hulls. We found that the level of electrolisis increased as the distance from the propeller shaft zinc increased, with the head thru-hulls in the bow having the highest metal loss, the seacocks showed similar wastage. With the flange type seacocks, the mushroom thru-hull fitting passed from outside of the hull, through the hull and plywood backing block, screwing directly into the bottom of the seacock. The threaded portion of the mushroom thru-hull fittings were cut too short, engaging 2-4 threads of the seacock, water and subsequent corrosion wasted away remaining exposed threads, was a shame, considering 3 of the 4 1-1/2" seacocks were otherwise restored to like new condition. Despite conflicting opinion, you can bet, if its under water we’re going to bond it! The next step in fighting galvanic corrosion is to install a galvanic isolator to isolate the shore power ground.

Shamrock has Spartan Marine Hardware, conical valve bronze seacocks as installed at the factory when built, we order new replacement for all today from:

We found it less expensive to replace the Spartan seacocks rather than fill all the thru-bolt mounting holes in the hull, 2 per seacock and re-drill for Groco BV series. We don’t mind disassembling the Spartan valves and servicing them at haul out, sort of a boating ritual. Besides, it nice to look inside the valve and see whats going on inside, something you can’t do with a ball valve. With the ball valve, best you can do is wrestle off the hose and look down inside and check the condition of the ball, applying grease through the hose barb realy doesn’t work as the nylon socket tends to wipe the grease from the ball as it is opened and closed.

Servicing is simple, remove the locking nut opposit the handle, backing nut and plate and slide out the plug and attached handle, degrease, clean with white vinegar, re-grease and your done. If the fit is not smooth and clean, use a fine grade valve grinding compound coating on the plug, reinsert the plug and rotate the handle back and forth 30 times, remove and clean, re-check to see if you have a clean mating surface of the plug and seacock body, if so, clean throughly, grease and reassemble, ok, maybe now your done…

In a pinch, and with a good diver, the diver can insert a wooden plug in the thru-hull fitting while the boat is in the water, sealing off the water and the Spartan seacocks can be service without hauling the boat.

The Spartan standard 1-1/2" model with the straight 1-1/2" hose barb cast into the top of the seacock, saves on buying additional fittings to adapt to scupper or galley sink hose. The engine inlet uses the 3/4" standard model with a 3/4" cast in hose barb. The head inlet and discharge use a “seacock with adapter”, instead of a hose barb, it has a male threaded barb for attaching 90 deg or straight fitting with a locking collar, both the 1-1/2" head discharge and the 3/4" seawater inlet use the seacock with adapter and 90 degree fitting.

We really liked the Groco BV series valves and the BVH with integral straight hose barb, considered the best in the industry; we ran into a problem finding hose-pipe fitting from Groco and Buck Algonquin which screwed directly into the seacock that were 1-1/2 NPT and 1-1/2 hose, our supplier did not carry the BVH Series, we could have used bushings or adapters to make them work, but by the time you add all the fittings the cost quickly rises above the Spartan valves by a fair margin. The Groco BV/BVH models require no maintenance and can be rebuilt; although I haven’t seen anyone who carries the repair kits, willing to bet they are almost as expensive as the complete seacock, probably better off replacing when they no longer seal properly.

The best buy in mushroom thru-hull fittings for us was Groco, excellent machine work, list price is $23 for the 1-1/2 and $6.5 for the 3/4" model, our distributor Svendsen’s Marine sells them below list price.

Hope you find this useful.

Best wishes,

Marty Chin, BCC Shamrock