About Fig Leaves And Installing Seacocks

Installing a seacock properly is not a trivial project.

First you need to install a backer plate and then you need to figure out how you will bolt the flange of the seacock down.

Yes, I know that many, perhaps most, boats do not have their seacocks bolted, but that is, in our opinion, a very poor practice since any force coming in contact with the top of the seacock or the attached hose, such as a clumsy foot—a problem I’m famous for—can exert an incredible sheer force on the through hull threads. And if those threads strip, things are going to get very damp very quickly.

Add an aluminum hull and a seacock that is made of bronze, like most of those in Morgan’s Cloud, and you need to figure out a way to keep the two electrically isolated. (See the pictures at the bottom of the post for how the bronze seacocks on Morgan’s Cloud are installed.)

Oh yes, and you need to make sure the seacock that you are about to install really is bronze and not some form of brass. This is particularly a problem in Europe where valves are sold for marine use as “tonval bronze”, which is not bronze at all, but brass.

Brass is really bad news in salt water since the zinc leaches out of it leaving a spongy and weak potential boat-sinker behind. One more thing: if you tee something off the seacock you will use a nipple and all nipples except t hose made by Groco, at least as far as I know, are made of brass, not bronze, so watch out for that.

With all of the above metal seacock hassles, when we needed to install a new seacock for the drain required for our new separator exhaust system, we decided to give a Forespar seacock made from Marelon,  a tough plastic, a try. An experience that can only be described as “out of the frying pan and into the fire”.

The installation manual said:

If it is desired to additionally fasten the king-nut to the backing block with screws, there is provision for such, but it is completely unnecessary.

Not only do we believe the above instruction to be just plain wrong, particularly with a plastic through hull, we don’t believe fastening with screws is adequate either. We through-bolt our flanges (king-nut) to the backing plate.

Wait, it gets worse: Despite the above assurance, there is no practical way to actually accomplish the above since one of the four holes provided is obstructed by the handle and the flange is so small in the way of two others that there is no way to get a screw head, never mind a washer, to bed in the space allowed. Despite this the manual states:

On the backside of the king-nut there are four (4) blind ¼” holes. These may be drilled through to the front side before installation to allow for round-headed screw fasteners.

I suspect that the non-functional holes and the associated text in the manual are only there to serve as a fig leaf—you were wondering how I was going to work that in, huh?—so that the company can say “Well, you could have bolted it down”.

This otherwise excellent product has been let down to save a few pennies by not providing a decent flange for proper fastening–a real pity. See the photos below for how we solved this problem.

The new bronze seacock, ready for installation, sitting on top of the plastic spacer that will separate it from the aluminum hull. The mounting holes have been bored out oversize to take insulating sleeves. This reduces the "meat" around the hole, but we feel that the addition of large washers will make this safe. (The original seacocks, also from Groco, installed in 1984, had much wider flanges—just another way that cost cutting diminishes a good product.
The new bronze seacock, ready for installation, sitting on top of the plastic spacer that will separate it from the aluminum hull.
The mounting holes have been bored out oversize to take insulating sleeves. This reduces the “meat” around the hole, but we feel that the addition of large washers will make this safe.
(The original seacocks, also from Groco, installed in 1984, had much wider flanges—just another way that cost cutting diminishes a good product.
The larger diameter end of the custom machined stud threads into the backing plate welded into the hull. The plastic sleeves with shoulder flanges isolates the seacock from the hull.
The larger diameter end of the custom machined stud threads into the backing plate welded into the hull.
The plastic sleeves with shoulder flanges isolates the seacock from the hull.
The Marelon seacock attached from underneath to a custom aluminum plate that we had made. As you can see, there is no way to screw the sea cock down from above as the manual suggests due to the interference of the handle.
The Marelon seacock attached from underneath to a custom aluminum plate that we had made. As you can see, there is no way to screw the sea cock down from above as the manual suggests due to the interference of the handle.
A close up showing the very small amount of room provided on the flange for fastenings. So small that parts of two of the nuts had to be ground off. There is absolutely no room for a washer.
A close up showing the very small amount of room provided on the flange for fastenings. So small that parts of two of the nuts had to be ground off. There is absolutely no room for a washer.
Another view showing the custom plate attached to the seacock. The four unused (in this picture) holes will take hex head bolts to fasten the plate down to holes that were bored and threaded into the backer plate before it was welded into the hull.
Another view showing the custom plate attached to the seacock.
The four unused (in this picture) holes will take hex head bolts to fasten the plate down to holes that were bored and threaded into the backer plate before it was welded into the hull.
The reinforcing backer plates ready to accept the seacocks.
The reinforcing backer plates ready to accept the seacocks.
The completed task. Who knew that it could be that difficult! If Forespar had given us just a little more flange width and had thought to offset the handle from the mounting holes, it would have been a whole lot easier.
The completed task. Who knew that it could be that difficult! If Forespar had given us just a little more flange width and had thought to offset the handle from the mounting holes, it would have been a whole lot easier.
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John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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