Free hand-me-down sea cocks and through hulls

Kidding! !

We replaced the through hulls last week on our 36 year old boat. Ever think about what's going on down there? Scary! !

Nice job on the new installation.
I'm surprised to see those old Groco rubber plug seacocks lasted this long. Did they start to leak?

Just about to embark on replacing all eight seacocks in Sarawana, decided to go with a composite NZ product.

Two of the seacocks for the toilets have built in cupboards around them , so the Tecma's will have to come out and a bit of carpentry undertaken with the mighty Fein (bit worried about the carpenter though, he can be a bit dodgy at times)

Sure you will do just Fein.

I was thinking of asking for that seacock that's at the 9:00 position in the picture, sort of along the left side about midway between top and bottom of the photo.


It would be kind of a funny rod holder for a stern mounted flag.


But it would probably just end up in my garage along with all the other junk I've collected over the years.

old Groco rubber plug seacocks last a very long time.
I have two. a 3/4 and 1.25 inch. They can be taken apart and cleaned and greased.
Mine are from 1970 and still fine, not rotten, metal still solid.
I don't have yellow rubber handle covers, just bronze rod.
Perhaps you should sell or give them to someone?

I think a big cause of death for these, and the reason we had planned to pull them all indiscriminately, was the wet wood backing blocks. The ac through hull would wiggle when opened or closed! The rubber plugs were chewed on the inside and the face seal leaked when exercised.

Gabe n Em said:

I think a big cause of death for these, and the reason we had planned to pull them all indiscriminately, was the wet wood backing blocks. The ac through hull would wiggle when opened or closed! The rubber plugs were chewed on the inside and the face seal leaked when exercised.

Click to expand...

Nice job!

Largely the same experience here. I replaced about a dozen of these seacocks below the waterline, although only one of them was stiff . . . and the dimple on the rubber plug that inhibits movement can be sanded out. The old rubber-plug Grocos are extremely robust, but over time, the bond to the hull weakened and became overly dependent on the through hull connection. The "backing boards" were plywood affixed with some kind of weak black mastic; some were saturated and would flex when operated. I could pull the whole assembly off by hand once the through hull was sawed off.

I went with new Groco ball-valves because I like their stronger composite backing boards and the ability . . . if you use their threaded flanges . . . to swap out a damaged or defective seacock without involving the through hull. The new flanges are glassed to the hull and use the proper threads to deeply engage the through hull. They're rock solid. (And yes, the mud daubers' nest is long gone )

Gabe n Em said:

I think a big cause of death for these, and the reason we had planned to pull them all indiscriminately, was the wet wood backing blocks. The ac through hull would wiggle when opened or closed! The rubber plugs were chewed on the inside and the face seal leaked when exercised.

Click to expand...

Yes, they can get scored, the other side, you tighten the handle, the rubber squeezes and seals the valve. Just the nature of them and how they work that they might leak a little. Mine don't leak when I loosen the handle and turn the valve. I am impressed with how they keep working being as old as they are, so a good design. I suppose if people never take them apart to clean the inside where the rubber rubs, using them a lot can scratch the rubber, if they are corroded on the inside.

I have not greased them recently, but I also mostly leave them open all the time.
I think a marine water resistant grease would be ok.

The two I have are on the head intake and the head outlet.

"but over time, the bond to the hull weakened and became overly dependent on the through hull connection.'


A proper seacock install will have them bolted ,3/8 bronze bolts minimum thru the hull.

The rubber items last almost forever IF you always remember to loosen the T handle before moving the operating lever.

FF said:

"but over time, the bond to the hull weakened and became overly dependent on the through hull connection.'


A proper seacock install will have them bolted ,3/8 bronze bolts minimum thru the hull.

The rubber items last almost forever IF you always remember to loosen the T handle before moving the operating lever.

Click to expand...

The 2 rubber ones I have are original to boat from 1970. Still in good shape.

You could probably resurface badly scored rubber with either Loctite s30 (even mixed with 1/32 fiberglass fibers which toughens the surface) , or some 3M5200

Andy G said:

Just about to embark on replacing all eight seacocks in Sarawana, decided to go with a composite NZ product.

Two of the seacocks for the toilets have built in cupboards around them , so the Tecma's will have to come out and a bit of carpentry undertaken with the mighty Fein (bit worried about the carpenter though, he can be a bit dodgy at times)

Click to expand...

One month later.

Well, after cutting out the access panels to the aft head, I got a close first hand look at the copper deck drain pipe attached to the below waterline thru hull fitting situated snug up against the hull.

Guess what, it had a slow leak, the pipe was virtually corroded away to nothing, one small tap and the slow leak became a large leak prompting some emergency plumbing, as the fractured pipe was about an inch or so below waterline. Why place a thru hull fitting below water line when there is absolutely no necessity to do so?

I am now cutting out access(viewing) panels for all thru hull fittings on the boat.

"Why place a thru hull fitting below water line when there is absolutely no necessity to do so? "

Deck wash and rain water is dirty , some folks prefer a no streak topside.

Not the way I would build the boat , but....

I pulled the thru hulls from the main and air conditioner yesterday off a 1986 Mainship 34'. It was on this year's maintenance list anyway but the visual of the pics above was motivation. The bronze was in good shape on each but both had wood backing plates that were deteriorated. Neither were bonded.