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Old 01-27-2021, 04:29 PM   #1
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GB 36 Classic Seacocks

Any GB 36 Classic owners, late 1980's in particular, know the sizes of the original Groco rubber drum type seacocks, aft head discharge in particula?
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Old 01-27-2021, 05:35 PM   #2
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Third Reef 1988 36' Classic

I will check ours for a size tomorrow but wondering if you have issues with the aft head SW supply. Mine is nearly impossible to cycle open and close, therefore I tend to leave open which I'm not crazy about. It feels like the rubber drum is swollen. I have lubricated but still no joy. Very hard to operate particularly in its location below the steps.

We are thinking of swapping out the aft head for a composting toilet which would enable us to eliminate both the supply and discharge but still up in air about this.

Is your discharge malfunctioning? I will go aboard our boat tomorrow and let you know the size.

Best regards,
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
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Old 01-27-2021, 06:00 PM   #3
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If you can’t work the seacock, then you should replace them asap or remove them asap.
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Old 01-27-2021, 06:02 PM   #4
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Aft Head Seacocks

The aft head seacocks, supply and discharge are original Groco tapered rubber drum type; the supply is capped off and in closed position. The toilets are Sealand electric fresh water flushed types still connected to the original discharge seacock. That is the one I want to replace when hauled out next month but wanted to order the new seacock before haul. I was sure the original boat information said what size each of the seacock thru-hulls are but can't find the info. The one I'm interested is hard to reach too under the aft head lav. Don't know where to look on the valve to see if there is a model number. If you can figure it out please let me know.
Thanks.
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Old 01-27-2021, 06:44 PM   #5
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I don’t think that they sell the rubber plug type anymore. All you really need to know to get a new through hull and seacock is the hose size. Then you can order it and have it on hand in time for the haul out.
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Old 01-27-2021, 06:47 PM   #6
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No the rubber drum types are obsolete; I was hoping to replace the seacock only, not the thru hull which appears to be fine. Are you suggesting both should be replaced as a matter of course?
Thanks for the reply!
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Old 01-27-2021, 07:03 PM   #7
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I would replace both since it isn’t that much more work. The old through hull is probably ready for replacement also. Besides it may give way when you are replacing the seacock anyway. This way you are prepared for that possibility. I took out a seacock last year. No way would it unscrew so I just took a grinder and ground the head off and pulled the rest into the boat. Very quick and easy, maybe about 5 minutes of grinding and it was out. I could have spent hours trying to get it apart.
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Old 01-27-2021, 07:10 PM   #8
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I have the manual for our 1984 GB 36 in my hands. It gives the locations for all thru hulls but not the size. I believe the original seacocks were the Groco SV series. I have one left. I have attached the instructions on servicing from Groco. I would give that a try.
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Old 01-27-2021, 08:06 PM   #9
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Thanks everyone for the info and feedback. I think I know now what needs to be done.

Cheers,
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Old 01-27-2021, 08:12 PM   #10
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Connector Plates

So, unrelated and not sure if it's cool to ask an unrelated question in thread but any of you folks know what the little connector plate in attached phots is for? It has four holes, each pair counter sunk from opposite side.
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Old 01-28-2021, 02:04 PM   #11
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Third Reef 1988 36' Classic

Hi K
I checked the size of the aft overbd under the vanity. The hose size is 1-3/4", couldn't see any size markings on valve.body and have to agree after looking at mine, if mine were not working I would replace the whole valve/ thru hull fitting as mine is looking pretty crumpy too.I

As I mentioned, we are leaning towards a composting toilet aft at first so will be able to eliminate 2 thru hulls....less the better.

The plate you referenced doesn't look familiar, do you know where on the boat it comes from? Or from the spare parts drawer? I h haven't seen anything like that on our 88. What year is your GB?

STay safe.
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
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Old 01-28-2021, 02:17 PM   #12
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Thanks Charlie for the tech manual for the Groco seacock. This will be very helpful in the spring when I service all on our boat.
Thanks again
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
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Old 01-28-2021, 02:54 PM   #13
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Quote:
Originally Posted by mbdana View Post
Hi K
I checked the size of the aft overbd under the vanity. The hose size is 1-3/4", couldn't see any size markings on valve.body and have to agree after looking at mine, if mine were not working I would replace the whole valve/ thru hull fitting as mine is looking pretty crumpy too.I

As I mentioned, we are leaning towards a composting toilet aft at first so will be able to eliminate 2 thru hulls....less the better.

The plate you referenced doesn't look familiar, do you know where on the boat it comes from? Or from the spare parts drawer? I h haven't seen anything like that on our 88. What year is your GB?

STay safe.
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
1 3/4” is pretty huge for a head intake.
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Old 01-28-2021, 03:16 PM   #14
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The little solid brass plate is one of 8 wrapped in a small plastic bag with #6-1/2" FH SS WD Screws, enough for all holes. I found the package in an engine room bin with spare parts. At first I thought they must be cabinetry related but yesterday searching for ground junction posts I saw some slightly larger rectangular gold plated electrical connector plates, not sure what they are to be used for but on considering the plates I have (don't have one with me now but will inspect on boat tonight) the color/tone of the metal is more gold-like than yellow brass when seen in person. IDK, it's a mystery. I can not fathom how they would be used in cabinetry or electrical.
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Old 01-28-2021, 04:46 PM   #15
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At this age I would replace those Groco rubber plug seacocks with Groco Ball Valve Seacocks.

The reason rubber plugs become difficult to turn is that when you snug up the T-handle it causes the rubber to swell into the openings. Eventually the rubber hardens and the bump remains in the openings making it hard to turn the plug.

If you need to keep using it for a while you can extend the life by removing the rubber and sanding down the bumps.
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Old 01-28-2021, 06:41 PM   #16
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The 1-3/4" line is on the head discharge.

Best
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
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Old 01-28-2021, 08:23 PM   #17
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Originally Posted by mbdana View Post
The 1-3/4" line is on the head discharge.

Best
Mike Dana
Third Reef
36' GB Heritage Classic
Potts Harbor Maine
207-833-5080
That’s a really odd size for a toilet discharge. The pretty much standard sizes for marine toilet discharge is either 1-1/2 inch or 1” inside diameter. You might want to check again. What make and model is the toilet?
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Old 03-01-2021, 12:51 PM   #18
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Sea valves

I bought GB 36 #736 (1986) last year. She had the old rubber valves. Don’t waste time trying to refurbish them. I replaced all 9 (4 with integral strainers) with the new Groco ball valves. Worth every cent. Easy to turn even with arthritic hands. The new handles are great as you can use a 3/8’s ratchet to turn them if they are hard to reach. Let me know if you have not had your question already answered and I will dig out the yard invoice for you.
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Old 03-01-2021, 01:52 PM   #19
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GB 36 Classic Seacocks

Hi Everfor,

The original post I asked is anyone new the size of the seacock and through-hull for the original aft head overboard. Never actually got a for sure answer (some one suggested 1-3/4"). I intend to replace it but had also asked about the through-hulls; assume that requires replacement too?
If the 7 seacocks you replaced were the original ones I would still be interested in what size the aft head overboard seacock is and whether you had to or did also the through hull.
Thanks,
RambleOn
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Old 03-01-2021, 02:25 PM   #20
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I know you didn't ask me, so I hope this is not an unwelcome contribution (but if so, I'm sorry).

First of all, I feel your pain. We had a cruising sailboat built in the 70's that had those Groco rubber plug seacocks. Even in the early 2000's when we were getting it ready for a longer cruise, we could only get the rubber part in certain sizes (off dusty chandlery shelves).

Anyway, except for some emergency type situation, I would be suspicious of any yard that would want to replace the seacocks without doing the through hulls. Especially if using (what I consider to be) proper seacocks with a backing flange that gets fastened (in the old days through the hull with fasteners; nowadays often to a fiberglass/ed backing block).

Here is why I say that.

1) Well just because I'd want to get a good look at 40-year-old bronze, so it'd be out anyway.

2) I'd want to get a look at or renew 40-year old sealant.

3) The big one for me is how you install these. Now I know every boat isn't this way, but oftentimes (my preference) you use a seacock with a flange that has holes in it around the perimeter. These holes allow you to fasten the seacock to the boat. In the old days, oftentimes right through the hull with big machine screws. Nowadays often with a fiberglass backing block that is permanently affixed to the hull, then tapped (or some other way) the seacock is fastened to that.

So if you visualize the installation (and I'm skipping some steps for hopefully clarity), you fasten the seacock to the boat and then from the outside you screw in the through hull with its sealant. All good.

But if you picture leaving the through hull in there (presuming the bronze and the sealant are still great after 40 years), now you are "unscrewing" the original Groco seacock, and then "screwing" the new seacock down onto the through hull (maintaining that old sealant on the through hull all the while so don't let it move at all), and then either trying to "hit" the holes you already tapped in the backing block, or tapping new ones once the seacock is in place. Okay, maybe that's no big deal, but I see possible problems with that. Even if re-using the existing through hulls, I would want to reinstall them into the already affixed new seacocks.

Caveat though: There is usually more than one right way to do things, and perhaps my worries aren't valid. But if nothing else they are one perspective.

(I can expand on the steps I take if it's of any interest; but I figured this was long enough already since I don't know your level of interest in my thoughts.)
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