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Old 27-06-2016, 14:10   #16
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Well... I can tell you what the US Navy does on a Carrier if they have to break the connection between the hull penetration and the valve.

The put a "cofferdam" over the penetration. A temporary box welded to the side of the ship to keep the water away from the hole.

The plunger idea is very similar... but missing 2 essential components:

Positive sealant to the hull
Apply some sealant. Non-hardening so you can get it off.

A way to ensure it doesn't slip.
The sealant will help... but run a line ALL THE WAY around the hull and apply pressure on the plunger to make it secure.

You aren't dealing with 30 to 40 ft underwater and a 4 ft diameter hole in the hull... So you don't need as robust of a cofferdam as we used on the carrier's main seawater inlet.

If your "exterior plug" is able to handle the pressure and stay in place it should be fine if you are not moving the boat. Especially since you are planning something that should only take a couple of minutes.

And for safety: Calculate the max flooding rate through the hole and have a sump pump (if you have shore power... maybe $50 or $100 to purchase) that can handle 2X that rate, in addition to your float operated bilge pump.

***************

Then we get to one of my pet peeves...

Boat makers don't put in adequate bilge pumps. Your AUTOMATIC bilge pumps should be able to pump out at a rate at least equal to the worst case single through hull pipe shear. Better would be if the bilge pump is rated for double that. (after the loss of rate due to the lift to get the water up to the pump's through hull)
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Old 27-06-2016, 15:20   #17
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

There is a product called Stay-Afloat. It comes in a plastic tub and looks like wax, but has more adhesion and strength. It is designed to...plug holes and cracks. A golf ball size of Stay-Afloat would plug a thruhull and keep the water out. One would be able to remove most or all of the Stay-Afloat after the maintenance project and clean up the thruhulls the next time the boat is hauled.

I haul my boat every winter, so I would wait for seacock servicing.
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Old 27-06-2016, 16:22   #18
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Quote:
Originally Posted by TurninTurtle View Post
Then we get to one of my pet peeves...

Boat makers don't put in adequate bilge pumps. Your AUTOMATIC bilge pumps should be able to pump out at a rate...
Perhaps...

I consider my electric bilge pump and float switch a housekeeping system...and expect it to take care of nickel and dime water from condensation, and shaft packing drips, and the odd topside fitting leak (think I have them all fixed), and ice box drainage.

For two years, I had a dry bilge in port and removed the electric pump and switch. I've reinstalled them because I get a little water in the bilge from the shaft packing and the icebox.

I have three tapered seacocks (four if you count the decommissioned head discharge valve, which is always shut with a plug in the outlet)...engine raw water, sea water to the galley, and galley sink drains. They are opened as needed, and closed when unneeded...always.

So they are closed when in port, where nothing short of lightning, big weather, or an out of control sailor hitting my boat with his boat can cause a leak greater than that my housekeeping pump can handle.

If underway and emergency dewatering is needed, the manual gusher pump is the go-to pump.
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Old 27-06-2016, 17:25   #19
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

Have you tried a rubber bung?
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Old 27-06-2016, 21:05   #20
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Re: Servicing seacocks, plugging thru-hulls, when the boat is in the water

This is a useful tool for working on seacocks.

Seabung Breach Control
Seabung

It won't help the OP as he wants to lap the cone with the seacock in place but it might be useful in other situations.
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