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Old 07-07-2020, 23:09   #1
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Heavy marine grease to protect valves on thru-hulls from corrosion?

I'm looking at a boat that has rusty valves/fittings/clamps on top of its thru-hulls.

What I'm wondering is why these valves and thru-hulls are not covered in heavy marine grease so that they are not exposed to air or moisture? I use heavy grease in non-marine applications to prevent metals from rusting over prolonged periods of time (like washing machine fittings that sit in contact with water for 10+ years). Typically this grease will not melt (under reasonable temps and if not exposed to direct sunlight and will not harden).

So why is this not used on boats? At least not the ones I've seen.


Anyone doing this to prevent corrosion from moisture and salt in the air?
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Old 07-07-2020, 23:13   #2
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Quote:
Originally Posted by George_SD View Post
I'm looking at a boat that has rusty valves/fittings/clamps on top of its thru-hulls.

What I'm wondering is why these valves and thru-hulls are not covered in heavy marine grease so that they are not exposed to air or moisture? I use heavy grease in non-marine applications to prevent metals from rusting over prolonged periods of time (like washing machine fittings that sit in contact with water for 10+ years). Typically this grease will not melt (under reasonable temps and if not exposed to direct sunlight and will not harden).

So why is this not used on boats? At least not the ones I've seen.


Anyone doing this to prevent corrosion from moisture and salt in the air?

Steel rusts. Steel should not be used for valves/fittings/clamps on a boat, unless of course it is a steel boat.
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Old 08-07-2020, 00:10   #3
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Indeed. If your underwater fittings are rusty, they are the wrong material.

Proper bronze ball valves have heavy chrome plated bronze balls which run in PTFE seats. You can put a little grease in the ball seats but otherwise grease is not needed.
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Old 08-07-2020, 00:20   #4
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Fit Marelon throughulls they are made of Nylon.
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Old 08-07-2020, 06:11   #5
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Quote:
Originally Posted by George_SD View Post
I'm looking at a boat that has rusty valves/fittings/clamps on top of its thru-hulls.

What I'm wondering is why these valves and thru-hulls are not covered in heavy marine grease so that they are not exposed to air or moisture? I use heavy grease in non-marine applications to prevent metals from rusting over prolonged periods of time (like washing machine fittings that sit in contact with water for 10+ years). Typically this grease will not melt (under reasonable temps and if not exposed to direct sunlight and will not harden).

So why is this not used on boats? At least not the ones I've seen.


Anyone doing this to prevent corrosion from moisture and salt in the air?


Paint the valve
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Old 08-07-2020, 06:59   #6
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

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Paint the valve

So they can rust out from the inside?
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Old 08-07-2020, 07:02   #7
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

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So they can rust out from the inside?
Huh ?
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Old 08-07-2020, 07:20   #8
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

The factory sprayed all the marine metal attached to my hull w/ Cosmoline during the assembly process.

All of my bronze seacocks were removed by me, polished to a shiny brass appearance, coated w/ metal prep, epoxy and Rustoleum, well over a decade ago.

They still have a glossy / shiny plastic appearance.
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Old 08-07-2020, 07:45   #9
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Take any steel plumbing off the boat.
If you want to protect something that is steel or iron, use CRC 5-56, it's like cosmolene.
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Old 08-07-2020, 08:10   #10
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

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All of my bronze seacocks were removed by me, polished to a shiny brass appearance, coated w/ metal prep, epoxy and Rustoleum, well over a decade ago.

They still have a glossy / shiny plastic appearance.
FYI, the steel steering linkage was painted by the factory and never looked great.

That was stripped to bare metal, also receiving the same metal prep, epoxy and Rustoleum. It also still looks glossy after over a decade.

There are other steel parts that also are faring well from this treatment, such as the water heater enclosure and central vacuum enclosure.


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Old 08-07-2020, 08:12   #11
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

If you havwe to protect through hulls and vaves from corrosion then for sure you have the wrong hardware. use bronze ore marelon! Nothing else!!!! And DO NOT use V4A for this!
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Old 08-07-2020, 09:26   #12
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

So as an example, here is a picture of the valve/seacock on top of the thruhull. Obviously this is pretty bad and it needs to be replaced. However, if covered in marine grease or maybe painted with Rustoleum like someone suggested - would this help to prolong longevity.

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Old 08-07-2020, 09:27   #13
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Paint it

Metal sweats , then corrodes
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Old 08-07-2020, 09:29   #14
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

Trudesign composite thru hulls and valves are superior to Marelon.
They don't seize if not used and meet ABYC standards.
I've had them for 6 years
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Old 08-07-2020, 09:33   #15
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Re: Heavy marine grease to protect valves on thru-hulls from corrosion?

I grease everything that moves, including seacocks and the head pump. I can't see a downside.

From the op post though I read it as a question about slathering the outside of the valves. To be clear, I grease the moving parts and use neversieze on fasteners, not outside surfaces.
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