why is my seacocks connected/wired to my engine

[Firefly625]

I see your point VicS. I have briefly thought about whether, as far as electrolytic corrosion on the seawater side is concerned, the urine can serve as the "solid connection" but then you get into complexity about electrolysis going on on the urine side too. I don't know, and will happily back down on the "pool of urine" argument

I still suspect there is an actual solid connection where the shaft passes through the body and where the shaft's retainer nuts contact the body. Do you think differently? Do you think they are fully isolated by plastic components, so they never touch? I thought the seal was made only by the contact of the ball with the plastic material whose edge you can see if you look up the pipe, and that there was no sealing required where the shaft passes through the body. In other words, it's metal on metal where the shaft passes through the body, I think. I'll be corrected if you know better but that's how I recall the standard form of seacock construction

I think a quality seacock would use a minimal quantity of plastic... precise engineering would ensure ball closure was exact and total. Plastics in time may break up causing failure .... just a thought.

 

[Tranona]

I think a quality seacock would use a minimal quantity of plastic... precise engineering would ensure ball closure was exact and total. Plastics in time may break up causing failure .... just a thought.

You can't have that with a ball valve. The PTFE is there for a bearing surface for the ball and to isolate it from the body so you don't get galvanic corrosion - that is the reason for not requiring an anode.

You can get solid bronze (now DZR) valves, but they are of the cone type such as Blakes where the seal against water is the tight machined fit of the cone and body - aided by grease as a lubricant.

If you read the various recent articles on failed seacocks, the failure is usually because they are not made of the correct material (DZR or bronze) and is usually in the skin fitting or the tail rather than the valve itself. Ball valves usually fail by seizing due to build up of deposits - either internal from the waste in the pipe or external from salts in the water. Regular operation (also recommended for plastic seacocks) minimises the chance of this happening.

If seacocks and fittings were prone to galvanic corrosion on their own, manufacturers would fit them with anodes in the same way as some stern gear , some heat exchangers and many drive components where there are mixes of metal have provision for anodes.

So, back to the basic proposition - there is no reason to bond skin fittings or seacocks/valves of the correct material to a hull anode in a GRP or wood boat.

 

[Scubadoo]

I was bought up on the basis that you always close the seacocks when you leave the boat or go to sea (apart from engine sea cock of course!!!),

Same here, I tend to leave the seacocks closed until required, even when staying onboard I close them when the toilet is not in use (I don't have one for the engine).

Good thread firefly.

 

[jfm]

The PTFE is there for a bearing surface for the ball and to isolate it from the body

You're sure about that tranona? You're sure there is no hard electrical connection between the ball and the body? You're sure that where the shaft passes through the body there is plastic bushing or something to keep the complete electrical separation? I'd say the ptfe is there just for the seal, and not to create electrical isolation

 

[Firefly625]

You can't have that with a ball valve. The PTFE is there for a bearing surface for the ball and to isolate it from the body so you don't get galvanic corrosion - that is the reason for not requiring an anode.

You can get solid bronze (now DZR) valves, but they are of the cone type such as Blakes where the seal against water is the tight machined fit of the cone and body - aided by grease as a lubricant.

If you read the various recent articles on failed seacocks, the failure is usually because they are not made of the correct material (DZR or bronze) and is usually in the skin fitting or the tail rather than the valve itself. Ball valves usually fail by seizing due to build up of deposits - either internal from the waste in the pipe or external from salts in the water. Regular operation (also recommended for plastic seacocks) minimises the chance of this happening.

If seacocks and fittings were prone to galvanic corrosion on their own, manufacturers would fit them with anodes in the same way as some stern gear , some heat exchangers and many drive components where there are mixes of metal have provision for anodes.

So, back to the basic proposition - there is no reason to bond skin fittings or seacocks/valves of the correct material to a hull anode in a GRP or wood boat.

thanks for that Tranona, very interesting info.

 

[Tranona]

You're sure about that tranona? You're sure there is no hard electrical connection between the ball and the body? You're sure that where the shaft passes through the body there is plastic bushing or something to keep the complete electrical separation? I'd say the ptfe is there just for the seal, and not to create electrical isolation

Yes. There really is not a problem of galvanic corrosion in the ball valve itself. Thousands are in use with no bonding to anodes. As I said the bonding is only necessary if the ball valve and through hull is connected to something else - for example with a copper pipe direct to an engine - not common practice these days.

Perhaps as a valued customer you should ask Fairline why they bond seacocks. Maybe they have an explanation, but MG Duff who are arguably the "experts" on galvanic corrosion do not recommend bonding seacocks.

 

[jimmy_the_builder]

I've recently had a generator installed, with inlet and outlet seacocks. All the other seacocks on my boat (Fairline Targa) are bonded together; these two new seacocks are not bonded - and they have very quickly gone very green. What's causing this?

Cheers
Jimmy

 

[VicS]

A mixture of copper copounds in particular basic copper chloride.

Are you sure the new seacocks are either bronze or DZR brass

 

[Firefly625]

You're sure about that tranona? You're sure there is no hard electrical connection between the ball and the body? You're sure that where the shaft passes through the body there is plastic bushing or something to keep the complete electrical separation? I'd say the ptfe is there just for the seal, and not to create electrical isolation

trying to find a schematic on a seacock... so far this is the best I have found... I will keep looking.

 

[jimmy_the_builder]

A mixture of copper copounds in particular basic copper chloride.

Are you sure the new seacocks are either bronze or DZR brass

They are DZR, from Aquafax. I think the tails are brass. (I might have to dig out the invoice now to check...)

Cheers
Jimmy

 

[VicS]

They are DZR, from Aquafax. I think the tails are brass. (I might have to dig out the invoice now to check...)

Cheers
Jimmy

DZR is Ok, next best after bronze, but ordinary brass not. Aquafax do bronze tails

 

[jimmy_the_builder]

DZR is Ok, next best after bronze, but ordinary brass not. Aquafax do bronze tails

I've got the invoices. The skin fittings are bronze; the lock nuts are brass; the seacock bodies are dzr, and the tails are bronze.

Cheers
Jimmy

 

[aquatom]

I'm sure that when a ball valve is fully open or fully closed that the metal stop on the handle contacts the metal stop on the body. Body (bronze) connected to handle (mild or s/s steel) to shaft and ball (s/s steel)

 

[MapisM]

Interesting thread.
Fwiw, I also think that it's pointless to bond fittings and seacocks to the engines, and that this can even accelerate the fittings corrosion (which IIRC was one of the conclusions of the previously mentioned MAIB report).
I can only think of one very specific reason for that, and it's with fittings located below the level of practically unavoidable accumulation of bilge water (though that shouldn't be the case with seacocks - or any other thru-hull fittings, for that matter).
In fact, in this case a corrosion circuit could be formed by any electrical wire which might accidentally reach the bilge water.
But even in such case, I'd rather put my money on proper marine grade fittings than on any kind of additional wiring.

 

[rhumbunctious]

Hmmm

In the case of a skin fitting made of a single material, eg a simple skin fitting pick up or drain with the fitting and backing nut made of the same material, then I agree bonding makes no sense in grp boat. But if the fitting is made of two metals (ie every seacock) then one of those is cathode and t'other anode relative to each other, and such a fitting should be connected to the ship's anode system imho to create the result that the ship's anodes become the anode relative to both metals in the seacock, so that neither will corrode. This is the practice of many reputable yards, including Hardy, and is how my sq78 is done. If I were commissioning a new boat this is how i'd insist it be done (though most good yards would do this anyway)

It makes perfect sense

As VicS says, the maib report on Random Harvest questionned this practice and suggested that thru hull fittings and seacocks should not be bonded. I gotta say, that was one lightweight report and it dumped 2-metal seacocks and one-metal thru hulls into the same discussion, which is totally lacking in science. Just cos MAIB say it doesn't make it right...

Would you then bond a bronze seacock installed with stainless bolts then?

(I recently refurbished my Blakes seacocks and reinstalled them with stainless bolts, as the phosphor bronze bolts were horrifically expensive and numerous posts I found seemed to reflect concensus that stainless was fine)

???

 

[Firefly625]

I'm sure that when a ball valve is fully open or fully closed that the metal stop on the handle contacts the metal stop on the body. Body (bronze) connected to handle (mild or s/s steel) to shaft and ball (s/s steel)

indeed, that is how my seacocks work...

 

[jfm]

Yes.

That's amazing, when any simple inspection of a normal seacock shows there is no plastic bushing where the shaft passes thru the body. I don't think I can debate with you when you take such a plainly wrong view of the facts of how a seacock is constructued. Firefly's pic shows no plastic bush either.

And JTB's post reminds us that the seacock body and the skin fitting can be different metals, and of course they are definitely hard-connected, so that's three metals hard-connected and immersed in salt water with no anode

 

[Firefly625]

That's amazing, when any simple inspection of a normal seacock shows there is no plastic bushing where the shaft passes thru the body. I don't think I can debate with you when you take such a plainly wrong view of the facts of how a seacock is constructued. Firefly's pic shows no plastic bush either.

And JTB's post reminds us that the seacock body and the skin fitting can be different metals, and of course they are definitely hard-connected, so that's three metals hard-connected and immersed in salt water with no anode

jfm, excuse my ignorance here, the reason for my post on Sunday was when I had my head down in my engine bay looking at my seacocks and the bonding wire the thought that I couldn't shake from my head was that I was bonding something that is a relatively soft metal to my engine; therefore what stops this from being an anode?

 

[Tranona]

That's amazing, when any simple inspection of a normal seacock shows there is no plastic bushing where the shaft passes thru the body. I don't think I can debate with you when you take such a plainly wrong view of the facts of how a seacock is constructued. Firefly's pic shows no plastic bush either.

And JTB's post reminds us that the seacock body and the skin fitting can be different metals, and of course they are definitely hard-connected, so that's three metals hard-connected and immersed in salt water with no anode

The real;ity is that seacocks of this construction do not suffer from galvanic corrosion. the vast majority of boats do not bond their seacocks to an anode for two reasons. Firstly it is unecessary and secondly even if they are connected to anodes designed to protect stern gear at the rear of the boat they will be out of sight of the anodes.

I have never heard of seacocks failing because of galvanic corrosion of the ball valve - although as usual am quite open to persuasion if you can provide evidence of this happening. As I have already noted, the "experts" do not recommend bonding, most builders don't do it and not once in all the discussions and published articles on the subject has there ever been any mention of ball valves corroding - always fittings that are not bronze or DZR. They could of course all be wrong, but I don't think so.

Just to reinforce - sitting on my desk now is a 1/2" DZR ball valve I took out of my boat after 18 years because the new engine needed a bigger size. It was in seawater 50 weeks a year fully open, so totally immersed. It is in perfect working order with no sign of any corrosion on any parts except a bit of rust on the mild steel handle.

 

[Ripster]

Can I ask a related question on this interesting thread. I will be replacing my Skin fittings and seacocks soon as I know two of them at least are CW617n brass, so taking no chances. But... is it OK to mix bronze and DZR. So a bronze skin fitting and a DZR cock? Or should it be one type only for each set?