Do you connect through-hulls to an anode?

[Kelpie]

I've received conflicting advice on this, and will probably be replacing a few seacocks soon; if it's better to wire them up then I will. However one source suggested that wiring them up actually increased corrosion! Hence my confusion. What does the panel think?

 

[VicS]

If skin fittings or seacocks are of a suitable material, glass reinforced nylon ( Marelon), bronze or even dezincification resistant brass, they should not need cathodic protection.

Any non ferrous fittings that do need cathodic protection should not be wired to the same anodes as ferrous fittings. That was one of the recommendations in the MAIB report into the near loss of the FV Random Harvest of Brighton several years ago.

http://www.maib.gov.uk/cms_resources.cfm?file=/random harvest.pdf

 

[Tranona]

There cannot be a simple yes and no response. However, as Vic says there is normally no need to connect skin fittings to an anode. Stern gear is the equipment most likely to suffer because of the mix of metals which is why props and shafts and stern tubes often need an anode, either directly or through bonding to a hull mounted anode - or both in some cases.

Rather than listen to "bar talk" (or even forumites!) suggest you go onto www.mgduff.co.uk for expert advice.

 

[boatmike]

There cannot be a simple yes and no response. However, as Vic says there is normally no need to connect skin fittings to an anode. Stern gear is the equipment most likely to suffer because of the mix of metals which is why props and shafts and stern tubes often need an anode, either directly or through bonding to a hull mounted anode - or both in some cases.

Rather than listen to "bar talk" (or even forumites!) suggest you go onto www.mgduff.co.uk for expert advice.

Well I think there IS a simple yes or no answer and Vic gave it very well. Assuming your fittings are bronze, DZB, or plastic (urghh!) you don't need to bond them and you may well cause more problems than you solve doing so. If they are NOT and you have other materials change them now!

 

[VicS]

or plastic (urghh!)

Well I have plastic boat!

 

[angelsson]

Spot on Mike

 

[alahol2]

Mine were wired when I got the boat and there has been no sign of corrosion or dezincification in the last 7 years so I am loathe to disconnect. My previous boat was not wired and showed no signs either. My guess is that it makes not the slightest difference in most cases.

 

[rogerthebodger]

That will apply to a plastic boat but not one of steel or aluminium.

 

[Tranona]

Well I think there IS a simple yes or no answer and Vic gave it very well. Assuming your fittings are bronze, DZB, or plastic (urghh!) you don't need to bond them and you may well cause more problems than you solve doing so. If they are NOT and you have other materials change them now!

Only no if you have a GRP boat. See Rogershaws post. That is why I directed the OP to an authoritative source on the subject.

 

[Vonasi]

I was under the impression that if a through hull is completely isolated, as most are on a GRP boat, then it is best to leave them unbonded.

The problem one is the engine cooling water intake which is very much attached via the water in it's pipe to lots of other metal, including a big piece with electrical equipment attached to it (the engine). This hull fitting should be connected into the boats earthing system and anodes to ensure it is protected against stray current corrosion. Mine is definitely connected and it is the only one on the boat that is.

 

[Ludd]

I was under the impression that if a through hull is completely isolated, as most are on a GRP boat, then it is best to leave them unbonded.

The problem one is the engine cooling water intake which is very much attached via the water in it's pipe to lots of other metal, including a big piece with electrical equipment attached to it (the engine). This hull fitting should be connected into the boats earthing system and anodes to ensure it is protected against stray current corrosion. Mine is definitely connected and it is the only one on the boat that is.

Snap!

 

[VicS]

The problem one is the engine cooling water intake which is very much attached via the water in it's pipe to lots of other metal

No wrong there I am afraid . The water in the hose between seacock and and engine does not constitue a connection. We are only concerned with wired or metal to metal connections.

 

[cimo]

Mine were wired when I got the boat and there has been no sign of corrosion or dezincification in the last 7 years so I am loathe to disconnect. My previous boat was not wired and showed no signs either. My guess is that it makes not the slightest difference in most cases.

Can become a significant difference if your are planning to ever connect to shore power. The shore powers' protective earth conductor effectively connects your boat to every other boat that uses shore power. Any bonded thruhull fittings are now part of the (bigger) galvanic corrosion circuit, and you may need to think about providing additional protective measures.
The degree of corrision will depend on who else is in the marina, which is beyond your control.

Not a fan of bonding thru hull fittings personally, and wouldn't bother connecting them. Potientially more to loose than gain in my opinion.

 

[cimo]

No wrong there I am afraid . The water in the hose between seacock and and engine does not constitue a connection. We are only concerned with wired or metal to metal connections.

Vic is correct. The water intake tubing isolates the seacock from the engine.

 

[boatmike]

Well I have plastic boat!

So do I Vic but it ain't made out of modified Nylon
Actually now't wrong with plastic used properly, but I have seen nylon skin fittings snap off when overtightened or stressed. I just prefer Bronze.....

 

[dam747iam]

bonding

blakes toilet seacocks circa 1976 not bonded still ok

 

[mitiempo]

I wouldn't bond them. If you do you are taking what are isolated items with no disimilar metals and adding them to the mix.

 

[Vonasi]

No wrong there I am afraid . The water in the hose between seacock and and engine does not constitue a connection. We are only concerned with wired or metal to metal connections.

So if it is 'wrong' then please explain why Westerly chose to connect this through hull fitting and this through hull fitting only. I'm sure they didn't do it on a whim, there must have been some sort of thought process behind it.

My personal feeling is that if the engine becomes live through an electrical fault then this hull fitting will also become live. It is mounted close to the prop, approximately the same distance as the hull mounted anode. If there were a problem then it would be make a lovely anode just after the actual anode disappeared. The prop is bonded, so why not a hull fitting next to the prop directly connected by a nicely conductive pipes worth of salt water?

 

[rutten]

plastic, or bronze

Well I think there IS a simple yes or no answer and Vic gave it very well. Assuming your fittings are bronze, DZB, or plastic (urghh!) you don't need to bond them and you may well cause more problems than you solve doing so. If they are NOT and you have other materials change them now!

the `urghh!´ is frightening
I just damaged the plastic speed/transducer of Autohelm st50 of my steel boat built 1976. Should I replace with bronze (plus a bonded anode)?

 

[mitiempo]

NO - use plastic.