anodes

[soda1]

I thought I had all the answers (or, at least most!) concering my particular situation, but, alas, I decided not!
I have a steel hulled sailing boat with a diesel auxiliary. I have installed the necessary anodes in all the vital positions on the outside of the hull but I am totally confused about how to deal with the engine vis-a-vis galvanic protection. The engine is on the usual rubber mounts. Do they isolate the engine electrically from the hull or is there still continuity via the bolts of the engine mounts? I believe the latter to be the case. But if not, should the engine be electrically connected to the hull?
Are there stray currents from the engine itself that could adversely affect the galvanic problem for the entire hull?
I intend to connect the engine to the propeller shaft using the special spring (?) like device commercially available through such manufacturers as McDuff but still not certain what to do with the engine itself, as described above.
Thank you all, fellow sufferers (!) in anticipation for your ideas.

 

[VicS]

Protection of the engine from corrosion is a totally separate issue from protecting the hull.

If the engine is directly seawater cooled it will probably have an anode, or anodes, in the cooling water system somewhere. It/they should be checked as recommended in the manual and replaced as necessary.
If it is indirectly cooled the engine is protected by the corrosion inhibitors in the antifreeze with which it is filled. There may or may not be an anode in the seawater side of heat exchanger. If there is inspect it as advised in the engine manual and renew as necessary

 

[rogerthebodger]

I also have a steel hulled yacht and I have had anodes fitted to the hull as recommended by McDuff but my engine prop shaft and prop are electrically isolated from the hull. In my case not only the engine mountings but also the mechanical engine control cables need to be isolated. My prop shaft runs in vesconite bearings and the flexable coupling also provides isolated.

In the 4 years since launch my hull anodes have wasted al little, so are working, but could go several more years before needing replacement. I have 2 shaft anodes which I will replace this year again after 4 years but they could so another year ro 2 at the max.

All fittings below water line are steel or stainless steel except my bow thruster prop and up until last year my prop was also bronze but replaced with stainless steel fabricated last year. I will be interested to see how the shaft anodes have wasted in the last year since replacing the prop.

This pic is at the time of first launch 4 years ago and you may be able to see some of my anodes.

BTW my 12vDC is totally isolated from the hull but the engine is a normal automotive diesel hence the total isolation from the hull.

Hull was grit blasted and coated with epoxy tar which I think helps.

 

[soda1]

Apologies for the slow reply..work pressures etc. Thanks for the ideas..interesting hull you've got there Rogershaw..already got some ideas for MY boat by looking at yours...so thanks twice!

I have, in the past contacted McDuff concerning engine/shaft arrangement but the advice I received was a little less than satisfactory. Their product I was interested in is a device referred to as an "electro eliminator"..not cheap so...anyone out there who has this thing fitted to your shaft?

 

[Tranona]

Apologies for the slow reply..work pressures etc. Thanks for the ideas..interesting hull you've got there Rogershaw..already got some ideas for MY boat by looking at yours...so thanks twice!

I have, in the past contacted McDuff concerning engine/shaft arrangement but the advice I received was a little less than satisfactory. Their product I was interested in is a device referred to as an "electro eliminator"..not cheap so...anyone out there who has this thing fitted to your shaft?

That is nothing to do with protecting the hull or the engine. Its purpose is to connect a hull anode to the shaft to protect the prop. Normally if the coupling to the gearbox is solid then the anode is bonded to the gearbox casing and therefore to the shaft. If you have a flexible coupling there is no contact between the gearbox and the shaft, so the two possible solutions are a strap or wire across the flexible coupling or the Duff electro eliminator. The latter is arguably more effective as it provides a direct contact to the shaft. However, in many applications, particularly on sailboats there is not enough room to fit it, so the bridge across the coupling is more common.