Flexible coupling and bonding question

[SO40]

Hello Forum!

I have a Jeanneau SO40. As with all french manufactured boats, nothing is electrically bonded. When I was checking things near the gearbox and Volvo shaft seal, I realised that when the R&D flexible coupling had been installed (several years ago), the shaft and prop became isolated from them engine/gearbox as the copper strip that comes with the R&D coupling had not been installed (was not necessary according to the mechanic).

However, not making the link to this, every year when the boat comes out for new antifauling etc, there multiple blisters on the (cast iron) keel plate and bulb. This has been ongoing for a few years, but I thought it was just and old paint issue. Last year I had the keel sandblasted and re-epoxied etc. And to my horror, when we pulled the boat out in December last year (so a month ago), there was a whole trail of little blisters again!!!

So trying to think back, the only thing I can think about that has changed, is the installation of this R&D coupling, which isolated the shaft and prop. Could this be the cause of this blistering on the keel??

 

[Pagetslady]

Hello Forum!

I have a Jeanneau SO40. As with all french manufactured boats, nothing is electrically bonded. When I was checking things near the gearbox and Volvo shaft seal, I realised that when the R&D flexible coupling had been installed (several years ago), the shaft and prop became isolated from them engine/gearbox as the copper strip that comes with the R&D coupling had not been installed (was not necessary according to the mechanic).

However, not making the link to this, every year when the boat comes out for new antifauling etc, there multiple blisters on the (cast iron) keel plate and bulb. This has been ongoing for a few years, but I thought it was just and old paint issue. Last year I had the keel sandblasted and re-epoxied etc. And to my horror, when we pulled the boat out in December last year (so a month ago), there was a whole trail of little blisters again!!!

So trying to think back, the only thing I can think about that has changed, is the installation of this R&D coupling, which isolated the shaft and prop. Could this be the cause of this blistering on the keel??

My keel was and has been for 20 years always very pot marked every year when lifted out to antifoul a couple of years ago I connected the keel to my engine earth and my anodes etc i also but a earthing strap over the flexible coupling, Since then the paint on the keel has been completely free of rust marks so I guess the keel has been suffering from electrolytic corrosion (is that what its called) over the years I have sand blasted it several times attempting to remove the rust spots it has had 7 coats of primer more than once but still the rust came through, now all it needs is washing off and another coat of antifoul.
Mike

 

[Tranona]

Galvanic corrosion on iron keels and centreplates is minimal and usually only because there are traces of other metals in the casting. so what you are seeing is just ordinary rust and bonding to an anode is unlikely to make any difference. The only real solution -and not infallible is to blast to a high standard and epoxy.

The anode you have is to protect your propeller and it will not do this if the R&D is not bridged.

There is no need to bond anything else on the boat. The arrangement you have is not unique to French boats, but pretty standard practice.

 

[Tammany]

If the keel is solid metal you could attach an anode directly to it like a steel boat.

 

[lw395]

....
The anode you have is to protect your propeller and it will not do this if the R&D is not bridged....

Question is, where is the anode?
If it's on the shaft or prop, there is no problem, and no point in bridging the coupling.

 

[VicS]

Galvanic corrosion on iron keels and centreplates is minimal and usually only because there are traces of other metals in the casting. so what you are seeing is just ordinary rust and bonding to an anode is unlikely to make any difference. The only real solution -and not infallible is to blast to a high standard and epoxy.

The anode you have is to protect your propeller and it will not do this if the R&D is not bridged.

There is no need to bond anything else on the boat. The arrangement you have is not unique to French boats, but pretty standard practice.

Question is, where is the anode?
If it's on the shaft or prop, there is no problem, and no point in bridging the coupling.

The OP does not mention an anode !

 

[Tranona]

Question is, where is the anode?
If it's on the shaft or prop, there is no problem, and no point in bridging the coupling.

Not an unreasonable assumption as the OP is specific about the bridging wire not being fitted. Jeanneaus come with a p bracket shaft drive and a hull anode bonded to the shaft through the gearbox. They do not have an R&D as standard, so if fitting one the bridging wire is needed.

 

[Tranona]

If the keel is solid metal you could attach an anode directly to it like a steel boat.

You could do, but it is generally a waste of time because the corrosion is simple iron in water rust, not the result of galvanic action.

 

[SO40]

Thank you for all your comments. I have one anode fitted on the shaft, one on the Maxprop and some time ago I put one on the keel. All of the same brand, as I have heard that using the same type of anode material is important.

But, why I doubt it is "just seawater reacting with the cast iron", is the specific trails of bubbles. To me it is clearly an electrical thing, as the bubbles neatly follow the front and rear of the keel plate. The middle of the keel plate is hardly affected.

Anyway, I am going to fit a McDuff electro eliminator and see if that makes a difference. As I have replaced all through hulls and seacocks with Trudesign composite units, I am not concerned about these fittings.

Question to Pagetslady: did you also bond your rudder stock?