Engine & shaft

[sanna]

We have a long keeled sailboat with a new engine (Nanni Diesel 21 HP). Exept for the charger we only use 12 V onboard. The engine has no zink in it. We have no ground plate outside the hull. I therfore wonder: Should we connect the engine to the shaft with a cable ? (There is a plastic coupling between the engine and the shaft).
I would be greatful for any advice - thank you in advance !

Sanna

(from Oslo)

 

[david_bagshaw]

Yes A good idea to have a bridging strip across the coupling, and the skin fittings should be joined by a wire to the anodes also a "brush" running on the shaft to connect to the anodes.

(a brush is usually a carbon rod in a holder so an electrical contact can be maintained with a moving piece of machinery, as in a small electric motor, in case you have not met the term.)

Good luck

David
www.euroboating.net

 

[vyv_cox]

If your new engine is fresh water cooled it has no need for a zinc (or any other metal) anode. The only exposure to seawater is at the heat exchanger and this will be made from a corrosion-resistant metal. Fitting a conducting strap across the coupling will not have the slightest effect on corrosion.

The reason for fitting a shaft anode is that there is inevitably a galvanic couple between the stainless steel shaft and the bronze propellor (and often a brass nut and key). One will corrode at the expense of the other(s). Fitting an anode ensures that the most electronegative metal, the anode, is the one that corrodes.

Where skin fittings are made of bronze, with bronze bolts, there is no need to protect them with anodes. Good quality bronze has excellent corrosion resistance and will last for many years in seawater without attack.

 

[Trevor_swfyc]

"NO" sorry David, if you do not have a connection between the engine and the shaft by design and it is isolated intentionally by a plastic coupling then it could be detrimental to set up a circuit.
I recall a similar set up on a outdrive which was isolated intentionally from the engine the maufacturer had gone to a lot of trouble to achieve this and claimed it protected the engine from galvanic loss.
Your arbitrator ultimatly must be the engine manufacturer/supplier.

Interesting to see more posts on this.

Over but not out!
Trevor

 

[jfkal]

WHY? Shaft and prop with ample zinc are more happy left alone. WHY hook it up to boat ground with a zoo of other metals or worse shore power without isolation.

 

[sanna]

The Norwegian supplier of Nanni is of the opinion that there is no need to connect the engine and the shaft with a cable. A Volvo dealer told me however that there should be such a connection.

regards

Sanna
from Oslo