Port Sided Zinc Wear

[Vincentc]

We went out to the island yesterday and had a fine time. It was the first day this year I felt up to getting in the water and checking the zincs.

The zincs on both rudders were completely gone. The aft port shaft zinc was gone and the forward shaft zinc had 10% left. However both stbd zincs had at least 60% left. I replaced the rudder and port shaft zincs and ran out of time and breath. I will do the stb shaft next time.

I last replaced the zincs 5 months ago. Any idea why there is such a difference in zinc wear between the port and stb shafts?

 

[MikeP]

Shaft zincs can erode at different rates depending on how well the shafts are "connected" to the bonding system. Unlike the rudders, which are usually connected directly to the bonding system, the shafts are not (at least on our older boats) directly connected. Their "connection" is commonly mades simply from the shaft engaging in the tranny and this is not really a reliable connection from an electrical viewpoint.

A recommended improvement for this is to add a "wiper" with a carbon brush (same as an elec motor uses) so that the brush runs against the prop shaft and the brush holder is electrically attached to the bonding system. This provides a positive connection for the shafts.

 

[Nonchalant1]

In did exactly that and it substantially improved zinc life on the shafts & props. I just got the largest carbon "brush" blocks I could find and made a straight arm to hold one over each shaft about 6 inches in front of the shaft packing gland. The steel arm was supported on one end by a bolt with stop-nut so it could swivel and the other end was just the weight of the arm and brush against the top of the shaft and ran the brush wire to my bonding strap nearby. I sanded down the shaft to clean bright steel. The shaft and prop both tested solid connection to the bonding system. Very simple to do and keeps the connection clean when it runs.

 

[Vincentc]

Thanks