1552 Feb 14, 2002

The heel casting has no zinc, but should have. It is in contact with the rudder shaft which is made of bronze propeller shafting. Some years ago I discovered that the lower end of the rudder shaft had developed electrolysis, or whatever it is when the bronze turns pink. The rudder shaft was repaired, with a section cut away, and another put in its place, with male and female threads machined to fit each other. Then zincs were attached to the heel casting. Since then the zincs corrode slowly and need replacing from time to time, but the rudder shaft and heel casting seem OK. Holes were drilled and tapped into the heel casting to fit the zincs, which are half-torpedo shaped. A lot of the deterioration of zincs may be due to improper electrical grounding of your boat or some other nearby boat.

Dick Weaver SWII75K

1559 Feb 17, 2002

It seems the heel casting on Don Bundy’s boat, one of the later ones, has a built-in provision for zinc, a recess where the zinc fits in. Earlier heel castings had no such provision and must be drilled and tapped for zinc. One of the half-torpedo shaped zincs is better on the earlier shoe castings as they are somewhat streamlined.

Dick Weaver SWII75K

1595 Feb 25, 2002

Thanks for the tip will look into adding zinc to shoe before launching in a few weeks.

The reddening of bronze, even worse with brass, is called "dezincification" and not uniquely due to electrolysis. The zinc is corroded selectively in the copper-zinc alloy matrix and its departure leaves a powdery copper residue in the most complete case.

Bert dF SWII80K