Join Date: Aug 2013
Thanked 19 Times in 19 Posts
Rep Power: 4
Re: Prop and Shaft Barnacles
Well, we have been here before.
Zinc doesn't repel barnacles, on the contrary one could say. The best metal for repelling is copper (Cu), which usually is found in marine propellors.
Propellors with Cu are made in either bronze or brass. It is often very difficult to distinguish bronze and brass by just looking at it, but they are quite different: Brass contain a considerable amount of zinc whereas bronze does not have any zinc (this about the definition of bronze).
In water, brass releases zinc ions, ie some of the metal disappears. This is a rather fast process, as Cu is higher up on the ladder (also compared to water). Consequently, brass metal in water needs an zinc anode.
- the zinc andode is usually consumed rather fast, which gives some indication of how much zinc may be released from the propellor.
Bronze however, is another matter, at least another alloy! Not at all the same process, there is no real need for a zinc anode. Without such, a small amount of Cu ions will be released and ... barnacles will not attach!
Thus, it is easy to get rid of barnacles if one has a propellor made of bronze.
Problem is, of course, to know that it actually is bronze. Very few, if any, propellor manufacturer state that they are using bronze - and some clearly use brass.
If one is using a zinc anode, the only way to prevent - to some extent- barnacles is to paint with some anti-fouling made especially for props. In that way one can enjoy a much higher price as well.