That confuses me just a bit … Casey says a few things about anodes:
"most common casualty is bronze or aluminum propeller on stainless steel shaft"
"electrical contact is essential" "metal to metal" "anode must be in contact with the protected metal"
http://www.boatus.com/boattech/casey/sacrificial-zincs.asp
Yet we attach the anode to the stainless steel shaft and the anode is close but not in contact with the bronze propeller. So what is that all about?
This website shows 2 forms of stainless. steel http://www.kastenmarine.com/metalparts.htm There is the more noble (than bronze) "passive" stainless steel and the far less noble "active" stainless steel.
This website https://performancemetals.com/pages/sacrificial-anodes-faqs explains that when protecting both the shaft and the propeller, we need to add a third metal - obviously the far less noble zinc or aluminum anode. But the diagram indicates that the anode should be in contact with both metals. We don't do that, do we? The anode is usually in contact with the shaft, which is obviously connected to the prop. But does that count?
I'm assuming that the prop shafts are usually Monel or the "passive" stainless steel, which is more noble than the prop. Are we really protecting the prop when we attach the anode to the shaft?
"most common casualty is bronze or aluminum propeller on stainless steel shaft"
"electrical contact is essential" "metal to metal" "anode must be in contact with the protected metal"
http://www.boatus.com/boattech/casey/sacrificial-zincs.asp
Yet we attach the anode to the stainless steel shaft and the anode is close but not in contact with the bronze propeller. So what is that all about?
This website shows 2 forms of stainless. steel http://www.kastenmarine.com/metalparts.htm There is the more noble (than bronze) "passive" stainless steel and the far less noble "active" stainless steel.
This website https://performancemetals.com/pages/sacrificial-anodes-faqs explains that when protecting both the shaft and the propeller, we need to add a third metal - obviously the far less noble zinc or aluminum anode. But the diagram indicates that the anode should be in contact with both metals. We don't do that, do we? The anode is usually in contact with the shaft, which is obviously connected to the prop. But does that count?
I'm assuming that the prop shafts are usually Monel or the "passive" stainless steel, which is more noble than the prop. Are we really protecting the prop when we attach the anode to the shaft?