Where to place the zincs on a 25?

[Maarten]

Hi, I think what you call zincs we in Holland call "anodes". The things that prevent other metals to be eaten by eloctrolysis. I hope you know what I mean.

So, the question is where to place them and how many there are needed? And what material? Most of the time we are not sailing in salty waters, sometimes in brackish waters.

[PeterYOW]

This may help in anode selection for the waters you boat in: https://www.defender.com/html/zincs_info.html

[Maarten]

Thanks, very helpfull information!

[WillieC]

I have one on my prop shaft, collar type, between end of new fiber style cutlass bearing and the bronze nut that is threaded onto the shaft inboard of the prop. I understand this is a bit rare with the nut serving as a built in prop remover. The WillieC is a 1973 Super Duper DeLuxe model A25.

This arrangement places the end of the prop shaft too close to the rudder to use the preferable bullet style end of shaft zinc, in my opinion. Bit of a long story here...I could have cut the shaft shorter when I swapped engines, but our installation incorporates an R&D Engineering shaft saver coupling. My prop guy suggested we leave the shaft long so that in the event of the coupling failure, we could limp home by removing the shaft zinc and failed coupling and direct connect the shaft to the transmission. The R&D coupling is about the same thickness as the shaft zinc. Everything would slide forward about an inch without the prop hitting the cutlass. We have had no indication of any problem with the R&D coupling in three years, knock on plastic.

The zinc we use in this location is 30mm inside diameter (shaft size) and maybe 3" overall diameter. About 1 inch thick. There are thinner zincs available if you don't have room for a one inch thick job. Make sure you leave enough room for water flow in and out of the cutlass, at least 1/4". Also note if your prop shaft travels in and out when changing direction. This may only apply to the original Volvo Penta MD3B set up with the RB style transmission. Make sure you don't bind this travel and leave enough for water flow.

We are moored in salt water, more to the brackish end only in the summer months. Our roaming range is the Salish Sea from Desolation Sound to Olympia. We keep the WillieC on a trailer in the off season. The water warms up at our home moorage in late summer. We go through two zincs to last the season. I could use three, depending on use.

Additionally, we have another collar style zinc on the skeg just in front of the lower rudder support. Here we are able to use an SAE 1-3/8" zinc and it lasts for multiple seasons. We could probably go without it. It is the absolute low point on the boat so on more than one occasion it has saved the skeg and rudder from road rash while trailering. That's all I have to say about THAT.

The R&D coupling completely isolates the prop shaft electrically from the engine. We have no brush or bonding arrangement of the shaft. We bond none of the six through hulls, all are electrically isolated from other metals by rubber or plastic connections. There is no indication of dezincification on any of them. There is one pencil zinc on the raw water cooled transmission, and two on the Sendure heat exchanger. These are checked annually with only one on the Sendure that shows any sacrifice.

Sorry if too much information.

[Maarten]

Thanks, not too much for me. Do you have none round the engibe? For example on the intercooler?

[WillieC]

"There is one pencil zinc on the raw water cooled transmission, and two on the Sendure heat exchanger. These are checked annually with only one on the Sendure that shows any sacrifice."

These are the zincs on my engine. The Sendure heat exchanger is what you might refer to as the intercooler. These old Volvo Penta engines were originally all raw water cooled. Most of them have been converted over to Fresh Water Cooling by the addition of these Sendure, or similar, heat exchangers. The only truly engine connected zinc is on the transmission, which is raw water cooled. This circuit is in line with the raw water side of the heat exchanger.

There are still some raw water cooled ancient VPs out there. Maybe those folks could weigh in as to where they find their engine anodes.

Maarten, what engine do you have in your A25?

[Maarten]

Sole diesel with heat exchanger.