Trojan Boat Forum

Hi, I have a F32 and was wondering where my shaft anodes should be placed.

A few inches in front of the strut.

You're likely to get a variety of opinions on this but a few good marine electrical books that I've read indicate very close to the front of the strut, like about half an inch or just under. I always place mine half an inch away.

Big D wrote:You're likely to get a variety of opinions on this but a few good marine electrical books that I've read indicate very close to the front of the strut, like about half an inch or just under. I always place mine half an inch away.

Mine are further ahead, but I guess your setup does double duty -- if the shaft coupling ever lets go, the anode will stop the shaft from being pulled out...

captainmaniac wrote:

Big D wrote:You're likely to get a variety of opinions on this but a few good marine electrical books that I've read indicate very close to the front of the strut, like about half an inch or just under. I always place mine half an inch away.

Mine are further ahead, but I guess your setup does double duty -- if the shaft coupling ever lets go, the anode will stop the shaft from being pulled out...

Yep, but it's more about electrical flow and protection of the shaft and prop, and the rudder and post as in both cases, dissimilar metals are in contact with each other so you want an anode as close as possible. I suppose you can move the shaft anode a little further forward if you had rudder anodes but what would be the point of moving them further forward. I've also read that anodes further forward can influence the balance of the shaft and induce a wobble under the right conditions. While it may not be noticeable, it can be measured. When it's very close to the supporting point of the strut, the possibility of throwing off the shaft's balance becomes negligible.

Big D wrote:

captainmaniac wrote:

Big D wrote:You're likely to get a variety of opinions on this but a few good marine electrical books that I've read indicate very close to the front of the strut, like about half an inch or just under. I always place mine half an inch away.

Mine are further ahead, but I guess your setup does double duty -- if the shaft coupling ever lets go, the anode will stop the shaft from being pulled out...

Yep, but it's more about electrical flow and protection of the shaft and prop, and the rudder and post as in both cases, dissimilar metals are in contact with each other so you want an anode as close as possible. I suppose you can move the shaft anode a little further forward if you had rudder anodes but what would be the point of moving them further forward. I've also read that anodes further forward can influence the balance of the shaft and induce a wobble under the right conditions. While it may not be noticeable, it can be measured. When it's very close to the supporting point of the strut, the possibility of throwing off the shaft's balance becomes negligible.

I can see the argument re balance.. if the anode is off balance and mid way between stuffing box and strut, it can cause maximum problems. Closer to the strut, it has less potential of actually throwing the shaft off.

Electrically though -- (I have Calder's book - still have to read it) -- electrons are electrons. Whether they have to migrate 30' or 32' to find a grounding victim, they are going to do it and do related damage. I would think a properly installed anode should do the same job no matter where it is along the shaft. I would think that with a properly bonded system, anodes should be able to protect all running hardware. I have anodes on shafts and on rudders. Rudder anodes were a mess this spring, and my rudder hardware is not part of the bonding system, so that is something I have decided to address this year.

captainmaniac wrote:.....Electrically though....electrons are electrons. Whether they have to migrate 30' or 32' to find a grounding victim, they are going to do it and do related damage. I would think a properly installed anode should do the same job no matter where it is along the shaft.....

One would think so but I have not found this to be the case in the field. Too many variables involved including the electrolyte (the water you're in) If you measure, you'll find a difference in potential the closer you get to your props and rudders, that's where I want a sacrificial anode to be. The further away you get from there, the less worrisome the measurement becomes. Prop nut anodes used to be more popular than they are now but there was a reason why they put them back there. New Gen Bravo III drives have prop nut anodes now and they have anodes all over them including an electronic impressed current cathodic protection system at the transom assembly. Even with this feature, several other anodes are still a must throughout the drive. The drives are aluminum of course but it serves to illustrate that if you were to simply add an anode to the transom in the general vicinity, the electrons wouldn't bother traveling the additional foot, they'll simply take the path of least resistance.

On another note, what is everyone using for anodes now? Come next season, I'll be switching over to aluminum for inboard applications and sticking with magnesium for sterndrives. Have been wanting to switch to aluminum for some time but found that distributors didn't have a wide enough selection on hand. That is changing as the move to aluminum becomes more popular.

Oooops, didn't mean to hijack the thread, anode type is a whole other can of worms. Like I said earlier, you'll get a variety of opinions on anode positioning but the important part is that you have anodes and that you replace them when necessary.

My primary boating area (Delaware River) is fresh water but I also take trips to the upper Chesapeake where it is brackish so I use aluminum anodes. They protect my running gear really well, even in the fresh water. No problems with corrosion.

Using zinc in salt water . I thought of trying aluminum anodes as a suppler had given me shaft and rudder aluminum anodes . But no engine anodes and you should not mix them so Zinc it is .


As far as placement One about 4''-6' in front of the struts

I checked a salinity map of the Chesapeake. Tragically, my boat spends 99.99% of the time in water that is 1% as salty as seawater, on average, so I switched to aluminum this year. Too early to report any results.

Oh, and I have two anodes per shaft -- one goes about an inch before rear strut, the other about an inch abaft the forward strut. Abaft -- I don't get to use that word every day.

I place mine 1 shaft dia: away from front of strut to not interrupt the flow of water to lubricate the strut bushing.

Can we get a simple deff of before the strut is prop side, after the strut is engine side!
Is two better than one!
Thanks