What size zincs on prop shaft strut

[Porchhound]

1986 C34 It seems the local divers don't keep zincs in stock so I have to go find mine. I know the shaft takes two one-inch collars, but not sure about the shaft.

[KeelsonGraham]

Am I the only one to be really confused by this post? 🤔

[Noah]

Nope!
I will guess. The Catalina 34 prop shaft is 1 in. Dia. That is the size zinc you need. Not necessary to put two zincs on the prop shaft—ok to do, but not necessary.
I would also recommend a 3 in. mushroom zinc on the strut. And if you have a propeller that use a cone-style zinc, replace that as well. Propeller zincs are proprietary to propeller brand, so can't help you there. My diver and I like SeaShield brand zincs.

[Ron Hill]

Guys : My SS drive shaft is isolated by a flex able coupling.  So I just use a single 1" Zn on the shaft about 2/3 of the way down (closer to the strut) and have NEVER had a problem - without a mushroom Zn on the strut!!!

A thought

[Noah]

Ron- I believe you meant you use a shaft zinc on the prop shaft, not a mushroom zinc. As for using or not using a zinc on the strut; whether you have a flexible or not coupling shouldn't impact whether or not to use a zinc on the strut—as it is also isolated from shaft due to the rubber in the cutlass bearing. However, it is a big, expensive, structural piece of bronze, and opting to protect it with its own zinc is a good idea, IMO.

[Ron Hill]

Noah : Thanks - it pays to proof read your comment before you hit SAVE/post

A thought

[Porchhound]

Thanks for the help. The question was regarding the strut zinc. I need to proof my questions! The shaft was self-explanatory, although one diver insisted I should use a collar zinc on the shaft, the other thought the football shaped one was better.

[High Current]

My strut was showing some dezincification when I bought the boat this spring and I realized that the cutlass bearing electrically isolates it from the shaft (and the zincs).  My strut bolts are exposed on the inside of the hull so I ran a bonding wire from one bolt to the engine block.  I'm not a corrosion expert but I believe this should also protect it since the shaft and engine are electrically connected, and I didn't have to go drilling holes in my strut.

[Stu Jackson]

My new strut zinc is a CRM-3.

[Ron Hill]

Porch : I'd guess that it's terminology.  In my mind a collar/shaft Zn is shaped like a football!!   Just make sure it has a copper BB in the inside for better contact!!

A thought

[KWKloeber]

Mainesail has a very good article on his website about how to prepare an anode before mounting it. 
I have argued to apply a preventive like Superlube ptfe gel on the surface to prevent creeping corrosion (the contact surface will inherently not be perfect throughout the length of the contact area and any minute space can begin to corrode.)  This is less of an issue if the anode is removed and reseated annually.