I posted a "where-to-get-the-part" query yesterday on the Cherubini (my boat) forum. But also thought to post my situation/question here for wider non-brand specific responses.
This week's haul-out revealed that the cutlass bearing finally needed replacement. But I decided to first to clean the 34 year old strut surface. Seeing some pink bronze, I was 75% sure that the procedure wouldn't succeed. But not much choice other than to go-ahead. At least a failure would flag that I couldn't continue to motor with a brittle strut.
Sure enough, the yard's dedicated hydraulic cutlass bearing tool cracked the strut's bronze after the bearing only moved 1/4". Condition of the strut metal = powder pink on the inside. (The work was done by yard staff -- experienced.)
Per the attached picture.
Granted it's an old strut. But what was the likely cause of the gone pink damage? Certainly in my seven years of ownership, the boat prop/shaft has always been zinc protected. And I use a "fish" zinc directly connected to the shaft with a shaft brush when I am at the dock.
But also, since the strut is isolated from the SS prop shaft by the cutlass bearing rubber, does it really need zinc to protect? My strut does not have a zinc fitting hole. (On a related point, I have spot scraped my bronze thru-hulls during this haul-out. I believe that they are 34 year old OEM. But still bright yellow bronze apparently good for more years of service. They are not bonded.)
Curiously when I dug down deep to get at the strut attachment nuts (the strut is off the boat now), I saw that a bonding wire was attached to one of the bolts. The wire had been shoved out of sight under the interior liner by a P.O. The wire ring connector was in clean condition on the strut end. But on the other wire end, not connected to anything. The ring connector on the loose end was very corroded - no longer a ring actually. So obviously at one point, the strut had been bonded. Maybe this was the time the strut bronze went bad, if the boat had been left un-zinced?
Anyway, what is the best practice to protect struts from galvanic attack? I would like to avoid replacing zinc on the strut with each diver change-out. And I presume that it is important to paint the strut with non-conductive underwater primer before applying copper bottom paint?
Thanks for information and insights.
rardi
This week's haul-out revealed that the cutlass bearing finally needed replacement. But I decided to first to clean the 34 year old strut surface. Seeing some pink bronze, I was 75% sure that the procedure wouldn't succeed. But not much choice other than to go-ahead. At least a failure would flag that I couldn't continue to motor with a brittle strut.
Sure enough, the yard's dedicated hydraulic cutlass bearing tool cracked the strut's bronze after the bearing only moved 1/4". Condition of the strut metal = powder pink on the inside. (The work was done by yard staff -- experienced.)
Per the attached picture.
Granted it's an old strut. But what was the likely cause of the gone pink damage? Certainly in my seven years of ownership, the boat prop/shaft has always been zinc protected. And I use a "fish" zinc directly connected to the shaft with a shaft brush when I am at the dock.
But also, since the strut is isolated from the SS prop shaft by the cutlass bearing rubber, does it really need zinc to protect? My strut does not have a zinc fitting hole. (On a related point, I have spot scraped my bronze thru-hulls during this haul-out. I believe that they are 34 year old OEM. But still bright yellow bronze apparently good for more years of service. They are not bonded.)
Curiously when I dug down deep to get at the strut attachment nuts (the strut is off the boat now), I saw that a bonding wire was attached to one of the bolts. The wire had been shoved out of sight under the interior liner by a P.O. The wire ring connector was in clean condition on the strut end. But on the other wire end, not connected to anything. The ring connector on the loose end was very corroded - no longer a ring actually. So obviously at one point, the strut had been bonded. Maybe this was the time the strut bronze went bad, if the boat had been left un-zinced?
Anyway, what is the best practice to protect struts from galvanic attack? I would like to avoid replacing zinc on the strut with each diver change-out. And I presume that it is important to paint the strut with non-conductive underwater primer before applying copper bottom paint?
Thanks for information and insights.
rardi
