Springtime Zinc inspection

[rpmerrill]

Last spring was my first season getting the boat going and into the water.

At that time I installed all new zincs. At that time the existing zincs were as follows:
Trim tabs pretty grubby but there was something recognizable there. New ones installed on unpainted surfaces of the trim tabs.
Thruster zincs were pretty much gone. Thrusters cleaned up and zincs replaced.
Prop ... completely gone along with the bolt. Installed new. (Tightly, I thought)
Engine internals; Pretty much eaten up. Replaced around mid summer. (No record that the previous owner ever replaced them. (1000 hours on the engine - 4+years)

This spring I was ready to replace the external ones.
Trim tab zincs are immaculate. Not shiny but barely pitted. I think I'll clean them up in place.
Prop zinc is gone again. I'm thinking locktite!
Thruster zincs are just a glob of white corroded zinc. I guess they did their job.

Before I go back to the marina I am a little suspicious of the trim tabs. If I do some exploring back around the transom, should I expect to find that the trim tab bolts are grounded? If they aren't would that explain why the zincs look so good? I'm under the impression that a zinc needs to be "in the circuit" in order to do it's work. Do the trim tab hinges interfere with the flow of current? Anybody have more experience with this? What should I look for?

 

[stwendl]

There is a good chance that the hinge is not a good contact and that the hinge may not be bonded inside anyway. On my r27, I think, the hinges are fixed to the hull with wood type screws which do not penetrate to the inside and are mostly not grounded. But then my boat came in trailer and they don’t put zincs on trimtabs then. Perhaps a stainless wire conductor would be called for.

 

[rpmerrill]

I found this on the Bennett Website.

(SALTWATER ONLY) To deter electrolysis, a zinc anode should be attached to the top of each trim tab. Zinc must make direct contact with stainless steel. Do not paint zinc. Do not ground trim tabs to other underwater appendages.

Website address: https://bennetttrimtabs.com/maintaining ... ab-system/

Well, I'm guessing that the zincs are there to protect only the stainless trim tabs and nothing else back there. Except of course, the tabs on my boat are pretty well covered with paint.

We learn as we go.

 

[jkhiser]

For complete galvanic protection, all underwater metal is typically connected internally with copper bonding wires, then to a sacrificial anode immersed in the water. Items that cannot be easily connected internally have stand alone anodes. Hence the anodes on the thrusters and trim tabs. Larger boats will have a shaft grounding brush to ensure the propellor and shaft are part of the common bonded circuit, so they are protected both by shaft zincs and the larger stern mounted zinc.

I would not worry about trying to add the trim tabs to the internal bonding circuit. The 3.75" buttons should provide one season of protection in normal conditions. There should be bare, clean metal beneath the zincs.

Keeping good protection for the propellor, shaft, and engine internals is more important. The engine internal galvanic environment is mostly separate from the main hull circuit.

J.K. & M.Q. Hiser
2013 C-28 WENNIWAY

 

[Cutwater28GG]

I would check your zincs more regularly. the prop zinc is likely failing and disappearing because enough metal has been eaten that the bolt fails to be tight.

my engine zincs are not quite gone but close within the 12 month service window. So they must be changed annually. its also amazing at how powdery they become when you remove them

the thruster zincs are tiny so will get eaten fast in hot marina's.

for the cost of replacing all these parts (prop, tabs, thrusters) get a diver down every 3-6 months and replace the zincs.