Prop zinc eroded in 6 months, thruster & trim tab zincs OK?

[Georgevb]

Yesterday I got my bill and work details from my semi annual diver service. Everything look good except for the large prop zinc, which was totally gone, The thruster and trim tab zincs were OK and would be changed out during the next service.
My prop shaft has the 'green' wire attached to it to help with erosion of zincs.

Does anyone have an idea why the prop zinc wears out completely while the thruster and trim tab zincs right above or next to the prop are still good?

 

[trailertrawlerkismet]

My experience is that the area around the screw hole erodes prematurely and the zinc falls off.....you said it was completely gone. I’ve taken an extra step and put a washer big enough to cover the end of the prop zinc and tightened it down, this seems to help.

Jim F

 

[Red Raven]

If you don’t have a transom or rudder anode the prop anode is the only anode tied to the bonding system on the boat. The thruster and trim tab anodes are not bonded so the prop zinc is protecting all the other underwater metal on the boat and will erode faster as a result. In addition, the design of the prop zinc allows it to get loose as it erodes. It often falls off because either the bolt backs out or it breaks up.

Search Tugnuts for Prop Zinc and you will find many descriptions of this and many solutions as well. I chose to add a transom zinc and a rudder zinc as well as a good application of thread locker and three spacing washers under the prop zinc. I pull the boat out annually after 6 months and it is pretty much time to change them all.

Curt

 

[SLyle01]

A lot of Yamaha O/B prop-zincs simply work loose and fall off. I'm on my 3rd in 3 years...and the O/B prop is always out of the water unless underway, so NOT due to anodization. Just poor design. Will use lock washer this time..we'll see.

 

[Georgevb]

Thank you for the information.

 

[Rocky]

Did it wear or fall off? IF it was missing entirely, it may have simply fallen off. That is not uncommon in our boats.
I just wanted to offer that possible explanation.

I hope it helps.

Rocky

 

[Rocky Lou]

I was surprised to see one of two trim tab anodes missing. I ordered one and the new OEM ones no longer have a tab: https://www.simyamaha.com/Yamaha_Trim_T ... -00-00.htm I am also guessing it fell off since the other one looks new. If you are not typically a DIYer, like me, come prepared with a 10inch ratchet extension and 12mm socket (for Yamaha 300). I spent quite some time staring down a hole wondering if something was missing. Covid is expanding my (limited) tool box.

 

[Georgevb]

The diver said the nut and washer were still there so the zinc wore out.

 

[BB marine]

The diver said the nut and washer were still there so the zinc wore out.

Curts explanation is spot on. You need more anode area. A galvanic isolator will help save the anodes if you keep the boat plugged in at a marina. Additional anode area will help protect the underwater hardware and may increase the prop shafts working time. The Trim tab anodes are protecting the Tab planes. The thruster anodes are protecting the Thrusters. The prop shaft anode is protecting the Prop, prop shaft, Rudder,Keel shoe, and swim platform brackets, and underwater thru hulls. Isolating your boat from other boats and adding more anode area will help.