300 Yamaha on 24C electrolysis on engine foot

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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Sun Jan 13, 2019 1:05 pm


Thanks for your confirming post that aligns 100% with my experiences. If you find there's no need for shore power connection it's the best cost effective way for reducing the boat's underwater zinc erosion, especially if you leave the boat for extended period with just having the solar panel proving a trickle charge for the batteries.

I have my boat in a covered slip so the benefit of the solar panel is greatly reduced so I visited (just a few minutes away from home) my boat once per month to connect shore power for 24 hrs - 48 hrs. My batteries were always kept charged and my zinc erosion was minimized to the extent I could easily go 9 to 12 months between diver service for checking/replacing the underwater zincs.

Note: The bow thruster will likely show weeping rust on the exposed screw/bolt and washer and should be periodically lightly scrubbed to remove the rust scum.

One of the nice design features of the R27/OB is that the swim step does not required bracing struts so there's no issue with bracing struts and the attachments (through transom screws/bolts) to the transom rusting in the water as on other RT models.

...and yes the lower bracket plate zinc for the engine can erode very quickly, and yes, my F300 when raised had very little left in the water; weight distribution can effort this though.

My Yamaha service shop told me the internal engine anodes should last for a very long time so long as the engine is back flush with fresh water after it being used.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby tedmunds4 on Mon Jan 14, 2019 3:49 pm

Many thanks to all for your varied?? opinions. Think I'll add the transom zinc and not plug in except for occasional battery charging and not use the refrigerator. Lesson learned. Thanks
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby guthriejp on Tue Mar 12, 2019 11:25 pm

I too went the galvanic isolator route AND used a separate zinc "fish". I believe neither helped at all! I have seen significant erosion after 3 months.

I am going to try and unplug my vessel and see if that helps.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby BB marine on Wed Mar 13, 2019 10:21 am

Unplugging your boat could help and if it does you should find out why. Something is wrong and should be fixed. You should be able to keep your boat plugged in with out damage to your Lower unit or any other metal components mounted under the water. The Galvanic isolator should be enough to protect your boat while connected to shore power but not always. You may have a issue with a DC connection in your boat's bilge or your neighbor may. If this issue is in your neighbors boat and is introducing 2+ volts DC in the water ( galvanic isolator blocks 1.2VDC or less) and you are plugged in the isolator will no longer protect you. If it is in your boat same issue. You need to find the issue.

The isolators purpose is to eliminate your anodes from protecting your neighbors boat. Without the isolator your bonding system in your boat is essentially connected to your neighbors bonding system. That means that your anodes are not only protecting your boat but your neighbors too. The isolator should help extend the life of your anodes.

Anode selection with an outboard should be aluminum for the best protection. Many use zinc in salt water areas to protect the Aluminum Lower unit and the rest of the metals. The aluminum alloy anode actually protects better then the zinc. Most outboard manufactures recommend protecting the boat and motor with Aluminum alloy anodes and some will void warranty if zinc is used. I use all aluminum anodes with my inboard C26. I am in fresh water but will still use the aluminum while in salt and feel I will be better protected. Zinc anodes oxidize when they are exposed to air. Each Time I pull the boat out of the water the zincs need to be sanded to remove this oxidation or replaced to allow them to be conductive. This coating that forms white powder appearance has now made the anode ineffective unless it is cleaned off. ( don't breath the dust it is harmful) The aluminum alloy used in Navalloy anodes is very different from normal aluminum. It includes about 5% zinc and a trace of Indium, which prevents the build up of an oxide layer.Aluminum anode alloy provides more protection and lasts longer than zinc. It will continue to work in freshwater and is safe for use in salt water. Aluminum is the only anode that is safe for all applications.

When raising the lower unit out of the water to protect it from marine growth ( if leaving the boat in the water) one of the anodes that is in place to protect the lower unit and mid section is out of the water.( trim tab mounted under cavitation plate, or some use a block anode mounted just above the cavitation plate) The only protection the motor is getting is the anode mounted on the bottom of the transom bracket. Adding an aluminum Fish off the transom would compensate for this. To make sure it is protecting the portion in the water there should be continuity between the fish and the prop this will confirm the lower unit has protection.

https://cdn.shopify.com/s/files/1/2245/ ... 1501872236

This issue has come up a few times here on TugNuts. Has anyone followed through with the marina, a Yamaha dealer or Fluid motion to find out where the issue is. When I was working with Mercruiser and a customer had corrosion issues with their drives, before warranting the issue we would fully test the boat in the water to find the culprit. It was 50/50 marina and boat issues. Standard procedure was Galvanic isolator, aluminum anodes, Mercathode system installs regardless of marina or boat issue. All of these helped with marina issues. If it was the boat we found the culprit and repaired it.
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