300 Yamaha on 24C electrolysis on engine foot

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300 Yamaha on 24C electrolysis on engine foot

Postby tedmunds4 on Fri Jan 11, 2019 1:06 pm

We keep our new 24C docked in the water on Back Creek in Annapolis and noticed the front of the engine foot had extreme electrolysis gouging when it was pulled for the season. We have not experienced any excessive zinc degradation on any past boats here and keep our boat plugged in for the battery charger and the fridge. Other boats with similar (Yamaha) outboards and some with stern drives located within 15-20 feet away whose engines also partially hang in the water show no corrosion or excessive zinc wear. Has anyone else who may keep their boat in the water for the season plugged in experienced similar findings. It seems when asking the dealer that I was told that we should change our zincs out every 90 days when left in. But, the 24C does not come with a transom zinc, as do all the other larger models. Me thinks there is electrical drain somewhere that grounds its way to the water through the engine. Apparently the 250 HP engines do not rest in the water, but we're told the 300 is heavier and doesn't lift totally out of the water even with little water in the tank or 1/2 full fuel. Poor engineering in my opinion. Cutwater recommends adding a transom zinc and possibly a galvanic isolator on my dime and the dealer agreed to come out in the spring to assess the voltage leaking situation at my dock. I plan to add the transom zinc myself and was wondering if any other 24ft Cutwater or Tugs have had similar issues??
Thanks
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Fri Jan 11, 2019 1:23 pm

For my R27/OB with the Yamaha F300 engine that is kept in the water year round in salt water with the engine tilted up only the small bottom fin is left in the water. When I had bottom paint applied before the boat was delivered to me in Aug 2017 I also had the lower section of the outboard covered with bottom paint to protect that portion of the engine that I presumed would sit in water when the engine was tilted up.

At first my diver service estimated I would need to replace my zincs; the engine's lower large transom bracket and trim tab's every 90 days. They did so after the first 90 days as the zincs were at 50%.

In researching this rapid erosion I adopted the following....

As I'm just a few minutes from my slip, I connected shore power for 24 hrs each weekend just to keep batteries topped up. This had a dramatic effect on the zinc erosion and diver service switched to replacing every 9 months. I think connecting Shore Power for 24 hrs each 2 weeks would provide even less zinc erosion, but never got around to doing this. With good/new batteries I would think the batteries would hold their charge over a 2 week period. They certainly did for a week not being on Shore Power.

I had thought about installing a galvanic isolator but having tried that on my earlier R-25 Classic with zero affect and having spent some $400 doing that, I decided not to repeat that wasted effort.

The effect of minimizing the use of Shore Power is IMO the best way to reduce zinc erosion. My diver service is in complete agreement with me about this.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby gsc3 on Fri Jan 11, 2019 3:00 pm

Below is a copy of my Tugnuts post from August 2018 about our similar experience, solved by installing a galvanic isolator:

Galvanic corrosion is a hazard for boats that are docked near steel seawalls or concrete seawalls reinforced by iron rebar and are connected to shore power. The problem is particularly bad for boats with underwater aluminum fixtures, such as outboard lower units. Unplugging the boat’s power cable from the dockside AC outlet should prevent the galvanic current that causes the corrosion. Alternatively, installing a galvanic isolator, which costs about $185, will stop the galvanic current, and the resulting corrosion, even with the boat connected to shore power.

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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Fri Jan 11, 2019 3:04 pm

Slade: A PROMARINER ProSafe FS30 30 Amp Galvanic Isolator will cost new from $300 to $350 today.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby CobyF on Fri Jan 11, 2019 3:54 pm

I had the same problem when I bought my R23 Ranger. I installed a galvanic isolator, and hang an additional zinc off of the stern connected to the engine mount....problem solved.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby gsc3 on Fri Jan 11, 2019 4:50 pm

Promariner 30amp galvanic isolator listed for $241.63 on Amazon, with free shipping.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Fri Jan 11, 2019 4:58 pm

When people say "problem solved" can they state exactly what the GI provided with respect to reducing the zinc erosion rate.

For example...

With boat in same location....and with shore power connected all the time the boat docked

Before GI installed: had to replace every 3 months with zincs at 50% gone
After GI installed: had to replace every X months with zincs at 50% gone

As I have said earlier, when installing a GI on my R-25 (Classic) I saw no significant change in the erosion rate and my diver service continued to replace the zincs at the same interval as before vs. afterwards. Diver service advised that the ONLY way to deal with the problem was to avoid connecting to shore power as much as possible, and this was based on their years of experience.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby BB marine on Fri Jan 11, 2019 5:14 pm

baz wrote:Slade: A PROMARINER ProSafe FS30 30 Amp Galvanic Isolator will cost new from $300 to $350 today.


For anyone looking to purchase a Promariner FS30 30 Amp Galvanic Isolator I found one at Anchor Express for 200.81 with 9.99 shipping. I needed to buy my aluminum anodes for thrusters, trim tabs and prop shaft and found West Marine had good pricing on them. I called to see if they would price match Anchor Express and they did. I purchased the Pro Mariner FS30 from West Marine for 200.81 and received good pricing on the anodes with free shipping. As Berry said average pricing is 300.00, Amazon 241.00 free shipping. Internet shopping you can't beat it!

Having the motor stored in the up position is the right thing to do. The only problem with that is the only anode that is protecting the Lower unit is the anode attached to the transom bracket. The trim tab anode is out of the water so less protection. The other check to make is to see that all the anodes are aluminum. Boat manufactures tend to stock one style anode Zinc or Aluminum. If the boat has zinc and the motor has aluminum this is not the best protection. I would install a galvanic isolator they do work and help if there is an issue with shore power at the dock. Has CobyF stated hang another aluminum anode off the stern grounded to motor this will make up for the anode that is not in the water. (Trim tab anode)
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Fri Jan 11, 2019 5:54 pm

I will add to what I installed on my R-25 (Classic) for dealing with zinc erosion....

I added a large transom plate zinc bonded to the engine.
I added a prop shaft brush between the engine and the stuffing box.
I added donut zincs to the base of the swim step braces.

Thus with the above plus the GI I experienced no significant reduction in zinc erosion. This is my basis for not doing this again. Having my shore power connected just a few short periods per month was the most significant in reducing zinc erosion by a factor 3 to 4 for me. This was true for my R27/OB as well.

As I'm purchasing the R29 CB shortly I will be following the same technique for reducing zinc erosion for the prop zinc, trim tabs, and small bow & stern thruster cone zincs.

I've docked my boat in various slips at my Marina and all have caused unwanted and significant zinc erosion so I have to assume my Marina is simply 'hot'.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby Red Raven on Fri Jan 11, 2019 8:39 pm

Regarding “Hot” marinas. Typically the marina facility is not at fault (I.e., not “hot”). It is your neighboring boats that cause the problem.

Think of each boat with its underwater metals and bonding system as a battery, with its negative post tied to the water as the ground and the positive post tied to the marina grounding wire. Dissimilar metals in salt water form a battery with a voltage somewhere between 0 and 2 volts depending on the type of metals. Since each of the boats (remember these boats are batteries!) at the marina when plugged in to shore power have their positive galvanic “battery” post tied to the marina grounding wire they are all either supplying current or drawing current from the grounding system. This current runs through each boat’s underwater metals to the water (ground) and will erode (corrode) the metals that are the most active. The anodes are chosen to make them more active than the metals you wish to protect. The surface area of the metals also need to be considered. If your neighboring boats (could be boats quite far away) are insufficiently protected they will use your boat’s anodes for protection!

A galvanic isolator adds diodes to isolate your boat up to around 1.4 volts to ensure this does not happen. If the galvanic isolator has failed, is wired incorrectly, the voltage exceeds 1.4 volts, or is otherwise not getting it done, then the only solution is to disconnect the power cord (and not just shut off the power) except when topping off the batteries.

You can measure all of this yourself with one of these (link below) and a multimeter.
https://www.boatzincs.com/corrosion-reference-electrode-specs.html

Curt
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Fri Jan 11, 2019 10:12 pm

Yes, I used 'hot' in a bad way blaming the/my Marina.... sorry about that.

So is it possible that at my Marina all the shore power pedestals share the 'same ground' electrical connection ? If so, then this would explain why placing my boat anywhere in one of the several hundred slips makes no difference to my zinc erosion rate. That is, I could be subject to a boat's poor bonding/grounding configuration at the far end of the marina which could be some 1/2 mile away ?

I understand how the GI is supposed to work, but for me it did squat and yes, it was installed correctly.... then maybe the 1.4 volts you mention was being exceeded.

No matter, disconnecting the shore power at the pedestal for weeks at a time is and has been my savior. :) :shock:
Last edited by baz on Sat Jan 12, 2019 11:53 am, edited 1 time in total.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby ixlr8 on Sat Jan 12, 2019 5:55 am

baz wrote:So is it possible that at my Marina all the shore power pedestals share the 'same ground' electrical connection ?
Yes, all power pedestals will share the same ground connection. The hot and neutral connections may be shared, or they may be isolated thru transformers, but all the ground connections will be tied together.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby BB marine on Sat Jan 12, 2019 11:48 am

Very good summary Curt. I am a believer in Galvanic isolators. I'm not sure why they are not standard equipment on any boat with shore power. I guess its $$$. I always advise boat owners that use shore power to install one. You never know how your neighbors boat is maintained. A couple installation and maintenance items I have always done when installing a Galvanic Isolator. Location dry, cool area as close to the shore power connection as possible. I put more stock in cool, dry and accessible location. Before installing the isolator test and record the voltage reading using a multi-meter on the diode check function. Check the isolator both ways and the readings should be close to 1 volt. example (my isolator reads .954 one way and reversed leads .943) doing this insures the isolator is a known good one. Once a year this should be on the list of preventative maintenance checks to make sure the isolator is working properly. Retest and confirm the readings are the same or close to your original readings. ( temperature can change the readings slightly. I like to test the isolator directly at the terminals. If the isolator is installed in a area that is hard to get to you can use your unplugged shore power cord and go between it and the green bonding terminal. (There can be some false readings doing it this way) Bottom line If you have a isolator and it doesn't appear to be working test it.
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby baz on Sat Jan 12, 2019 3:20 pm

I don't deny that Galvanic Isolators (GI) will work in most/many cases. However, my experience is that after installing one there was no noticeable improvement with my zinc erosion rate. This was obviously disappointing and especially having paid out for the GI and the effort for installing it and not able to return it for a refund. I'm sure it's still on my sold R-25 (Classic) which is owned by another TugNut person and kept in the salt water at the Des Moines Marina just south of Seattle. I have to wonder if its GI is in fact helping with the boats zinc erosion rate at that Marina ?
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Re: 300 Yamaha on 24C electrolysis on engine foot

Postby Maggie Anne on Sun Jan 13, 2019 10:47 am

I've also found similar issues with using the shore power cord. In my R27OB, the motor mount zinc was completely gone after roughly 7 months of staying 100% of the time in slip in salt water). The boat was delivered new in August and the zinc seemed fine (slight corrosion) later in the year when I plugged in the shore power cord to run the cabin heater and dehumidifier for the winter. When I pulled the boat in early March for the spring oil change I was surprised at the amount of corrosion. The other zincs (trim tab, fins) were about 50% gone at that time. Newbie mistake, I should have checked more frequently, anyway after reading Baz's note I decided not to plug in the shore power cord at all this year and so far after 10 months now the motor mount zinc is still mostly intact and the trim tab zincs show very little wear. I don't keep the refrigerator on and no other electronics and it seems like the solar panel has been keeping the batteries charged.

BTW, the 300 HP Yamaha on my boat seems to sit completely out of the water by about an inch when tilted up.
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