Hunter 30 is eating zinc

[saltygator]

My Hunter 30 is eating zincs like they are going out of style. My prop is starting to suffer too. Here are the observations so far:1.) An ohm test between the motor and the steel keel shows almost a direct short.2.) A voltage test between the motor (-) and the steel keel (+) shows almost a .5 volt.3.) There is a measurable current flow between the above two.4.) Turning off shore power, D/C main, A/C main has no effect on these readings.5.) Disconecting the lightening grounds from the mast, and any other connections to the keel bolts has no effect on the voltage readings between the two.I'm stumped, anybody got any ideas? I'm thinking of isolating the prop shaft from the motor and connecting the motor (D/C and A/C ground) to the steel keel.Any comments and/or suggestions are welcomed!

 

[mike]

stray juice

it may not be your boat. the current may be leaking from either the marinas electrial system or one of the boats in your vincinty. try disconecting your boat fro the grid and re check it. also ask your dock mates if they are havingissues too. hope that helps some.later mike

 

[s sauer]

Shore Power

I'd disconnect from shore power and shut off the battery selector switch ; then run the same voltage checks. Also look for equipment added by the previous owner(s), often not connected correctly. Our 28.5 had electrolysis partially eat away the strut and one or more thru hull fittings when a slipholder about two slips away had his live power cord dropped into the water, probably at least a week and it didn't trip the shore side circuit breaker. I routinely keep two zincs onthe prop shaft as a little cheap insurance for such unforseen events.

 

[saltygator]

It has crossed my mind.

Especially the boat next door plugged into the shore power with a regular extension cord and I have yet to see the owners in six months. Others have had issues in the past, but they are not having them now. It is a witch hunt. I have just purchased (tonight)Don Casey's "Sailboat Electronics Simplified" and I am going to go through all the test in the next couple of days. Maybe I'll find the nugget!John

 

[Bob R.]

Bilge Pump Wiring

Check your bilge pump and float switch wiring connections. I had the same problem last year and didn't discover the source of the problem until the wiring connection between the pump and level switch actually shorted out and broke the connection when the boat was put back into the water this spring. Hunter used heat shrink connector for the wiring but didn't do a good job of shrinking them tight when they were installed. You won't see the stray current unless the bilge pump in running.Bob RS/V Unfurled 2002 H356

 

[saltygator]

Well, I tested everthing

in the Casey book and everthing is where it should be. The only thing that boggles my mind is the voltage between the motor and the keel. I realize the stainless prop shaft with the bronze prop, and zink anode are one side of the battery, and the steel keel is the other. But, .73 volts seems like a lot. Oh yes, the voltage almost doubled when I replaced the zinc on the prop shaft. An old salt on my dock just laughed at me and told me to grab a bid chunk of zink, and wire it to negative side of the DC circuit and throw it in the water and forget it. So, I'll give it a try. See what happens over the next couple of weeks.

 

[Don S/V ILLusion]

start with the basics

JohnWhen you get advice like that ("An old salt on my dock just laughed at me and told me to grab a bid chunk of zink"), it's time to go back to the basics. I'm presuming you have confidence in your voltage readings.By adding more zinc under your circumstance, you are effectively increasing the size of the unwanted battery being created between dissimilar metals. Not a good option. One thing you could do is just tie in both the keel and engine to a common ground but it sounds like you have multiple ground points creating the voltage potential so I'd first verify that only one single ground point exists. You really need to do some searching to identify the source of the voltage potential between engine and keel by selectively de-energizing every electrical item including the bilge pump. Having a common ground as described above usually serves to mitigate the problem but only after you've found the problem source which can be as simple as a bilge pump wired in reverse polarity.

 

[saltygator]

A little knowledge is dangerous

and that is exactly where I am. After looking at the diagram on page 167, and this quote from you, "One thing you could do is just tie in both the keel and engine to a common ground but it sounds like you have multiple ground points creating the voltage potential so I'd first verify that only one single ground point exists."And a quote from Casey on the same page, "The preferred configuration is to isolate the propeller shaft from the engine so the prop doesn't provide a ground, then use the Lightening grounding plate for all ground connections."Since hunter gave me 3800 pounds of steel hanging in the water for a lightening ground, and all of the dc and ac grounds run to the motor. Why wouldn't isolating the prop shaft from the motor, and connecting the motor to my keel solve my problem?Assuming of coarse that I carefully go through every circuit and make sure that I do not have any stry current from the dc side of the house.

 

[Don S/V ILLusion]

easier said than done

To answer your question - "Why wouldn't isolating the prop shaft from the motor, and connecting the motor to my keel solve my problem?", it may depending on how, why and where the current is flowing. Also, it is not impossible but not easy to isolate the prop. If you do so and it isn't a totally isolated metal, you might simply exacerbate an already bad situation.I'm unfamiliar with Casey but have seen Calder's books which have some excellent explainations of how your situation can be created and more importantly, how it can be corrected but only after identifying the source(s). As an example, you could spend hours and lots of effort and money trying to fix a problem eventually identified to be caused by a neighbor's boat.Your inclination to go through every circuit is a good one and is sound routine maintenance as well during which you can often find problems before they become evident in crucial situations

 

[BoulderDon]

Similar Issue with Hunter 31

I had a similar problem with our 1985 Hunter 31. I was keeping the boat behind a friend's house here in Cape Coral about a year ago. We had to replace the zinc every month. We started putting two zincs on and could get about two months. The boat was not plugged into shore power so we felt the problem was caused by transient voltage leaks from one of the other boats or lifts in the canal. When I moved the boat several miles away behind another friends house the problem stopped. Still not generally plugged into shore power. I've only started plugging in to shore power in the last month so I can run a dehumidifier. We'll see how the zinc looks when we clean the bottom next week.DonSunday Silence1985 Hunter 31