life span of zincs?

[Home Cookin']

I keep my boat in the water year round, salt. fiberglass hull. 2003

I put a zinc on each trim tab, the ones that are about an inch square and half inch thick, and they are gone in a few months. My tabs are lenco electric, not hydraulic.

The big zinc under the motor looks fine.

I have a battery switch and always turn off all power (except bilge pump). I do not have shore power and closest docks with power are about 100 yards away.

Thoughts?

 

[Georgesalmon]

Re: life span of zincs?

using up zincs depends on a lot of other things besides just your boat. Other boats nex to you can add to problems as can the specific water you are in. Don't worry about it, just keep putting on new ones when you need them and make sure your bonding system is connected to everything that contacts the water.

 

[Home Cookin']

Re: life span of zincs?

bonding system?

 

[Texasmark]

Re: life span of zincs?

They are doing the job for which they are intended. As long as electrical currents (electrolysis) are moving about the metallic things in the water you will have erosion of metal. Zinc is one of the softest metals and yields easily, that is why it is used as the "sacrificial" element. Part of leaving your stuff in the water. You probably can't get rid of all currents, but cleaning things up as George said can help.

Mark

 

[Chris1956]

Re: life span of zincs?

Use bigger zincs and they should last longer. SS prop increases erosion. SS trim rods increase erosion. I used to put zincs on the I/O trim rods, trim tabs and the normal ones on the outdrive. They would last 9 months or so.

 

[SolingSailor]

Re: life span of zincs?

From what I have read, I think your zincs should be lasting longer. Perhaps you should investigate the electrical system on your dock. First confirm correct polarity. Then you may benefit from a ground isolation device, either the diode or transformer type. This prevents your zincs from sacrificing themselves to underwater metal not on your boat, such as on other nearby boats, or grounded dock fittings.

 

[Home Cookin']

Re: life span of zincs?

I think they should last longer, too. but as I said, I have NO POWER to the dock. the closest boat and dock is 100 yards away.
I do have a SS prop, but it is out of the water when moored.
All power is shut off when moored except the bilge pump (on a float switch--and it doesn't come on much b/c the boat is self-bailing.) I would think the erosion is occuring while moored, not while running, since that is a few hours a week compared to many hours idle.

 

[Chris1956]

Re: life span of zincs?

Do you have an outboard or I/O? You could connect the zincs to the outboard mounting bolts or to the outdrive, with a piece of wire. That may help. Maybe the other boat has a current leak? What do his zincs look like?

 

[Georgesalmon]

Re: life span of zincs?

Bonding system: everything in the water is bonded together with wire usually #6 and green. Keeps everything at the same potential in relation to each other so no current going through the water from one to another. Bronze, SS, aluminum, etc. Places wher I worked had everything tied thgether, engine, rails, cleats, struts, trim tabs, rudders, and logs, even the shafts had wipers on them (inboard). Not to be confused with the 12DC negative wiring system.

 

[Home Cookin']

Re: life span of zincs?

so maybe I should connect a green wire to the trim tabs themselves and then run it back to the motor bracket (OB motor Yam 150) and one of its grounds. Hate to have wires running across the transom, though, and also leave enough slack for the tabs to operate. Maybe I can sneak them in through the main wire hole and find something inside to hook to.

Think I should attach to the tabs (flat planes) or the actuator? I'm thinking the tabs

As I said, I'm suspicious of the tabs, being electric and that the zincs there last about as long as an alka selzer. OK not really but 4 months, and meanwhile the zinc on the motor (under the braket, in the water) shows no age.

Thanks for the suggestions.

 

[Chris1956]

Re: life span of zincs?

Maybe there is current leaking thru the tab actuators? Usually you would check for stray current with a galvinometer (spelling), in the water. You could check with the batteris connected and then w/o batteries connected.

Do you turn off the batteries when not using the boat? Try that, obviously direct connecting the bilge pump to the batteries, so she don't sink.

 

[Home Cookin']

Re: life span of zincs?

yes as I said I have a battery switch which is always off when moored and no power gets to the tabs or motor, just the bilge lfoat switch direct wired works. And no power at the dock or nearby; no boats nearby. that's why it seems odd.

But that presumes all the wiring is correct and no "leaks". I had a short once in a house that leaked power but not enough to trip a breaker. Drove me crazy.

 

[Texasmark]

Re: life span of zincs?

Has been awhile, but this subject has come up before. There are accurate answers somewhere in the archives.

As discussed, if current is flowing from one dissimilar metal to another it takes a voltage to cause the current and the resultant ion migration. Hence one surface will be at a different potential than others. Just because you have your electrical sources disconnected, doesn't mean that the water the boat is sitting in isn't charged, or if there is a current, it possibly could cause the difference of potential.

I have no idea as to how small the voltages are and would assume they are DC. So you might get a digital voltmeter and with the DC scale on the lowest range, put your leads between different metallic objects and see if you can read a difference of potential. The potential could be as low as 0.1V, but if you are eating sacrificial elements as fast as your are, I'd bet the voltage could be a lot higher....possibly 1V.

For the record, Mil-Std-454 is the USAF manual for their electronic equipment materials compatibility set up in 4 groups. Each group contains a listing of metals that have the least reaction with each other when in contact; didn't say NO reaction, but the least. Materials in marine applications just happen to fall into Group II and are:

Alum.
Alum Alloys
Zinc
Cadmium
Tin
SS
Tin-Lead (solder)

So, we are using friendly metals and other than coating them (Zinc excluded for obvious reasons) we are doing the best we can do from a metallurgical standpoint.

HTH,
Mark

 

[Georgesalmon]

Re: life span of zincs?

Best to hook up yout trim tabs if you want to is by using an attachment bolt on the inside. Unless they are screwed on. Mu experiencs has been most are bolted thru the hull someplace, at least on larger boats.

Example. One of my fuel fill fasteners is a bolt so a wire can run from the fill to the tank. This wire is not for corrosion its for static electricity but the concept is the same. Keeping the fill and tank at the same potential and Keeping all the wires inside the boat.

 

[Texasmark]

Re: life span of zincs?

Use bigger zincs and they should last longer. SS prop increases erosion. SS trim rods increase erosion. I used to put zincs on the I/O trim rods, trim tabs and the normal ones on the outdrive. They would last 9 months or so.

The reason is that most SS is unprotected (as the MiL states) whereas alum is protected by primers and paints designed for the application. Otherwise alum, being a softer metal would follow Zinc in sacrificing.....just look at the corrosion on an alum prop or lower unit where the paint/primer has been worn off or nicked.

Mark

 

[dingbat]

Re: life span of zincs?

so maybe I should connect a green wire to the trim tabs themselves and then run it back to the motor bracket (OB motor Yam 150) and one of its grounds. .

The last thing you want to do is ground that tab to earth. Talk about starting a chain of events.
The problem could be caused my variety of reasons. I could write a thesis for you on the cause and affects of the nobility of materials but that would tell you absolutely nothing about what is going on without an in-depth analysis of the materials and the circumstances surrounding the phenomenon. There are over 100 different stainless steel alloys in production today. Each would behavior differently in a given situation. You also have to take into consideration the composition of the water, the temperature of the water, the use of bottom paint, etc. Far too much to get into here.

Let’s start here. Disconnect the leads from the batteries and connect your volt meter to your negative battery post. Then check to see what kind of residual voltage you’re getting from the water. Seawater is extremely reactive by nature of its composition. Throw in pollutes and stray currents from other sources you can get a pretty decent battery going.

Next, pull the fuse for the trim tabs and let’s check for stray current paths. Check for continuity between the positive and negative battery posts and the trim tab plane. If you have continuity you’ve found your problem. A brush going bad or the insulation on the armature has been compromised is the most likely cause.