e-Letters to the Editor

To Brett Dingerson - Brett, I have a 2001 Skipjack 30 in Marina Village. My hull cleaner is replacing my trim tab zinc at least three times a year.

Do you think this is excessive? In the log book from the previous owner, I found a note from his mechanic saying that he was concerned about excessive zinc wear. I recently replaced some of the ground wire in the engine area as some were corroded.

Thanks- Great column! - James B. - Scottsdale, Az.

James - That actually doesn't sound too excessive - once a month would be excessive. Since you have read my column, then you've heard me talk about galvanic isolators.

Every boat that plugs into shore power on a regular basis should have a galvanic isolator in the shore power ground wire. This ensures your zincs are not being used to protect other boats in the marina.
- Brett

To Brett Dingerson - Brett - The battery for my generator, a 12v group 24, goes dead after sitting for a short period of time. The battery is pretty new and don't believe it should be discharging.

The old battery I replaced was doing the same thing. I have put a meter between the cable and positive battery post and it did not show any current draw. It is in a wooden battery box. I have put a wire from the positive post to the negative post in the dark to see if there was any spark, but there was none.

Any suggestions on how to find the cause? I am probably going to put it on a battery switch, but would still like to understand the problem. - Dave G. at the Hyatt Regency Mission Bay Marina.

Dave - Make sure the alternator on the generator is working and charging the battery when it's running. For example, if you install a fully charged battery and start the generator, it will draw power from the battery to run the generator. If the alternator is defective, then the battery will supply the power without being recharged. When the generator is shut down the battery will already be discharged.

You might not notice it until its time to start the generator again, at which time the battery will be dead and make you think it happened while at rest.

Put a voltmeter on the battery and record the voltage before, during, and after use. That should lead you to the problem.

To Brett Dingerson - Brett - UL has, for over a year, yet to answer my question about which is better to protect bottom metal and underwater persons from a AC jump to ground - an isolator or an open AC/DC ground system.

My argument is that leaving the AC ground open is better. Why? Because of ground fault protection is far safer than dependence on an isolator that could still leak capacitance for corrosion. I also don't think UL has approved isolator for marine environment. Do you know? My guess is UL doesn't know what to do! I am a retired EE and electrical contractor with a 25 yr. old Catalina 30 that suffers short zinc life from all the neighbors with connected grounds. And the Marina can't help! - Walt T.

Walt - Galvanic isolators are a basic shore power component to reduce zinc use. Every boat that plugs into shore power, in any marina, should have one. NewMar makes a good product, but my clients get "Fail Safe" isolators built by DEI Marine, you can purchase one from Ward's Marine in Riviera Beach, Florida. They are considered the best on the market by the corrosion specialists of the country. - Brett

To Brett Dingerson - Brett - Are you certain a properly bonded boat should go a year before replacing zincs on the prop, shaft and keel? I seem to get a bill for one or more zincs approximately every three months.

I'm at the Southwestern Yacht Club and this schedule seems to be pretty common from what I've heard and the bottom cleaning guy hasn't commented on premature zinc replacement. I've used three different bottom cleaning services over three years on two different sailboats and zinc replacement seems to be the same.

I guess I don't understand why you say a zinc should last 1 year before replacement. This is not my experience nor does it seem to be true for other boat owners. Can you explain why there is this seeming discrepancy? - Bob C.

Bob - The rate of zinc use will differ with every single boat. I won't bore you with the details, but there are formulas that corrosion specialists use to calculate the amount of zinc a boat will use in one year. That formula would no doubt suggest using more zinc than you are now using, which means that the zincs on your boat are probably just not properly sized to last a year.

There isn't anything unusual about that on a pleasure boat - bigger zincs are more commonly found on commercial fishing boats.

I owned and operated a steel 50' Salmon/Albacore boat in the 80's. I hauled out once a year to paint the boat and replace my zincs. I also kept the bonding and electrical system in perfect shape and never replaced my zincs prematurely due to abnormal wear.

Trust in this - keep your electrical and bonding system in top shape, install a galvanic isolator or isolation transformer, and keep the diver going down on a regular basis. Your zincs might not be big enough to last a year, but you'll get your money's worth out of them. - Brett

Editor's Note: Brett Dingerson has over 25 years experience as a marine electrician, with a specialty in marine galvanic corrosion protection. He has worked with a wide range of sailing and power vessels and is the owner of San Diego-based Marine Electric. If you have a sailing question for Brett, send e-mail to brett@BlueSkyNews.com