By Our Technical Editors

Introducing, Our New Ask The Experts Team

This month we begin a new column devoted to the technical challenges that frustrate all boat owners. Standing by with the answers you need is the top tech team in boating.

Boat ownership requires you to have a sixth sense, to think quickly on your feet, and to use every arcane skill you've ever learned in your life to root out what's wrong with your boat, then fix it — often by yourself, usually at the worst possible moment. This month, to help illuminate the darkness, we present a new, ramped-up version of our popular "Tech Connection" column, now called "Ask The Experts," comprised of your questions, answered by the top technical team in boating:

How To Find Leaking Current

A couple of boaters in our marina reported a high degree of corrosion to their outdrives. So, we decided to have an electrician measure the amount of current in our marina. But no one seems to know what an acceptable level is. Are there any standards set for this? Our findings:

  • 6/10/10-19.8 mv and (different locations)
  • 8/12/10-33.8mv and 82.5mv
  • 9/17/10-25.2mv and 44.8mv

We plan one more reading after all boats are out of the water. Can you shed light on this test and whether we're within normal, safe range?

Don Casey: Voltage between the 120V AC grounding socket and the water should be zero. Any reading other than zero indicates a leak. If your electrician will switch the scale to amps, he or she can measure the magnitude of the current leak. If the leak is DC, any reading above 10mA is damaging the underwater components of your tenant boats. However, the fault may well be a boat in the marina rather than the marina wiring. Identify the source by plugging in (or unplugging) one boat at a time. Theoretically alternating current should not contribute to corrosion, but AC leakage into the water can be lethal for swimmers, particularly in fresh water. Stay with this until you've identified the leak source and stemmed it.

Time For A New Cable?

The Morse shift control on my starboard engine became stiff over the winter. The port control is smooth as silk. Is the problem in the cable or in the control lever?

Tom Neale: Most likely the problem is in the cable. It's not unusual for corrosion or a buildup of grease and gunk to occur. If there's rust inside, you'll hear a crunching sound when you twist the cable. Also, inspect under the jacket. Disconnect the cable from the engine and try it out to see how easily the cable moves when you move the shift control. If the problem persists (it probably will), disconnect the cable from the shift control. Operate the shift control and see if it moves freely. If it does, then the problem is probably in the cable. Cables come lubricated for life, and manufacturers recommend not lubing them, as it can cause the sleeve to swell. Just replace the cable. However, if the shift control works stiffly after the cable is removed, that's probably where your problem is and it might just need some lubrication and cleaning. Typically these controls are complicated. Last time I disassembled one, it took me a day to figure it out and a lot of luck getting all theparts back together. If this part of your system isn't working well, it could present a serious safety hazard, so deal with it before you use the boat. Only take the steps I've suggested if you're confident you can do it safely and well yourself.

Rampant Galvanic Action

I have a 2850 Bayliner, purchased new in 2001. We've had outdrive service performed annually, and at each haul-out the lower unit appeared as new. However, upon haul-out for outdrive service this year, the lower unit was corroded, with several deep pits and loss of metal, and the zincs were fouled with corrosion. The boat has always been moored in the same slip, under cover in Lake Washington fresh water. We've always used shore power to keep batteries charged, and to power a small heater/dehumidifier. When I checked the boat last winter, the heater/dehumidifier was off; I found the plug-in connection for shore power was dead at the dock. The marina replaced the plug, and the heater/dehumidifier worked fine thereafter.

When I saw the corrosion or electrolysis this spring at haulout, I became very concerned about the damage: much loss of metal on the thinner parts of the outdrive, lots of pits, and severe corrosion on the zincs. As part of the outdrive service, the zincs were replaced. Several weeks later I had another haul-out for bottom painting, and found the new zincs to again be severely corroded. It seems that whatever was causing the damage to the outdrive lower unit was also affecting the zincs. I tested the shorepower plug on the dock; it had no grounding. Other plugs on the dock had grounding, and none of their lower units appeared unusual. Did the lack of shore-power grounding lead to grounding into the lake via the outdrive, resulting in electrolysis?

Don Casey: That seems to be exactly what's happening. Some appliance on your boat — probably the battery charger — connects both to the shore-power AC and to the battery, which grounds to your engine. Any current "leakage" in a three-wire AC appliance should find its way to ground via the grounding wire. Without the grounding wire, that leakage flows through the DC ground to your engine and into the water via the outdrive, taking metal with it.

As bad as accelerated corrosion is, there's worse. If the normally grounded metal case of your battery charger or any AC appliance aboard is or becomes energized, it represents an immediate and real risk of electrocution. In addition, the AC flowing into the water around your boat due to missing or disconnected grounding can kill a swimmer, and the problem is made more dangerous in fresh water. Unplug your boat immediately and talk to your marina management, with the term "liability" in your conversation. While they get the outlet wired correctly, buy yourself an outlet tester (around $10 locally or from Amazon) and check this outlet and every outlet you use for both proper ground and proper polarity every time before you plug in. (You'll need an adaptor to plug a tester into a standard shore power outlet. If you continue to leave your boat plugged in, you should consider installing a galvanic isolator.)

Drinking Down A Sand Smoothie

I have twin crusader engines in a 1976 Gibson in the Mississippi River. Last year I ran aground on a sandbar; at first the starboard engine ran about 40 degrees hotter than normal. Also, the left bank of this engine felt hotter than the right and the water discharge reflected that. I changed the impeller and thermostat; that made some difference. The port engine ran normal. Several weeks ago on a short cruise, the port engine went to 180 degrees. Exhaust water was fine at first, then after warming up, water flow was minimal and temp stayed at 180 to 190. I replaced the impeller, checked the oil cooler for blockage (OK), checked thermostat (moved freely), removed one drain plug on block (little or no sand).

Don Casey: If the engines ran cool before the grounding and hot after, sand is the problem. When grounding in sand, almost everyone tries to reverse off. That inevitably feeds the raw-water pump a sand slurry. There are multiple possibilities, but all related. If the sand (or lack of water) caused your impellers to shed rubber, those impeller bits are downstream somewhere still restricting flow. Sand-loaded water also can wear the inside of the pump housing so that the seal between impeller and housing becomes so degraded the pump has inadequate pumping capacity to meet the cooling demands. Most likely, sand is clogging the cooling passages in your engine; not only does this result in overheating, but where passages are blocked or restricted, you can have damaging hotspots. Back flush all the cooling passages inside these engines. Depending on the raw-water plumbing, this may not be that difficult, but you have to dislodge whatever is blocking the passages. Compressed air may be helpful.

Leaking Mast Step

The mast step on my 1992 Hunter Passage 42 leaks. The tech folks at Hunter recommend unstepping the mast and redoing it as they did when it was new. I can't get this done right now. Any suggestions?

Tom Neale: I'm assuming your mast is stepped on deck. If the mast is stepped on the deck and the deck is leaking under or around the step, you may have a dangerous structural problem that should be addressed by a qualified yard in consultation withthe manufacturer. The cause of the problem may be minor, such as a leak in the wiring passage, but this would still probably require unstepping the mast and other serious damage could have resulted from the leak. If the mast comes through the deck and is stepped on the keel, and the leak is where the mast comes through the deck, follow the manufacturer's recommendation where you can.

Check out products such as Mast Boot Tape or Universal Mast Boot available at West Marine. Or, for a more temporary fix, try heavy-duty Rescue Tape. Be sure to follow the instructions; it's different from the sticky tapes to which you may be accustomed.

Wind Generator Affecting Autopilot?

The Raymarine autopilot on my 33 footer has worked well for five years. I installed an aft-mounted wind generator and now my autopilot won't calibrate. I've replaced the flux compass with the same results. I plan to re-route my power wires from the generator to the batteries to keep them as far from the compass as possible. Will it help to twist the power cables?

John Adey: Absolutely! Close-proximity cables, especially originating from a DC motor such as your wind generator, can carry a huge amount of magnetic distortion; wind generators normally have a very strong magnet in their motors. The National Marine Electronics Association (NMEA) publishes installation standards that discuss this very arrangement, noting that any electrical conductors run near the compass should be twisted. Because of the amount of interference that this wind generator may cause, I can't guarantee this will take care of the problem entirely. Your original thought is my recommendation as well; your boat is only 33 feet, so relocating your power cables or your compass, whichever is more practical, may also do the trick.

Connecting Two Solar Panels

Can I connect two solar panels (135-watt and 65-watt) to the same 30-amp controller?

John Adey: The key here is the capacity of the controller and the capacity of the wire you're using. Converting watts to amps (watts/ voltage=amperage) at 12 volts gives us 16.7 amps from your panels, which is less than the capacity of your controller. So, yes, you can connect the additional panel as long as the maximum output doesn't exceed the controller capacity. That said, ensure that the associated wiring is able to handle the amperage as well. See ABYC Standard E-11 (AC & DC Electrical Systems on Board Boats, specifically table VI A.) You can access the standards on a five-day free-trial basis at The standards have "ampacity" tables that will tell you how many amps you can put through a given conductor. In this case I'd err on the side of caution and size the wire for 30 amps (future expansion) and size the fuses for 150 percent of the amperage currently used (16.7 X 150% = 25.05 or 25 amp fuse/breaker). Also, check with the manufacturer of the panels to insure that using the two on the same circuit and controller won't result in one dampening the output of the other.

Get In Touch With Our Experts

Contact these three experts at the BoatUS Ask The Experts site at where you'll also find hundreds of questions and expert answers already archived, with new questions and answers uploaded regularly by our team. Online, you'll also find 11 other experts in different fields, ready to help. From your questions, we'll select a few of the most generally interesting for use in future magazine columns.

We look forward to hearing from you. The best part? This service is free to members.

Don Casey
He's been one of the most consulted experts on boat care and upgrading your boat for 30 years, and he has been on our BoatUS "Ask The Experts" website for the past decade. He and his wife cruise aboard their 30-footer, part of the year in the eastern Caribbean. His books include "Don Casey's Complete Illustrated Sailboat Maintenance Manual", and the recently updated "This Old Boat", a bible among do-it-yourself boaters.

John Adey
The VP/Technical Director for the American Boat & Yacht Council (ABYC), John grew up boating. He's been in the industry since 1990, with diverse experience from a yacht brokerage and boatyard to owning a marine supply store. He and his family sail their classic 1976 Irwin ketch, a boat that he completely restored, including the hands-on installation of all systems. John is a trusted source for technical information for industry professionals.

Tom Neale
He's maintained, lived aboard, and cruised long distance on boats with his wife and family for most of his adult life. He can take apart and fix almost every system aboard a boat, has written two books, filmed a two-set DVD on East Coast cruising, served in numerous editorial and columnist positions for top marine magazines, and has won seven first-place awards from Boating Writers International and many awards for his technical writing.

Generator Ground Wire Causing Reverse Polarity

BoatUS Magazine's reference to the Honda generator in the Aug.-Sept. 2010 issue struck a nerve. I've recently purchased this unit (EU2000i) but when I use a 30- to 15-amp converter (Marinco #83A) to plug the unit into my Maxum 2700SE's shore power receptacle, my breaker panel on the boat shows "reversed polarity." Can you shed any light on whether I should worry about the "reversed polarity" issue, if I should ground the unit to my boat while it's in use, or if there's a third option?

John Adey: A reverse-polarity indicator senses the reversal of the black and white (hot and neutral) wires. The generator manual states that the neutral and ground are not connected and therefore will not test like a typical home outlet. The reverse-polarity light is glowing, not indicating. You can stop this by connecting the neutral and ground together at the generator (call Honda customer service, I'm sure they get this issue with both RVs and boats and can tell you the safe, correct way to do this) or by using a cable that does this for you.

Bernie, I work in boating safety and every week I receive reports (Boating Accident Data [BAD] reports) with news clips of every accident across the country that involved a boat. Carbon Monoxide and portable generators are a popular topic on those lists. Accidents ranging from CO sickness and severe poisoning to deaths occur all too frequently. The Consumer Product Safety Commission (CPSC) has been following portable-generator accidents and is looking at legislation for the control of exhaust gases. I won't use a portable generator on my boat based on my experience with these CPSC reports and the accidents I've seen. If you continue to use a portable, regardless of what's said here, I urge you to do the following:

Install a CO detector in each sleeping area, and don't use the generator at night, or while sleeping. The more alarms and detectors, the better.

Don't operate the generator in a crowded anchorage or while rafting up. Just because you've taken the proper precautions to direct exhaust gases away from your boat and have CO detectors, doesn't mean your neighbors have. Keep in mind that even though CO detectors are not required on diesel-powered boats, you should still use them if you insist on using a portable. Maintain the unit. These items aren't built to be used in a saltwater environment. I've seen generators strapped to swim platforms, which is about as hostile an area as you can get for equipment. The lifespan of the unit may be significantly less than what it would be on land.

Close hatches and portlights. CO is a silent killer. I've read accident investigations where the CO source was 25 feet away and still lethal concentrations entered the boat through an opening. Remember, you have an engine intake as well. Engine rooms may not be sealed enough to keep the CO from migrating through the engine intake or even something as small as an air conditioner condenser overflow without a "P" trap.

Until we see portable generators with catalytic converters (they're coming!), CO is a danger while using these devices. Further reading:,