Generating Danger?

Ask The Experts: Solutions from the BoatUS Tech Team

Wrench illustrationPhoto: Bill Roche

My family loves to swim from our boat when we're away from the dock. If my boat's generator is running, is there a risk of electric shock drowning (ESD)?

Beth Leonard: As long as you're not using your generator to charge another boat's batteries or run another boat's equipment, the chances of current leaking into the water while running a generator are an order of magnitude smaller than when plugged in to shore power, but not completely nonexistent. Electricity always wants to return to its source; in this case, the source is the boat. So if any electricity does get out of the correct pathway, it should return to its source on the boat without traveling through the water. The exception would be if there were an electrical fault on the boat and the bonding system were not intact; it would then be possible to get current flowing between two underwater fittings. We recommend installing an ELCI on the boat that will shut the current off if any of it is not returning along the correct pathway. Or, if you want to be absolutely sure, wait until the swimming is over to run the generator.

Don't Screw It!

I'd like to install a swim platform on my Sea Pro center console, but can't install washers or backing plates on the transom through-bolts. Could I use stainless screws instead of through-bolts? Would they pull out over time?

John Adey: You're correct to doubt the wood/lag-screw method of your install; it's not acceptable. My choice would be marine-use-specific blind fasteners by Garelick, made of stainless steel toggle bolts with zip ties attached. Drill through the transom and insert the bolt. A plastic collar slides down the zip ties holding the toggle bolt in place. They come in 1/4-20 and can be used in thicknesses up to 3 5/8 inches. Go to and search "toggler" for details. I have experience with these and highly recommend them. There will be a 1/2-inch hole in your transom now, so seal it up well around the bolts with something like 3M 4200. Check instructions. Where it calls for through-bolting, you now have a solution.

Tracing A Foul Smell

Do waste-holding tanks become permeable over time or is it just the hoses? Is there an easy way to remove the rear holding tank on a 1985 32-foot Carver aft cabin?

Don Casey: I don't know who supplied the holding tanks to Carver in 1985, but a properly made (read, thick) plastic tank should not become permeable over time. If the smell is coming from the tank, either the tank is cracked or one of the fittings is leaking. Most often, however, toilet smells originate from the hoses, which can become permeable (See "Don't Get Hosed By Busted Hoses"). Inadequate tank ventilation also contributes to smelly interiors. With enough oxygen, aerobic bacteria dominate, which greatly reduces the odor the tank produces. Increasing the size of the vent to reduce smell seems counterintuitive, but that's exactly the effect. As for tank removal/replacement, most often boatbuilders install tanks permanently, building the boat over the top of the installed tank. I don't know specifically about your boat, but if you do find the tank at fault, expect to do major surgery to replace it.

Anchor Rode Geometry

I just installed a Lewmar Profish 700 series windlass on my 20-foot Pro Line. In placing the chain stopper between the bow roller and the horizontal windlass, where should the cleat be in correlation to the chain stopper?

Don Casey: The chain stopper needs to be located so that the chain runs fair through it between the bow roller and windlass. Locate the cleat to one side or the other. Generally the cleat is placed forward of the stopper so that when the rode is cleated, it comes from the roller to the cleat without passing through the stopper, which would otherwise be a source of chafe. Of course, if the foredeck configuration requires locating the cleat farther aft, the rode can just as easily be grasped forward of the stopper and taken to a cleat behind the stopper. The only critical issue is that you want the rope to be subjected to as little chafe and deflection as possible when the strain comes on the anchor.

Fitting Frustration

What's the best way to install a flanged through-hull fitting in an aluminum hull 1/4-inch thick?

John Adey: First, through-hull selection is critical. Bronze should not be used because of galvanic issues with the aluminum over time. You can try to mechanically isolate the bronze from the aluminum with some type of barrier, but this is a difficult, permanent application. My advice is stainless steel, Marelon (a glass-reinforced nylon) or an aluminum pipe nipple welded in (my preference) by someone who has the equipment and experience with TIG or MIG welding. For installation, you'll need a backing plate to keep the install from flexing and cracking the surrounding aluminum. Your choices are aluminum (to be welded) or a "marine lumber" such as Starboard by Taco Metals — a fairly amazing poly material. However, it can be challenging to get adhesives or sealants to bond to it. Since you are sealing, not gluing or bonding, and relying on the mechanical fasteners, you can use 3M 5200. Flame-treat the Starboard before applying the sealant as described on their website (go to, click on "application support" in the menu, and choose marine lumber).

I've done this with excellent results. Just have patience; the drying process takes several days. Also coat the whole surface like you're installing tile in your house. I cut a round piece, bevel the edge and scuff up the aluminum with a Scotch-Brite pad and clean as stated on the website. The nut from your through-hull should do an adequate job of clamping the hull and backing plate together. Do not use wood! This will capture water between the aluminum and the wood and cause corrosion that may go unnoticed until failure.

What Do Those Numbers Mean?

I use a website for tides on the Potomac River. The numbers given are puzzling. As an example: Low 4:27 a.m. 0.1, High 10:04 a.m. 1.9, Low 4:39 p.m. 0.1, High 10:28 p.m. 2.0. I know what High/Low means and I understand the times. However, what does the other number mean? I'm sure they don't indicate the total height of the water.

Tom Neale: Those numbers indicate the height above or below chart datum. Check your chart for the depth given for a certain area (the datum). The datum is usually given for MLLW (Mean Lower Low Water). If your chart shows 5 feet at MLLW, then the low tide for that date at 4:39 p.m. is expected to be 5.1 feet (0.1 feet above chart datum) and the high at 10:28 p.m. is expected to be 7 feet (2 feet above chart datum). Remember, velocity and direction of the wind can affect tidal height, as do the lunar state and other factors. MLLW usually takes into account the lowest low that can be expected in normal conditions, and the tide tables usually reflect the expected lunar influences. So you'll probably see negative low tide numbers during full and new moon phases. They're only estimates and don't indicate direction or velocity of the current at that particular spot.

Shaken, But Not Stirred

I use gasoline with ethanol in it, but it's not practical to drain my fuel tank for the winter. My boat is on a trailer in an enclosed area, so is it OK to move it enough to slosh the fuel around to prevent phase separation? I use an additive and keep the engine room at 55 degrees.

Beth Leonard: Unfortunately, simply sloshing the tank around won't stop phase separation or reverse it once it's started. If it's not practical to drain the tank, the best thing to do is to add a good stabilizer, fill it almost full (leave a little room for expansion), and leave it. Having a warmer engine-room temperature would help to retard phase separation because the amount of water ethanol can absorb without phase separating increases with temperature. As long as you don't leave the fuel for too long (six months or more), it should be fine. I hope you're not keeping the engine room temperature at 55 degrees using a space heater; we see far too many fires and freeze-damaged engines when people rely on heaters in the winter!

Dry Run

I'm getting ready to launch a restored Catalina 22. I am thinking of doing an on-trailer test of the Honda outboard, including mounting the motor, adding some gas to the tank, connecting fuel lines and wiring (to test battery charging), and installing flushing muffs with garden hose water supply. By doing so, I should be able to start and run the motor to assure all systems are functional. Do you have any advice?

Tom Neale: If you buy flushing muffs that totally cover the intake ports and have plenty of water pressure to them, you should be fine unless the manufacturer advises against it. Always follow the manual. Some manufacturers sell muffs specially designed for the motor and it's worth it to get them. When you turn on the water, you'll see it squirting out from around the muff and other places. This is normal. Let the water flood in for a while to be sure it reaches the impeller before starting. As soon as you start the engine, water should be seen coming out the pee hole and other outlets to confirm that water is in the pump and it's working. Take great care not to shift into gear when the prop could contact the hose OR anyone or anything else. Also have somebody watching to be sure that the muff doesn't come off. This could ruin your impeller quickly.

I wouldn't run it for long, and if you put it in gear, do that very briefly and don't rev it up at all. Remove the fuel tank afterward for storage outside the boat in a safe place, if it's a portable tank. I'm not sure what's involved on your boat with connecting fuel lines but take great caution with gasoline. You've done a lot of work on this boat, so it's extremely important that you check carefully to be sure that there are no leaks in the gas tank or any gas lines or connections. If you've installed a built-in tank, there's even greater need for caution, and probably it would be advisable to have the installation and fuel line checked by a qualified professional. Connect and carefully check any wiring prior to adding gas. 

— Published: February/March 2014

Meet the Experts

Photo of Beth Leonard

Beth Leonard BoatUS Magazine's technical editor, Beth Leonard, grew up powerboating, waterskiing, and fishing on Lake Ontario. Since 1992, she and her husband have completed two circumnavigations on two sailboats, doing all maintenance themselves. They also installed the systems on their 47-foot aluminum sloop. Beth has written The Voyager's Handbook, the how-to bible for offshore sailors, and hundreds of technical articles.

Photo of Tom Neale

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

Photo of Don Casey

Don Casey
One of the most consulted experts on boat care and upgrades for 30 years. He and his wife cruise 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, the bible for do-it-yourself boaters.

Photo of John Adey

John Adey
The president of the American Boat & Yacht Council, John has been in the industry since 1990, with 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 he completely restored.


BoatUS Magazine Is A Benefit Of BoatUS Membership

Membership Also Provides:

  • Subscription to the print version of BoatUS Magazine
  • 4% back on purchases from West Marine stores or online at
  • Discounts on fuel, transient slips, repairs and more at over 1,000 businesses
  • Deals on cruises, charters, car rentals, hotel stays and more ...
  • All For Only $24 A Year!

Join Today!