Ask The Experts

Solutions from the BoatUS Tech Team

Uncooked Electronics

I read your article on lightning in the June eNews. I put my radios and backup GPS in our sailboat oven during electrical storms while cruising, thinking that the oven is similar to a Faraday cage with only a small glass window. Is there any evidence to support using the onboard oven to protect electronics? We have a ketch rig with antennas on both masts, monitor the lower mast radio during storms, and disconnect the main mast antenna. I also rig a chain from baby shrouds into saltwater from the mast during lightning storms, even though the main mast is grounded.

Don Casey: There's ample evidence that an enclosing metal cage or box provides good protection from the electrical field that accompanies a lightning strike. Thus putting your electronics in the oven should protect them from nearby strikes and possibly even from a direct hit. Sailors have taken this precaution for decades and all reports I've seen suggest a good outcome. A glass front should be closed with a cookie sheet or similar metal shield to perfect the enclosure.

Grounding masts, disconnecting cables, and putting electronics in the oven pretty much exhaust your opportunities to mitigate the consequences of a strike. I've seen scant evidence that dissipaters and other such devices have any effect. Giving lightning a good path to ground offers the best protection for people aboard. Chain can work, but because aluminum is a much better conductor than stainless steel, the bulk of a lightning strike is likely to travel down (or maybe up) the mast. That makes grounding the base of the mast with as direct a conductor as possible far superior to chain clipped to a shroud.

While a well-grounded mast offers you protection, all that electricity looking for paths of least resistance will surely cook connected electronics. Even if they're disconnected, the enormous electrical field associated with a strike is likely to induce sufficient currents in exposed proximate electronics to destroy internal components. Your make-do Faraday cage will be their best shield.

Smooth Bottom

I have a 1985 Wellcraft with black bottom paint. I only trailer the boat; it's never moored or in a slip. I want to remove the bottom paint back down to the gelcoat. It looks like there may only be one layer to remove. What's the best way to tackle this? Can I sand through the bottom paint using progressively lighter pressure and smoother grit, getting to the point where I can wetsand and buff it out? Or are chemical strippers the way to go?

John Adey: Personally having done this a number of times, I wouldn't sand the bottom. If you want good-looking gelcoat without wet-sanding and buffing for days (did I mention most of this is on your back?), strippers like Peel Away and others do a nice job, leaving behind the gelcoat. One coat of bottom paint should not be a hard job to strip chemically. Make sure you cover your trailer, as any splashes or drips ruin any finish (paint, galvanized, or aluminum trust me, I have experience on this). You could also have it "soda blasted" by a marina or autobody shop. This will "haze" the gelcoat but nothing like sandpaper. Either way, I hope you find a clean bottom with no crazing or blisters!

When You Can't Wash Your Feet

The shower well on my 42-foot boat doesn't drain. The pump and float switch work fine. I couldn't open it with a plumber's snake, plunger, or by flushing it with a hose. What would you recommend next? Muriatic acid? Is that safe for hoses?

Tom Neale: I wouldn't recommend pouring muriatic acid down the drain. We really don't know whether it would be safe for the hose because we don't know what's there, or what the hose is made of. Also, there could be a leak or a leak developing that would let it out where it could really do damage. Muriatic is inherently dangerous if not used in the right circumstances.

I assume that the plumber's snake met with some obstruction and didn't come out at the sump end? You need to be sure that it's a blockage rather than something like an air lock (which is very unlikely).

It's possible that the hose has collapsed down there, particularly if it's an older boat. This would explain the failure of the methods you've used. Sometimes, particularly where there's a bend in the hose, it will collapse. Sometimes the inner walls will separate from the outer walls and collapse, although the hose looks OK from outside. Frequently a shower hose will have one or more bends in it. I'd suggest replacing the hose. I know this is easier said than done, but it may be the only thing to do, considering your efforts already. I don't know how tight your hose run is, but usually if you get a new hose of the same outside diameter, and couple it to the end of the old hose, you can pull it through. If you use a plastic hose barb butt-end coupler, you'll probably need to sand off any protruding ridges at the middle that could hang up in tight areas, and you wouldn't want to use hose clamps for the temporary butt-end connection because they could also hang up as you pull the hose through. Have someone feed while you carefully pull.

If you can't access the underside of your shower pan to pull the old hose off the drain, you may need to extract the drain from above, hopefully bringing up at least a short section of the hose with it. Usually these are metal fittings "glued" into the shower pan with a sealant. Also, consider calling the boatbuilder and telling them the year and model of the boat, as well as the problem. They may have a much easier solution.

Shaft Packing

I need to know how to determine what size flax is needed for the stuffing box female nut and how many rings of flax are needed.

Don Casey: The best way to make this determination is with a caliper because it's more accurate than eyeballing a ruler and it measures inside diameters. Measure the shaft diameter and the inside diameter of the stuffing box the big female nut. Subtract one from the other, then divide that in half to get the proper packing size. For example, if the shaft is 1 inch and the inside of the box is 1 3/8 inches, the difference is 3/8-inch, so you need packing for half that, or 3/16-inch. Most stuffing boxes require three rings of packing.

You don't want to fill the box so much that it fails to thread easily and engage several threads.

Healthy Charge

I replaced the starting battery for my Yamaha four-stroke outboard and retained the house battery. The voltmeter shows 12-plus volts, and each battery will start the engine. However, when the engine is running at idle to 1,100 rpm, the voltmeter shows 14 volts. Does this indicate that I'm overcharging the batteries and something is wrong with the voltage regulator?

Don Casey: No. A fully charged 12-volt battery at rest, meaning not being charged or discharged for several hours, will register around 12.6 volts. The charging voltage your Yamaha provides will be somewhere around 14 volts. So if the batteries are fully charged and you don't have any high-draw appliances on, the charging voltage will drive up the voltage your meter measures to close to 14. You always want to see 13-plus volts on the meter when the engine is running above idle, or you can assume you have a charging problem. A voltage reading as high as around 14.4 volts is unlikely to do your batteries any harm with normal use patterns.

A boat that runs for hours or days will do better with a 13.8-volt regulator, but a day-use pleasure boat makes good use of the quicker charging a higher voltage provides.

The Elusive Zinc?

I am attempting to replace the 10 pencil zincs on each of my diesel engines. I located all 10 caps, but when I went to inspect the zincs, some were not connected to the caps. I can see them inside the hole. How do I get them out? I was told you can push the zincs in, if you can't grab them, but that just doesn't sound right to me. These diesels are Cat 3126s.

John Adey: If you can't reach them with a pair of long needle-nose pliers or medical forceps (one of my favorite tools!), then yes, you can push them in. I've discussed this with a friend at Windward Power Systems in Massachusetts, and he says that they'll dissolve eventually. This is something that happens when the zincs aren't changed with enough frequency; they swell and separate from the holder. Your only other option is to push them in, then remove all the engine components related to the cooling circuit, and fish them out. There are several "odd" needle-nose pliers that may fit your needs. Good luck!

How High The Poop

I have a Silverton 38 convertible and am having trouble with my holding-tank gauge, which is no longer reading at all. I just finished thoroughly cleaning out the tank chemically and flushing multiple times to no avail. I've checked the wiring from the tank to the gauge, which is located by my electrical panel. It's my first season with the boat and I'm not yet familiar with how many flushes before I have to pump out, and don't want to risk overflow, so the gauge would be helpful. It did work early on this season. Any suggestions?

Tom Neale: This is a common problem. Gauges in holding tanks frequently go bad even good ones. I assume it has to do with the environment they "work" in, but I've seldom seen any that work for long. Causes of failure include deterioration from caustic gases created in a holding tank and obstruction by solids and sludge. I'd get a high-quality gauge and replace the entire thing. If you have reasonably good access to your tank, it shouldn't be a very difficult job, although certainly not very pleasant.

Holding tanks create dangerous and explosive gases under certain circumstances. Be sure the tank and surrounding area are well-vented before working on it, and if you're not sure, get a qualified professional to do it. This is not a new boat, so clean the entire system with some environmentally safe products designed to help you deal with such problems. Raritan and Thetford both make products to dissolve calcium-like deposits in the system. I've just used Raritan's new C.H. product and was impressed with how well it worked. Deposits not only clog the plumbing, but can break off, get into the holding tank, and obstruct some types of gauges.

Anchoring Gear

I have a 34-foot Sea Sprite, full-keel sailboat. I sail primarily in the Chesapeake with mostly mud or grass bottoms. I don't plan on anchoring in a hurricane, but squalls can produce 40-knot winds. How much chain should I have to keep the anchor (a spade type) stable, what size should it be, and what size nylon rode should I have?

Tom Neale: I prefer an all-chain rode. I base this on years of living on the hook in most types of weather and anchoring over most types of bottom. Within reason, the more chain and the heavier the chain that you have, the better your anchor will hold.

Of course, the rule of thumb is that you should deploy at least five to seven times the length of rode as the depth of the water, plus the height of your anchor roller above water. But sometimes you need more, as in storms or certain poor holding bottoms such as really loose mud.

Chain also helps to keep the boat from "kiting" about on the hook. As to anticipating wind velocity, it's unrealistic to think you won't be anchoring in hurricane-force winds. Thunderstorms often generate that much wind.

If you must use both nylon and chain because of storage and/or weight issues, use as much chain as is practical between the nylon and the anchor the more the better. Never carry so much weight in the bow that it could impair your boat's performance and stability.

Chain size can vary with the product. Manufacturers have charts for their particular products. The best bet is to buy quality products and consult the manufacturer's recommendations regarding size for your boat, then go up. There are "rule of thumb" charts available at anchoring, but you should give priority to the manufacturer's recommendations.

Two For The Price Of One

I have a 1977 bass boat with a 50-hp Johnson outboard that puts out almost 15 volts of charge, and the starting battery is the only one of two batteries being charged. If the dedicated battery for the trolling motor needs to be charged while on the water (away from the dock and shore power), do I need to switch cables, or batteries? Or could I just run a jumper wire while the motor is running between the two batteries and charge both at the same time, even if it is at a lower rate?

John Adey: It's not the voltage we're concerned about here when it comes to charging, it's the amperage.

I can only assume that your alternator puts out around 15-20 amperes. This can adequately charge a starting battery but not a discharged deep-cycle battery in a reasonable amount of time. If you wanted to keep it "topped off," you could consider connecting both, but with a device called a battery isolator so one battery will never discharge the other one (if you have them connected without this, you'll use both your starting and trolling batteries, leaving you with two dead batteries!).

There are some very smart isolators by companies such as Sterling Power and Blue Seas that do an excellent job at isolating and determining when to charge what battery. I wouldn't connect them together without one of these devices.

Lighter Touch Or Feel The Abrasion?

We had the gelcoat on our motoryacht compounded and waxed about three years ago by one contractor, then wet-sanded and waxed a year-and-a-half ago by a different person. We're due for a fresh waxing and have asked both contractors, as we were equally pleased with their earlier results (although in a certain light, we do see swirl marks and dull areas). One contractor says the gelcoat needs a heavy compounding, then wax, while the other says it needs a fine wet sanding and wax. Each says the other's treatment removes more of the gelcoat's surface. What do the Experts say?

Don Casey: Both procedures remove more of the surface than should be required for a five-year-old gelcoat surface that was "new" (via wet sanding) just 18 months ago and protected by waxing. The original gelcoat on a boat hull is typically around five to eight times thicker than a painted surface, so it will tolerate repeated peelings. However, gelcoat is also softer than paint, so more material is lost to an abrasive.

There are significant differences in rubbing compounds, but you will not be too far off pegging the abrasiveness of a typical rubbing compound at somewhere around the equivalent of 1,500-grit wet sanding. Rubbing compound should be used only if a finer abrasive is insufficient. Likewise, wet sanding should be reserved for significantly weathered surfaces.

As with compounding, wet sanding isn't all the same. Gelcoat restoration typically involves working through increasingly finer grits, starting with one as coarse as 600, and finishing with 2,000-grit. This process inevitably thins your protective gelcoat. Before you allow anyone to sand your hull, you'd be wise to determine what the intended procedure is.

The swirl marks you see are from wet sanding. They can be removed with polish. Because of product mislabeling, there is a lot of confusion between polish and wax. A polish is a fine abrasive that smooths the surface. A wax is a coating that fills imperfections to create a smooth surface. Both are useful, but to remove swirl marks, you need polish.

Without seeing the hull, I suspect that all you really need is buffing with a fine polish, followed by a wax coating. If you will renew the wax coating every nine to 12 months, you should not need additional polishing for some time, which will save money and insult to your gelcoat. 

— Published: October/November 2012

Meet the Experts

Photo of Don Casey

Don Casey
He's been one of the most consulted experts on boat care and upgrades for 30 years, and a panelist on our "Ask The Experts" website for a 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, the bible for do-it-yourself boaters.

Photo of John Adey

John Adey
The president of the American Boat & Yacht Council (ABYC), John grew up boating. He's 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. John is a trusted source for technical information for industry professionals.

Photo of Tom Neale

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, written for top marine magazines, and has won seven first-place awards from Boating Writers International and many awards for his technical writing.

Photo of Bob Adriance

Bob Adriance
The editor of Seaworthy, the damage avoidance newsletter of BoatUS Marine Insurance, Bob has written hundreds of articles on safety, loss prevention and causes of boating accidents. His 2006 book, Seaworthy, Essential Lessons of Things Gone Wrong, is based on 20 years of real claims files. He's owned Folkboats to J-Boats and currently sails a 36-foot sloop.

Photo of Beth Leonard

Beth Leonard
BoatUS Magazine's new 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.


In Search Of A Dry Bilge

We've had readers ask us lately how to stop that annoying weeping of water into their bilges from their stuffing boxes; they're tired of tightening the packing nut every other week, they say, to no avail. There are three ways to accomplish this:

Photo of a stuffing box on the inboard end of the stern tubePhoto: Courtesy of Tides Marine and PYI

1. Most older pleasure boats rely on a stuffing box on the inboard end of the stern tube, which uses a large nut to compress grease-impregnated flax packing against the shaft. No water should enter the bilge when the prop shaft is not rotating if the nut is properly adjusted, but a small amount of water (two to three drips/minute) comes through the packing while the shaft is rotating to lubricate the gland and prevent overheating. The nut must be tightened as the flax wears; eventually the packing must be replaced. New packing materials made from synthetic carbon-based fibers and impregnated with modern lubricants like PTFE (Teflon) resist overheating better than traditional greased flax. With these materials, less water needs to pass through the stuffing box to maintain lubrication, but some water will still find its way into the bilge.

2. Traditional stuffing boxes can be made almost watertight by replacing most of the packing material with self-lubricating Drip-Less Moldable Packing. While several times more expensive than flax packing, this clay-like substance conforms to the shape of the stern tube and all but eliminates drips. If used on boats with extremely fast shaft rotation, or if over-tightened, Drip-Less Packing can overheat. But if used appropriately, it can provide an almost dry bilge for a fraction of the cost of replacing the stuffing box with a shaft seal.

Photo of a Shaft sealPhoto: Courtesy of Tides Marine and PYI

3. Shaft seals offer a truly dripless alternative. They can be retrofit on many older boats and are becoming increasingly common on new boats. Some designs rely on a mechanical face seal where a stainless-steel rotor on the propeller shaft is compressed against the flat surface of a stationary carbon flange. Others use a PTFE bearing with a nitrile lip seal to keep water out. (See illustration, left.) In both cases, an articulating hose or bellows connects the stern tube to the shaft-seal housing. To prevent overheating, the prop shaft must be cooled at the shaft seal. On high-speed boats (those capable of 12 knots or greater for the PSS brand), the shaft seal is plumbed into the engine cooling system and cool water is injected directly into the seal. On lowerspeed boats, an open vent hose attached to the injection hose barb and led well above the waterline is enough to keep water circulating around the shaft seal.

In addition to keeping water out of the bilge and eliminating the need to tighten the packing nut, shaft seals reduce vibration and shaft damage due to misalignment. However, if the articulating hose ever fails or if the set screws work loose on the rotor in a faceplatetype seal, the boat will begin to take on a lot of water, fast. To avoid these problems, shaft seals need to be inspected regularly, and the bellows needs to be replaced at the first sign of wear or cracking. Neither the traditional stuffing box nor the new shaft seals are maintenance free. If your goal is to reduce the amount of water in the bilge, the new packing materials offer a simple and inexpensive way to do that. But shaft seals, if properly installed and maintained, provide a vibration-tolerant, completely drip-free alternative.


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