The BoatTECH Files

By Don Casey and Our BoatUS Tech Editors

Insight has arrived! Next time you need to do a project or repair aboard your boat, chances are one of our experts already has written an authoritative guide to help you through it.

BoatTECH, BoatUS's vast archive of technical stories, constitutes one of the most invaluable and popular pages on our website. Written by the top technical writers in the country — most are among our own trusted tech team of BoatUS experts — BoatTECH is filled with in-depth advice for members on how to do everything on your boat from plumbing to polish. This month, we're unveiling our all-new presentation of the site. We've made it easier to use, and enriched it with more useful photos and advice than ever before. Here's just a sampling.

Gelcoat Scratch Repair

Surface scratches can be buffed out of gelcoat with polishing compound, but deep scratches must be filled. When the gelcoat surrounding a scratch is in good condition, the filler of choice is gelcoat paste, which provides both filler and finish in a single application – but not in a single step. The surface of the cured paste will be uneven, so sanding and polishing are required to smooth the repair and blend it with the rest of the hull. Except for color matching, gelcoat repairs are easy and straightforward.

Never try to repair a scratch by simply painting over it with gelcoat. Gelcoat resin is too thin to fill a scratch and gelcoat paste too thick. Instead of penetrating scratches, gelcoat paste will bridge them, leaving a void in the repair. To get a permanent repair, draw the corner of a scraper or screwdriver down the scratch to open it into a wide V.

Work the gelcoat paste into the scratch with a flexible plastic spreader. Let the putty bulge a little behind the spreader; polyester resin shrinks slightly as it cures, and you'll sand the patch, anyway. Don't let it bulge too much or you'll make extra work for yourself. Gelcoat Scratch Repair on

Anchors Aweigh

Scope is often defined as the ratio of the length of deployed anchor rode to the depth of the water. That is so wrong! Scope calculations must be based on the vertical distance, not from the sea bottom to the surface of the water, but from the sea bottom to the bow chock or roller where the anchor rode comes aboard. For example, if you let out 30 feet of anchor rode in 6 feet of water, you may think you have the appropriate 5:1 scope, but if your bow roller is 4 feet above the waterline, your scope is actually only 3:1. Scope is required to make the pull on the anchor horizontal; the more upward pull on the anchor, the more likely it is to break out. Minimum scope for secure anchoring is about 5:1, and 7:1 is better. A length of chain between the line and the anchor (at least 20 feet) helps keep the pull horizontal. Anchors Aweigh on

Bedding Hardware

Think "gasket" when you bed hardware. The mistake most of us make is squeezing the sealant out of the joint by over-tightening. While the sealant is wet, snug the fasteners down just enough to form a continuous bead of sealant around the perimeter of the fitting. Crank down on them only after the sealant has cured for 24 hours (one hour for silicone). Turn the nuts only so you don't break the seal on the bolts. Tightening fasteners after the sealant cures puts it under compression, greatly extending the life of the seal. Bedding Hardware on

Rolling And Tipping

The key to getting a flawless paint finish is the thinner. Too little thinner and the surface shows brush strokes; too much and the paint sags or runs. Start with the paint manufacturer's recommendation, then test the mix on a glass panel — window glass, not fiberglass. Using a foam roller, roll some paint onto the test panel, then tip it out by lightly dragging a dry badger-hair brush horizontally through it. Give the surface a couple of minutes to level out. Because you have painted glass, all flaws are in the paint. If you see brush strokes — the usual result — add a capful of thinner and test again. Stop adding thinner when the stroke marks disappear. Adding paint, because you have to mix it, is more troublesome than adding thinner, so try not to go too far — evidenced by sagging or running. Rolling And Tipping on

How Important Is Changing Engine Oil?

Not only does the grit in dirty oil wear precision surfaces, the acids the contaminated oil invariably contains dissolve internal engine parts while the boat sits idle. Frequent oil changes ward off breakdowns and extend the life of your engines by thousands of hours. Engine manuals typically specify changing the oil every 100, 125, or 150 hours, but no less than once a year. If your boating is seasonal, once a year isn't often enough. Change the oil when you commission your boat in the spring, and when you winterize it in the fall. You'll never get a better return on a $40 investment than from changing your oil twice a year, or every 100 hours.

Running the engine is always a prerequisite to an oil change. You want the oil warm enough to flow freely, and you want the contaminants in the oil, not lying in the bottom of the pan. Drain the oil cold and a lot of the contamination stays behind. Because a quality oil filter should be good for 200 to 300 hours of running time, engine manufacturers sometimes specify a filter change with every other oil change. But filters harbor a significant amount of oil. Not changing the filter is like pouring this morning's coffee over an inch of yesterday's coffee remaining in the cup. When you change the oil, change the filter. How Important Is Changing Engine Oil? on

Using Rubbing Compound To Restore Gelcoat

If your gelcoat is weathered so badly that polish fails to restore its shine, you'll need the stronger abrasives rubbing compound contains. Wax on the surface can cause the compound to cut unevenly, so first remove all wax by "sweeping" the surface in one direction — not back and forth – with rags saturated with de-wax solvent or Toluene. Select a rubbing compound formulated for fiberglass and use it exactly like polish, rubbing it with a circular motion until the surface turns glassy. The gelcoat on your boat is about 10 times as thick as the paint on your car, so compound shouldn't cut all the way through as long as you're careful not to rub in one place too long. If the gelcoat starts to look transparent, stop. After the surface has been compounded, polish it, then coat it with wax and buff it. Provided the gelcoat has an adequate thickness — your boat might have been compounded previously — this process will restore the shine to fiberglass in almost any condition. Using Rubbing Compound To Restore Gelcoat on

Battery Charger Voltage

Because 12-volt gel batteries cannot tolerate a charge voltage above around 14.1 volts, multi-stage chargers generally limit charging voltage to that level. This makes the charger safe for gel batteries, but slower to charge wet-cell batteries. Weekend boaters won't notice the difference, but for those needing to recharge only wet-cell batteries in the shortest time possible, battery chargers with a higher output voltage — typically around 14.4 volts — are available. When the battery reaches full charge, multi-stage chargers switch to a lower voltage. The intent is to maintain the charge without gassing the electrolyte. Chargers are not perfect at this, however, so check the water level in the batteries frequently. If the boat will be unattended for more than a week, plug the charger into a lamp timer to limit its operation to an hour or two per day. Battery Charger Voltage on

Zinc Anodes

The longevity of a sacrificial anode is a function of its weight. The amount of protection it provides depends on its surface area. When a zinc lasts less than a year, you need one with more weight. If the protected metal shows signs of corrosion despite the zinc, you need more surface area. Check all anodes at least annually; if half, or more, of an anode has been lost to corrosion, replace it. Don't forget to check the zinc pencil inside your engine's heat exchanger; you'll find it (or not) under a brass plug in the exchanger. Zinc Anodes on

Adding An Inverter

An inverter can be a marvelous convenience, but take care not to overlook the load it places on your boat's batteries. AC appliances draw 10 times their rated amp when running on 12 volts. For example, a 1,000-watt coffeemaker draws 8.3 amps at 120 volts (1,000/120), but 83 amps at 12 volts (1,000/12). Add about 15 percent for inverter inefficiency and the actual battery draw for that pot o' joe is close to 100 amps. This likely exceeds your starter-motor draw, so the effect on your batteries of a 10-minute brew cycle is roughly the same as cranking the starter for that long. Unless you're willing to run the engine while the inverter is in use, limit inverter wattage to five times your battery's rated amp-hour capacity. In other words, don't expect a 100-AH battery to power an inverter larger than 500 watts. Adding An Inverter on

Shore Power

Straight-blade receptacles — like those in your home — are increasingly less common at marina outlets, for good reason. Water and electricity are a potentially lethal combination, and straight-blade receptacles have no provision for preventing rain or washdown water from reaching the contacts. Even if shore-power demands can be met with a 15-amp service, equip your boat with a 30-amp inlet fitting to allow the use of a shore-power cord with waterproof plugs. In addition to the safety benefit, you'll find that because the 30-amp locking receptacle has become the norm at most U.S. and Caribbean marinas, a 30-amp inlet on your boat will minimize or eliminate altogether your need for adapters. Shore Power on

Head Maintenance

Saltwater and uric acid (don't ask!) produce calcium scale inside marine toilets and discharge hoses. Such deposits cause the toilet to get progressively harder to flush and can lead to total blockage. Avoid this unpleasantness by pouring a pint of white vinegar into the bowl once a month and pumping it slowly, a single stroke every four or five minutes, through the toilet. The mildly acidic vinegar dissolves fresh scale deposits. To keep the pump operating smoothly, follow the vinegar treatment with an ounce or two of mineral oil or a lubricant specifically formulated for marine toilets. Head Maintenance on

Chemical Strippers

The resins in paints and the resins used to build fiberglass boats are chemically similar — too similar for most paint strippers to notice the difference. That means hardware-store paint strippers will dissolve your boat, too. There are strippers specifically formulated for use on fiberglass — the only kind you should contemplate using — but even these can damage gelcoat, if you leave them on too long. So if you use a stripper on fiberglass, don't make the mistake of thinking that leaving it on longer will be better. Chemical strippers can be used safely on wood surfaces and are very good at removing varnish and other wood coatings. However, avoid strippers containing methylene chloride, an extremely hazardous chemical. There are health-friendlier alternatives. Chemical Strippers on

Aerial Or Handheld Flares?

Are aerial flares better than handheld? Not necessarily. A 12-gauge aerial flare reaches an altitude of around 250 feet, making it visible over a much longer distance than a handheld flare that reaches only a few feet above the water. But the meteor burns out in just six seconds while some handhelds burn for three minutes. The best choice for you? Where do you do your boating? If you're almost always in sight of shore or other boats, handheld flares have a better chance of drawing attention because of their longer burn time. If you boat well offshore, aerial flares can signal your distress over greater distances. Safety-conscious skippers carry both, plus smoke flares for daylight signaling. Parachute flares combine high altitude with long burn times, making them the most effective nighttime distress signal. Aerial Or Handheld Flares? on

Oiling Teak

Oil intensifies the colors and grain patterns of wood and gives the wood a rich, warm appearance. Because it simply enhances the inherent beauty of the wood, oiling is arguably the most attractive of all wood finishes, and it restores some of the teak's natural oils and resins. Unfortunately, the benefit of oiling exterior teak is transitory. The sorry truth is that teak will last just as long if you don't oil it – longer really, as repeated between-coat scrubbing wears the wood away.

Teak oils are primarily either linseed oil or tung oil, bolstered by resins to make them more durable. Linseed oil tends to darken the teak, but is significantly cheaper. Tung oil doesn't darken the wood, and is more water resistant than linseed oil – a notable advantage for boat use. However, a month or two after application, it may be hard to discern that much difference as both oils carbonize in the sun and turn dark. Proprietary teak oils address this problem with various additives, including pigments, UV filters, and mildew retardants. Some that perform admirably in one climate are reviled in another. If you're going to oil your teak, make your teak oil selection based on the recommendations of boat owners in your area.

Apply teak oil with a paint brush. Immediately wipe up (with a spirits-dampened cloth) any drips or runs on fiberglass or painted surfaces, or the resins in the oil will leave dark, nearly-impossible-to-remove stains. Watch out for sneaky runs below the rail. Oiling requires multiple coats. The wood will initially "drink" the oil, and thinning the first coat about 20 percent with mineral spirits or turpentine will encourage it to penetrate the wood more deeply. By the third coat, oil will begin to stand in some areas. Wipe up excess oil with a cloth. Continue to brush on the oil and wipe away any excess until the wood is saturated. The wood should have a matte finish without shiny spots. Oiling Teak on

Install Two Bilge Pumps

A bilge pump big enough to deal with a real emergency will do a poor job of keeping the bilge dry because the water in the discharge hose drains back into the bilge when the pump shuts off. And a big pump requires a big hose. The ideal bilge-pump arrangement is a small (400-GPH) automatic bilge pump mounted in the sump to dispense with rain and shaft-gland leakage, combined with a high-capacity pump (3,500-GPH) mounted higher to deal with more serious ingress. Stepping the discharge hose from the small pump down to 1/2-inch minimizes the backflow from the hose when the pump cycles, maintaining a dryer bilge. The large pump can be wired to a float switch if you prefer, but a manual switch makes more sense. An added advantage of this bilge-pump configuration is that the high-capacity pump sits high and dry, extending its life indefinitely. Install Two Bilge Pumps on 

For more detailed information on all these topics, and many more, go to

— Published: August/September 2012

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