How Long Is My Boat?

Ask The Experts

Illustration on how to determine the length of a boat Learn your LOA from your LWL, which is measured stern to bow at the loaded waterline on the centerline of the boat.

How is a boat's centerline measured? It's my understanding that the centerline is the length from the top edge of the transom to the longest point of the keel (bow), not including the bow pulpit. If the bow pulpit is included, then that would be the LOA.


John Adey: The centerline is just that, the boat split in half down its length, and it is not used in and of itself as a boat measurement, but as a reference point for other measurements. Measuring parallel to the centerline at various points (e.g., at deck level, at the waterline) can give you LOA (length overall), LWL (length of waterline), and so on. LOA is defined as the straight line measurement from the foremost part of the boat to the aftermost part of the boat at deck level, measured parallel to the centerline and to the design waterline, including any integrally formed, molded, or welded components. ABYC standards carry definitions of these items. The document titled "S-8: Boat Measurement and Weight" is the one you may be looking for. Very often, property-owners' associations contact ABYC to settle slip or mooring disputes, and this is the perfect document for that. The discussions often result in a change in the bylaws of the organization to reflect the ABYC definitions. Brochures and online sales specs for boats often talk about terms that really don't exist in the design world but sound great at boat shows. They may quote LOA but really mean what we call "maximum length," which is the tip-to-tail measurement including any accessories installed.

Stick It To It

What is the best adhesive/sealant to attach a rubber gasket to a Bowmar aluminum deck hatch?

Robert Millard
East Falmouth, MA


Tom Neale: You refer to a specific brand but this issue is relevant to many brands and products. For your situation, I talked to Bob Touton, product manager of hatches and portlights for Pompanette, which now owns Bowmar. He told me that a lot of their new gaskets have UHB (ultra-high-bond) backings. This makes them very easy to install and you shouldn't need a sealant. Use superglue to glue the butt ends. But Bowmar has been around for 40 years so you first need to know which deck hatch you have. Aluminum can be cast or extruded. Some of the extruded aluminum hatches have gaskets that are wedged into a molded "groove" with butt ends glued together. With this type, a small coating of black silicone will usually help if there's a problem. Call the manufacturer's customer service number or email them and send a picture or two of your hatches so that they can tell what you have. If you have a part or model number, that's even better.

Windlass Size

I'd like to install a windlass on my Sea Ray Sundancer. Any advice on best model and size to use for this installation?

Robert Pernal
Valley Stream, NY


Don Casey: The windlass should have a pull capacity of not less than three times the total weight of your ground tackle. I don't know what size your Sundancer is, but for example, if you have a 35-pound anchor attached to 100 feet of 5/16-inch HT chain, the chain weighs about 115 pounds. A windlass with a 450-pound capacity or more (35+115=150 times three) should do the job for you. You might want to raise the minimum capacity to four times the tackle weight, in case you buy a larger anchor later. When it comes to anchoring gear, it's rare to be too conservative. I don't recommend brands simply because I have experience only with those I have used. Others may be better, so you'll need to do your own research on what model to choose.

Charge It!

I have an outboard with two batteries and a parallel switch. I'd like to install a solar cell or a battery charger to keep both batteries charged while the boat is on its lift. How should I set the parallel switch, and how should I connect the batteries to the charger? I assume the batteries can be charged in parallel. They're identical.

Charles Peele
Frisco, NC


John Adey: For optimum battery charging, I recommend you bypass the switch and go right to the battery terminals themselves. (Make sure you install a fuse in the wire going from the charger to the terminal.) This prevents you from making the mistake of leaving the battery switch set at "Off" with the charger on. A single charge into the parallel switch will not charge both batteries equally — even identical batteries won't charge at the same rate. You want each battery charged independently so that one battery does not pull the charge from the other. Solar is not going to give you the same charge as a 120v AC charger. If you decide on solar panels, you can also wire them directly to the individual batteries with a fuse, assuming they go to a regulator first.

Photo of two batteries and charger with parallel switch

Here's my recommendation: Buy a marine two-bank battery charger and follow all recommendations for installation. They have them prewired with a standard plug on the end and ring terminals ready for battery installation. Keep your battery switch off so they charge independently. Connect a GFCI-protected extension cord to the charger and be confident that both batteries will be ready to use when needed. If you have a shore-power system on the boat, you can't use the extension-cord option; you would need a permanently wired charger, adding an appropriately sized breaker to your panel.

Dirty Caulk

On my boat there is sealant or caulking where the radar arch mounts to the gunwale and around covers over the engine air vents. The caulking is embedded with dirt or mold that will not scrub out. I don't think it needs new sealing but I'd like to clean it up. Do I need to dig out the old caulking or can I put a coat over the existing caulk?


Don Casey: When caulking on a boat is done properly, the only part of the caulk that should show is the thin edge between the hardware and the hull or deck, like the edge of a gasket. Unfortunately, a lot of owners and more than a few professionals seem to think that a bead of sealant around the hardware, like caulking a bathtub, adds to the security of the seal. It doesn't. All it does is provide an environment for unsightly mold to flourish. If the hardware on your boat has been bedded properly, simply slice away the sealant that's discolored. To avoid scoring the fiberglass, use a plastic razor blade. (If the sealant bead is thick, you may have to use a real blade to cut almost all the way through, then the plastic blade to complete the separation.) Of course, the bead of sealant you're seeing might also have been applied topically in an effort to seal the hardware from the edge. In this case, when you start to cut away the bead, it's likely to peel away entirely, reopening whatever leakage precipitated its application in the first place. The only solution is to remove the hardware in question, clean the mating surfaces free of all old sealant, then rebed them properly.

Zinc Or Swim

I currently have zinc anodes on my 30-foot Sea Ray, which is in fresh water. There are anodes above each prop on the outdrives and clamshells on each of the stainless trim tabs. I also have a Mercathode system with a large rectangular anode on the bottom of the hull. I have been told that I should use magnesium anodes for the trim tabs and above each prop.Is this a wise move or should I stay with zinc?


Beth Leonard: Aluminum anodes are the best choice for nearly all boats kept in salt, brackish, and fresh water. Magnesium will work in clean fresh water if you can't locate aluminum, but don't use zinc as it will not offer sufficient protection in fresh water. Also, upgrade your Mercathode to the freshwater kit if you haven't already, and check it periodically. They require a constant source of power and if a wire corrodes or a fuse blows, your drives will be unprotected.

Drip Drop

I have a 30-foot sailboat and when I cranked the Yanmar diesel last week, I noticed a small drip coming from around the shaft, just behind the engine block. How serious is this, and do you think it may be something that could be fixed while the boat is in the water?


Tom Neale: First, identify the leaking substance. Is it water? Transmission fluid? Lube oil? I'll assume you're talking about water and that it's coming through your shaft seal. A small leak at a shaft seal isn't unusual. As the boat sits without running, the stuffing may dry some, and if you run it, there may be a little seepage. The seal should leak a little while running to keep the stuffing lubricated; it should not leak at rest.

It's usually easy to fix this in the water. Just back off the retaining nut and tighten the adjusting nut as needed. Too much can cause the stuffing to overheat, so never tighten it more than needed to stop, or just barely stop, the seepage. Remember, the seepage will increase when running. Some water may come in as you do this, but it shouldn't be a problem with a good bilge pump. For a more detailed discussion read Don Casey's article "Servicing Your Stuffing Box."

Excessive leaking can also occur when the stuffing needs replacement, the housing is damaged, the shaft has become worn inside the gland, the prop is impaired as with barnacles and/or seaweed or is bent, or the cutlass bearing is worn. These would normally require a diver or hauling to remedy and you'd feel some vibration when running. If you have a different type of seal, such as some of the so-called "dripless seals," you may have to take very different steps, such as hauling.

If the fluid is oil or transmission fluid, there's a seal going bad on the engine that will eventually have to be replaced by a qualified mechanic. This can usually be done while the boat is in the water.

Starter Stutter

I'm having trouble starting the engine on the port side of my boat. The starter is giving a rattling sound every time I turn the key. We started the engine by using 24 volts, and after it turned over, we switched to 12 volts and the engine started like new. I let it run for 10 minutes, turned it off and on several times, and it worked normally. I went to start the engine again a couple of days after that and the same problem reappeared. What is the problem here? I've replaced the starter, battery cable, and the battery but the problem persists.


Don Casey: In my experience, starter problems are most often related to low voltage to the starter solenoid due to undersized wiring or poor connections. You can confirm this by jumping the positive battery cable terminal on the starter solenoid to the ignition terminal also on the starter solenoid. This bypasses all of the ignition circuit — the key switch, the start button, and the wiring delivering the current to energize the solenoid. If the starter spins vigorously when you jump these terminals, the ignition switch wiring is the problem. It might be the ignition switch. It might be the starter button (if you have one). But most likely it's that the circuit from the battery through these components to the solenoid has too much resistance — small wire or corroded connections.

You can rewire with larger wire, but the ignition wiring is often contained in the wiring harness, making this a bit more challenging. Often an easier option is to install a second solenoid near the starter and reroute the ignition wire to energize this unit rather than the solenoid on the starter. To the other two terminals on this auxiliary solenoid, connect heavy cables to the battery terminal and to the starter solenoid's now-empty ignition terminal. Now your ignition circuit only needs enough voltage to energize this electric switch, and when that happens, the voltage delivered to the starter solenoid should be close to full battery voltage. Reliable starting will be the result.

Abandon Ship?

I'm leaving my sailboat in the water at a marina in Key West, Florida, this summer. What maintenance needs to be done while I'm away? A friend suggested timed-release chlorine tabs in the raw-water strainers for my engine, generator, and air conditioner to prevent algae growth. I've never left my boat in the water before, so I'm really anxious.


Tom Neale: First, I wouldn't leave my boat in water storage, while I'm away, in that area during hurricane season. I'd store it on the hard, properly prepared and secured. But if that's not an option, here are a few things I would do. Close all thru-hull valves. Post warning signs on all start switches for equipment (such as engine or air conditioning) that uses raw water so that no one will inadvertently start it while the valve is closed. Don't put chlorine tablets in water strainers. The chlorinated water might damage the system and growth is slow there because of lack of light and oxygen. I'd consider buying a Sea Flush system to clear passages when I put it back into service, but you probably wouldn't need to do that after only one summer.

Get a smart three-stage battery charger set for your particular type and size of battery to keep the batteries properly charged. Empty the water tanks and leave the fuel tank filled. Add a good stabilizer additive. Rig lines, including spring lines, to handle extreme tides and blows. I'd double my lines and take great care to add and secure good chafing gear. I use Tide Minders, but the pilings must be tall enough and without obstructions. The dock should have strong and very tall pilings. Remember, you're leaving it there during hurricane season. Remove all sails and the bimini/dodger. Even if there's no hurricane, tropical storms and bad thunderstorms can generate very high wind gusts. If you have a dinghy, remove and store the outboard (no gas belowdecks), pull the dinghy onboard, turn it upside down, and tie it down well. If it's an inflatable, deflate it and store it below. If you can, carefully store your dinghy ashore in a safe place.

Have someone check on your boat: lines, deck, bilges, batteries, including checking for vermin, preferably once a week, but the more the better. They should also check for bird droppings. If left uncleaned, they can stain gelcoat and induce rot in fabrics. Leave written instructions for starting systems and running the boat should there be an emergency. Have at least one loud high-bilge alarm (preferably two, separately wired) that will attract the attention of those on the dock and/or ashore. Be sure your insurance covers you where you are and under the circumstances.

Leave the boat with fresh zincs in your engine and in any other internal components that use zincs. Have a diver check your bottom every month or so for excessive electrolysis. The diver should replace zincs if needed, and if excessive electrolysis is occurring, the cause should be determined and corrected. He may need to clean off the shaft, prop, and struts occasionally to prevent barnacle buildup. Lastly, find a good yard/mechanic to call should you need one.

Move It Or Leave It?

Should the sterndrive anti-ventilation plate (above the prop) be even with the bottom of the boat? Mine is 1/2-inch below the bottom with the manual tilt rod/pin in the center hole. Right now it would be fairly easy for me to raise the outdrive mounting collar on the transom a half-inch to make it even. What effect would it have on speed, turns, and bow attitude? The boat is a 20-foot bowrider. With 56 gallons of fuel in the stern, it gets heavy. I'd like more speed, and less porpoising. Would I risk getting ventilation on turns by raising the ventilation plate?


John Adey: There really is no reference to the location of the anti-ventilation plate to the bottom of the keel. If you take a look at any of the installation manuals online, you will find that the drive template location is found by determining the driveshaft center, based on transom height and angle, and then there's a small allowance for performance. We have to assume that the builder performed testing to determine the acceptable performance. Moving the drive up could contribute to ventilation and cooling problems from interrupting the flow of water to the raw-water intakes. I'd hate to see you change the height and re-glass the transom only to have complicated the issue.

You might see excellent straight-line performance but then the prop loses its bite going into a turn. You didn't mention any experimentation with prop pitch; this will be the single largest improvement you can make instead of taking a shot in the dark at drive height that you may seriously regret later. Many boats have the stern-weight issue you're experiencing. For starters, put 20 feet of anchor chain in the bow, see where that gets you, then experiment with your propeller pitch. I'd trust the boatbuilder on this one, and keep the height the same.

Photo of a truck trailering a boat

The Trailering Guys

Photo of Dustin Hoover and Ted Sensenbrenner

Ted Sensenbrenner of the BoatUS Foundation for Boating Safety and Clean Water has been pulling, fixing, and studying boat trailers — and every type of trailer problem! — for years. He's our man.

Dustin Hoover of Legendary Trailer Repairs fame is a top service provider for BoatUS TRAILER ASSIST in Annapolis, MD. There's nothing he doesn't know about trailers (

Ted and Dustin write the popular "Trailering Guys" column in BoatUS Trailering Magazine — one of the many great benefits of covering your trailer and tow vehicle with BoatUS TRAILER ASSIST, the 24-hours-a-day roadside-assistance service.

Going To Ground

I just replaced all the lights and wiring on my trailer, but I still have a problem with the lights blinking off and on while driving. Sometimes they work fine, and I'm not sure what is causing it.


Dustin Hoover: Every trailer has a white ground wire that must be directly bolted to the trailer from the tongue plug. Make sure this wire is good. If you have a tilt trailer, make sure there's a jumper wire between the trailer tongue and the trailer frame. Many tilt trailers will lose their ground at this point, thus the need for the jumper wire. After you've checked the ground, test it without the trailer down on the ball. If it works, then you know that you're not relying on the ball for a ground. Check all other connections as well, and, if you want, grease your connection to help prevent corrosion. If you can't get the trailer lights to work without the ball being hooked up, then put a pair of jumper cables between the truck and the trailer to make the ground. If this works, go back to the truck wiring and make sure it's feeding the trailer a good ground.

Fed Up With Rot

What's the difference if you replace trailer tires with passenger car tires with the same load rating? My friends and I are fed up with the sidewalls of trailer tires dry-rotting after two or three years, even when stored inside.


Ted Sensenbrenner: There's a big difference. The sidewalls on trailer tires are stiffer to prevent swaying. It's dangerous to put light-truck or car tires on a trailer. For a trailer, use only ST-rated tires ("Special, Trailer"). If you get into an accident while towing your trailer, using the wrong tire, your insurance company may deny your claim. We all wish that trailer tires lasted longer. One way to extend life is to remove the wheels during long periods of storage. 

— Published: August/September 2013

Check Your Zincs!

Assuming you do not have a problem with stray current corrosion, 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 will find it (or not) under a brass plug in the exchanger.


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.


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