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Sea Savvy

Life is better with bow thrusters

Life is better with bow thrusters

Forget that gold braid cap and yacht club burgee. Forget those European lines and fishbowl windows. I can do without all of that as long as I’ve got the grind. I don’t care if it’s flat calm, no current and I’ve got a straight shot into the slip; I’m going to push that toggle and thrust and grind.

 It used to be that the only thing I could grind was my transmission or my rubrail, but now when I grind I get respect. A bow thruster can make even me look like I know what I’m doing. I ran boats for 47 years without a thruster.


 I’ve had one for the last six years on my 53-foot single-screw motorsailer, and I love it. And now I’m seeing them more and more on smaller boats.

Tom Gillikin is president of Florida Bow Thrusters ( of Merritt Island, Fla., which specializes in installing Vetus bow and stern thrusters. Gillikin says when he started the business in 2001 he installed 30 thrusters. Last year he installed more than 300 on boats ranging from 25-footers to megayachts and high-performance boats.

“Business really took a turn in the last year and half or so toward the 30- to 33-foot range,” he says. “We recently did a [Sea Ray] 260 Sundancer.”

Gillikin says a typical 36- to 38-footer would need a unit with 165 pounds of thrust and would cost around $10,000 installed, with parts representing around $6,300 of the total. He says the required motor thrust is determined by a formula that takes into account the boat’s draft and square footage above the waterline.

Joe Molinaro, owner of East Coast Bow Thrusters in Youngsville, N.Y., ( ), which also specializes in Vetus thrusters, says he attributes his increase in sales in part to the fact that there’s a tendency toward lighter boats, with shallower draft and higher freeboard and superstructures. This, he says, coupled with tighter slips (to get more boats into the marinas), has made thrusters more desirable.

Peter Nolet, product manager of thruster systems at Imtra of New Bedford, Mass., which sells Side-Power thrusters, says thrusters are getting to be like power steering was in a car. “At first you didn’t see it on every car, then you started seeing it on them all,” he says. Nolet also says Imtra is selling more and more stern thrusters ( ).

A multipurpose tool

Most people use thrusters for docking, but they can save the day in many other common situations, particularly with single-screw vessels. For example, a thruster can really help when you must hold in confined quarters with current and/or wind, such as waiting for a bridge to open. Frequently there’s a lot of current pushing the waiting boats toward the bridge, with strong winds blowing across the channel or toward the bridge.

In some places — along the Intracoastal Waterway, for example — the channel may be narrow with rocky and/or precipitous sides. These circumstances may require you to turn around to point into the current. In the “old days,” I did this by backing and filling while trying to avoid breaking off a rudder on a bank. With my thruster, I easily make the turn. Once the bow is into the current, I can hold with the engine and rudder.

Often, however, I know the wait will be short, and I don’t want to turn and point into the current. This brings up a seldom considered use for a thruster: helping you steer astern. For twin- and some single-screw boats, steering while backing down in tight quarters isn’t an issue. But for many sailboats and displacement trawlers, it’s a severe problem, especially when there are eddies bouncing off channel banks, the wind is blowing from any point off the bow or stern, or there are other boats milling about.

On our 53-footer, my tactic for reversing without the thruster is to steer with the rudder and shift into forward with a short power burst when needed to kick the stern around. This keeps the boat aimed in the direction I want to reverse. When steering astern with my Side-Power thruster, if I want the stern to go to port I thrust the bow to starboard in an arc appropriate to the conditions and to the degree I want to turn, and let the propeller pull the boat in that direction. (Your rudder likely will be amidships unless your boat’s steering characteristics require a different angle or because of other conditions, such as eddies or wind.) This requires some practice, but I’ve found it gives me much more control in these conditions.

This points out another advantage of thrusters: They can save wear and tear on a boat’s transmission. Without a thruster, the reversing tactic described above involves multiple shifts from reverse to forward, often in rapid sequence. And docking in less-than-ideal conditions may involve the same. Under ordinary use, most transmissions are designed to take this. However, the more you shift, the sooner you’ll have to replace or repair your transmission. That’s an expensive job. It’s easier and cheaper to replace a bow thruster.

We’ve found other somewhat unorthodox uses for a thruster. When anchoring, for example, you must find a good spot on the bottom for the hook to dig in. Most of us anchor in waters where we can’t see the bottom and really don’t know precisely where the best holding is. But in some areas the water is clear enough that you can see the bottom and find a spot of good sand or mud among poor-holding grass or rock. The Bahamas is one such area. Many times, as I stand on the bow ready to lower away, I’ll signal to my wife, Mel, to move the bow a few feet to port or starboard so that I can place the anchor exactly where I know the best spot to be. In the past we usually had to run off and circle to do this and were likely to not find that spot when we returned. But with the thruster all it takes is a push of the toggle.

Thrusters also may help get you off the bottom if you run aground. In a soft grounding along a channel, the deeper water often is to one side of the bow because the vessel has run into the shallows at an angle to the channel bank. Motoring ahead may dig the keel in deeper. Reversing may work, but you will have less power backing down and, depending upon the configuration of your hull and running gear, you may be unable to steer toward the deeper water. We’ve found that one of the more effective ways to get off in these circumstances is to pivot the bow toward deeper water. The full thrust of the prop can then push the boat in that direction and can also push against the rudder to better turn the boat in that direction.

There are several ways to pivot the bow, but one of the easiest and perhaps safest is to simply use a bow thruster. Most thrusters weren’t designed for this type of heavy use, and your boat may be too hard aground for this tactic to work, but it’s certainly worth a try if the circumstances are right. Take care that you don’t overdo it and damage the unit. You’ll know pretty quickly whether it’s going to be a wasted effort. Sometimes fore and aft thrust from the prop may loosen the boat enough for the thruster to work. Also, it might help to use the thruster as the bow is lifted on a wave or wake.

You can also use thrusters as a supplementary aid when executing other maneuvers, like warping around a piling to get into a slip, or using a spring line to get off a dock when wind and/or current are pushing you into it. There may be too much current or wind for these tactics to work safely without something extra, and sometimes a supplementary push or two from the thruster is just what it takes.

We’ve used our thruster to help shorten an upwind dock line when we’ve wanted to pull the bow farther away from the dock during a storm. The thruster is seldom adequate by itself, but it often provides that extra margin to allow us to pull in the line manually. (If the thruster won’t do it, consider using the anchor windlass.) We use only short thrusts as we simultaneously pull in and secure the line each inch of the way.

Power to the thruster

A good power supply is critical to a properly performing electric thruster. With electrical units, you can choose from AC (if you have a generator and run it all the time) and DC power. In general, 24-volt DC units are considered more efficient than 12-volt units and use lighter-gauge wiring. Even if your boat is rigged for 12 volts, you can establish a dedicated 24-volt power source by wiring in series two dedicated 12-volt batteries and providing a 24-volt charging source.

With a DC unit you’ll need either adequate wiring from your main banks or a bank of batteries forward near the thruster motor. Powering a thruster from the main house bank usually requires very heavy gauge wire, probably 4/0. If you read the specs for your thruster and consider voltage drop over distance of the run, you might be surprised at what’s required.

I’ve used another method that I’ve found effective on my boat. I gave my thruster and windlass their own independent power source. I installed a sizeable battery bank in the bow, charged by a dedicated Xantrex Truecharge 20+ ( located close to the batteries. This is a “smart” charger designed to charge in three stages according to the needs of the battery bank. You can set it for various types of batteries and for several ambient temperature ranges. This keeps that bank optimally charged, which is important because the thruster may not operate well when you seriously need it with poorly charged and/or maintained batteries. Special issues arise with this method, but that’s a subject for another time.

While a bow bank may not be the best solution for you, I prefer it because I didn’t want to run heavy gauge cables through my boat. Even with a bow bank, however, these cables would be needed if there’s no charger for the bank — not only for charging but also to handle overdraft from the bow bank during times of heavy usage.

You can charge a bow bank from the boat’s house bank by running heavy cables between the two. However, since a bow bank would be used differently from the house bank and normally would be of a different temperature, and because it may consist of different battery technology, you should consider using smart monitoring and inline charging equipment, such as a Duo Charge by Balmar ( ) and Echo-Charge by Xantrex. As is true of any equipment, the manufacturer’s specifications, operating parameters, warnings and instructions should be carefully observed to avoid serious problems, particularly when there is excessive draw from the thruster or windlass that results in high amperage current in the wires between the two banks.

Since installing the Truecharge 20+ on our boat, Xantrex has introduced a new XC series of battery chargers, which it says will charge three separate sets of batteries, each according to its needs and temperature, even though the batteries use different technologies (flooded lead acid, gel, AGM). This charger is said to accept a wide range of voltage and cycles. If I were to install a charger for my bow bank now, I’d consider using an XC to service that and my other two banks if it were practical to install an adequate 12-volt wiring run from the charger to the bow bank.

Thruster busters

Certain conditions can limit the effectiveness of even a powerful thruster, including simply being under way. Water moving past the tunnel can reduce side thrust, though this sometimes can be improved a little by a skilled installer. Factors that may help are the tunnel’s location in the hull, hull configuration around the tunnel openings and faring. (The discussion above about using a thruster to steer in reverse is an exception because you’re moving very slowly.)

The speed that negates a thruster’s effectiveness varies with the boat and circumstances. Imtra’s Nolet says some sportfishing boats use bow thrusters for trolling slowly, and that Simrad is offering an interface to a Side-Power bow thruster control with some of its autopilots.

We once had to perform some close maneuvering in a commercial basin in 40-knot wind gusts. The spaces were so tight and the wind so strong that I thought I didn’t have space or time to back and fill to get my bow around. Uttering a prayer of thanks for the thruster, I hit the toggle. I heard the sound of the motor, but there was no bow movement in either direction. We looked for the telltale swish of water coming from the hole but saw nothing. I’ve thrown my propellers, I thought, amazed that they could both have spun off.

Fortunately, I was able to safely maneuver using old fashioned fore and aft thrust from the diesel. When we got into clear water and less wind, I stopped and looked over the bow as Mel worked the thruster switch. Both sides were jetting out water normally, and the bow was responding to the toggle. I realized that the wind on the beam had given the boat enough forward motion through the water to completely overcome the effect of the thruster.

Never assume that a bow thruster will always be a cure-all. Even if you’re not under way, wind and current can overcome a thruster, which can occur as you’re trying to get off a dock. We never take it for granted that the thruster is going to work, so we have alternate plans ready — even if the thruster has the power to get the bow far enough out to get away without being pushed back and tangling with a piling or dock.

Just a little burst must do

Many of the uses for thrusters mentioned above highlight one of the most important concerns: Manufacturers mean business when they say not to run them for very long, and use only a few short bursts. It’s easy to damage the motor or wiring by running a thruster too long, and great care is needed to prevent this. While not overdoing it, you’ll need to learn to avoid ineffective very short bursts in favor of bursts that are long enough to begin the desired momentum. (Hydraulic thrusters can be run for long periods of time, but they are usually much more expensive and found on relatively large boats.)

Electric thruster motors are in many respects similar to a starter motor for an internal combustion engine (though they’re greatly improved and becoming more suited to the purpose than early versions). They’re designed to work very hard and consume a huge amount of power as they do so, but only for short spurts. Failures usually occur because of the heat generated by the load. Bearings, bushings and coils heat up quickly and can become so hot that components melt or seize. Also, power source wires will become hot, even if they are properly sized. This frequently occurs at terminals, where the wires are connected to a battery on/off switch or the studs to the motor.

Terminals, even if well-executed, provide extra resistance that causes heat buildup. A good installation will have a properly sized circuit breaker, and the motor may have an overheat safety shutoff. But it’s unwise to assume that these devices won’t fail, as with every other device on a boat. The result of this failure could be a ruined thruster motor, melted terminals or even fire.

The strength and survivability of a thruster and its load capacity are affected by its size, installation, type, wiring, power supply and your boat. If it’s undersized for your boat it may burn out more quickly because it’s not doing what you want it to do, and you’ll be tempted to thrust longer.


It’s obviously important to follow manufacturer-specified maintenance, but here are a few tips that may not be included.

We all know that barnacles and other growth on propulsion propellers impair performance. This is even more of a problem with bow thruster props. Just a few barnacles will make a noticeable difference. And barnacles attached to the wall of the tunnel also can significantly affect performance. If you paint the bottom every year this shouldn’t be a great problem, because you can apply anti-fouling to the inside of the tunnel. (You still should regularly inspect the tunnel.) Operating the thruster every week or so, even while sitting at the slip, also will help to keep it clear.

I generally haul my boat every three years, and toward the end of that time I usually must clean the thruster propellers. I do this by going into the water with mask, flippers and snorkel. (Be absolutely certain power to the thruster is disconnected before doing this or any other maintenance.) If your thruster has two propellers, like mine, you might find it difficult to reach and clean the interior blade surface. I’m usually able to reach around the propellers and knock off the barnacles with my fingers. I wear heavy-duty work gloves that the barnacles can’t cut through. Knocking barnacles off inside the tunnel is relatively easy with a long knife or large screwdriver.

While looking into the tunnel, check the zinc that likely is attached to the unit, and look for signs of wear on the tunnel wall caused by the propeller blades. The tolerance between the outer tip of the blades and the tunnel normally is quite close, and if you see indications of impact it could mean that the unit has been installed poorly or there may be some play in the hub of the propeller or shaft — a sign of trouble to come.

Another critical maintenance job is making sure the line between the oil reservoir and the bearings (or comparable equipment, depending upon your unit) is clear and that the bearings are well lubricated. Also, if possible (and it should be), check the contact points of any solenoids that switch the thruster motor on and off from one direction to another. If these are mechanical, normal usage over a few years may cause pitting from the arcing. This pitting could reduce conductivity and/or cause them to hang up in one position — a time that you’ll be glad you have an easily accessed bow thruster battery switch and that you know where it is.

Also, whenever safe and practical, look over the sides before operating the thruster. A major cause of damage is simply trash in the water that gets sucked into the tunnel and chips or jams the prop. Protective grates are sometimes installed over the tunnel openings.

Making a hole

Few owners install their own thrusters. In theory, it seems easy. You just saw two big holes in the side of your boat, slip the tube through, glass it over, and hook it all up. Say what? Saw two big holes in your hull? Unless you really know what you’re doing, this is a time for experienced professionals. Fortunately, many boatbuilders now offer thrusters on new boats. If you’re getting a new boat, consider at least ordering a tunnel or plug in place if it’s an available option.

As we’ve seen, placement of the tunnel is important. A rule of thumb is that the farther forward it is, the better the thruster will pivot the boat. But it’s not that simple. The tunnel also must be deep enough to avoid cavitation. Gillikin of Florida Bow Thrusters says it must be at least half the diameter of the hole from the water surface to the top of the tunnel — preferably deeper. And depending upon the contour of your hull in the area of the tunnel, you may need special faring so that the tunnel won’t cause flow interference while under way.

Even if you know the best theoretical location for the tunnel, you may not be able to put it there. Interior support timbers, decks or other equipment might be in the way. And there must be space not only for the tunnel but for the rather large motor, and its support and accessories. Also, there must be space to work on and around the motor.

Once the tunnel location has been determined, there comes that moment of truth when your hull is opened up to the light of day. It’s important that the two holes are properly aligned so that the tunnel won’t be cocked. Some professionals use what is essentially a large and very long hole saw to cut through a fiberglass hull from one side to the other. This expensive tool helps, but you still have to line it up correctly. The tunnel tube comes ready-made and should be blister-proof.

As stated above, more owners are opting for stern thrusters in addition to bow units. Depending on the boat, they may be installed in the aft end of the keel or on the transom. If they’re on the transom, it’s important that they also be within a tunnel. “A thruster without a tunnel is like a garden hose without a nozzle,” says Imtra’s Nolet.

There have been times I’ve wished for a stern thruster. But at some point we all need to remember that there’s a rudder back there, and we should know how to use it. As more people get into boating, there’s a tendency to turn the key and go without learning basic boat handling and seamanship skills.

Know when to hold ’em

I once watched the proud new owner of a $2 million dollar trawler dock bow first in a wide slip in an enclosed basin with no wind or current. The boat had bow and stern thrusters, and for almost 20 minutes the skipper would toggle and grind, toggle and grind, moving his boat around in minute increments, each with a flourish of water shooting out from the sides of the bow or stern. Finally the yacht was precisely lined up, its bow pointing straight into the slip. It was the moment of truth. As he stood on the flybridge, coolly looking over the heads of admiring spectators on the dock, he shifted gear and gunned it hard. He had shifted into reverse.

Learn how to drive your boat before you learn how to play with your joystick. Even though thrusters have many attributes, they can seldom take the place of the propeller, rudder and skillful use of the two. The list of tactics you need to know sans thruster is almost endless — springing off a dock with prop wash against the rudder, warping around a piling, backing and filling to hold place, forward burst coupled with slow reverse to turn around in a tight spot — and these more truly define your ability to safely operate your boat and have fun. The thruster will sometimes do a job by itself, but it more likely will complement your skills and other equipment, not to mention your ego.

Speaking of which, I’ve made a recording of my thruster’s grind so that I can play it through my loud hailer if the thruster ever breaks. This will avoid an extreme ego crash should I have to dock without it, while greatly increasing the comfort level of other boat owners at the dock. They’ll have the illusion, if only for a while, that I won’t hit them as I come in.

Tom Neale is technical editor for Soundings and lives aboard a Gulf-star 53 motorsailer. You can buy his book, “All in the Same Boat,” at .