Take Control
Bow thrusters are not just for bigger boats—today, there’s no reason not to have one on all but the smallest of vessels.
Gary DeSanctis, President of the AIM Marine Group, the parent company of this magazine, bought a new boat this summer, a 24-foot Jeanneau NC 795 with a pilothouse and a single outboard. DeSanctis spends lots of time at the helm of a variety of vessels, most of them larger, often much larger, than his Jeanneau. But he discovered that, like many outboard and single-screw inboard boats, the pocket-sized Jeanneau can be a handful to maneuver in close quarters: The boat’s shallow draft and light weight make it skittish in a crosswind; to complicate things more, DeSanctis’ berth is alongside a floating dock, tucked between two other boats, in an area of strong tidal currents. Bottom line is, the wind, the current and the limited room for error frequently made docking maneuvers unduly thrilling.
Rather than limit himself to using the boat only on calm days at slack tide, DeSanctis decided to install a bow thruster. It’s no longer the 20th century, when thrusters were only for big boats—today, there’s no reason not to have one on all but the smallest of vessels. Before purchasing a thruster, consult an expert so you select the right one; there are many variables to consider—not only its power, but its physical size, electrical requirements, flexibility in mounting and more. The Vetus Bow Pro 42 KGF DeSanctis chose has plenty of power to push the Jeanneau around in stiff winds, and it has three features that improve its function and reduce maintenance when compared to similar thrusters from other manufacturers. It also fit in the tunnel that the forward-thinking Jeanneau installed in the boat at the factory, making installation a lot easier.
Why the Bow Pro?
What’s the Vetus Bow Pro got that many similar models don’t? First, it’s a proportional thruster. Most thrusters are full power on or off; the joystick is just a switch. This is fine for a big, heavy vessel that needs all the thrust available, but a small boat like the Jeanneau often requires just a nudge, and that means cycling the thruster on and off repeatedly. A proportional thruster—some people call them variable-speed thrusters—generates thrust proportional to the deflection of the joystick, which is no longer a switch, but a rheostat. For a little thrust, move the joystick just a bit; for max thrust, move it all the way. This lets the skipper fine-tune their docking maneuvers while reducing wear on the thruster motor.
Second, Bow Pro thrusters use a brushless induction motor, a feature that shortens the list of maintenance chores. Most thrusters use motors with brushes, small blocks of carbon that conduct current from the power supply to the rotor, which causes it to spin inside the stationary stator. (These terms are part of basic electromagnetism; you can look ‘em up.) Springs push the brushes against the rotor, where friction will eventually wear them down. Inspecting and maybe replacing brushes is a yearly maintenance chore, but repeated cycling of the thruster off and on will shorten its life.
Induction motors energize the stator rather than the rotor. Since it doesn’t move, the stator can be hard-wired to the power source, in this case a battery. An electronic controller uses the juice from the battery to create a rotating magnetic field in the stator; this induces the rotor to rotate as well. Induction motors are more efficient than brushed motors, have fewer moving parts and therefore last longer with virtually no maintenance. You might think induction motors are the wave of the future, but they’ve been around since Nikola Tesla invented the first one in 1887, using alternating current to excite the stator coils. They are not yet all that common in bow thrusters for small boats, however.
Third, the Bow Pro’s tailpiece, sometimes called a drive leg—it’s the part that lives in the tunnel—is sealed, so there’s no need to check or change the oil. It’s essentially maintenance-free; the only serviceable part is the anode, which, like any other anode, should be replaced when half gone. It’s behind the propeller, held in place by a couple screws. You’ll need to remove the prop to paint the inside of the tunnel, so change the anode then. Grease the shaft before replacing the prop.
A Job for a Pro
DeSanctis called New England Bow Thruster in Mystic, Connecticut, to install the unit; the job was done by Andrew Ziolkovski, the company’s service and technical supervisor. In his eight years with NEBT, Ziolkovski has completed close to 400 bow thruster installations, by his own estimate, so this was a simple job for him. For you and me, maybe not so much; I recommend hiring a pro for this kind of project, especially since in most cases step one is to cut two large holes in the bow of your boat.
No need for the hole saw on this job, though: The tunnel was already in place, taking away about half the effort of installing the thruster. According to Ziolkovski, the Jeanneau had a nice compartment to work in; it would have been easy to install the tunnel, but that’s not always the case. “Sometimes we have to go ‘spelunking’ on the boat to reach the place where the tunnel should go,” he said. It should be as far forward and as low as possible. Always start on the inside of the hull when situating the tunnel, he said, to make sure there’s room and nothing’s in the way.
The deadrise and fore and aft curve of the hull mean the holes for the tunnel aren’t round, but more or less elliptical. Pros lay out the holes using a jig that takes the hull form into account so the tunnel fits snugly and a minimum of filling is necessary. Once the tunnel is fitted, the installer will lay down layers of fiberglass—usually a biaxial fabric and epoxy or vinylester resin—on the inside. This is the structural glass that keeps the tunnel in place and the water out. He’ll then fill and fair the outside joint with epoxy putty. This takes skill to make a neat, structurally sound job. Again, it’s best left to a pro.
Measure Twice, Cut Once
The thruster should be positioned in the tunnel so the propeller is within easy reach from outside the boat, not necessarily on the hull’s centerline—not an issue for the Jeanneau with its short tunnel. The thruster motor can be mounted vertically, horizontally or at an angle, but if it can’t be mounted vertically, the installer must support the weight of the motor with some kind of structure. Again, not a problem here—there was plenty of room to mount the motor vertically.
Using a pattern provided with the thruster, Ziolkovski cut one large hole in the tunnel for the drive shaft and drilled two smaller holes for the machine bolts that hold the drive leg in place. He drilled a third hole to accommodate a lube fitting on the drive leg, even though it’s no longer functional because the leg is sealed. All holes must be lined up on the exact centerline of the tunnel, so it’s worth taking extra time to precisely position the pattern before drilling. Ziolkovski then fitted assorted packings and shims, along with sealant, on the drive leg—which he had already barrier-coated to make the antifouling stick better—and while standing outside the boat pushed its shaft up through the hole in the tunnel.
The drive leg is held in place from inside the boat by a cage-like bracket (Vetus calls it an “intermediate flange”) that sits atop the tunnel like a saddle. Two machine bolts pass through the bracket and tunnel and thread into the drive leg; tightening these bolts sandwiches all the parts together. If the installation is correct—and after 400 thrusters, Ziolkovski gets it right the first time—the thruster prop will spin freely in the tunnel with at least 1/16 of an inch clearance all around. The thruster motor then mounts atop the bracket, secured by four bolts and connected to the drive shaft by a flexible coupling.
Juice and Joystick
Even a small thruster, like the one on DeSanctis’ boat, takes beaucoup amps—250 when the Bow Pro is running at max power. Connecting to the boat’s existing 12-volt power would mean snaking two stiff (and expensive) 4/0 cables all the way aft to the ship’s batteries to keep voltage drop to an acceptable level. The NEBT guys don’t take this route. Instead, Ziolkovski installed a dedicated battery close to the thruster, with a slow-blow fuse for circuit protection and a magnetic remote inline switch, wired to the helm, to cut the power when the thruster isn’t needed. Any Group 31 marine battery will do the job, said Ziolkovski. He installed a Stationary Power Systems M105B, a fast-charging 105Ah battery with 820 cold-cranking amps. About the size of a briefcase, the M105B fits nicely against a bulkhead, held in place by straps. For recharging, Ziolkovski installed a Victron Energy battery combiner that feeds current from the outboard’s alternator to the thruster battery once the Jeanneau’s starting battery is fully recharged.
Vetus offers two joysticks for the Bow Pro. The standard model is typical—it moves back and forth and operates the thruster. When you release the joystick, it centers itself and the thruster cuts off. But an optional model has a “hold” function: Pushing a button on the joystick locks in whatever thrust level the Bow Pro is set at. Pushing the hold button again, or moving the joystick, releases the hold. DeSanctis said the upgraded joystick is well worth the extra cost. For example, he can set the thruster to keep the bow alongside, then go forward and rig his lines without the wind blowing the boat away from the dock.
Once the Bow Pro was installed and the Jeanneau was back in the water, DeSanctis spent about half an hour in open water practicing with the thruster. He said the learning curve is very easy, and he was soon able to make the boat go sideways with the engine and thruster. His tight, current-plagued berth isn’t a problem anymore, and he no longer thinks twice before using the boat in less-than-ideal conditions. “Now it’s cake,” he said. Maybe it’s time to think about adding a thruster to your boat.
