At the most basic level, the common bow thruster comprises one or two propellers driven by an electric or hydraulic system placed in an athwartship tunnel to draw water from one side of the boat and move it, through the tube, to the other side - moving the bow of the boat sideways in the process.
However, installing a bow thruster involves quite a bit more than taking a giant hole saw to the bow below the waterline - though that's admittedly one of the more exciting steps.
Before anyone cuts a hole, it's important to determine correct bow thruster size and placement. The two variables are interrelated: positioning the thruster farther forward from the boat's pivot point provides more leverage, but different hull designs and configurations may limit options. A more powerful thruster, however, can compensate for less-than-ideal placement.
New England Bow Thruster developed and prototyped a "laser-induction system," which projects a virtual laser tunnel from the inside boat - typically pinpointing the tunnel location within five minutes, says owner Bill Jennings. The company then worked with a local engineering firm - Mystic, Conn.-based Race Rock Associates - to further develop and fabricate the system.
"The system we've designed basically guarantees we're maxing out leverage on the boat," says Jennings. "It makes taking the complex measurements a much simpler, efficient and highly accurate repeatable process."
Before making the first cut, the team must ensure they won't disrupt plumbing, wiring and other systems already in place. They do this through visual checks and the help of special cameras. "These allow us to inspect areas that in the past would have been near impossible," says Jennings.
To get clean water, he says, the tube should be submerged at least one tube diameter below the waterline. Tube length and other hydrodynamic factors affect how the thruster draws water, too. Properly shaping the tube where it meets the hull compensates for shorter tube length and mitigates drag when the boat is under way.
Proper shaping is critical to extracting all the available thrust in a given system, as it works in conjunction with proper placement, tube length and hydrodynamic flow, says Jennings.
"These are not inexpensive systems so it's important that we attend to all the details that contribute to maximizing the performance," he says.
A typical installation takes two to three days with half of that time spent shaping the tube to the hull.
New England Bow Thruster has installed single-thruster systems on boats ranging from 23 feet to 90 feet, Jennings says. The price tag for a fully installed electric system ranges from $5,000 to $28,000, he says.
Other available systems include stern thrusters as well as retracting thrusters, where there is no tube and the thruster is launched through a door at the bottom of the boat, says Jennings. The company is also now bringing in a new line of retracting thrusters from Sweden called RMC and, as of February, is the exclusive U.S. distributor, says Jennings.
In the end, the system has to work well and it has to work every time, Jennings says.
"The thruster is only as good as the installation," he says. "It's a wonderful thing when you know you've done all the homework."
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This article originally appeared in the New England and Connecticut and New York Home Waters Sections of the April 2010 issue.