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Why Is My Bow Thruster so Loud? 3 Common Causes of Noisy Thrusters

Is your bow or stern thruster too loud? Whether your thruster has been noisy from the day it was installed or if it just started getting louder over time, here are three factors that contribute to noise, and ways to solve them.

What Makes a Bow Thruster Loud?

The most common cause of noise in a tunnel thruster is cavitation. Cavitation, in the context of a bow or stern thruster, is air bubbles mixing with the water as it passes through the tunnel. Simply put, more air in the tunnel means a louder thruster, so the process of reducing the noise of your thruster is simply to reduce the cavitation. So what causes cavitation?

Marine Growth

If your thruster hasn’t always been loud, but seems to be getting louder every time you use it, the additional noise is most likely related to marine growth in the tunnel. If there are barnacles, weeds, or any other form of marine life growing on the inside of the tunnel or on the propellers and gearleg assembly, more air bubbles will form as the water flows over them. The fix to this issue is simple: clean out the tunnel and scrape away those barnacles.

Sharp Tunnel Edges

If the tunnel installed on the boat doesn’t have properly rounded edges, the waterflow over a sharp edge will cause bubbles to form, which will both make the thruster louder, and reduce the thrust and efficiency at which the thruster runs. Therefore, properly rounded tunnel-edges will quiet your thruster down and help it perform more efficiently & effectively. The video below from Side-Power illustrates this phenomenon quite well.

Poorly Insulated Thruster Compartment

Another cause of a loud thruster is simply a lack of sound insulation where the thruster motor is mounted. Most thruster installations involve mounting the motor in the bilge of the boat, which can be echoey when the motor runs, and reverberate throughout the hull. If there’s room to add some foam around the bulkheads in the thruster-motor compartment, this can help reduce the noise level of the thruster. It is important to be careful not to over-insulate the compartment, however, as the motor does need enough air around it for heat to dissipate so that the motor doesn’t get too hot when running and trip the thermal overload, rendering the thruster inoperable until it cools back down.

When checking on a noisy thruster, it’s always best to start with the easy solution first. Check the tunnel for marine growth and scrape away any barnacle or other obstructions in the tunnel. Once the tunnel & gearleg assembly are confirmed clean, check the compartment where the thruster motor is mounted and see if it’s echoing throughout the boat. If it is, consider adding some sound installation. Then, if neither of those solutions reduce the noise, check the edges of the tunnel to make sure they’re rounded well, and do the necessary fiberglass work to smooth them out if not.

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