Bow thruster not producing much thrust

[HeadedToTexas]

I see neighbors and online videos of people whose bow thrusters move their boats around with ease, but my Vetus 75 Kgf bow thruster has always been rather weak. It is unable to overcome much more than a light breeze and does little to aid turning the bow on our single screw boat. It makes noise and I can see water moving laterally off the bow when running, but it does little to move the boat. Vetus indicates that the 75 Kgf is "suitable for Yachts and Powerboats up to 15m (50ft)." Escape is a 2007 40' Mariner 37.

Our bow thruster is powered by the house bank which lives in the lazarette almost 60 wire feet away. Cables between the house bank and the bow thruster are all 2/0, though they connect through a 1-2-Both switch and a main busbar along the way. Other than the anemic output from the thruster, I've not had any electrical issues with the motor or controls and they all appear to be original equipment.

I can not say the same for the Lofrans Kobra 1000 windlass (above right). First the down terminal on the motor lost continuity and then the up terminal went dead leaving the motor unresponsive. The picture is old and the contacts have been cleaned to a shine. The power arrives at the terminals on the motor, but the motor does not run. The 1000 watt windlass motor is also powered from the house bank nearly 60 wire feet away. Lofrans explained that low voltage and the resulting increase in amperage is a common cause of electrical contact failure on their motors and controls, though living in the wet environment of the anchor locker is a much more difficult life than living in the dry space above the bow thruster tunnel.

Point is, both motors aren't performing like they should. Is it unusual for the batteries powering these significant loads to be so far away? Are new Helmsman 38s designed the same way, or do they have dedicated thruster and windlass batteries in the bow? I have not yet put a meter on the thruster when it's running to measure current draw or voltage, but might that be why it seems to produce so little thrust? Yes, it could be something in the thruster prop or tunnel, but output has always been less than expected.

 

[O C Diver]

The simple answer is to check voltage under operation. Hold a digital volt meter on the bow thruster lugs and have your wife give a 2 second pulse to measure voltage drop (while the boats is in the water). Both the bow thruster and the windlass motor are DC which is absolutely effected by voltage drop.

On my boat, changing the bow thruster from the house bank (30'+ away) to 24 volts 2' away, easily double the effectiveness and reduced pulse duration buy 75%.

Ted

 

[SteveK]

Many discussions on why not to use house bank as starter batteries. Often I have said my preference is to have windlass on the Start battery while the engine is running.
Line loss and the fact that house banks usually do not output a continuous starter load (I consider a thruster as a starter load) from two feet let alone 30 feet away on 2/0 cable.
You see water flow comparable to a garden hose instead of a fire hose as a result.

 

[HeadedToTexas]

On my boat, changing the bow thruster from the house bank (30'+ away) to 24 volts 2' away, easily double the effectiveness and reduced pulse duration buy 75%.

Doubled the effectiveness and reduced pulse duration by 75% meaning that your thruster put out that much more flow? That is impressive. Did you replace the 12 volt thruster motor with a 24 volt motor?

 

[Hippocampus]

Yes need separate batteries for thrusters load test them first. If that’s ok then voltage drop test when in use. If that’s ok it’s the thruster itself or something with prop or tunnel. You can get minor movement or misalignment which will drop effectiveness

 

[HeadedToTexas]

Many discussions on why not to use house bank as starter batteries. Often I have said my preference is to have windlass on the Start battery while the engine is running.
Line loss and the fact that house banks usually do not output a continuous starter load (I consider a thruster as a starter load) from two feet let alone 30 feet away on 2/0 cable.
You see water flow comparable to a garden hose instead of a fire hose as a result.

I have read those discussions from a perspective of battery life and charging rather than from the perspective of starter (or thruster) motor speed, but it makes perfect sense. Suppose my 75 Kgf thruster hypothetically spins its propeller at 200 rpm when the motor is getting 12 volts. Does that mean it only spins the prop at 150 rpm when the voltage drops to 10 volts due to line losses?