Bow thruster not producing much thrust

[HeadedToTexas]

$59 is quite a bargain for an AC charger, but I am seeing the same roughly $250 for a Blue Sea ACR, a Victron DC to DC charger, or a simple AC charger. We have both the engine alternator and the inverter/charger feeding the house bank with old L-Series automatic charging relays keeping main engine and generator start batteries charged.

Not surprisingly, Blue Sea recommends automatic charging relays and Victron recommends DC to DC chargers. The consensus here seems to be AC chargers. What is the best way to keep a bow thruster battery charged? Does it come down to preference?

 

[tiltrider1]

It comes down to location, preference and usage. In my case AC was already available. DC was a long ways away. Generator usage or dock power happens daily so AC had no short comings.

A boat that never visits shore power, uses solar over generator would prefer a DC method.

Because my house is 12v and thruster is 24v a DC to DC charger would make the most sense if I were to install a DC method.

I might still do that. For now I wanted to be out of the yard and functional. I may or may not be done with this project.

 

[HeadedToTexas]

A boat that never visits shore power, uses solar over generator would prefer a DC method.

I don't currently go many days without connecting to shore power, but I aspire to go much longer between connections. My sense is that DC is the way to go for me.

 

[Jeff F]

My sense is that DC is the way to go for me.

You have a robust 12v feed now to the thruster. It seems like a no-brainer to me to repurpose that line to supply power to a DC charger.

 

[Jeff F]

Lot to be said for a battery at the bow thruster.

Even more to be said for a 24 volt motor and 2 smaller batteries in series at the bow thruster.

Ted

My belief is that in the power range being discussed the performance difference between a 12v and 24v system will be negligible if the same pair of batteries is used and the cable run is short.

I get the need for higher voltage to support more powerful motors, but unless going bigger than 95kgf there is no requirement for more than 12v, and marginal benefits to going to 24v IMO.

What am I missing? I have a 24v stern thruster and a 12v bow thruster, both the same power and both with identical pairs of dedicated starting batteries. Both work perfectly.

 

[O C Diver]

My belief is that in the power range being discussed the performance difference between a 12v and 24v system will be negligible if the same pair of batteries is used and the cable run is short.

I get the need for higher voltage to support more powerful motors, but unless going bigger than 95kgf there is no requirement for more than 12v, and marginal benefits to going to 24v IMO.

What am I missing? I have a 24v stern thruster and a 12v bow thruster, both the same power and both with identical pairs of dedicated starting batteries. Both work perfectly.

IMO, an electrical circuit voltage drop is the sum of all its parts. My system went from 350 to 175 amps (12 VDC to 24 VDC). I seriously doubt that the two batteries is post #86 would spin the specific motor as well in parallel as opposed to other in series. From my inspection of the 12 volt and 24 volt motors, there was no difference except the actual windings. Between the brushes, solenoid contacts, electrical connections and everything else, I've got to believe 175 amps has less resistance going through the circuit than 350 amps.

Ted

 

[Jeff F]

Between the brushes, solenoid contacts, electrical connections and everything else, I've got to believe 175 amps has less resistance going through the circuit than 350 amps.

Agreed. 24v is better, all things being equal. But I don't have reason to think that increased resistance plays a material role in thruster performance or longevity, assuming the motors are appropriately designed and engineered.

I seriously doubt that the two batteries is post #86 would spin the specific motor as well in parallel as opposed to other in series.

I'm picking on you in part because you have well thought out decisions, but also because we use the same batteries and (I think) have the same thruster, except that mine is 12v. I haven't had reason to complain in 4 years of regular usage, but have little to compare to.

When it comes to power delivery, I can't see why drawing Xkw from a pair of batteries is any different whether they're wired in series or parallel. Apart from cabling loss it's all the same to the batteries, right?

 

[O C Diver]

Agreed. 24v is better, all things being equal. But I don't have reason to think that increased resistance plays a material role in thruster performance or longevity, assuming the motors are appropriately designed and engineered.



I'm picking on you in part because you have well thought out decisions, but also because we use the same batteries and (I think) have the same thruster, except that mine is 12v. I haven't had reason to complain in 4 years of regular usage, but have little to compare to.

When it comes to power delivery, I can't see why drawing Xkw from a pair of batteries is any different whether they're wired in series or parallel. Apart from cabling loss it's all the same to the batteries, right?

As no two batteries are exactly the same, one battery will experience higher amperage draw than the other. Failures on individual batteries within a bank while not common ,do happen. My guess (while I have no proof) is that at the half life point for starting batteries in parallel, there is a decided CCA (cold cranking amperage) difference between the two. In series, the amperage is more balanced.

You will notice that I specifically stated "starting batteries" as thrusters mimic the the draw of engine starting not low amperage draw over hours. In the picture posted in post #86, those original batteries lasted 8 years of heavy cruising. I attribute that life to in series batteries, lower amperage draw, and complete recharging after use.

Ted

 

[OldDan1943]

I moved bow thruster from the 4D start battery to the house bank, 3x4D. The Cummins main engine would shut down when the battery voltage dropped to about 10.9 vts. Gotta keep main engine running so off to to the house bank.

 

[Mountain man]

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.

View attachment 158822

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.

View attachment 158823

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.

That's a long run for high current application. You would be well served by installing a dedicated high amperage battery near the thrusters motor and find a way to keep it charged. I had a similar problem and used this approach with good results.

 

[grandbanksbayfield]

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.

View attachment 158822

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.

View attachment 158823

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.

Nine meters is the limit for the cable. It should be putting out a strong gush of water like a little outboard would.

 

[slowgoesit]

HTT, any resolution on your anemic thruster?!?

 

[HeadedToTexas]

Sorry guys, no resolution since the boat is now on the hard for the winter. I will measure volts and amps at the motor while thrusting once back in the water this Spring. My guess is that it will be quite low with the thruster running.

Realizing that my Cummins QSB will freak out if its start battery voltage drops below 12 volts, my plan is install a new dedicated battery in the bow right at the thruster. It will have a remote disconnect using the existing battery switch on the lower helm dash. It will be charged by either a DC-to-DC charger or an automatic charging relay.

 

[slowgoesit]

Okay, thanks for the update. It's just that some of us, with no lives, hang on a thread for resolution of posted problems! Best of luck with figuring it out this Spring, but, for what it's worth, I think you're on the right track with a dedicated battery.

 

[HeadedToTexas]

Thank you. Fingers are crossed!