Bow Thruster Question

[Theresamarie11]

Hi, I have a bow thruster question. We didn't really use it much last year (our first) because we trailered, but this year we're using a slip and sometimes have a good cross wind.

I'm finding that after two, 5 second bursts of the thruster, the performance seriously degrades to where it seems to be hardly working. I don't have a dedicated battery and not sure which battery it runs from (starter or house). The batterys both seem fine and strong for other uses (starting, etc).

The thurster is a lewmar 140TT 2.2Kw with 92 lbs of thrust and a 200A fuse. Since the batteries are strong I don't think it's a battery issue but I will be checking voltage this weekend as we use it. The cables are huge and seem to be professionally installed. The prop seems undamaged and doesn't rub the tunnel.

Is there anything else to check?

When I read the manual it says it'll turn off automatically after 3 minutes of constant running and reading other posts from people who have one, it seems it should run a lot longer than a couple of 5 second bursts (a lot longer). I do understand that it's likely never going to be used for a minute or longer, but, we had need for more than 2 5 second bursts and it was clear it was barely working.


Thanks for any ideas.

 

[katricol]

Have you checked to see if it needs oil?

 

[Theresamarie11]

Have you checked to see if it needs oil?

Thank you for the suggestion, but don't know that it uses any oil for anything? It's an electric, and not hydraulic, motor. Are you thinking lubrication or did you think it hydraulic?

 

[BON DIA]

Check your thruster props for debris, ie plastic bags, rope, etc, causing loss of thrust. I wouldn't think there's any because it deliver full power initially but it never hurts to verify.

 

[Theresamarie11]

Check your thruster props for debris, ie plastic bags, rope, etc, causing loss of thrust. I wouldn't think there's any because it deliver full power initially but it never hurts to verify.

Thanks, I will check but like you said, since it works perfectly for a small while it seems unlikely something is lodged in there.
I think I'm going to take the hatch off in the cabin and see if the motor can be disassembled to check for any problems inside.

 

[Theresamarie11]

Check your thruster props for debris, ie plastic bags, rope, etc, causing loss of thrust. I wouldn't think there's any because it deliver full power initially but it never hurts to verify.

Thanks, I will check but like you said, since it works perfectly for a small while it seems unlikely something is lodged in there.
I think I'm going to take the hatch off in the cabin and see if the motor can be disassembled to check for any problems inside.

 

[tobnpr]

You say the cables are "huge", but that's all relative...
My bet is that the cables are undersized and there's a huge voltage loss problem.
200 amps is a lot of juice- two to three times what a windlass would draw.

Given that there is no dedicated battery bank forward, that's a very long run from your battery- especially if it's near the stern as I suspect it would be with an I/O.

You're talking about a conductor run in the neighborhood of 50'- handling 200 amps at 12 volts. The conductor sizing charts I have don't even go that large...

That's similar to locating a 2000 watt inverter up there- it wouldn't work. Too far from the batteries.

 

[Theresamarie11]

You say the cables are "huge", but that's all relative...
My bet is that the cables are undersized and there's a huge voltage loss problem.
200 amps is a lot of juice- two to three times what a windlass would draw.

Given that there is no dedicated battery bank forward, that's a very long run from your battery- especially if it's near the stern as I suspect it would be with an I/O.

You're talking about a conductor run in the neighborhood of 50'- handling 200 amps at 12 volts. The conductor sizing charts I have don't even go that large...

That's similar to locating a 2000 watt inverter up there- it wouldn't work. Too far from the batteries.

Thanks for the reply. It just begs the question why it works so well for some amount of time. I guess I'll to put my EE hat on and do some calculations as well as measure the voltage at the motor. I was just hoping someone in a similar situation could help.

 

[PlayDate]

Terri,

Sometimes your ears are the best diagnostic tools for a bow thruster problem. Does the sound dramatically change after 10 seconds of use? If it does then it is slowing down for a reason. If the noise level remains about the same......there might be a drive related problem. I have seen broken shear pins that behave as you describe.

John

 

[The Bill Collector]

Hi, I have a bow thruster question. We didn't really use it much last year (our first) because we trailered, but this year we're using a slip and sometimes have a good cross wind.

I'm finding that after two, 5 second bursts of the thruster, the performance seriously degrades to where it seems to be hardly working. I don't have a dedicated battery and not sure which battery it runs from (starter or house). The batterys both seem fine and strong for other uses (starting, etc).

The thurster is a lewmar 140TT 2.2Kw with 92 lbs of thrust and a 200A fuse. Since the batteries are strong I don't think it's a battery issue but I will be checking voltage this weekend as we use it. The cables are huge and seem to be professionally installed. The prop seems undamaged and doesn't rub the tunnel.

Is there anything else to check?

When I read the manual it says it'll turn off automatically after 3 minutes of constant running and reading other posts from people who have one, it seems it should run a lot longer than a couple of 5 second bursts (a lot longer). I do understand that it's likely never going to be used for a minute or longer, but, we had need for more than 2 5 second bursts and it was clear it was barely working.


Thanks for any ideas.

My batteries had to be replaced after 1 year. The battery combiner unit failed and killed the brand new batteries after 1 year.... And yes I have 1 OTT (?) cable.

 

[Theresamarie11]

My batteries had to be replaced after 1 year. The battery combiner unit failed and killed the brand new batteries after 1 year.... And yes I have 1 OTT (?) cable.

Thanks Bill, sounds like I have another thing to research. I'm not sure what a battery combiner does unless it's to make a 24 volt system from multiple batteries. I don't think my system runs 24V. This is a smaller boat with a pretty small thruster (92 pounds of thrust). But I will research, thanks.

 

[Theresamarie11]

Terri,

Sometimes your ears are the best diagnostic tools for a bow thruster problem. Does the sound dramatically change after 10 seconds of use? If it does then it is slowing down for a reason. If the noise level remains about the same......there might be a drive related problem. I have seen broken shear pins that behave as you describe.

John

John, thanks. It sounds perfect and strong for a while (couple or few bursts up to 5 sec each). Then all of a sudden (not decreasing slowly), it'll sound like it's got no juice and barely be working. It's not a slow decrease and the battery still shows strong on the meter. So I was wondering about some kind of thermal effect in the motor or maybe an increase in resistance at a contact somewhere when it heats up. In any case, I'll be crawling through it this weekend as well as trying to measure the voltage at the motor as it slows down. That should at least tell me if the problem is at the motor or power delivery.
I read the Lewmar manual and it talks about cleaning out carbon residue in the motor and I'm not sure prior owners have ever done this.. Not really sure what this causes in symptoms. I'm an EE, but nothing to do with motors... (semiconductors).

 

[tobnpr]

measure the voltage at the motor.

That's exactly where I would start; have someone else run the thruster while you have a DVM on the motor leads. If it's voltage drop as I suspect, that'll tell you.

 

[Theresamarie11]

That's exactly where I would start; have someone else run the thruster while you have a DVM on the motor leads. If it's voltage drop as I suspect, that'll tell you.

That's todays job...since it's raining, seems like a good thing to go do after housework is done

If it is the drop, I have more than enough room to put a battery up front, which I may do. I guess I can use the existing cables to run charge lines. One thing I am not clear about is how to vent the compartment where the battery is, and to where?? One place for the battery is in the same compartment as the thruster which is more or less sealed under a step that the table column goes into just before the berth. Seems like venting into the cabin isn't the greatest of ideas.

Thoughts on this are welcome.. in the event I have to go here.

 

[manfredr]

My 420 Sedan Bridge uses a separate Battery bank and 24V for the thruster for good reason. The current can reach 300A even with the 24V system. I assume you have only a 12V thruster. Smaller boat, but still huge currents and potential voltage drops. Your best bet is to get a dedicated battery for your thruster, as close to the thruster as possible. I doubt there is anything wrong with the thruster itself.
Best Regards,
Manfred

 

[mvoellinger]

Im no expert on the enclosed space batteries, but an Optima blue top doesn't vent under NORMAL conditions. If it gets cooked, it may still vent.

 

[Theresamarie11]

My 420 Sedan Bridge uses a separate Battery bank and 24V for the thruster for good reason. The current can reach 300A even with the 24V system. I assume you have only a 12V thruster. Smaller boat, but still huge currents and potential voltage drops. Your best bet is to get a dedicated battery for your thruster, as close to the thruster as possible. I doubt there is anything wrong with the thruster itself.
Best Regards,
Manfred

Thanks, I have been thinking 24V as well, I'll be less sensitive to the voltage drop and the current should be 1/2 for the same power. I know my on-board charge will support 3 batteries but not sure how I need to isolate the two batteries connected in series when they're charging. Something more to research.

 

[Theresamarie11]

Im no expert on the enclosed space batteries, but an Optima blue top doesn't vent under NORMAL conditions. If it gets cooked, it may still vent.

I suspect this is the ideal solution. If I can't figure out another solution this is at least part of the next step.

 

[Theresamarie11]

Well, was at the boat today. Besides rinsing out the tank after putting chlorine into it yesterday. I checked out the voltage on the thruster. Seems to initially start out around 12.8 volts (running) and after a few (5 or 6) 5-7 seconds bursts it went down to 10.8 volts and then starts to dog it. I was still connected to shore power at the dock. The cables are at around 3/4" in diameter (huge) and seems like it was factory installed as there is no indication that the finish in the area looks different from anywhere else (tube, etc). Very clean install.

It's being sourced from a single battery, the deep cycle battery number 2 and it has it's own switch and 200A fuse (doesn't go through the 1-2-both-off switch). I'd guess the length from the battery to the thruster is 20' or less.

Since it worked better when being fully charged, I suspect my habit of running on the deep cycle for several hours at anchor and then switching back to '1' starting battery and running off that until I dock isn't helping matters (i suspect my deep cycle is discharged a bit to start). So at a minimum I need to charge on both back to the dock.

My deep cycle is also only a 750 CCA (i don't see a AH rating but since it's not super heavy it's prob not too high-maybe 50ish) with 160 min of reserve (i guess that how many minutes at 25A before it hits somewhere around 10.8V).
This doesn't seem like a very big battery for the thruster.

I need to get back to documentation to see if there's any recommendations for battery sizes.

 

[Theresamarie11]

You say the cables are "huge", but that's all relative...
My bet is that the cables are undersized and there's a huge voltage loss problem.
200 amps is a lot of juice- two to three times what a windlass would draw.

Given that there is no dedicated battery bank forward, that's a very long run from your battery- especially if it's near the stern as I suspect it would be with an I/O.

You're talking about a conductor run in the neighborhood of 50'- handling 200 amps at 12 volts. The conductor sizing charts I have don't even go that large...

That's similar to locating a 2000 watt inverter up there- it wouldn't work. Too far from the batteries.

I just wanted to respond to your post more fully:
I just checked the lewmar table for cable sizes, for a 40' run AWG 1 is the correct cable size. 00 is good for 60'. Since the cable I measure is approximately 3/4 inch outside (including insulation) I'm assuming the conductor I can't see must be around .5" and that would make it at least AWG 00 (or bigger). After measurements today I believe my battery hasn't been fully charge and/or it's undersized for the job.