Sluggish bow thruster

scubaman

scubaman

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Recently the bow thruster has become sluggish. It operates on both directions with very limited power, occasionally giving short more powerful bursts. I haven't used it much so only now started to look into it. Obvious thing to check would be the propeller to see if there is anything restricting it from spinning, but I'm in a marina and don't fancy taking dive in here.

The power comes from domestic batteries in the back of the boat. I measured voltage at the bow thruster and it was 13,6 V ish dropping below 10 V when operating the thruster. Measuring the same from the battery terminals showed around 11,3 during operation, so there seems to be a good volt and a half missing at the thruster.

Is this to be expected considering the long run of cables to the bow or is it more likely to due to corroded terminals, etc? Terminals at the batteries look good as do those in the heavy duty 12 V box. Also, connections looks clean at the bow thruster end.

Investigating the propeller will have to wait until our next stop.

Any thoughts most welcome.
 
Did you open up and have a look at the internal parts of the motor, K? Any rust?
The fact that you get occasional more powerful bursts would make me fear that there's something giving up inside the motor.
In fact, I can neither imagine how that could happen if the electrical connection were bad, nor with a knackered prop.
 
My t40 needed a new motor. It ran slower and slower. Boats.co.uk replaced under warranty. Prior to that I had done the end to end electrical etc which was fine.

I suspect it actually needed new brushes
 
Hmm, doesn’t sound good. Do you know if the brushes can be replaced? Or if the thruster can be removed with the boat in the water (it looks as if it could)?
 
It does sound like you are measuring volts drop over a long run of cable, but since this is a new phenomenon, it is possible that either the batteries are not putting out the cranking amps you need or you could have a disconnected brush or poor connection within the motor. Also worth bypassing any battery switch in case it has become high resistance too. Bow thrusters should be connected to a starting battery as it is basically a starter motor that you are running, so high amps required.
 
scubaman said:
Recently the bow thruster has become sluggish. It operates on both directions with very limited power, occasionally giving short more powerful bursts. I haven't used it much so only now started to look into it. Obvious thing to check would be the propeller to see if there is anything restricting it from spinning, but I'm in a marina and don't fancy taking dive in here.

The power comes from domestic batteries in the back of the boat. I measured voltage at the bow thruster and it was 13,6 V ish dropping below 10 V when operating the thruster. Measuring the same from the battery terminals showed around 11,3 during operation, so there seems to be a good volt and a half missing at the thruster.

Is this to be expected considering the long run of cables to the bow or is it more likely to due to corroded terminals, etc? Terminals at the batteries look good as do those in the heavy duty 12 V box. Also, connections looks clean at the bow thruster end.

Investigating the propeller will have to wait until our next stop.

Any thoughts most welcome.
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prop and tunnel fouling make a big difference. Doesn't have to be a restriction on spinning the disrupted flow makes a huge difference.

I have the sidepower thruster which has twin props. This was a mistake as it is tricky to get the prop off in the water and getting the prop off is the only way to clean the back side of the blades and the middle section of tunnel.

11.3V sounds low to me at the battery end. That is with engines running I take it? I wonder if one of your batteries is on its last legs dragging the bank down. Is starting more sluggish than before?

You won't have voltage drop in the cables any more than you had before. Any voltage drop will be at connections. Clean and remake them both ends.

You could rig up a local battery with heavy duty jump leads (in parallel with the feed from the back of the boat) as the final test before concluding it is the motor.

edit ps i agree with MarkDJ too I took a call mid typing so had the window open a while and didn't see what he wrote.
 
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I doubt fouling will be the issue, since you only relaunched a couple of months ago. When this issue arises with one of our workboats which is a heavy use “thruster”, 90% it’s a failing battery.
 
scubaman said:
Hmm, doesn’t sound good. Do you know if the brushes can be replaced? Or if the thruster can be removed with the boat in the water (it looks as if it could)?
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Yes you can Remove without taking from the water. It bolts to a gearbox. It is HEAVY!!!

I assume that you can change the brushes on any motor of size. Mine was just running about half speed and did almost nothing !
 
Did some further testing today. First off, the domestic batteries are only one year old, which of course isn't to say that they couldn't be failing, so I swapped the batteries around and tried with the other pair, but the result was no different. Btw, the harbour captain kindly popped into the boat and did some testing of his own. His assessment was also dying batteries, hence my test.

Cranking has been fine with both engines (the other is fed off the domestic batteries, the other has a dedicated battery) and I have no other reason to doubt their condition.

There is noticeable black dust on the surfaces of the bow thruster, whether this is normal or not, I have no idea.

I still would like to have a look into the tunnel, just in case there isn't anything tangled around the prop, but am starting to lean on the motor needing fixing/replacing. When operating the thruster, the lights in the forecabin dim noticeably. Intuitively, to me this supports the theory of a restricted prop.

A dedicated battery next to the thruster would be a good idea in any case.

There is a Sleipner installation partner close by, I'll contact them in the morning.

Thank you for all your input so far!
 
I had a sluggish bow thruster action earlier this year with a few surges apparent. I was quoted about 1,000 plus vat for new motor, but found this guide online and thought it was worth a try.

https://www.imtra.com/Collateral/Documents/English-US/Products/Guide_for_checking_motor_brushes.pdf

One can of compressed air later and a couple of hours work (max) and blowing out a load of dust, the bow thruster was back in place and has been much better since and seems back to normal operation.
 
Thank you Dan! That's a good find and very interesting. At the end it's says that the typical operating voltage at the thruster is between 9,5 and 10,5 volts. This is where my voltage sits, so that in my view confirms that the batteries are fine.

There's something to do for the rainy day tomorrow.
 
Could I ask your views on one further thing before I start dismantling the thruster.

If the brushes were worn and the power output was down due to this, would this be likely to affect the operating voltage, ie. less power draw -> higher operating voltage?
 
I had a similar experience last year. I dived in to clean and check the prop, no problem. I tested the batteries cold cranking output, no problem. Connected to a portable battery pack, didn’t help. Cleaned the dust, checked the brushes (which were remarkably easy to access :encouragement:) in the end I determined that the motor must be knackered (even though it was a nearly new Quick unit). The technician agreed, changed the motor under warranty and so far (touch wood) it’s been perfect.
By the way, my dedicated bow thruster batteries are right next to the motor as it the stern thruster’s.

Ps there are rudimentary fault finding lights on the thruster control box. But they merely indicate the problem rather than isolate the cause.
 
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My thruster has a high current solenoid switch . The contacts on these can become burned which affected the thruster power on my friends boats with the same thruster.
 
My thruster did the same and was hardly working at all. It got taken apart, cleaned up and put back together again with no new parts and works fine now. It had just accumulated a load of dirt and crud over the years.
 
Result! Encouraged by your pointers and the excellent pdf Dan linked to, I decided to take the bull by horns and remove the thruster for further inspection.

It turned out that 3 out of 4 brushes were firmly stuck in their holders. Following the instructions in the pdf, I removed them one by one, carefully sanded and cleaned the surfaces and put them back. I also purchased some compressed air cans to blow the dust away. Don't know if this made a huge difference, but can't have hurt either.

Put it all back together and hey presto, the familiar rattle was back!



I was feeling rather pleased with myself, but I wouldn't have gotten this far without your help. So big thank you to each and everyone of you for taking the time to contribute! A glass is raised to you. :encouragement:

Edit: one thing to add is that the carbon dust is a bugger to clean off. I setup workshop on a large cardboard sheet but the very fine dust is easily blown about and sticks very hard even on the clean fiberglass.
 
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Good to hear that the clean up seems to have worked, like me you are probably glad of spending a couple of hours to do this rather than spending £1,000+ on a new motor!!
 
Dorset Dan said:
Good to hear that the clean up seems to have worked, like me you are probably glad of spending a couple of hours to do this rather than spending £1,000+ on a new motor!!
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I am indeed. Was already searching for resellers. Now I just have to think what to do with the money I saved .
 
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