Intermittent Bow Thruster

I have a Nordhavn 43 with a Side Power SP95T bow thruster. last August, the drive leg was replaced with a sealed unit. We have been cruising down Mexico, and we are currently in Huatulco, preparing to cross the Gulf of Tehauntepec. A couple of weeks ago when we arrived in Ixtapa after an overnight cruise from Caleta de Campos, the drive leg failed to engage. The motor would spin in either direction, but no prop spin from the thruster. Later that morning in the dock, it worked fine. When we left the dock on tow different occasions, it worked fine. But when we returned, no operation. This is a pattern now - no operation after a cruise, but it works perfectly moments later. I have tried silly things, like stopping and starting the engine, resetting the breaker, etc. When we were in Acapulco attempting our first med-moor (not an easy task for a single screw with no bow thruster!), I repeatedly tried to engage it, and it finally did work. When we arrived here in Huatulco, no operation again. I am at my wit's end trying to figure out what could be wrong, and why it only fails after a long cruise. Has anyone experienced something like this before? Any ideas? Again, it doesn't seem to be electrical, and when it works, thrust is good in both directions.

Attached (I hope) is the TS guide for my Side power unit. Also check your oil reservoir. As these units use a flexible motor/shaft coupling engaging shouldn't be the problem....

OK, the PDF file exceeds the allowable limit. If you PM me an email address I will forward the file to you.

Good luck!

We have a similar thruster. Our "intermittent" problem it turned out to be caused by tired batteries. A few times, the thruster did not seem to operate properly and we tried to identify the cause. Then when most needed, the thruster packed in completely!! Replaced the batteries with 2 new 4Ds and problem solved. These thrusters draw up to 350 amps, so batteries need to be in good condition. If not the batteries (definitely check these first with a good load tester) then check/clean the carbon brushes and look for signs of corrosion at terminals/connections to the motor. If like ours, your thruster is in a water-tight compartment, then high humidity can do a number on the wiring connections.

Having read your post again, have you considered that the problem might be in the switches/controls and not in the thruster itself. Perhaps a loose connection after the breaker going to the thruster. Do you have a solenoid switch going bad?

So the motor runs, but no thrust? That sounds like a coupling between motor and leg, the leg itself, or the props slipping. Are you sure the motor is turning and props not turning? Not clear exactly what is happening.

Suggest you submit your problem to the experts:

questions@imtra.com

Go for the easiest fix first: start at the batteries and check their water, check the voltage, check the connections, follow the cables and check the fuses/breakers, check the connections at the solenoids, at the motor. Check them all for tightness and corrosion, if you take them apart, make sure they're clean and reassemble with dielectric grease. Spray some contact cleaner inside the helm switch and work it about.

I don't know how this particular system works. It obviously has a solenoid for the motor, does it have one for the transmission? Solenoids seem to be the main source of failure in these systems, look closely at them. There is probably 4.

Motor not running or running slow, often intermitent: likely lots of carbon build-up, worn brushes, stuck brushes (due to carbon) or a combination of these. Easy fix and you should find the guide on the Imtra site. They will also email you the relevant documents. We had this problem on the Tug.

Motor runs, but thruster prop doesn't engage: likely the shear pin. I've heard that sometimes the pin can break and get stuck in such a way that the thruster will still turn the prop intermitently, but have not seen it happen first hand.

If neither of these, most likely electrical - switch, solenoid, etc. Again, I'd contact Imtra. Their customer service is supposed to be excellent on the tech side.

Carolena said:

...the shear pin. I've heard that sometimes the pin can break and get stuck in such a way that the thruster will still turn the prop intermittently...

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Good idea to check. It sounds like a coupling issue so it's a good place to start.

Not that good a place to start if he's not hauled?

Xsbank said:

Not that good a place to start if he's not hauled?

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He's in Mexico!! He can jump in the water and check it!!

That's a foreign concept to those up in Vancouver, I guess.

Does the thruster work in one direction but not the other?? Is your "intermittent" for both port and starboard thrust?? Perhaps you have lost one of your two thruster props??

Xsbank said:

Not that good a place to start if he's not hauled?

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Depends on the manufacturer. Our bow thruster (Vetus), the "safety" or shear pin can be changed in the water. Disable the electric, unbolt and lift the motor. The shear pin is right there. You can turn the input shaft with a screwdriver to see if rotates easily and verify there are no obstructions in the tunnel and then convince yourself that there are no more obstacles and reassemble.

On our Sidepowers there are two shear pins. One is on the prop and the other between the motor and the gearleg. The gearleg one can be checked (and replaced) with the boat in the water by removing the motor.

Clever. Thanks for clarifying.

It's a Nordhavn: isn't the thruster hydraulic?

Aquabelle said:

It's a Nordhavn: isn't the thruster hydraulic?

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Usually smaller nordhavn's aren't equipped with the hydraulic package (Stabilizers, windlass, thrusters, emergency bilge pump, anchor wash, etc) although I think their are some 47's with it, but I believe no 40's, or 43's due to lack of engine room space for the equipment but I could be wrong.

Blender boy, I'm curious if you have pulled the motor to inspect the coupling and drive system? That seems the most likely culprit based on the advice here and from the Nordhavn Owners group.

If this thruster operates normally when it works - that is you hear the motor run normally, the thrust is good both to port and to starboard, but sometimes it just does nothing, then the cause is most likely an electrical problem. Other defects as suggested would most likely display other symptoms such as no thrust in one direction, harsh noises, etc. If it operates normally when it works, begin with the simple (hah ha!!) things like batteries, switches, wiring, solenoids. You indicated that the breaker does not go off, suggesting that there is no current overload as might be the case with a motor binding, bad bearings, or something jamming the system.

Ski in NC said:

So the motor runs, but no thrust? That sounds like a coupling between motor and leg, the leg itself, or the props slipping. Are you sure the motor is turning and props not turning? Not clear exactly what is happening.

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Yes, this is exactly what is happening. The motor spins, but no prop thrust, and this only happens after we have been cruising. Five minutes later at the dock, it works just fine. I have contacted Imtra, and they have provided me with a list of things to check, but they are mostly electrical. Since the motor operates correctly at all times, I don't think there is an electrical issue. As you noted, I suspect there is an issue with the coupling between the motor and the drive leg. But what I can't figure out is why the problem is so consistent - it always fails after a cruise, and always works before a cruise.

dwhatty said:

On our Sidepowers there are two shear pins. One is on the prop and the other between the motor and the gearleg. The gearleg one can be checked (and replaced) with the boat in the water by removing the motor.

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Imtra was skeptical that the shear pins could be the problem, but they sent me the troubleshooting guide anyway.

With the power off, I would hop in the water and check both propellers. Would check to see if they were tight on the shaft, and if the shaft could move in and out. Also, always good to make sure the tunnel is free and clear of anything that might make the props cavitate.

Ted

Engine room temperature? Try cruising with the bilge blowers on.

hmason said:

Engine room temperature? Try cruising with the bilge blowers on.

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Really??? I guess if your engine room was in the bow, Never seen a set up like that.

Had a similar problem after relaunching with new anti fouling. The props were binding on the paint buildup on the ends if the blades. The motor would run, but the props were not turning - there is a safety clutch as well as shear-pins, at least there is on the hydraulic Side Power that I have.
Fortunately, the boat was still in the travel-lift slings when I discovered the problem so lifted up again, pulled the props and scraped off the excess paint.

I don't know if this is helpful but there could be something intermittently fouling the props- maybe some fishing line. I have even seen a thruster bought to a halt by a fish jammed in the tunnel!

I've also just replaced a joystick which failed after 10 years. It was intermittent but an easy diagnosis because I have two stations and could just swap the joysticks.

someone suggested to me this...

"take a look at the flexible coupling and see if there is any sign of rubber dust around it.

Rubber expands when heated so if it is slipping it will heat up,"grab" and function until it cools off again and shrinks."

I trust his judgement...might be worth a look...