Bow thruster problems

Nostrodamus

Nostrodamus

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www.cygnus3.com
We have a Vetus bow thruster.
After a month in one port it seemed to be playing up.
The motor was turning as per normal but there was no thrust. I suspect there may have been growth after a month that was stopping the prop turning.
Eventually it seemed to free up a little and now works perfectly thrusting to port but although the motor sounds the same there is very little thrust to starboard.
I believe the prop in the tunnel is plastic and I was wondering if it had been damaged or deformed.
I cannot work out another reason why it should only partially work one day.
Anyone with more brains than I (which is everyone) got any suggestions?
 
Nostrodamus said:
We have a Vetus bow thruster.
After a month in one port it seemed to be playing up.
The motor was turning as per normal but there was no thrust. I suspect there may have been growth after a month that was stopping the prop turning.
Eventually it seemed to free up a little and now works perfectly thrusting to port but although the motor sounds the same there is very little thrust to starboard.
I believe the prop in the tunnel is plastic and I was wondering if it had been damaged or deformed.
I cannot work out another reason why it should only partially work one day.
Anyone with more brains than I (which is everyone) got any suggestions?
Click to expand...

sheer pin broken
 
Nostrodamus said:
I can look... its knowing just what I am looking for!!!!
Click to expand...

Should be pretty obvious if it's an obstruction and if a shear pin had gone props. would be free to rotate. Symptoms don't really indicate a shear pin problem.

I'd pull the fuse or better, disconnect the power feed to the bowthruster before going near it. Think of it as a large mincing machine, not good if it starts with your arm inside the tunnel.

I have a max-power unit and the props look pretty symmetrical to me. Seems logical that they would be, so should work equally well in either direction and failure of one prop. wouldn't result in zero output from one side. I'd agree that the most likely cause is something caught on one prop. and being either blown out or sucked in and blocking the system.
 
If the screws that hold the prop to the hub are not fully screwed in the in one direction the prop would move away from the shear pin and loose drive the other way the prop would move onto then shear pin and be held there by the thrust of the prop

The screws are long self tappers in plastic so could be partly striped.

Unlike the max-power the vetus only has one prop no two as the max-power
 
Hi Mark,
We have the same bow thruster and had a similar problem, but ours was just after the anode had been replaced.
I doubt the shear pin has gone from your description, but if you have replaced the anode it is possible the prop has not been fully seated on the shear pin. The pin is located through the shaft and the prop pushes on to the shaft but has a "C" shaped slot in the plastic to locate over the shear pin. When you fit the prop it can feel as though it's located okay but is just sitting on the pin rather than being fully pressed home. You can even tighten up the locking nut and it still does not fully "home". When you put the prop on make sure you feel it click fully home before tightening the locking nut. You will have to remove the prop to get at the anode by the way.

As advised above, make sure the motor is isolated!!

We are still sitting in Cartagena, will be heading to the Baliaric's via Torrevieja and Alicanti in a week or so.
 
Networks and the others,
Thank you for the replies. We are looking at getting hauled out shortly so I will be better able to look at the problem. I just didn't want to get on the hard and pay money for it to sit there whilst we wait for parts.
At least I now know some of the things to look for. I am fed up of turning to port all the time. (should have gone the opposite way to Dylan).
Networks. We are planning on spending the summer in the Balearic's and winter in Scilly. Hopefully we can meet and compare bow thrusters.. over several beers of course.
 
Rogershaw said:
If the screws that hold the prop to the hub are not fully screwed in the in one direction the prop would move away from the shear pin and loose drive the other way the prop would move onto then shear pin and be held there by the thrust of the prop

The screws are long self tappers in plastic so could be partly striped.

Unlike the max-power the vetus only has one prop no two as the max-power
Click to expand...

Makes perfect sense and actually sounds even more likely to be the cause than a blockage. You should be able to diagnose by feeling the prop moving on the shaft if you push or pull and also try to rotate it. I'd forgotten that some makes only have one prop. :D

It will be trickier to fix when afloat as it won't just involve cutting something caught on the prop. It's a pity bowthrusters are fited at the narrow pointy end (well they are Errr. bow thrusters). I remember someone fixing the prop. on a smaller boat by putting a case of beer in the bows and having a party. It didn't take long for the stern to lift enough to reach the propeller. Unfortunately, you have a much larger boat and there's a lot of buoyancy at the stern so might need 2 crates of beer to get the party started (plus a rugby team carrying a Mini or even two :().
 
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