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Bow thruster problem

Posted by AD23 
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Bow thruster problem
10 May, 2018 21:02
My bow thruster decided to go on strike last weekend! I can hear the motor spinning but there's no thrust, so my guess is that the shear pin has sheared. Unfortunately I haven't got a manual or any other documentation that might help me to install a new shear pin. One of the key questions is whether or not the shear pin can be replaced without taking the boat out of the water. The unit was installed circa 1996 and is a Technautic bow thruster but I cannot see a model or serial number anywhere. I contacted Technautic who were unable to help except to tell me that these units were supplied by Nobels. Nobels have not yet replied to my e-mail. If anyone can offer any advice about this, I will be most grateful.
Re: Bow thruster problem
11 May, 2018 14:16
I have some experience with a little sleipner bow thruster, so the answer may not be entirely relevant, but it's a pretty straight forward matter of taking off the covering and the pin should be quite close underneath. A straightforward job and no dry docking required. The pin usually goes after a bit of heavy handed operation, thrusters are disappointingly delicate, hence why I keep a couple of spares winking smiley
Re: Bow thruster problem
11 May, 2018 14:20
On most of bow thrusters the sheer pin is on the motor shaft you should be able to remove the motor while still on the water, if you are worried just loosen off the bolts a bit and see if any water gets in, maybe beach the bow just to be sure to be sure smiling smiley

Re: Bow thruster problem
14 May, 2018 09:13
Many thanks for the advice - I'll (carefully!) explore the possibility of repairing it while on the water.
Re: Bow thruster problem
17 May, 2018 13:24
Hi AD23
How did you get on with the Bow thruster problems you were having
Re: Bow thruster problem
18 May, 2018 08:53
Just back from the marina - here's an update.
I removed the motor from inside the boat and discovered that it connects to the gearbox with a woodruff key instead of a shear pin (it does the same job). It turns out that the woodruff key is not sheared (see pics attached) which means that the problem is further down and it'll have to wait until the next lift out. In the meantime I'll have to improve my boat handling skills!! For the sake of completeness, I should mention that the shaft connected to the motor by the woodruff key turns very easily and smoothly.
Re: Bow thruster problem
18 May, 2018 10:58
Hi AD23
Sorry to hear you didnt get sorted yet.
Can I ask did you check the motor is working correctly and one other thing you could try..... check the tube for blockages ie weed or twigs blocking the propeller.
Don the wetsuit and goggles and jump in and poke about, make sure you have someone with you for safety.
I had issues with my Bow thruster recently and it turned out to be the Brushes were burnt out and they had arked on the Armature and scored it badly, as they didnt offer enough pressure via the springs.
I removed the motor and filed the armature clean and true again and replaced the Brushes,
It is working fine now
I dont actually need a Thruster, as I have twin screws, but ocassionally use it in a tight spot, they do come in handy
Re: Bow thruster problem
20 May, 2018 08:43
Thanks for the suggestion. I know there's no problem with the motor - I can hear it spinning away when I try to activate the bow thruster.
I have a friend with an underwater camera, so the plan is to take photos of the prop and tunnell to see what's going on down there.
Re: Bow thruster problem
14 June, 2018 08:21
A friend of mine took some pics with an underwater camera (see attached) which show that the prop is still there as is the retaining nut. Being an eternal optimist I am now thinking that this might just be a case of replacing a shear pin on the prop shaft. If that is the case the repair could be carried out in a few hours with the boat still in the lifting slings rather than jacking her up on the hard stand. BUT I would need to have a replacement shear pin with me on the day - does anyone know what the spec is for the prop shear pin on a Nobels bow thruster? Also the size of the split pin holding the retaining nut? Thanks for any help you can offer.

Edited 1 time(s). Last edit at 14/06/2018 08:22 by AD23.
Re: Bow thruster problem
05 July, 2018 07:47
The underwater camera was used to make a video of the bow thruster prop shaft while the bow thruster was being activated and unfortunately for me it shows that the prop shaft is not turning. The problem must be in the gearbox (and not a shear pin as I had hoped) - I'll have to wait until the next haul out to dismantle the gearbox and see what needs replacing. I'll post another update with a few pics then.
Thanks again to all contributors for their suggestions/observations and support.
Re: Bow thruster problem
20 April, 2019 09:20
This story has a happy ending. Last week I took the boat out of the water and removed the bow thruster with the help of my ever willing nephew! When I dismantled it I discovered that the pinion gears are held on the vertical and prop shafts using roll pins and that the roll pin on the vertical shaft had sheared.
The shafts, pinion gears, seals and bearings were all in excellent condition. The gear box was still full
of oil. I replaced the roll pin (cost of 1 euro!), reassembled the gear box and filled it with gear oil and
it was ready to be reinstalled in the boat. Total time from start to finish of 4 hours.
For the benefit of anyone with one of these Nobels bow thrusters the following details are provided;
The fibreglass cover on my bowthruster says Technautic but it was actually manufactured by Nobels.
Both the vertical and prop shafts have woodruff keys instead of shear pins. The woodruff key on the vertical shaft can be accessed from inside the boat when she is in the water.
There are 4 grub screws which must be removed before the end caps on the prop shaft can be removed.
After the prop shaft has been removed the vertical shaft can be removed using a punch through the oil plug hole.
For extra strength I replaced the damaged roll pin and then put a smaller roll pin inside the new roll pin (known as a double roll pin).
If you need parts, motor, carbon brushes etc contact
Thanks to all who read and contributed to this thread.

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