Bow Thruster Problem Advice sought

AD23

AD23

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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.
Adrian
 
Usually yes. The thruster connects to a mini gearbox and that’s is water tight. Removing the motor does not least to water in he boat The pin is typically between the motor and the gearbox

Do bear in mind it sheared for a reason and that may require a lift !
 
Unlikely that the gearbox to motor pin (if it has one) has sheared - usually it's the prop pin or the prop itself that gets damaged,
 
Generally speaking with regards to DIY preventative maintenance

It’s not mportant to refresh the anode on the gearbox when the boats out of the water .
If you don,t then the thing corrodes .If that happens at the output shaft(s) , then the seal knackers and you get water ingress .
Symptoms are a rattle noise ever increasing as the gears rough up = eventually ceasing leading to shear pin # .
This happened to me with a QL VP type .If it’s an old ish boats there’s parts availablility issues which may end up you needing a whole complete unit .

Some like say Vetus have a oil reservoir as high up under the bed as possible.
Idea is a +ve pressure / head of oil so the direction of flow of fluid through the output shaft(s) is OUT .
Thus mitigating water ingress and above ^^ gear corrosion.
Now and agian remove the mattress and rummage about to find that reservoir - about the size of a jam jar .

Yes the internal motors can be removed to expose the top of the gearbox and the water tight through the hull fitting .
Here you will see the shear pin allready described .Just a couple of three bolts .

Obviously something like a bag or piece of wood in the tunnel may jam the prop(s) ,,and it may be a one off - tbo that’s wishful thinking I,am sorry to say .

Msg to everyone with a bow thruster - ck your oil reservoir :encouragement:
 
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With our Vetus in 2004-2007, the pin sheared a few times - something like a piece of wood, or similar caused it each time. You just dismantled it from the top down, and the pin was inboard through the shaft that drives the prop.
 
Many thanks to all for their comments and suggestions - I am very grateful that you took the time to respond to my call for help.
Adrian
 
When my Volvo Penta bow thruster stopped thrusting it was the plastic propeller that had failed rather than the shear pin.
 
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 (I have some pics but for some reason I'm not allowed to post attachments???) 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.
Thanks again to all who offered advice - you gave me the confidence to get this far!!
 
DiscoVolante said:
Like I said it's almost always the prop shear pin or prop that breaks first.
Click to expand...

You would think they would design the weakest link to be the one inside the boat, given that it's the easiest to get at, and saves lifting the boat out.

My Vetus internal shear pin was the one that sheared each time there was an issue - (cant remember if it was 2 or 3 times in 6 years).
 
Update and some questions:
I managed to get access to an underwater camera to inspect my bow thruster prop without lifting the boat. What I found was that the prop is still present and the nut holding it onto the shaft is also still in place. So now I think there is a real possibility that a shear pin has gone on the prop shaft and that I might be able to replace it in a couple of hours with the boat lifted in slings rather than taking it onto the hardstand (I'm an optimist!!). Can anybody answer some of the following questions, please;
(1) Does the Nobels bow thruster have a shear pin on the prop shaft?
(2) If so what is the spec of the shear pin (so that I can get the correct replacement before lifting the boat)?
(3) What is the spanner size for the nut that holds the prop on the shaft?
(4) What is the size of the split pin that secures the nut on the prop shaft?
If anyone can answer some or all of these questions and/or offer advice on the repair I will be most grateful.
Thanks in advance.
 
AD23 said:
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 (I have some pics but for some reason I'm not allowed to post attachments???) 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.
Thanks again to all who offered advice - you gave me the confidence to get this far!!
Click to expand...

Is it feasible to get a snorkel and mask and a waterproof torch. get down there and have a look while someone turns the shaft inside the boat ?
previous owner of my boat found a drinks can had jammed in there. Anything to save the inflated prices of lifts as far as I'm concerned.
 
Thanks hg2016 for the suggestion but the photo taken by the underwater camera showed that the prop is not impeded by anything.
 
AD23 said:
Thanks hg2016 for the suggestion but the photo taken by the underwater camera showed that the prop is not impeded by anything.
Click to expand...

Have you managed to spin the prop under the water? Do you feel resistance like it is trying to turn a motor? If not, and the sheer pin or woodruff key is in tact then I think it is likely that your problem could be below the water line. If your camera is of the video type, get someone to turn the shaft and look to see if the prop is turning at the same speed. But going back and reading your post It looks kike you have already worked this out. I'm sorry, but I cant help you with questions 1,2,3 or 4 on your previous post. I'm sure that someone will soon drop in and give you some answers.
 
Update:
I used the underwater camera to make a video of the bow thruster prop shaft and it showed that the shaft was not moving when the thruster was activated. This indicates that the problem is in the gearbox (and not a shear pin as I had hoped!!). Now I'll have to wait until the next haul out to dismantle the gearbox etc. I'll post an update here later in case it might be useful to someone else in the future.
Thanks to all contributors for their advice and support.
 
All the Vetus thrusters I've seen only have a prop shear pin - nothing internal from motor to gearbox.

To have a gearbox fail is very odd unless it's very old?
 
DiscoVolante said:
All the Vetus thrusters I've seen only have a prop shear pin - nothing internal from motor to gearbox.

To have a gearbox fail is very odd unless it's very old?
Click to expand...


Common issue see my post #4 - the shaft seals fail and there’s an ingress of water .
Coupled with neglect of refilling the oil reservoir or overheating as it cools water is sucked in then over time there’s an inevitability of corrosion = bang !

To the op is there some sort of +ve pressure gravity fed oil reservoir nearby ?

Of course a foreign body jamming the prop will fracture a shearpin(s) .
Problem getting parts as said .

To the Op you not mentioned anodes ? —— there’s should be one on the gearbox either under it directly attached or if a single wheel on the end of the prop bolt ?

Interesting to see the contents of the gearbox when opened .
 
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