Cetus bow thus tear

[Nigel Twigg]

Hi 

we have a Venus bow thuster that has stopped working.

we have power to the thuster confirmed with a volt meter.

the sound the motor makes is high pitched like it is not engaging with the prop.

we have changed the shear pin between the motor and the gear box.

we can spin the propeller by hand through the weed hatch but this dose not turn the spindle on the top of the gear box. If we turn the spindle the prop dose not turn.

 

Is the gear box broke?
Is there a second shear pin on the prop that we can’t get to in the water.

 

Can anyone help, I don’t know what else I can check ?

[matty40s]

You need a new leg.

 

Example only, please ensure that you order the correct one. 

 

https://www.vetus-shop.com/lower-unit-compete-for-vetus-bow-thruster-75kgf-p-3014.html

 

Edited August 26, 2023 by matty40s

[Tractor]

Lift the motor, by releasing the four bolts which secure the motor flange.

Check the the drive coupling is secure.

 

[Nigel Twigg]

Hi Tractor I’ve lifted the motor and I’m left with this, with 2 bolts. I take that the two bolts will hold the leg and the prop. I don’t want to remove the bolts if the  leg a prop fall in the tube. 
 

The motor turns Ok and the shear pin is fine .

The bow thuster is old it’s a Venus 50kgf. I’m not sure wher I would find the drive coupling on my model 

[Tracy D'arth]

1 minute ago, Nigel Twigg said:

Hi Tractor I’ve lifted the motor and I’m left with this, with 2 bolts. I take that the two bolts will hold the leg and the prop. I don’t want to remove the bolts if the  leg a prop fall in the tube. 
 

The motor turns Ok and the shear pin is fine .

The bow thuster is old it’s a Venus 50kgf. I’m not sure wher I would find the drive coupling on my model 

It will but you fish it out via the hatch.

Why not just not use the BT and enjoy cruising without one like most boaters?  Will save you lots of money.

[Nigel Twigg]

Yes think that’s a good idea, just wondered if it was a quick fix but looking like it could be the foot that’s expensive 

[Sea Dog]

Struggling to recall if there's  a shear pin through the prop itself, or if that is just a drive pin?

[Tony Brooks]

5 minutes ago, Sea Dog said:

Struggling to recall if there's  a shear pin through the prop itself, or if that is just a drive pin?

 

I don't know the details, but we have had rubber bush drives on OB props for years and eventually they do slip and not drive.

[magnetman]

The prop according to Vetus is this. 

 

Where does the pin go? 

 

https://webshop.vetus.com/storage/SET008920000_7.webp

 

 

 

 

[Nigel Twigg]

Thanks for the advice everyone.
I will undo the two bolts and take the foot and prop off through the hatch and have look if there is a drive pin or shear pin. 
I’ll come back with some photos if I’m struggling. 
 

[Thames Bhaji]

I might have missed something here, but it looks like the boat is in the water and if you remove those 2 bolts to let the leg drop into the tube there’s nothing keeping the water out anymore is there? 
 

You should be able to remove the prop from the leg through that hatch using a Philips screwdriver - it’s tricky but can be done. I’ve done mine at full arms-length while in the water so via that hatch would be luxurious! If you can do that you’d be able to tell whether the gears in the leg have gone, or whether the prop is free-spinning on its spindle for some reason. If it’s like the one in the photo then I don’t think the pin would shear as it’s steel. It might shred the plastic of the propeller until it spins freely, or if the prop has been able to come forward from its proper position then I think the pin wouldn’t be engaged anymore. 

Edited August 26, 2023 by Thames Bhaji

[blackrose]

11 hours ago, magnetman said:

The prop according to Vetus is this. 

 

Where does the pin go? 

 

https://webshop.vetus.com/storage/SET008920000_7.webp

 

 

 

 

 

The shear pin goes through the spindle on the prop shaft and locates in a recess on the other side of the prop in your picture.

Edited August 27, 2023 by blackrose

[Nigel Twigg]

Yes good point I was worried about taking those bolts out.

I will try taking the prop of first via the hatch. 
The propeller is spinning very freely, there is no resistance there. So it’s either the foot or a problem with the propeller. 
it will be coming out for blacking in the spring so may be a job for then if we can’t solve it in the water. 
 

[magnetman]

 

 

40 minutes ago, blackrose said:

 

The shear pin goes through the spindle on the prop shaft and locates in a recess on the other side of the prop in your picture.

Thats a good picture as it establishes that there isn't a rubber bush drive as Tony Brooks suggested. Is that in fact a shear pin or a drive pin? 

 

Thames Bhaji in their post above seems to imply that it is a drive pin. 

 

 

17 minutes ago, Nigel Twigg said:

Yes good point I was worried about taking those bolts out.

I will try taking the prop of first via the hatch. 
The propeller is spinning very freely, there is no resistance there. So it’s either the foot or a problem with the propeller. 
it will be coming out for blacking in the spring so may be a job for then if we can’t solve it in the water. 
 

 

I can't believe the interior parts of the leg  would be weaker than the propeller blades. Surely the blades or a pin would go before any internal damage occured to the gearbox from a propeller foul. 

 

I wonder if as Thames Bhaji has suggested the prop is loose and has come away and perhaps the drive pin has dropped out or is not engaging. 

 

I reckon thats what it is. Loose propeller. 

 

How or why I don't know but if its just two self tappers holding it in place perhaps it can vibrate loose over time? 

 

removed as wrong. 

 

So the plastic two piece end cap is what keeps the propeller in place by clamping into the groove in the end of the shaft then two screws to secure it to the propeller. 

 

 

 

 

 

 

 

Edited August 27, 2023 by magnetman
edit to remove incorrectness

[Sea Dog]

12 hours ago, Tony Brooks said:

 

I don't know the details, but we have had rubber bush drives on OB props for years and eventually they do slip and not drive.

I've done a new Vetus prop like the OP has and it's definitely a pin (as a later photo of the kit confirms), but whether it's a solid drive pin which won't be the issue or a  weeker shear pin which might be the cause I'm not sure.

[magnetman]

I know someone with a dual prop bow thruster and he lost all the blades off both props when a rope was ingested. It stripped everything. 

I was surprised. It was a good quality thruster not sure which make. 

 

One would expect a shear pin there but perhaps with the awkward positioning it is a drive pin. It still could break. 

 

 

 

 

[blackrose]

57 minutes ago, magnetman said:

Thats a good picture as it establishes that there isn't a rubber bush drive as Tony Brooks suggested. Is that in fact a shear pin or a drive pin? 

 

It's both - but it doesn't always shear.

 

I took the prop off mine once while I was in a dry dock to inspect the leg and found the pin was bent on both sides in opposite directions making it impossible to remove and replace. In the end I had to take the guard off a 4" angle grinder to get it into the tunnel and cut off one of the ends of the pin flush with the prop shaft. Then I clamped a pair of mole grips onto the other end and tapped the grips with a hammer to remove the pin.

Edited August 27, 2023 by blackrose

[pearley]

In our old boat a piece of 2 X 1 managed to get through the grill and snap one blade off the prop. Neither the shear pin or drive pin broke.

The drive pin is fitted into the shaft first, with the hole needing to be horizontal or it simply falls out. The prop then fitted so the cutouts shown locate over the sticking out bits of the pin. Then the two white bits of plastic are located over a grove in the shaft and pushed together and secured with the screws.

I did mine out of water. Wouldn't want to try it through a weedhatch.

[magnetman]

ABCstore.co.uk

https://www.abcstore.co.uk › Bow-t...

Bow thruster shear pins & misc spares

 

Vetus electric bow thrusters have a drive pin located behind the propeller, which is designed to fracture if the propeller becomes jammed by debris, .

 

 

So it IS a shear pin. 

 

Hopefully that'll be it then. Broken pin. 

 

 

ETA I see Blackrose already pointed this out. 

 

 

 

 

I suppose the designers had it in mind that if you are using a bowthruster your boat may be in a compromised position so you don't want a shear pin which breaks too easily. 

 

 

[blackrose]

3 minutes ago, magnetman said:

So it IS a shear pin. 

Hopefully that'll be it then. Broken pin. 

 

 

Yes that's the most likely thing, or a bent pin and mashed up recess on the back of the prop.

[Nigel Twigg]

Thanks everyone for this advice.

We have owned our 57 foot narrow boat since March this year, it’s a live aboard and we are new to boating. Learning as we go along, so this advice is great, from people who have hands on experience.
I’m reluctant to try and fix it in the water, as pearly suggests may be a step too far so we will probably wait till spring when it is out of the water for blacking. 

[Sea Dog]

1 minute ago, Nigel Twigg said:

I’m reluctant to try and fix it in the water, as pearly suggests may be a step too far so we will probably wait till spring when it is out of the water for blacking. 

Well, of you're desperate to fix your bow thruster, it's probably gonna do you good. If you really don't need a bow thruster, it'll be a handy extra tool once it's recommissioned. 

[Nigel Twigg]

Yes Sea dog it’s broke so can’t make it any more broke🤣 and might be good experience for me. I’ll let you know how I go on. 

[blackrose]

30 minutes ago, Nigel Twigg said:

I’m reluctant to try and fix it in the water, as pearly suggests may be a step too far so we will probably wait till spring when it is out of the water for blacking. 

 

I don't mean to be patronising but just make sure you buy a new prop and shear pin before coming out the water because if you're only out the water for a week you and you wait to order it you probably won't get it delivered in time. If you find you don't need it just keep it as a spare.

[Nigel Twigg]

Great suggestion thanks blackrose I’ll do that. I’m also considering using a underwater go pro to help with the fault finding