Bow thruster problem and improvement

Eloi Bamberg

When i hauled out this fall, i cheked my bow thruster, i had to rebuilt 2 month earlier with an original kit from Amel. I always wondered what was the first part to fail. When i opened it i found cracks in the tefnol axis around the 2 holding pins!

Maxime from Sav@Amel sended me a new axel. The alignment of the pinholes was not corresponding to my gear. I just turned the axel 90 degres and drilled new holes. I believe the holes are not strong enough to take the force of the propeller, so i added a transversal axel, like the one of the propeller through the gear and the axel. I drilled a 5mm hole and to be sure of a tight fit i cuted the shaft of the drill as pin. It will be hold in place by the bearing. I spoke to Maxime of this modification who was very intrested and wanted to havd some pictures to discuss it with his provider. So maybe we wil have modified kits in the future.

SM2k 426  RedLion

George Green

Your modification, which looks good to me, brought to mind a parallel concept.
I would imagine that many SM bowthrusters have issues, not just from torque factors on the shaft, but from issues arising from lack of ,and or contaminated,  lubricant oil.
To remove and reinstall the SM bowthruster just to check and replace oil  is to me ,  a pain, for such a simple item of maintenence. 
I cannot see any engineering reason, as a qualified engineer, why an oil drain on the bottom and a flush fill point on the shaft could not be fitted.
I would be most interested in comments from the officionados of  the Amel community as to the practicality of my concept.

COCO,  SM 434


This could not be done in the water.

Bill Kinney


Maintenance of the bow thruster involves a lot more than just changing the oil.  You also need to change the seals on the shaft, and the process of removal of the bow thruster drive from the motor is also a key task.  If this is not done regularly, it can become an extremely difficult problem to solve.

An Amel needs to be hauled every year or two for maintenance work on the C-drive, even if the bottom coating is in good shape. The removal of the bow thruster when the boat is hauled for other routine bottom work is a pretty easy job. 

I have worked on a good number of Amel bow thrusters.  There are two problems that I see regularly.  
  • Bow thrusters that are extremely difficult to remove from the motor because they have been neglected, and left in place for far too long, and
  • Serious damage to the area around the prop shaft seal by people using screws to pull out the seals instead of properly disassembling the unit.
I think you’ll find if you are doing all the other work that is required to keep these bow thrusters running smoothly into their third decade, the time it takes to drain and refill the oil is pretty trivial, and not worth the risk of introducing two additional potential leak paths.

Bill Kinney
SM160, Harmonie
Le Marin, Martinique