SM2000 Bow thruster service


Mike Ondra <mondra@...>
 

We just completed servicing Aletes' bow thruster on the hard,
postings from this BB in our greasy hands. Yet upon completion we
have concerns about the water tight integrity of the bow thruster.

1. Fundamentally, is the penetration through the hull above or below
the water line when at rest in calm water? It appeared to us that it
was slightly below the water line, which conflicts with the concept
of dropping out the propeller/shaft assembly while in the water and
raises images of the boat with water where it should not be.

2. What is the seal strategy of the assembly? We found only the 2
closed cell foam rings on the shaft outside the hull that are
compressed against the hull opening when the bow thruster is fully
up. Other postings refer to up to 5 seals: 1 just behind the
propeller, the 2 we have around the shaft just outside the hull, 1 at
the hull opening, and 1 foam ring above the opening that would be
compressed when the truster motor is in the full down position.

3. The 2 foam rings outside the hull were adhered to the foot of the
shaft and the gear box and rode up and down with the shaft. It would
seem that if they were adhered to the bottom of the opening in the
hull they would seal to the shaft as well as be compressed when the
assembly was full up. However the friction of the shaft moving up and
down could wear the seal and/or pull the rings away from the
adhesive. Also that surface up in the bow thruster well is oily
(difficult to adhere to) and not very accessible for cleaning up
adhesive in preparation for a new seal.

4. The sleeved penetration in the hull, about 2" tall, had 2 grooves
in it. Is this or are there other provisions for a seal at this
location that would not move with the assembly and seal to the shaft?

5. We did not find any seals on the top side of the hull. Should
there be a foam ring on top to seal when the motor is down?

6. Is there a seal required behind the propeller and what does it
look like and do? The propeller shaft has a seal pressed into the
gear housing, and should that be replacable?

7. Again, what is the total seal strategy? Although we have had only
a very minor amount of water in our forward bilges, what we found
seemed to be profoundly not leak proof.

8. Our shaft assembly took a full quart of 90 wt oil instead of
the .3 liter described in the manual. Are there different models that
require different amounts of oil and may have different seal
strategies?

As this is a bi-annual service usually done out of the water, it
would be nice to be very clear about what is required to maintain the
water tight integrity of the boat!

Mike Ondra
Aletes SM200#240

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