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Subject: [worldcruising] Diagnosis Needed - Follow-up
From: John Bankside (john.bankside@XXX.XXX)
Date: Wed Aug 30 2000 - 02:25:40 EDT
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A few months ago I posted the cry for help below. This is just to thank
everyone who responded and let you know that the mechanic did resolve the
problem by machining 3-4 mm off the bearing, thus increasing the gap between
this and the hub of the prop. Quite why the problem should suddenly have
started in the first place is another question, although a friend has
suggested that some extra play may have developed somewhere - eg. the
gearbox - as he says, it would only have taken a 1 mm movement to have
created the problem.
My delay in providing this follow-up is due to the fact that I've been
keeping the boat in Amsterdam this year and I was only last week able to do
a proper test (14 hours motoring plus lots of manoeuvring in locks and
harbours!).
Thanks again everyone.
John
----- Original Message -----
From: "John Bankside" <John.Bankside@XXX.XXX>
To: <live-aboard@XXX.XXX>
Sent: Wednesday, May 24, 2000 6:08 AM
Subject: Diagnosis Needed Please
> I'd appreciate help on the following...
>
> I have a Yanmar 3GM30F engine and a fairly large (not sure what size)
> 3-bladed prop. I re-engined Callisto 3 years ago and the engine has about
> 300 hours on it.
>
> When cruising under engine on reasonably flat water, I normally run at
about
> 2300 rpm and get 5 knots.
>
> Last month I was motoring back to my home mooring and found that above
about
> 1900 rpm, there was a continuous grating/grinding type sound at the back
of
> the boat. When I reduced revs to 1800 or below, the noise disappeared and
> the engine sound was normal.
>
> I had not experienced this on the way out. The only thing that happened on
> the day was that I had to do a lot of moving in and out of forward and
> reverse to get myself out of a tight downwind spot in the small harbour I
> was visiting.
>
> Believing I'd got something wrapped round the prop, I had the boat hauled
> when I returned to my home harbour - but there was nothing round the prop.
> (As a footnote, the prop is protected by Callisto's long keel and I've
never
> had anything wrapped round it, so don't know what this would sound like.)
>
> I discussed the situation with the local mechanic (who has a very good
> reputation in the area) and he identified that there was a lot of play in
> the prop shaft - he diagnosed a worn or broken bearing.
>
> He replaced the bearing but the noise is still there. The mechanic is now
> theorising that the gap between the prop and the bearing (about 1.5 mm) is
> too small and, when under load, moving through the water, the prop is
> rubbing against the bearing, thus generating the noise.
>
> He is proposing that I need to have Callisto hauled again so that he can
> increase the gap - by reducing the size of the bearing.
>
> The only other piece of information I think I can usefully add is that the
> noise doesn't occur when I put Callisto in gear and run the engine at more
> than 1800 rpm while still tied up on the pontoon. So I guess there is
> something about load/moving through water in the problem.
>
> So ... help! I'd be very grateful for thoughts on this problem. Is the
> mechanic on the right track?
>
> All this hauling out is getting expensive!
>
> Thanks
>
> John
>
>
>
>
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