Re: [Amel Yacht Owners] Speed vs. RPM

ianjenkins1946 <>

Hi Claude and others. Sorry to read of your experience. I dont know if my Bruntons Autoprop is different to yours ( Pen Azen is June 2000, no 302, standard Volvo/Perkins engine) but after nearly 2,000 engine hours, usually cruising at 1900 revs with a burst of 2,800 for about ten minutes every 6 or so hours, I cen happily get 8.6-8.8 knots on a calm day with a full cruising load aboard.
Twice I have had the revs stick at about 2200 in gear even though I was getting 2800 in neutral. On each occasion the boat had just been put in the water after several months ashore. All I did on each occasion was to keep revving up and down for ten minutes or so and the thing cleared itself.
So far, performance hasnt been affected by small amounts of sealife. On one occasion, in UK waters, I couldnt exceed 7 knots at full throttle and on diving I found the prop absolutely covered in barnacles between one and two centimeters across. I was amazed that it functioned at all.
I confess that I have never seen how high I can rev astern, but going ahead I have found nothing to complain of.
Bruntons claim that you should think of changing the bearings after 1000 hours or so. I think this depends on revs and the condition of the water you sail in. I will do it next time the boat is out of the water. Fair winds, Ian and Judy Jenkins, Pen Azen, Rio de Janeiro ( just about the dirtiest water you can find!)

From: Claude Roessiger <>
Subject: Re: [Amel Yacht Owners] Speed vs. RPM
Date: Wed, 8 Mar 2006 09:10:49 -0800 (PST)

I have had no end of trouble with this combination.
Amel aren't playing this straight with us. Every owner
I have met with the Volvo-Auto prop combination has
similar woes. I think the source of the trouble is the
prop. In reverse, do you get 3500 RPM? If so, it says
a lot.
This darned prop (and I have had unsatisfactory
exchanges with Bruntons, the maker) is unbelievably
sensitive. Unless it's polished to perfection, it
seems to just not give power. Expensive as it is, I
think to change it.
At full power the SM ought to give you 8 kts +.
I have had similar woes in waves as you describe, no
power, no speed.
The Volvo turbo-diesel is itself less torquey than a
straight old diesel as in the old Maramus,
bullet-proof engines.
This said, an 80 hp engine should do the job. I think
the prop is suspect.
If anyone has made a prop change successfully, it
would be good to know.
Claude Roessiger

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