Autoprops and revs


ianjenkins1946 <ianjudyjenkins@hotmail.com>
 

I wouldnt rush to give up the Autoprop. Ours is no. AP 3294LH, which was recalled for a new locking plate so we fitted the fixed prop to take us from the Caribbean to Ecuador, involving 6 days of motoring in the Pacific.Unless you put two Amels side by side with the different props its impossible to be sure which gives the better performance but we certainly felt the Autoprop had the edge under power and clearly has less resistance under sail.
We are in Brazil at the moment , between Santos and Rio, good motoring country as there is no wind here. Yesterday we did a little test. Bear in mind that Pen Azen is in full cruising mode, including a 15hp outboard,4 anchors, 500m of shorelines,every locker full to overflowing, 600l water , 350 fuel plus 100l in jerry cans in the lazarette, which also holds the second dinghy whilst we were towing the rib with a 2hp attached.Bimini was down but we had sun awnings up, covering both booms. With minimum wind, (4 knots apparent on the beam), we achieved these knots at these revs
1500--- 5.9
1600 6.0
1700 6.4
1800 6.8
1900 7.1
2000 7.4
2100 7.7
2200 7.8
2300 8.0
2400 8.2
2500 8.3
2600 8.5
2700 8.6
2800 8.7

In each case we took a conservative figure for the speed, taking the first decimal pint, so that if we were doing, say, 7.27 we recorded 7.2. Our top speed was 8.89, the pull of the rib making it inconsistent.
These figures are marginally down on the same test conducted when the boat was new, but we must now have an extra ton of stores on board and we didnt have a rib to tow in those days.
Is the log accurate? In 25,000 miles we have never had any reason to consider it anything other than the most accurate log we have ever had on a boat.
To me , this suggests that certainly the standard Volvo and Autoprop are well matched and maybe the performance of the turbo is the most likely culprit.
Happy motoring! Ian and Judy Jenkins, Pen Azen, SM 302, Ilha Grande, Brazil.

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