Re: Propeller recommendation


Martin Birkhoff
 

Hi Alex,
before we got our A54 we sailed a Reinke Super 11. This is an aluminium bilge keel design of German origin, overall length 39 feet. It was fitted with an Daimler-Benz OM 616 with 54 hp and a fix 3-bladed prop of 19" adjusted to this engine power. The boat had an extreme tendency to weather helm in gusts. Sailing performance was poor - we never set sails with less than 10 knots of wind. Standard speed on engine had been some 6 knots at 2200 rpm. 
After some research we changed to an Autoprop of 19" specified for our engine. Result: The boat was able to sail in light wind conditions down to 5-6 knots of wind properly, even downwind, sailing speed had increased 1 to 1.5 knots depending on sea conditions, the tendency of weather helming disappeared nearly, speed under engine increased to 6.5 kn at 2.000 rpm. Fuel consumption was reduced. Power going forward/backward was more or less identic. The side shift of the propeller going backwards was more or less similar to the fix-bladed.
Disadvantages: the Autoprop needs a certain amount of time to adjust its blades (or a strong push with the throttle) by manouvering. With the fix-blade prop the boat started immidiately when clutched in. With Autoprop it needed some seconds or a strong push as mentioned.
We sailed the Autoprop from 2000 to 2008 and later from 2010 until we sold the boat in 2016. Always pleased. 
Except once: In very rough but short seas in the LeMaire Strait we tried "to escape" to a small bay. We run the engine but steering against this seas we had no effect. First we thought to have lost the prop. So we decided to sail out of the channel to open waters and turned, figuring out the prop was still on the shaft and pushing. It must have been a rare combination of wave shape and intensity, boat movements, position of the prop on our boat etc. which caused this effect. We believe there never was sufficient time for the blades to adjust properly because of extreme fast changing conditions at the prop. We never had this again in all conditions we had to face later on, and we never heard a similar story from other owners of this kind of prop. 
After damaging the prop by hitting lots of wooden trunks in South American rivers we got a 4-blade SPW prop of 19". We chosed 4 blades to get more or less the same propulsion compared to the former Autoprop. The blades of this prop are connected and are turning their narrow sides to the bow while sailing. It´s not a foldable prop. 4 blades were needed because of the different design (blades are absolut symmetric). It was adjusted according to the needs of engine of course by limiting the blades rotation to to adjustable angles (forward and backward). 
Result: More or less similar than the Autoprop, but starting faster to move the boat on one hand, on the other hand less effective going backwards because the prop pitch was limited to a certain angle. We sailed these prop for some 15 month.
Our A54 is fitted with an Autoprop. It is performing absolut reliable. We cannot imagine to face the problem mentioned above with an Amel due to the props position in deep water behind the keel. 

Our conclusions outcoming of our experiences and experiences of friends is
- there is no good prop which is a cheap prop as long you avoid a fix-bladed one
- all props with moving parts need a certain specific amount of maintenance
- if you vote for a fixed-blade prop you have to know that your sailing speed will decrease and a weather helming can show up.     

Martin
Mago del Sur - A54#040

 

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