I installed an H6 Autoprop on my 1984 Contest 48 in the spring of 1999. There were several things that prompted me to chose this model: The first being the article in Practical Sailor, which ranked the Autoprop as amongst the best compromise between fixed and feathering props. The second were the claims of increased cruising speed from the same engine
RPMs. Also, our boat had a terrible ‘prop walk’ towards starboard in reverse – we had provided hours of entertainment to those watching us try to dock
the boat up and down the west coast
of North America.
The Autoprop did indeed increase our cruising speed. With our fixed blade prop at 2,400 RPM
, we’d make about 6 knots. With the Autoprop at the same RPMs, we’d do 7.5 knots, a significant increase.
However, we did not experience any improvement in our ability to back up straight. The boat walks to starboard badly so we’re still providing the entertainment our dock
In April of this year, while anchored off of Manzanillo, I removed the Autoprop and replaced it with my original fixed blade prop. This is why:
The Autoprop requires annual maintenance
and this cannot be done in the water
. Either the boat has to be hauled or the prop removed. We discovered this the hard way once when we had a boat full of guests and one of the blades had ‘frozen’ in the reverse position, making forward progress very slow regardless of the RPMs. I had a diver remove the prop and after overhauling the prop and reinstalling it, Rutea moved as she had in the past.
A word about overhauling the Autoprop: It’s a relatively simple process that requires no special tools or skills. The only measurement the manufacturer specifies is the torque setting on the spanner nut that retains the blades. I did not use a torque wrench while rebuilding my Autoprop instead I just monitored the effort it required to turn the blade as I tightened the nut. I assumed that there should be zero free-play and that the nut should be tight yet the blade must be able to spin freely. This seemed to work fine plus I was able to approximate the torque setting specified.
needed to overhaul
the Autoprop are readily available from Autoprop or you can get most of the parts
from any local bearing supply house. I say most of the parts as I was unable to locate the lip seals
from anywhere other than from Autoprop. These seals
don’t have anything unique to their appearance, in fact, appear to be surprisingly inadequate for the job they have to do. However, at $50.00 apiece, there must be something special about them but what it is escapes me. I was able to purchase
the bearings for about $10.00 each and there’s two bearings per blade; one lip seal per blade. In the course of owning the Autoprop for 10 years, I overhauled it twice, averaging about 300 hours of motoring per year. The last time I overhauled it was during a haul-out in February of 2008.
In February of 2009, my wife and I took Rutea on a 4-month cruise
. While anchored off of Manzanillo, I dove the prop and found one blade to be very loose. I removed the prop and disassembled the loose blade. I found that the tab washer that locks the spanner nut had broken. The inside tab that indexes the washer to the stud had broken off, allowing the spanner nut to loosen. It was only a matter of time before the blade fell off altogether. I stowed the Autoprop in the bilge
and reinstalled my original fixed-blade prop.
In all fairness to Autoprop, the propeller
was due for service
. However, the design that allows this small, inexpensive yet absolutely critical part (the tab washer that’s obviously prone to failure) that is required to retain the blades on the hub, is poor engineering. I feel that there must be a more positive method for locking the spanner nut – a cotter pin, a set screw or something that won’t fail as easily as the tab washer.
I had a conversation with someone from Autoprop where I asked if they were aware of any blades being lost
. They said they were. This further supports my theory that while the Autoprop is a very clever concept
, there are refinements required to it’s manufacture before the product is suitable for installation
on a cruising sailboat.
Furthermore, according to a Segeln Magazine test http://www.propelspecialisten.dk/dow..._test_2008.pdf
the Autoprop created almost as much drag while sailing as did a non-rotating fixed blade prop. It also shows that the thrust in both forward and reverse is amongst the best of any prop.
After extensive research
, I have chosen a Gori 3-blade prop.
Fair winds and calm seas.