I use a Bruntons Autoprop on a Bav 40 Ocean (2001) and I'm basically pleased with it - more on its performance than it's robustness.
I just had a full bearing kit service and learned that there's a dissimilar metal issue in the ball bearing race that allows the race to pit to the point that even with new bearings, one feels the flat spots through a blade as the balls roll past the pitted areas. I'm not too impressed with that design - a bit similar to the aluminium rudder housing issue.
I managed to collect some 80-kilo test fabric-covered nylon line between the sail drive anode and the brass back plate of the auto prop. It must have been there some time as it created sufficient heat to form the nylon into a solid disc the diameter of the anode. Getting the prop off for service required forceful effort, which is not usually the case with Nashira. Inside the autoprop housing is a spline coupling that mates to the sail drive splined coupling employing a vulcanised rubber combination.
It appears the heat and tension of the nylon line may have created a torsion effect that when I removed the prop the vulcanised rubber twisted the spline out of centre position, which makes re-installation a low-odds proposition. I had to have the s/s spacer machined at 22.5 degrees to allow an inelegant mating on the drive shaft. Certainly this is not a permanent fix.
Back in the water today and I didn't notice any adverse vibration. My advice is that only Bruntons is able to replace the vulcanised rubber bushing... Sending the prop to the UK, repair and return shipping seems as if a new prop might be less expensive - and a hell of a lot quicker.
One would imagine that given my new understanding of the limitations I'd give Bruntons a miss on the next prop. But... I'll likely end up with an replacement Bruntons shortly. Why? Performance!
Today I wanted to test prop performance and selected a racing bouy as a reference and tracked toward the bouy at WOT of 7.4 knots into the 8-knot wind. When the bow came abeam the bouy, I brought the throttle to idle briefly and added full reverse power. The boat stopped in less than 1/2 it's length. I'm not an expert by any means, but that seems pretty good to me. Given the broad and high profile of Nashira, I have to keep 2.5 knots steerage way to keep her under control in any wind conditions going into the berth. Feeling secure that I'm going to be able to stop positively makes the Bruntons my choice.
Presumably, other props offer similar performance. For me, it's better the devil I know.
