Tech Wiki

Autoprop Installation

Autoprop 1

by Bob Kovich, Big Dog #1424, Port of Sheboygan, Wisconsin

I have a slightly different take on the installation and operation of the Autoprop. I purchased an Autoprop in spring of 1999 and had my boatyard install it. They also ran into trouble when running the blades through the 360-degree swivel that they must do for reverse. The blades would hang up on the strut and refuse to rotate. They called Steve Armitage at Autoprop and was told there were two solutions to the problem.

1. Install a flexible Drivesaver between the engine flange and the propeller flange, which would extend the shaft out through the hull about an inch. This would give the Autoprop enough clearance to rotate freely. The problem with this solution is that every time you extend the propeller away from the cutlass bearing you increase the potential for vibration. Also because the Autoprop is about 3 times heavier than the standard Michigan Wheel three blade 15 X 9 propeller it was replacing, there could be increased stress and wear on the cutlass bearing.

2. Grind away at a portion of the bronze strut enough to allow the Autoprop to clear. The potential problem with this approach is the weakening of the strut and the catastrophic failure of the strut, propeller shaft and propeller. Despite the potential problems I choose option #2 and had the yard grind out enough of the strut to allow for 1/4 inch of clearance for the Autoprop. (See photos)

After one year of operation I find no problems with this approach. There is still plenty of support for the shaft and I don't have any vibration when motoring or sailing. There has been no appreciable wear on the cutlass bearing. The extra control and lower RPM when motoring was impressive but it is the change when sailing that really makes the Autoprop Pay off. In light air of 8-12mph true, I can see as much as a 3/4-knot increase in boat speed. Once the wind builds to 15+ I am moving pretty much at hull speed and the Autoprop becomes less effective.

You do have to get used to putting the transmission in forward, not reverse, to lock the shaft and allow the Autoprop to correctly feather into the water when sailing. I don't have any problems with the shaft rotating when locked in forward. It is fun to informally race some of my friends when the transmission isn't in forward and the Autoprop isn't feathering. Putting the transmission in forward locks the shaft and the Autoprop feathers, which allows me to pull away just like kicking into overdrive.

I will keep the group posted on the status of the bite out of the strut to see if there are any failures down the road but things are looking good so far into year two.

Autoprop 2

by Rick Hildahl, Attitude Adjustment, 1989 C-30 #5630, Ballena Isle, CA (SF Bay)

This weekend I installed an Autoprop on my '89 Catalina 30. I chose the route of adding the Drive Saver between my transmission and driveshaft instead of modifing my strut. I went this way mainly because I didn't want to haul out just to change props. I was able to swap them while free diving (one breath at a time!)

These are 8 benefits I received by using the Drive Saver instead of cutting my strut:

  1. No haulout necessary.
  2. No modification to hull or strut is necessary.
  3. Additional 1 inch clearance from strut gained by moving shaft aft.
  4. I also gained additional prop tip clearance from the hull.
  5. The engine/transmission are now electrically isolated from the prop and shaft (less electrolysis).
  6. The rubber bisket absorbs minor vibrations for smoother running.
  7. The Drive Saver will break before any other part of the drive system in the unlikely event the prop were to hit something and suddenly stop.
  8. Because the Drive Saver flexs, flange alignment is less critical.

After I gain more experience with this setup I can decide if moving the prop aft does create other problems. If it does then I can always undo this modification during the next haul out and then try notching the strut.

Autoprop 3

by Steve Ritter, Night Flyer #687

I installed an Autoprop just prior to my trip to the Bahamas and wanted to let you know my impressions and problems. It's unscientific and I really don't know a way to check the sailing performance increase, but I think I'm doing better than one kt difference in wind speeds of 5-10 kts. This was borne out by a 335nm passage from Man of War Cay to Fernandina Beach in 65 hrs, all but 14 under sail in light winds. My previous best was 72 hrs in a stiff breeze. Naturally, in winds above 15kts little speed increase was noted since the boat was approaching hull speed regardless. Under power, I'm getting about 6.7 kts at 80% of max rpm, and approach hull speed at max power. I'm very pleased!

There are some glitches, however. When I initially installed the prop, the prop would contact the cutless bearing strut when the prop reversed and the blades swung forward, so to increase clearance I installed a Drive Saver which positioned the prop 1" rearward, which was enough by 1/4". The only other problem so far is shaft rotation under sail above 3kts boat speed, which (naturally) gets faster at higher speeds. This occurrs regardless of whether the transmission is in reverse, forward, or neutral, and has a dramatic effect on boat speed since the prop won't fully feather if it's rotating. I'm presently using Vice Grips on the shaft to secure it under sail, which is obviously not suitable. I'll have to install a shaft lock which can be controlled from the cockpit before my anxiety level about the situation will be under control!

The people at Autoprop are excellent. My first prop lugged the engine, so they really hustled to fire out another smaller one before my trip, and basically said get the first one back to them when I could! As time passes, I'll let you know of problems with maintenance, fouling, etc. So far I'm ecstatic with the increase in performance!