Does anyone have any info on the sailing specifics of an Autoprop? I have read conflicting advice regarding shifting into Reverse, Neutral, and Forward with an Autoprop. I know that my owner's manual states that the tranny should NEVER be sailed in forward, but beyond that I'm wondering about the characteristics of the Autoprop. 1987 C36 w/Universal 25XP. Thanks in advance.
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Jon W.
Autoprop
Tom, I went through this with an Autoprop and a Universal M25 and Hurth transmission. You are correct that the manual says never sail in forward gear. THIS IS WRONG WITH AN AUTOPROP! The Autoprop freewheels in the opposite direction compared to other props. The whole idea is that for the Hurth transmission, freewheeling in neutral is ok, but never let the shaft spin in gear. After watching my shaft spinning while in reverse I called the Autoprop Company and confirmed that forward is the gear that will prevent freewheeling due to the counter rotating design of the Autoprop. If you check the shaft rotation with the engine off, you will see that it locks in one direction and spins in the other. Shifting from forward to reverse just changes the direction to lock. Regardless of which prop you use, it really doesn't matter if it takes forward or reverse, as long as it locks. This will be the forward gear with the Autoprop. I also had verification of this fact from other Autoprop owners. Again, you can use neutral, but the Autoprop doesn't feather very well when it's spinning.
Tom, I went through this with an Autoprop and a Universal M25 and Hurth transmission. You are correct that the manual says never sail in forward gear. THIS IS WRONG WITH AN AUTOPROP! The Autoprop freewheels in the opposite direction compared to other props. The whole idea is that for the Hurth transmission, freewheeling in neutral is ok, but never let the shaft spin in gear. After watching my shaft spinning while in reverse I called the Autoprop Company and confirmed that forward is the gear that will prevent freewheeling due to the counter rotating design of the Autoprop. If you check the shaft rotation with the engine off, you will see that it locks in one direction and spins in the other. Shifting from forward to reverse just changes the direction to lock. Regardless of which prop you use, it really doesn't matter if it takes forward or reverse, as long as it locks. This will be the forward gear with the Autoprop. I also had verification of this fact from other Autoprop owners. Again, you can use neutral, but the Autoprop doesn't feather very well when it's spinning.
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Tom Soko
Thank You!!!
Jon, Thank you immensely!! You've cleared up what has been a huge mystery to me. It all makes perfect sense now. Tom.
Jon, Thank you immensely!! You've cleared up what has been a huge mystery to me. It all makes perfect sense now. Tom.
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Ernie April
Agree with Jon and more...
Hey, Tom-- For me, Autoprop ranks right up there with all-chain ground tackle and radar. What Jon said about locking in forward is correct. It keeps the blades feathered - otherwise (unlike feathering props) the passing stream of water develops a pitch which causes rotation. Unlike fixed props, the locked shaft never jams in gear. Even if left to rotate, the shaft never turns as rapidly as with a fixed wheel. There has been much discussion on the boards recently about Autoprop vs other folding or reversing-blade props. What seems to have been missed is that the big Autoprop advantage is self-pitching. Getting the correct pitch on other adjustable pitch props is a real hastle. With Autoprop its a non-issue in that pitch is infinately and automatically variable depending on RPM as well as boat speed through the water. This advantage really comes into its own when motor-sailing. Low shaft RPMs with water moving past allows the blades to take really big bites. It's amazing how much boost occurs. I almost never motor-sailed before having an autoprop, now I do it not infrequently because at low RPMs it really rather quiet and you can supplement the wind. No other prop behaves quite this way and so efficiently. Also in rough conditions, the blades constantly autopitch for maximum efficiency. I plotted RPMs vs speed both with my previous fixed blade and with the Autoprop under absolutly calm conditions. At about 1800 RPM, I get an addition 1.5 kts with Autoprop. It tapers back on either side to 1.25 kts at 1400 RPM and 2200 RPM. However, top speed (3800) is still 7.5 kts with either prop. At idle speed (800 RPM) I get about 2.5 kts vs 1.4 kts which I do not find too fast for docking. I prefer this speed because the helm responds better. Backing is not a problem. In fact, it is extremely powerful since the blades flip completely around. You just have to start to back with determination. Once backing, it goes straight as an arrow. Last summer I backed straight out of a narrow 100+ foot-long slip at the Newport Harbor Marina to everyone's amazement - including my own. The only disadvantage might be the price - but the increased efficiency at cruising RPMs and the increased range that a tank of fuel will provide will eventually pay for the difference. The best reference is the MIT Propeller Test Report - Autoprop will you a copy on request. Of course, the MIT engineers rated Autoprop on top. Ernie April (WindCatrcher, C-42)
Hey, Tom-- For me, Autoprop ranks right up there with all-chain ground tackle and radar. What Jon said about locking in forward is correct. It keeps the blades feathered - otherwise (unlike feathering props) the passing stream of water develops a pitch which causes rotation. Unlike fixed props, the locked shaft never jams in gear. Even if left to rotate, the shaft never turns as rapidly as with a fixed wheel. There has been much discussion on the boards recently about Autoprop vs other folding or reversing-blade props. What seems to have been missed is that the big Autoprop advantage is self-pitching. Getting the correct pitch on other adjustable pitch props is a real hastle. With Autoprop its a non-issue in that pitch is infinately and automatically variable depending on RPM as well as boat speed through the water. This advantage really comes into its own when motor-sailing. Low shaft RPMs with water moving past allows the blades to take really big bites. It's amazing how much boost occurs. I almost never motor-sailed before having an autoprop, now I do it not infrequently because at low RPMs it really rather quiet and you can supplement the wind. No other prop behaves quite this way and so efficiently. Also in rough conditions, the blades constantly autopitch for maximum efficiency. I plotted RPMs vs speed both with my previous fixed blade and with the Autoprop under absolutly calm conditions. At about 1800 RPM, I get an addition 1.5 kts with Autoprop. It tapers back on either side to 1.25 kts at 1400 RPM and 2200 RPM. However, top speed (3800) is still 7.5 kts with either prop. At idle speed (800 RPM) I get about 2.5 kts vs 1.4 kts which I do not find too fast for docking. I prefer this speed because the helm responds better. Backing is not a problem. In fact, it is extremely powerful since the blades flip completely around. You just have to start to back with determination. Once backing, it goes straight as an arrow. Last summer I backed straight out of a narrow 100+ foot-long slip at the Newport Harbor Marina to everyone's amazement - including my own. The only disadvantage might be the price - but the increased efficiency at cruising RPMs and the increased range that a tank of fuel will provide will eventually pay for the difference. The best reference is the MIT Propeller Test Report - Autoprop will you a copy on request. Of course, the MIT engineers rated Autoprop on top. Ernie April (WindCatrcher, C-42)
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Tom Soko
Also thanks...
Ernie, I also thank you for your input. I've already purchased an autoprop, and I was hoping to learn about the details without a huge "trial and error" period. Everything I've heard and read about them has been wonderful. Can't wait until spring! tom.
Ernie, I also thank you for your input. I've already purchased an autoprop, and I was hoping to learn about the details without a huge "trial and error" period. Everything I've heard and read about them has been wonderful. Can't wait until spring! tom.
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Thom Reeves
Sailing with Autoprops
Tom, Congrats on the AutoProp. We had one on our 36 and now have one on our 400. Inspite of what the tranny people say you have to put it in forward to stop the prop rotation and thus let the prop feather. Try it and you will feel you boat lurch forward when it feathers. When you put the boat back in neutral it will feel like you just hit a kelpbed. In neutral you can feel the vibration from the turning of the prop. And reverse was just about the same as neutral. But forward gear did the trick. See you Sunday in Westport. Thom.
Tom, Congrats on the AutoProp. We had one on our 36 and now have one on our 400. Inspite of what the tranny people say you have to put it in forward to stop the prop rotation and thus let the prop feather. Try it and you will feel you boat lurch forward when it feathers. When you put the boat back in neutral it will feel like you just hit a kelpbed. In neutral you can feel the vibration from the turning of the prop. And reverse was just about the same as neutral. But forward gear did the trick. See you Sunday in Westport. Thom.
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Tom
Did any of you that put an Autoprop on your boat
have to grind out the strut to take the possibility it wouldn't hit when it swung backwards. I knew that this might be a problem when I put it on So over the weekend I put it on and saw that it indeed would be a problem. It looks like about a 1/2" at the worst I'll have to grind out. (I don't want to put a drive saver on there). So who else ground out a 'divit' in their strut? How much did you have to grind out? Have you seen any problems from doing that? Are you concerned that structurally the strut is now compromised since you took out a "chunk"? Any mechanical engineers out there that are not concerned? BTW I brought this up to Gerry Douglas (Lead design engineer for Catalina) and he said that I shouldn't be concerned doing that because most of the strength in the strut is in the middle....and the newer Catalina 47' has the "chunk" ground out of its strut (but then again that strut is huge compared to mine and possibly over engineered)
have to grind out the strut to take the possibility it wouldn't hit when it swung backwards. I knew that this might be a problem when I put it on So over the weekend I put it on and saw that it indeed would be a problem. It looks like about a 1/2" at the worst I'll have to grind out. (I don't want to put a drive saver on there). So who else ground out a 'divit' in their strut? How much did you have to grind out? Have you seen any problems from doing that? Are you concerned that structurally the strut is now compromised since you took out a "chunk"? Any mechanical engineers out there that are not concerned? BTW I brought this up to Gerry Douglas (Lead design engineer for Catalina) and he said that I shouldn't be concerned doing that because most of the strength in the strut is in the middle....and the newer Catalina 47' has the "chunk" ground out of its strut (but then again that strut is huge compared to mine and possibly over engineered)
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Bob Kovich
Grinding the Strut
I also ground the strut to receive the Autoprop. I suppose it was about 3/4 of and inch or so to allow 1/4" clearance for the Autoprop. After one season no problems whatsoever.
I also ground the strut to receive the Autoprop. I suppose it was about 3/4 of and inch or so to allow 1/4" clearance for the Autoprop. After one season no problems whatsoever.
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Ernie April
Another clearance solution...
When I installed the Autoprop on my C-42, I also added Spurs. The latter needed additional clearance. I inserted a 1/2-inch spacer in the coupling which extended the prop shaft by that much, providing the necessary clearance. Spurs sells a large range of spacers of different widths and bolt-hole patterns. My only caution is not to extend any more than you need. Ernie April
When I installed the Autoprop on my C-42, I also added Spurs. The latter needed additional clearance. I inserted a 1/2-inch spacer in the coupling which extended the prop shaft by that much, providing the necessary clearance. Spurs sells a large range of spacers of different widths and bolt-hole patterns. My only caution is not to extend any more than you need. Ernie April
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Jon W.
Ground Strut
There is a picture of my ground strut and some comments on my webpage at www.home.earthlink.net/~jobawhite/ (go to the bottom of the “UPGRADES” page) On spacing of the prop body to the strut, the recommendation from Autoprop is to have no more than one and a half times the shaft diameter for space. We chose to grind. It is true that the tapered aft section of the strut contributes only a small proportion of the overall strut strength. When we put our second smaller prop on, we lengthened the notch in the strut and radiused the corners slightly. We’ve had it on for a year without problems.
There is a picture of my ground strut and some comments on my webpage at www.home.earthlink.net/~jobawhite/ (go to the bottom of the “UPGRADES” page) On spacing of the prop body to the strut, the recommendation from Autoprop is to have no more than one and a half times the shaft diameter for space. We chose to grind. It is true that the tapered aft section of the strut contributes only a small proportion of the overall strut strength. When we put our second smaller prop on, we lengthened the notch in the strut and radiused the corners slightly. We’ve had it on for a year without problems.
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Tom Soko
What about hull/prop clearance?
I've heard from some autoprop owners that had problems with vibration, and they seem to think it's the lack of adequate clearance between the blades of the prop and the hull. According to David Gerr(?), it should be 15% of the diameter of the prop. Mine is only 8-9% and I'm wondering if I'll have vibration problems when I get launched. Any thoughts?
I've heard from some autoprop owners that had problems with vibration, and they seem to think it's the lack of adequate clearance between the blades of the prop and the hull. According to David Gerr(?), it should be 15% of the diameter of the prop. Mine is only 8-9% and I'm wondering if I'll have vibration problems when I get launched. Any thoughts?
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