Ball Bearing Autoprop Assistane

[MikeHoncho]

I hope you enjoy yours as much as I have enjoyed mine for the last 22 years. It has never given any problems.

One thing to note is that you must lock the shaft or it will create more drag than a non-spinning fixed 3-blade prop. If it cannot turn, the blade feather and create almost no drag and takes almost no force to keep it from spinning. On distance races when I need to run the engine to charge the batteries, I tie a single piece of builders string to one of the coupler bolts which holds the prop with the engine running in neutral.
As soon as you release the shaft, it starts to spin in the reverse direction which is why on my Hurth transmission I need to leave it in forward gear rather than reverse. once it starts to spin, the blades increase the angle of attack and start creating drag which makes it spin faster and create even more drag. It is like sailing with the engine running in gear in reverse.

I know that everything says to shift a Hurth into reverse but Bruntons (and Hurth) will tell you to do the opposite to normal with an auto prop because it freewheels in the opposite direction.

Awesome input. Thanks

 

[MikeHoncho]

Well after almost a year I finally got the prop on. I ended up designing and building a dive hookah system to do it and it took forever to get my dry suit. Keeping in mind I researched the prop specs with the manufacturer prior to purchase......it doesn’t fit. It just touches the bottom of my boat. I was able to sand down the bottom paint and got it to clear with about 1/8”. Took it out and the thing flys at low rpm. I could not get the engine above 2800 without it blowing black smoke but I was at hull speed at about 2200. Pulled it and sent it to a prop shop that cut it down from a 16” to a 14”. Although I didn’t get it out in the open, a US distributor said the right way to check for proper diameter it to run it through the Rpms while tied up at the dock. Did this today and max rpms is 3200-3300, right in the sweet spot! I didn’t have time for a sea trial so that comes next week. I’m looking forward to the results both under power and under sail.

 

[sailme88]

Had my Autoprop rebuilt last year ( before COVID) Because of an overheating issue all last year I was unable to appreciate the overhaul. This year, overheating resolved I can report the the prop rebuild was/ is successful.
My M25 will only run up to 2800 RPM when in gear. At 2500 RPM I get about 6.8kts over the bottom..

 

[MikeHoncho]

To my surprise I wasn't able to get rmps up above 2800 and for the majority of the time the max was 2500. I can really tell how the blades self pitch. I can hammer down on the throttle from a stand still and RPMS rise quickly and as the speed picks up the rise of the rpms slow. Going into current lowers the max rpm and going with current raises it. All the characteristics are by design of the prop. My issue continues to be diameter. I started at 16" and had it cut to 14" with a gain of about 500rpm while keeping the same mph. I don't want to do another 2"'s but I would like to get the RPMS up to at least 3000-3200 which is the engines hp rating rpm. I do have concerns with loading the engine at such low rpms. I take off for a week trip in a week so I'm going to leave it for a while and maybe have it cut down again a inch. The issue is each time I have it cut down its $400.

 

[MikeHoncho]

Had my Autoprop rebuilt last year ( before COVID) Because of an overheating issue all last year I was unable to appreciate the overhaul. This year, overheating resolved I can report the the prop rebuild was/ is successful.
My M25 will only run up to 2800 RPM when in gear. At 2500 RPM I get about 6.8kts over the bottom..

What is your engine and what diameter is your Autoprop?

 

[sailme88]

What is your engine and what diameter is your Autoprop?

My engine is an M25 and I'm sorry to say that I don't know the diameter of the wheel. Were I to guess, I'd say that it is 12"

 

[Hayden Watson]

Mine is an M25XP and the max RPM I can get in gear is ±2400 At WOT in neutral, I get 2800. My AutoProp is 13".

 

[sailme88]

Mine is an M25XP and the max RPM I can get in gear is ±2400 At WOT in neutral, I get 2800. My AutoProp is 13".

Thinking that our numbers are about the same in spread.. So I think that maybe the difference is your tach. I 'm of the belief that the neutral WOT should always generate 3000 RPM. The 200 RPM difference could simply be a calibration issue, and when you add that 200 to the 2400 you're now at 2600, and that is close to my in gear WOT..

 

[Hayden Watson]

I have very seldom run at or near WOT because I would get harmonic vibrations at 2400. My good speeds were 1400, 1900, 2200. At all other RPM's the stove and dishes rattled like crazy.
I always attributed this to the AP but I recently replaced my motor mounts and after some at-dock testing the dishes are quiet at all RPM's so I may try the higher revs.

 

[MikeHoncho]

My max rpms are indicated by black smoke from the exhaust. I’d like to get the rpms up to the rated hp rpm of 3200 but cutting the diameter from 16” to 14” gave me only about 500. I wouldn’t want to go any smaller than 13”.

 

[sailme88]

Had this post in mind yesterday. Set my RPMs at 2200 . Steaming into 16-18kts of wind I was seeing 6.2 its over the bottom. As I entered into the the river part of the harbor the out going tide that was augmented by the river flow cut my headway to 5.6 kts. I got back to 6 kts when the wind got partially blocked by a marina,,

 

[MikeHoncho]

Did a 6 day trip to the San Juan’s while motoring about 95% of the 244 mile trip. It was really interesting how the prop works with its self pitching characteristics. Going against the current I was able to cruise at higher RPMs due to the higher velocity of water through the prop and going with the current I was limited. Average RPM was about 2200. I started to develop a slight chatter that was more prevalent when goin with the tide ( higher engine loading/ lower rpm capability). It sounds like either a luging diesel ping or a flex plate chatter, probably both. Under sail ( we got a great couple hour run from Lopez. I swear it has added a average of .75 to 1 knot with winds in the 12knot range. Probably ” new prop’itis”. I’m going to pull it and have it cut down another 1inch and change out the motor mounts. I failed to write down my starting Hobbs meter hours so I can’t do a hour per gallon figure but I did go through only 16 gallons in total.

 

[jssailem]

Nice. No such thing as prop’itis. Old wives tale.
Fun to feel refreshed and more powerful.

 

[MikeHoncho]

Ok, its been two years of use. A lot has changed........After my trip to the islands and getting a little chatter and lower RPMS, I decided to have the propr cut down a little more. I think it was another 1/4 inch. I think the shop cut it down more than than but it is what it is now. The prop now allows the engine to max out at 3300 RPMS which is right where it is suppose to be but I have lost some of the noticable self adjusting properties I felt before. This doenst mean it isn't doing it, I just don't feel it like it did. Took the boat for our two week cruise to the islands and within 40 minutes of push back I hit a log and produced a immediate RPM specific vibration and significant chatter sounds. I completed the trip with it on (I couldn't get it off in current). I got back and switched it out with my original three blade that was fine when taken off.......vibrations and chatter was significanly more. I had anxieties that I bent the shaft. I ran the engine in gear (no prop) while diving on it (I got my scuba cert) and I could not notice any travel of the shaft but when I put pressure on the shaft I noticed material coming from the shaft log....the shaft was almost touching the log. The strut was not bent. Rewind 1 year earlier when I changed the motor mounts. I lined up the and aligned the engine to the shaft as it sat. It was obvious to me now that over the years, the mounts had collapsed and the hose that connects the packing gland to the shaft log in the hull had developed a memory and was low in elevation allowing the shaft to rub on the log. The engine is a repower so everything is a little different than original so when I tried to adjust the mounts higher (I was shooting for 1/8 inch) they were maxed out. I ended up fabricating 1/2 inch spacers to place between the mounts and the stringers. While doing so I added larger lag bolts as two of them did not tighten down all the way. I used a wood clamp to raise the shaft 1/8 of a inch from original and aligned the engine to the relocated shaft. Installed the repaired prop and everything worked perfect. No chatter, no vibration. I believe the chatter from the start was the shaft rubbing on the log. I considered having the shop add the 1/4 inch back on but I figured why mess with something good.
Additional lesson learned with the Brunton.... when you check on the boat, run the engine and spin the prop. I haven't had it out since September but cleaned the bottom regularly. The prop blades froze from growth around the bearings. I ended up pulling it and servicing/cleaning it finding calcium like deposits between the outer (smaller) bearings causing the blades to rotate rough.