Autoprop ?

[Astrid]

I wonder what the diesel mechanics say about obtaining cruising speed at just above idle. My thought is that this is nice for noise and fuel economy and a disaster for the life of your engine. Or am I missing something?

That is not quite right. Let's say with a fixed prop you are getting a cruise speed of 4 knots at 2500 rpms. An auto prop gives you greater efficiency at same or near same rpms. With an Autoprop, you could probably realize a cruise speed of 5 at the same rpms. You do not adjust your rpms down to match the old 4 knot speed, you merely accept the one knot increase. Most fixed blade props are pitched at some ratio where best efficiency is at a certain rpm where as a self adjusting prop will maintain top efficiency throughout the rpm operating range.

[CFR]

Hi to all, i just got my offer for a Autoprop H6 for my 44 feet boat and ofcourse searching all info prior to buying, I have on question in respect of underpowered boats. i have a small 30 HP 2 cyl Sabb engine with a continous rating of 1850 rpm with a Hurth 1:2 gear. So the Prop is turning only max 900 rpm . My boat is arround 15 ton and i can reach max 7 kn at calm condition, with head wind it will go down to 3-4 knots. Does a autoprop really give me better speed although my engine might be to small in horsepower, i can not believe such miracle. reducing rpm would be nice if i could hold 6 knots but will it change max speed and thrust in waves and headwind. Here i actually feel not so happy with my 20 x 13 stainless stell fixed prop. please also let me have some positive replies not only the negatives.......

[Astrid]

In a nutshell and somewhat simplified: Fixed pitch props have an rpm range in which they are most efficient; any more or less and your efficiency goes down--i.e., the amount of thrust is optimal only over a very narrow rpm spectrum. With an auto adjusting prop, it automatically adjusts its pitch to give optimum thrust at what ever rpm or direction the prop is turning, so at rpms where the fixed prop is not efficient, the auto prop will be. There will be a lesser difference in efficiency at the old best rpm your engine and prop had before, since your fixed prop was optimized for whatever rpm that was, but outside of that range, you will have considerably better thrust figures.

[msponer]

Originally Posted by CFR

Does a autoprop really give me better speed although my engine might be to small in horsepower, i can not believe such miracle.

I believe it will, at least, that was my experience with a ~14 ton 40' boat. You should go faster in most conditions. But I would have no idea how to predict how big the difference will be for you. For my boat it was pretty substantial.

[nhschneider]

For what it's worth, my Autoprop did everything it was advertised to do except minimize prop walk in reverse. We gained a full knot of boat speed at the same engine RPM. I doubt that it had a significant impact on our speed while sailing as that's hard to measure in a 20-ton, 48-foot ketch. I loved having the maneuverability in close quarters - I could keep the boat speed fairly high but still stop in amazingly short distances.

Whereas the Autoprop is an intriguing design, I think it's poorly manufactured. The use of steel bearings, tab washers, etc in a component that lives and spins in salt water is a disaster waiting to happen. We never threw a blade but that's because I would dive the prop regularly. I overhauled it several times in the short time I had it on our boat and even though I did the work myself, it was still expensive as I could not find any source for the lip seals other than AB Marine. Theoretically, you can lube an Autoprop - which is required annually - without removing it but I found the prop to be a very high maintenance item.

We now use a Gori and have almost 1,200 hours on it. No maintenance whatsoever other than changing the zincs. I think it's the only 2-speed prop on the market without going to an adjustable pitch prop. Since we now have a hydraulic transmission, the fact that it folds completely is a real blessing as there's zero prop turning while under sail. I've read tests that the Gori has almost no drag when folded. I bought ours from AB Marine and got good service from them.

Fair winds and calm seas.

[Dockhead]

Originally Posted by CFR

Hi to all, i just got my offer for a Autoprop H6 for my 44 feet boat and ofcourse searching all info prior to buying, I have on question in respect of underpowered boats. i have a small 30 HP 2 cyl Sabb engine with a continous rating of 1850 rpm with a Hurth 1:2 gear. So the Prop is turning only max 900 rpm . My boat is arround 15 ton and i can reach max 7 kn at calm condition, with head wind it will go down to 3-4 knots. Does a autoprop really give me better speed although my engine might be to small in horsepower, i can not believe such miracle. reducing rpm would be nice if i could hold 6 knots but will it change max speed and thrust in waves and headwind. Here i actually feel not so happy with my 20 x 13 stainless stell fixed prop. please also let me have some positive replies not only the negatives.......

No, I'm afraid, sadly, the Autoprop will not magically make more horsepower than your engine can produce. 30 horsepower is too small for a 15 ton boat. Autoprop (or any self-pitching prop) will help you make the most of what you have, and will particularly help in partial-throttle situations. But trying to punch through a head wind (with head seas) in a 15 ton boat with 30 horsepower -- the numbers just don't add up.

[CFR]

jep this is my concern also, maybe better to save 4-5000 usd and invest later in a bigger engine. actually 30 HP is ok for a sailing boat old style and for calm weather, with headwind one has to sail, normally no problem i allways prefer to use my sails instead reying on my engine especillay if it is windy. maybe i try a bigger prop first, i have 20 x 16 but was recommend a 22 x 14 .

[Astrid]

I agree with Dockhead and CFR. A 30hp engine may serve you well getting in and out of an anchorage or navigating a calm inland waterway, but is really too small for quite a number of situations where you might need some reserve power to get you out of harm's way. A self pitching prop will help a little, but not that much for your power to weight ratio. You are working with about 2hp/ton with your current set up, while at least in years past, the minimum was considered 3hp/ton. You should therefore consider upgrading to a larger engine to give you more reserve power for when you need it.

[chala]

When considering the suitability of an autoprop it is wise to consider propeller curves. A 30hp motor is normally rated at 3600rpm which is not sustainable. I have a 30hp motor with an autoprop I do easily 5 ½ knots at 2200rpm again a 34 knots wind in a confused sea. The boat is 37 foot and weight 14 metric tons. I could elaborate.

[CFR]

Interesting info, as i have the boat only 2 years so i only had one situation where everything came together. headwind force 7, 1.5 m seas, a fouled propeller , maybe 3 cm of barnacles, which i realized after get the boat out of the water and this resulted in 2,5 knots. luckily after 1 mile i could hoist my sails and it was a wunderfull sailing with 8 knots.......
My engine is a little special it is a old SABB diesel with 1.9 liter and 30 HP at 1900 rpm, which is rated as continous operation. the engine was used for fishingboats up to nine meter and sailboat up to 14 m. So i have slowturning prop with max 900 rpm and a 20 x 16 stainless steel prop. I already got the advice to go with a 22 x 14 prop. maybe i should try this first before considering this bloody expensive and complicated feathering or auto props.
Does anybody has experienced with this campbell prop which is not known here in germany ?

[osirissail]

Originally Posted by CFR

. . . So i have slowturning prop with max 900 rpm and a 20 x 16 stainless steel prop. I already got the advice to go with a 22 x 14 prop. maybe i should try this first before considering this bloody expensive and complicated feathering or auto props. . .

We don't know what kind/type boat so it is hard to give anything but very generic and general opinions. However, you do not normally switch to a larger diameter propeller until you run out of "pitch" or the shape of the boat forward of the propeller is blocking the propeller's access to free water.

- - The bigger the diameter of the propeller the more "flat plate" surface you have putting "drag" on the boat when the propeller is not being used to drive the boat. If the boat is a sailboat then with fixed blade propellers the smaller the diameter the better to reduce drag when the boat is sailing with the engine shut down.

- - And "performance" sailboats (versus motorsailors) can make good use of feathering or folding propellers which greatly reduce drag. But for boats where the bottoms periodically resemble a coral reef I would suggest staying with a fixed wheel propeller as feathering/folding propellers do not tolerate much, if any, fouling before you do potentially expensive damage to them.

[CFR]

yes and as everything with sailing it is allways a compromise....... I have a nice sailing boat with a full body a shaft drive and skeg hung ruder. medium sized fin keel. how about a big / 24 ") 2 blade prop. the old sabb engine could be ordered with such a big 2 blade but manual pitch control via the shaft, mainly for towing fishnet

[osirissail]

Before the folding/feather propellers, the 2-bladed fixed props were favored as the propeller shaft could be marked and the engine shut down the propeller could be manually aligned vertically with the keel, sort of hiding it behind the keel while sailing. But for sailboats they were not variable as there was little need for it as the engine was only used to exit a port/marina or enter again.

[Astrid]

Yes, Saab did make a CPP with manual pitch control, and still does to my knowledge. One can also look into Helseth, Hundested (Denmark) and Novga, Heimdal, West Mekan, and Servogear (all of Norway). In the US and Canada, CPP systems are not so common as they are in Europe, but with rising fuel prices they are catching on.

[fstbttms]

Originally Posted by osirissail

But for boats where the bottoms periodically resemble a coral reef I would suggest staying with a fixed wheel propeller as feathering/folding propellers do not tolerate much, if any, fouling before you do potentially expensive damage to them.

Or they could consider properly maintaining their boats, have the hull cleaned on a regular basis before it becomes a reef and enjoy the benefits of a folding or feathering prop and a nice, clean bottom. There is no reason to lose performance to a dirty bottom or a foul prop.