Autoprop ?

[chala]

Ray thanks you for your reply.
I found Autoprop a very interesting piece of engineering.

Originally Posted by Pete the Cat

I think that most diesel mechanics will suggest that diesels need to be run primarily around 80% of max RPM….

I think that most diesel mechanics will suggest that diesels need to be run primarily around 80% of there rated power output. Take for instance a diesel generator the speed of the generator as to remain constant but it will be better if the diesel engine could be loaded to at least 80% of its rated output.
With a standard propeller it is quiet possible that 80% of max RPM will also be 80% of its rated full output and every body is happy.
In my 1989 print of Dave Gerr's Propeller Handbook, Dave make no mention of Autoprop but do mention controllable-pitch propellers as a very simple solution of matching pitch to variable loading conditions. It also demonstrates well in “Effect of Low Propeller Power at Slow RPMs” the low percentage of loading the engine is subject to, 22HP for 60HP available, 36% instead of the 80% recommended.
I have no data available for the Autoprop but by experience I would said that my engine is better loaded by an Autoprop but not overloaded and it is what I find special with an Autoprop it is the continuous automatic adjustment of the pitch. Your’s experience suggest that the motor is overloaded and it is possible then that the Autoprop installed is not the correct match for the boat and engine. I found an advantage that the Autoprop will reach speed at lower RPMs, in doing so using less fuel and making less demanding engine noise. When manoeuvring, to reduce speed, I have no problem in disengaging the propeller, bearing in mind this is often required of boats with standard propeller.

[godzillaboat]

I have maxi prop for sale it is twin blade 32"dia. for a 2' shaft I bought it for a 65 ft steel schooner , it did not work well to windward (cavitation). Company said to set it at what I put it at.
Anyway its been years sitting , anyone want to make an offer ?

[k7cej]

Re the Autoprop: we have an Autoprop H6driven by the Yanmar 4JH3-TE (75 HP) in our Outbound 44. Having over 20,000nm under the keel, including cruising from Alaska to Australia, I will say that it has worked very well and I am quite satisfied with it. It takes out boat to hull speed in flat water at 2100 rpm vs. 2600 for the original fixed 3-blade prop. We also get a significant boost when sailing and battery charging at a fast idle, as well as being able to pull red-line rpms tied to the dock. The nylon anode screws always seem a little flimsy but I have never had one break or come out.

[chala]

Originally Posted by PugtSounDav

Would changing over to an Autoprop maximize the limited power available?

This thread may have the answer but you can also ask this question to Autoprop themselves.

Originally Posted by PugtSounDav

Since Autoprops "self-pitch", do they somewhat protect the engine from over-loading/lugging by self-pitching to a finer pitch when the motor can't produce any more power?

I know that I can stall my engine (30 hp, 3 blades autoprop) if I put to much load (1100 VA inverter, or inrush current of starting a battery charging cycle) on my 12-24Vcharging alternators when idling or maneuvering. Proper management of the plant overcome this.

[chala]

Originally Posted by Astrid

Autoprop adjusts its pitch in a similar way to an airplane equipped with a mechanical self adjusting prop. At low rpms the Autoprop pitch is very coarse to give a greater bite into water to maximize thrust. As you increase rpm, the pitch becomes finer to reduce strain on the engine; at faster rpm, the prop has less bite into the water, but maintains its thrust by turning faster. The main advantage of the Autoprop is that it adjusts to be efficient at any rpm forward or reverse, and of course when under sail, and with the shaft locked by a brake, it auto feathers to reduce drag.

I think there is more to Autoprop than the above description.
I would assume that you own an Autoprop and would have realized that at constant rpm, the boat will go faster and faster. This is what most people using Autoprop dislike, reaching hull speed at idle. Obviously in that type of “sea” condition idle HP is all that is required from the engine. To achieve this (acceleration at constant rpm) the pitch of the propeller must change and “grab” more water. Indeed a beautiful piece of engineering.

[chala]

more info

[Eleven]

The principle is fine in a steady state condition but I have been on a boat that failed to drive into confused seas and wind. Not really clear if that was a horsepower or an auto-prop problem. In normal use, in normal seas these props do, theoretically, give much more miles per gallon by optimising thrust over a wide speed range, (i.e. the boat keeps accelerating until it's at the max for the power input) but I am concerned that the diesel engine management system can confuse the issue as diesels control by setting the target speed and adjusting fuel to suit, nowhere near as simple as a petrol engine, and can lead higher fuel burns than tick-over might suggest.
The auto-props are, however, great for motor sailing where the prop will adjust to absorb supplied horsepower, i.e. making up for what the wind fails to deliver.
I have seen a sail boat with a manual adjustment of pitch, continually engaged, providing reverse to max forwards with the smooth movement of a lever, independant of throttle.
For those who maintain a good watch, and tinker (trim) sails often to seek the optimum then this might be a more comfortable way of operating. Certainly it is much easier to get the fine adjustments needed when docking with this system.

[j.g.evans]

I had a 3B Autoprop and cruised 3000 miles before a blade fell off and was lost. Communications with Brunton has been nil. I did not see the magic "chata" refers to. I carefully took boat speed versus RPM data in calm water. The boat did not accelerate to hull speed at lower RPM. The speed-RPM relationship was identical to my fixed prop except for pitch. That is, linear until hull speed. The Autoprop was identical in performance to a fixed prop with 2" higher pitch. Higher pitch was the wrong direction and I could not achieve max engine RPM without 3GM30 overload. The Autoprop autorotated while sailing and the transmission had to be put in forward. Difficult to go to neutral to start the engine while sailing. I now have a feathering prop which I adjusted to get the pitch right. No autorotation.

[Eleven]

More info please, for others, on the feathering prop. Is that the permanently engaged manual type as thread #262?

[osirissail]

I was an Autoprop dealer many years ago and had one on my boat - it fell off due to a design fault. I put the old fixed 4-blade back on and got better speed and more efficient fuel burn.
- - If you sail a lot versus motoring and want a feathering prop get a MaxProp - they are tried and true over many years by all kinds of boats.

[Windgeist]

What was the design fault you speak of?

[steelev]

I've had an Autoprop for 15 years and was reasonably pleased with it's perormance, until it shed a blade last weekend. Autoprop wants $1500 to replace the blade (maybe not so unreasonable?), but on closer examination, one of the other bades is also cracked.
In my mind, the Autprop seemed awfully heavy and blades seemed to have a good deal of play, even with new bearings. I worried about fatigue and stress corosion, but thought that the bronze material might mitigate the problem. Anyway, I won't be repairing or buying another autoprop. Something that costs as much as an Autoprop should the lifetime of the boat, though I understand 15 years of moderate service is a long time.

[j.g.evans]

Re: ELEVEN's request for more info on the feathering prop. I bought an Autostream because I could adjust the pitch under water. I had to do this once. I also like a SS prop on a SS shaft for electroysis prevention. Unlike the Autoprop and a fixed prop, it does not autorotate once you stop it in gear and then shift to neutral.
I believe the more expensive Maxprop can be adjusted under warter too.

[Astrid]

Early Maxprops were not adjustable underwater, but the latest ones are adjustable without removing the prop.

[j.g.evans]

Autoprop Customer support still bad. I sent my Autoprop missing a blade to A-B Marine, the Autoprop importer, with them promising to consider repairing it or making it into a 2 blade and we share the proceeds from selling it. After 6 months of it being at the "top" of the to-do list and nothing happening I asked for it back. Anyone need parts?