Autoprop ?

[Moby Dick]

Alan - I fully agree with you last post (power/prop size)!

Ernest - it doesnt matter where the blades are 'at rest'. If '100% pitch' - blades parallel to shaft, minimum sailing drag - then they will swing to their thrust position as soon as the shaft starts to rotate due to rotational drag.

If the blades are at 'zero pitch' - blades offering maximum drag to normal sailing but minimum rotational drag to rotational flow, then centrifugal forces will cause the blades to swing to their optimum thrust position.

Both - I know somebody with twin Autoprops on a cat. When sailing, you can put engines in gear at near tick-over and significantly increase speed (over a knot). This is because the flow of water during sailing reduces drag 'seen' by the propellor and allows the weak centrifugal forces (weak because the prop is only slowly rotating) to open and contribute some thrust. What is happening in effect is that whatever speed you would see normally on tick over (no sails) is added to your sailing speed - say 1 + 5 knots. A normal prop would not keep up with the water flow, and would just contribute drag.

When a boat is at tickover with an Autoprop (not motorsailing) the centrifugal forces are low, but the rotational drag is high, so the blades do not 'open' far and pitch is small - hence speed is LOW (as normal)


It is all VERY clever.

[Alan Wheeler]

What is happening in effect is that whatever speed you would see normally on tick over (no sails) is added to your sailing speed - say 1 + 5 knots. A normal prop would not keep up with the water flow, and would just contribute drag.

Abosultly not. I have a conventional fixed three blade prop. If I am undersail in say 12kts, and I start the engine and allow it to just "tick over" I get an intant and dramatic speed increase.

[ernest]

OK, I give up for a while. I am still very fond of the Autoprop design. It seems so clever ( maybe more clever than I thought) and it beats my brain.
I will probably buy one just for the fun of it. None that I know of here in Sweden has got one and there will be a lot of discussions in the marina. Some will think I am mad when they here the price.
Then I probably also have to get me an underwater movie camera so I can admire its operation.
Alan, dont ever say it is dumb. It is a hydromechanical wonder with advanced computational power. A very limited instruction set though - but still ...
- Ernest

[Benny]

Alan - is the increase in boat speed due to reducing the drag because the prop is now turning or because the prop is contributing to forward thrust - or both?

[Benny]

Just looked up the Autoprop for my boat - the H5-430 - ONLY!!! $3599.00 US at Defender - YIKES - even if it lives up to all it's claims, isn't this priced for the lunatic fringe buyer (no insult intended for any of us who bought one) and is it worth an extra knot of boat speed - maybe? I would have a hard time justifying this cost instead of say new sails or standing rigging etc.

[Alan Wheeler]

Alan - is the increase in boat speed due to reducing the drag because the prop is now turning or because the prop is contributing to forward thrust - or both?

Good question. I only take RPM to a little above idle so as it sits in a nice sweet spot. With no sail, this is around 2-3kts for engine power only. So it is about the same for just sail. With both, powering the boat, I pick up extra speed. So at that speed, it is probably extra power fromt eh prop. As the wind speed increases and the boat starts to climb to say 6kts, if I then start the engine and set the same RPM, I pick up a good kt or two. I would say this is reduced drag. However, if I am at 5kts, I seldon runt he engine, I am very happy to tick along sail only at 5kts. When I get to 9kts, then she is all on. The boat feels awesome.

[Moby Dick]

I believe the Autoprop really DOES auto-variable-pitch (not just forward-low drag- reverse) positions and that is what I wanted to 'prove' here. I am not going to get involved in the debate on real life performance, usefullness or disadvantages, as I dont have enough experience running them. Others can contribute here.

(However, from a theoretical point of view, I cannot see how a normal propellor running at a speed which causes a water flow LESS than that caused by sailing (eg when motorsailing) can contribute thrust. Reduce drag, yes, but not thrust. It would be like walking slowly on a fast backward moving escalator. So I assume the effect Alan sees is increased speed due to reduced drag. On the cat I mentioned, there is no (or little)prop drag when sailing, as the props are in the low-drag position. So the increase in speed is due to increased thrust. Also, again when motorsailing, a normal prop would be unloaded until it is spinnning at a rate that has caught up with the water flow. This would be BAD for the engine. The Autoprop would have the engine under load, increasing until it reaches cruising revs, which is ideal)

To summarise. the Autoprop:

- DOES autopitch to various settings according to sailing and load conditions
- It does NOT autopitch according to engine power
- it DOES NOT cause excessive speed on tickover or cause hull speed to be reached at below-cruising revs. If it does, you have the wrong sized prop for your engine!

Whether this is good, bad or inconsequetial others can debate.

Inciently, in in IK a 2 blade Autoprop for a 40ft cat is a about £1k, so not much different from other (albeit 3 blade) feathering props.

[Tom Spohn]

I have been very happy with my 3 blade Flex-o-fold.
Comparing Flex-O-Fold to Feathering and Fixed Propellers

[Moby Dick]

Originally Posted by Tom Spohn

I have been very happy with my 3 blade Flex-o-fold.
Comparing Flex-O-Fold to Feathering and Fixed Propellers

speaking of which, has anyone seen the original material from the Cruising World or 'TECHNISCHE UNIVERSITAT TEST' tests refered to by Flex-O-Fold? I have seen the Practical Sailor 1995 report (which incidently confirms Autoprop motorsail/headwind advantages) but not the others.

[dkall]

The following is my email to Autoprop after doing all but one of their requests. I emailed them Monday and have not yet received a response. I'll give them until Friday before I contact them again.

I've finally completed all the requests except I've not hauled to find out if there is any run out in the shaft.

The measurements I have on both the Westsail 43 and 42 are as follows.

As you implied earlier Adrian, there are some differences between models. The WS 43 has a slight downward slope to the prop shaft, even though the shaft is identical in length and dia because the engine is a V drive it sits higher and the shaft angles down enough that the shaft is in the middle of the aperture. On the WS 43 there is approx 14 1/4" between the center of the prop shaft and the top and bottom of the aperture. On the WS 42 there is more distance in the bottom than in the top (the shaft exits the boat almost parallel to the waterline). On the WS 42 (our boat I measured from the top tip of the propellor to the hull is 1 1/2". When I ordered the prop I was never able to get the drawing mailed to me and had to have it faxed. I don't know if there was any change in the dimensions of the drawing by being faxed (faxing to one maching from another sometimes causes changes in both the x and y axis) and there was no key on the fax ie this distance is to equal 1" or this distance is to equal 5 cm, so I have no way of telling. All I know is that I used the paper to transfer it to some tag board (hard firm paper) and then cut it out and held it to the shaft as instructed.

Further measurements / information are as follows:

3 5/8" from stern bearing to the front of the hub for the Auto prop.
There is no discernible play in the stern bearing.
4" from the bottom of the shaft to the closes hull below the prop.
From all the vibration or from some other issue I've lost the zinc on the back of the propellor.
Every blade turns and rotates freely.

I've replace all the mounts on the engine and realigned the engine to be a much smaller tolerance than normal.

The results are as follows.

At the dock I ran the engine up to 2100 rpms with the prop engaged and there no extreme vibrations did not appear. I'm on a floating dock and didn't want to go any higher (than 2100 rpms). Remember that with the last setup I received the extreme vibrations at 1800 rpms.

The water test too was much improved as I did not get any differences in vibrations thru any of the engine rpm ranges. I ran the engine up to 2200 rpms under way and all was ok. Remember that prior to this at approx 1400 rpms I had extreme vibrations.

We still have the problem of the speed; hull speed at 1300 rpms is not going to be acceptable.

Because of the clearance of the blade tip and the boat speed being too great at such a low rpm, I still feel that the prop is oversized for the boat although it may be the correct size for the engine and for modern day surfing boats.

I don't know if you've been able to confirm the other Westsail 42 owners prop spec yet, he did indicate that he had sent Autoprop the prop information to get replacement zincs.

And finally, if we're going to resize the prop I need to purchase 2 zincs and a prop puller for the Autoprop. If I"m going to send it back to you to rework the blades or whatever you need to do I'll still need to purchase a prop puller as I believe the Autoprop uses a special one because of the larger then normal prop hub.

Please advise as soon as possible as to our next step.

[Alan Wheeler]

MATE!!!!, this is really taking some time isn't it. I feel very sorry for you that it is taking so long to sort this out.
Do I understand correctly that you are dealing with the US distributor, or are you dealing now directly with Bruntons ???

[dkall]

Part of the time it is taking is mine. They had asked for many thing to be done, measurements as well as replacing the engine feet. That was a feat.

As for dealing, I'm cc'ing the mailing to the CEO and cc'ing to the US distributor. They're not the best in dealing via email but for me it is the best to have a record of everything that happens. If I don't hear from them by Thursday pm my time I'm calling Autoprop Friday am, noonish their time to see what is up.

Thanks for keeping abreast of the situation. Support from other sailors helps.

Fair winds.

[Yachts66]

And thank you for keep us up to date. I'm considering Autoprop for my new boat and am mosted interested in how they work with you as it will greatly influence my decision on whether to give them a go or not.

Regards,

TJ

[dkall]

My recent reply from Autoprop and my response

On Apr 30, 2007, at 7:05 AM, Autoprop wrote:

Dear Dave,

Thanks for the information you have sent. From the information you have
given I read that the vibration problem has been pretty much solved. The
concern now is the engine loading aspect. Have I read this correctly?.

You say that you have taken the revs up to 2200rpm with no vibration. Is
this the maximum engine rpm you can reach or will it go higher?. Can you
see any black smoke at all.

If you can answer the above we will make our final decision on the best
solution.

Dear Autoprop,

Thanks for your reply. I look forward to resolving this issue and getting on with sailing.


Yes, you're correct that the vibration is basically solved. It does seem noisier than I believe it should but I've not used an autoprop in a fully enclosed aperature before. There basically is no more noise at 1500 vs 2200 rpm, just that my boat speed is not changing.

At the dock, as the rpms increased there wasn't any smoking; definitely not "black smoke" from an overloaded engine, simply more exhaust. The engine does not appear to be lugging in any way and I wasn't at my full throttle and had more throttle to go ( I hadn't reached the throttle stop. ). The engine will run up to the full rpms of 2600 out of gear. I didn't run it up that high at the dock as I said it was a floating dock nor did I on the out on the water test as my speed wasn't changing and I felt no need to push it further.

On the moving test away from the dock; basically I didn't notice any excessive smoke and I wasn't looking for any either. I do think had it been there I would have noticed. The boat is a center cockpit boat and the exhaust is out the side immediately adjacent and aft of the cockpit. It is just that I my boat speed didn't increase. The speed stayed flat from about 1300-1400 rpms. My tach divisions are close together so I can't say where exactly in that range.

What I'm concerned about is not about the engine being over loaded (although if I thought that was the case or had any data suggesting that overloading was the cause I would be concerned) but about constantly running the engine at less than it's optimum rpms (I've not spoken with any diesel manufacture that recommends continuously running an engine at 50% of full rpms; 80% seems more to their liking). And with your literature saying that one generally reaches hull speed at 80% of full engine rpms I felt this was a great fit. Further idling along I'm doing over 5 kts. This makes boat handling in congested areas much more difficult.

And I am concerned about the clearance at the top of the propellor tip. As I mentioned I had used a faxed copy of the needed clearance to fit the propellor and am a little concerned that it is as close as it is. 15% of 21" = 3 1/8 " or there abouts and what I've measured is 1 1/2" from the tip top of the propellor to the hull. Any research I've noted on the topic indicates 15% of diameter of the propellor not 15% of the radius.

Sincerely,

In a seperate post I added an addendum:

One post script to my earlier post.


I did have the extreme vibration "whirling" once when I shifted from reverse to forward and ran the rpms up my guess is too rapidly. I'm assuming this might have more to do with my method in manuvering in close quarters than the prop setup.

[Yachts66]

Any more developments on the situation?

Thanks,

TJ