Autoprop ?

[Alan Wheeler]

David, I got a very quick response form Adrian Miles. Sounds like he is a great guy and is going to be of tremendouse help. Here is the Email and his response.
David, couild you Email him. He will be expecting you.

Dear Alan,

Thanks for your email which I received this morning. It is obviously of concern to us that one of our customers is getting a poor response from our dealer in America.

I am not aware of this particular problem, however I am keen to try and help resolve the issue. For that reason I would be very happy if you can put me in touch with the owner concerned and I will see what I can do.

As this is a one off issue which will need certain information specific to the job I don't think the forum is the right place to undertake this sort of communication, however I have no problem in you posting this response, or any others that you or the customer may feel he wants to.

There are many thousands of very happy Autoprop customers around the world, one more would be nice!

Kind Regards
Adrian Miles
Managing Director
Bruntons Propellers Limited
Oakwood Business Park
Stephenson Road West
Clacton-on-Sea
Essex
CO15 4TL
UK
Tel +44 (0)1255 420005
Fax +44 (0)1255 427775
Mobile +44 (0)7850 621235 Skype adrianmiles1
Web www.bruntons-propellers.com

From: Toby Ramsay
Sent: 26 January 2007 08:49
To: Adrian Miles
Subject: FW: Autoprop problem

From: Alan "Wheels" Wheeler [mailto:wheels@hyper.net.nz]
Sent: 26 January 2007 06:08
To: Toby Ramsay
Subject: Autoprop problem

Dear Bruntons propellers. Could you please ensure that the Managing Director is forwarded this Email. It is very important.

Dear Adrian Miles,
I am writing you on behalf of a member of our boating community forum called Cruisers Forum. This is a large web forum specialising on the subject of cruising for both sail and power. We have a membership of over 4500 people.
The person I am contacting you on behalf of, has installed an Autoprop to his vessel. But there seems to be a rather serious problem with it. I believe he has tried to solve the issue with your US based dealer, but is having a very poor result so far. Please be aware that our site does not tolerate members that rant about possible issues. We consider it hearsay when the other side can not address the issue. Because this member has shown significant maturity and patience, I volunteered to contact you on his behalf and see if you maybe able to help resolve this issue.
Please go to this link. http://www.cruisersforum.com/forums/f114/autoprop-4299.html
Any help would be greatly appreciated and I think would help your product somewhat.
Please note that to reply requires you to join the membership. this is free. However, if you would rather not, then replying directly to me will ensure your reply is placed on the board.
Or, if you wish to communicate directly and only with the member, then that would also be acceptable and I am happy to place you in contact with him.
Thank-you for your time

Yours Sincerely,
Alan Wheeler
Administrator for Cruisers Forum.
www.cruisersforum.com

[dkall]

Alan,
I sent you a private post with my email address. I don't see his address in the email (which makes sense with all the spam). Thanks

[dkall]

Thanks to Alan the managing directory sent me an email saying he would look into the issue and was out of the office for this week.

I gathered all my notes and sent him a summary of what's happened up to this point.

I will let this board know of what happens - hopefully good; when it does.

[dkall]

For anyone following my saga; I wrote Adrian when he responded to me last week. He indicated that he would be out all week. I sent him a summary of my situation with respect to the Autoprop. He said he would look into what I have to say and contact the US Dristributor. Today I received a reply from him that he had received my email and would get back to me by the end of the week. Hopefully so. I keep my fingers cross.

[dkall]

I've now a response from Adrian. He provided several things to look at and said they would reexamine the prop if needed and finally that if all else fails they'll refund my monies.

I'm replacing the feet on the engine and will check the other areas he suggested.

I send a follow up about what were doing, that I like the prop and want to get it working.

I'm further concerned (of which I had said in my earlier correspondences to Autoprop) about the boat reaching hull speed at 1300 rmps when the designed max on the engine is 2600.

As things progress I'll further keep this board updated.

[ernest]

I will be very interested to hear about the progress since I am very interested to get an Autoprop with my new engine installation.

Today I have got a 35 hp VP35D and intend to replace it with a 87 hp Lombardini 2204MT. The main reason is that I want a an engine that just hums along at cruising speed.
The VolvoPenta makes a terrible noise and the Southerly has a second indoor steering wheel which would be lovely to use in a cold and rainy autumn weather.

Now to my question.
Since the Autoprop feathers to an optimum pitch and I will have an abundance of power - will I be able to go slowly forward with engaged gear?
It would be very awkward having a boat that will run along at 5 knots with the engine at idling speed.

Is there anyone that can share his experience with me? Guesses are fine too.

[Alan Wheeler]

There is a slight error in understanding this prop. It is not Auto feathering. It is Auto pitching. A feathering prop means the angle of attack can be altered. So yes, in a case like that, a slow reving motor could perhaps be made to push a boat along at 5kts. In a self pitching situation, all that is happening is that the blades are balanced in such a way as to "set" at a designed angle in the water. The actual "pitch" is determined by blade shape inthe factory. The rotary desing at the base of each blade ensures the blades swing to a "balanced position. So when select reverse, the blade swings 180 degree's and offers the best angle and blade face to the direction it is swinging. When Fwd is selected, it once again swings 180 degrees and offers the same in the other direction. Apart from that, the blades do not change shape to suit engine Hp of RPM or boat type or what ever. A feathering propellor is required for that, and Feathering are mechanical, expensive and need special shafts to work them.

[ernest]

OK, we should not fight over words. I used the word feathering wrongly. Of course it is self-pitching.
As I understand it the Autoprop is balancing available power at the propeller shaft with the hull resistance at a certain speed by the blades swinging to the right pitch.
If you have a powerful engine the boat could go quite fast at low revs since the engine still has lot of of power and could drive a high pitched propeller.
5 knots was just a guess.
I have not asked Brunton yet about their opinion. I think hands-on experience is more important to me.
As the Englishman says:"The proof of the pudding is in eating it"

[dkall]

My experience and it isn't after 100's of hours of use is that I travel at hull speed at about 1300 to 1400 rmps. My engine turns at 2600. I've an 85 hp diesel and full keeled boat. I never checked the knots at idle but it is well over 1 kts. The prop will throw a bunch of water. Elsewhere on this board is my contact with Autoprop and we're working out some problems. I get what they call a "whirl" which in my book is a big thunking - shaking the boat and I go at hull speed at half my engine rpms. They have however offered to refund my money. I give them that. I am making some changes to the drive train (putting in new engine feet) and taking some more measurements, then getting back to them. I like the basic concept of the prop and it will throw lots of water without cavatating, but hull speed at 1400 rpms and the whirl has got to change.

[Alan Wheeler]

As I understand it the Autoprop is balancing available power at the propeller shaft with the hull resistance at a certain speed by the blades swinging to the right pitch.

No that is not correct. It is not possible. I have not read the wording of any of their promotional literature, but I can only assume this understanding has come from reading such. The "understanding" seems to be the norm.
The blades are "dumb". That means they simply swivel. They have no way of knowing how much Hp the shaft can deliver. They have no way of knowing what the Hull speed could be at what revs. They have no idea of what friction throught the water one hull will have over another. They have no idea if a wave or wind is friction or just a force against momentum. So they can not change pitch to compensate. If they did change pitch, the engine RPM would be all over the place as load constantly altered.
The only time the pitch maybe able to change is perhaps by centrifugal force. As the blade hub spun faster, the Blades may want to slightly change position. but that is really a guess. I imgaine in reality that the blades are balanced such that rotation will not alter them.
OK so what is "auto" with them? Well firstly, Pitch and diameter is determined just like any propellor. They need essential figures to work out the size and pitch. The actual pitch is determind by the blade itself. It is shaped to a pitch ratio just like any other "fixed" blade. The difference in these props and fixed props is that the blade can fully rotate. As I said earlier, it means the leading edge when in forward becomes the same leading edge in reverse. Unlike a fixed prop where it is the trailing edge that becomes the psuedo leading edge in reverse. In this situation, the fixed prop is nowhere near as efficient in reverse as it is in fwd.
Back to the auto prop. The blade bases are shaped such that as the shaft rotates, the leading edge flicks around the blade and presents the leading edge into the direction or rotation. The blade base is offset from the Blade itself and this design is what causes the blade to always maintain the same attitude of attack, or pitch into the water.
In Daves situation, I am guessing, or at least initialy guessed that one blade may have a slightly different pitch placeing the blade out of balance, or the leading edge of a blade is damaged or the actual blade is bent or something along all those lines. But I guess that the people helping Dave should have gone over all those scenarios by now, So I guess my guess was wrong.

[cooper]

Hi Alan
What happens to the pitch when the shaft is not rotating but the boat is travelling through (sailing) the water ? Do the blades align with the water flow ? Ie..is it the rotation of the shaft against the friction of water on the blade that provides the power to create the pitch ?

[Alan Wheeler]

Yep exactly. When the shaft stops rotating, the Blades simply align themselves to the flow of the water.

[ernest]

Hi Alan,
thank you for all the the trouble you have taken by answering my letter to the forum. Unfortunately I cannot follow you.

You say that the Autoprop is dumb.
Maybe it is me that is dumb instead because this is how I understand the action of an Autoprop:
I consider the Autoprop quite intelligent. A very limited intelligence of course but it does what is expected.
Namely it self-pitches in a preprogrammed way and the pitch is the result of the water pressure on the propeller blade which makes it swing into position.
I define pitch in this case as the angle between the propeller blade and the streaming water.
The water pressure in its turn is depending on how much power you have available on one hand and the hull speed at a particular instant on the other hand.
Isnt this exactly the good thing about Autoprop when motorsailing?

A fixed propeller on the other hand could be considered as quite stupid.

Hopefully you will bear with me when I give a little background to my original question.
I have used methods and diagrams in David Gerr's wonderful and intriguing book "The Nature of Boats". If you want to dive even further into the subject I recommend "Propeller Handbook" from the same author. I dont know if I can share these diagrams with you since they of course are copyrighted by the author.

Anyway here is how it goes:
Basic data about my boat: lwl 33 feet, displacement 18000 lbs, future engine power 87 hp at 3000 rpm.

In the Displacement Speed Chart (Page 246) we will see that for such a boat 45 hp is needed to reach the maximum hull speed of 8 knots.

Now, how much power is necessary to reach 5 knots?
From the diagram we can see that 10 hp is enough.

My future Lombardini of 87 hp at 3000 rpm will deliver 10 hp at 800 rpm as I can see from the power vs. rpm spec. This is about idling speed.

Now back to the Autoprop issue.
If the Autoprop does what the advertisement promises it will automatically assume the optimum pitch due to its self pitching characteristics.
With optimum pitch in this case I mean a pitch that with the available engine power of 10 hp will drive the hull as fast as possible.

Will it be 5 knots??? That would be disturbing, I want to be able to go slower.

All the above are of course calculations although well founded.
Is there any support for my findings in real life?

-Ernest

[ernest]

Hi Dave,

I believe that your findings point in the same direction to what I calculated in my former letter.
You seem to have about the same engine performance as I have. My engine specification shows that it would deliver about 25-30 hp at 1300-1400 rpm.
David Gerr's Displacement Speed Chart (still my boat) shows that the speed then would be 6.9-7.2 knots.

How fast is your maximum hull speed? I have not found this in your letters to the forum.
What I am aiming at is that if you have a boat with less displacemnet than mine you might very well reach your maximum hull speed at 1300-1400 rpm.
At least you might be very close to it.

I cannot give you the solution to the big chunking you have experienced but a 21 inch prop on a 1.25 inch shaft does not seem right.
If you also have a couple of inches between the propeller hub and the cutlass bearing you can really get vibrations and oscillations from the prop shaft.
If then the free distances around the propeller are minimal and the propeller throws a lot of water the turbulence will be large.

I once had a motor boat and experimented with a big 18x12" Michigan on a 1 inch shaft. The combination made a lot of noice and and vibrations depending on the rpm.
Careful balancing of the propeller. measuring the straightness of the shaft and you name it made no difference. The cure was a smaller 16x11" propeller and now everything was smooth like a turbo.

It seems from your letter that you are on the same track yourself.

-Ernest

[dkall]

Ernest,

My hull speed should be 7.23 kts. Waterline lenght is 33.5'. My displacement is 31,500 lbs and a full keel boat. There is a couple of inches between the end of the shaft log and the begining of the hub for the propellor ( I don't yet know how much as the water is rather cool; but soon I'm going to dive and take some measurements. )

I've two concerns with them, first is the "whirl" which it sounds like you had too on your powerboat when it was over proped, and second that I'm abusing my engine if I can't go over 1400 rpms.

Do you have some formulas your working from? Are they online anywhere?

Thanks,