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Old 31-12-2010, 08:42   #16
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A recent comparative test...

from French sailing mag 'Voile magazine' is available here (in French infortunately)
http://www.bomarine.net/index.php/do...pril-2009.html.
The winner (?) is the Autoprop.

As an owner of a (3-blade) Kiwiprop on a (rather light) Jeanneau 36', I, (partly duplicating previous posts), can report
- tremendous performance in reverse
- lack of vibration
- necessity to tune the factory pitch setting (mine was overpitched), which is not difficult, but requires CARE, as you do it independently on the 3 blades
- tendency to free-rotate slowly under sail
- lubrication to be a pain in the ... unless you have the proper nozzle on the grease gun

The French test makes it clear that feathering props are a bit less efficient wrt milles per gallon/(liter ) performance than folding or self-pitching ones.

I'd argue a Kiwiprop is good value for money (the prop itself and extra blades are rather cheap) although it may not be the ultimate in design / performance

FWIW someone with a large engine w hydraulic clutch recently complained on a French forum about some stopping rod ending up twisted. He reported good service from the French distributor.
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Old 31-12-2010, 08:47   #17
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"Do be aware, though, that ALL feathering props share the difficulty of being less efficient than either fixed or folding props. This is due to the requirement that their blades NOT have any twist in them in order to make the feathering work. The lack of twist means a less efficient conversion of shaft horsepower into thrust, and this in turn means poorer fuel economy. In our case, changing from a good two blade folder to the Autostream cost us 25% in fuel usage."

I have had an Autostream for 15 years and about 20K with no problems (even picking up a 3/4 in poly line that ripped out the bolts in the shaft facing and tore out my cutless bearing did nothing to the prop) and the fuel consumption has been exactly the same as my old fixed prop but with better cruising speed. I thought I read somewhere where twist is irrelevant to thrust until you get into higher speeds characteristic of powerboats--teens and above. Was this in David Gerr's book? Or was it in Practical Sailor article? The ability to tune it easily with external adjustments is important--I would not have wanted to pay a diver or haul the boat the several times I have had to adjust it to get it perfect. Also, I adjusted it for heavier weight of a two year cruise and back when the cruise ended. Added a half knot of speed to sailing speed. One of the best investments in performance on my boat.
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Old 31-12-2010, 09:01   #18
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Quote:
Originally Posted by sailorF54 View Post
from French sailing mag 'Voile magazine' is available here (in French infortunately)
http://www.bomarine.net/index.php/do...pril-2009.html.
The winner (?) is the Autoprop.

.
.

That looks like a great article from what I can get from the graphs. If only it was in english
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Old 31-12-2010, 09:20   #19
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Nigel Calder did an exhaustive review of folding and feathering props about a year ago in Professional Boatbuilder magazine as part of his hybrid boat project. Lots of graphs and such. I can't find my copy. Hopefully someone will correct any faulty memory:

The props looked surprisingly close (at least to me). The autoprop was a bit of an outlier. It had substantially better efficiency under power but also substantially more drag.

The Flex-o-fold and Varifold were his "winners" but only by a little.

The biggest difference by far was caused by props that were mismatched to the boat/engine. Under propping made a prop perform much worse than any brand difference. Of course, over propping has it's own problems to your engine. So getting this right is really important and it often appears to require some amount of trial and error.

My own experience is that too little distance between the blade tip and hull (or aperture) and even the shape of the hull right over the prop can cause substantial vibration. The people who get in trouble seem to be right at the manufacturer's minimums. If you are in that position, I'd go one size smaller on the diameter and increase the pitch accordingly.

Carl


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Old 31-12-2010, 09:42   #20
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We have a Max Prop on our Little Harbor 38. While I cannot compare it to others I do want to say that it took three seasons before we figured out the right pitch even with the manufacture help. Don't expect to get it exactly right the first try.
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Old 31-12-2010, 10:22   #21
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.

That looks like a great article from what I can get from the graphs. If only it was in english
Don, Yachting Monthly did a comparison test recently. You can either buy a copy from YM or down load it from here:


Folding Propellers - Flexofold

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Old 31-12-2010, 11:16   #22
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Don, Yachting Monthly did a comparison test recently. You can either buy a copy from YM or down load it from here:


Folding Propellers - Flexofold

Pete
Thanks. I did find this article a little while go. The interesting thing was that a lot of the manufacturers statements didn't really get supported. And that some of the differences between folding and feathering props were a lot smaller than one would believe based on the hype.
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Old 31-12-2010, 11:42   #23
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I put an autoprop on my previous boat, but the blades hit the strut in reverse. I discovered this problem while the boat was still on the hard, fortunately. The rep said this was no problem, all I needed was to install a shaft saver. I came up with a better solution and returned the autoprop, after which I installed a Flexofold. Liked it so much that I went straight to flexofold on the next boat.
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Old 31-12-2010, 12:50   #24
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I put an autoprop on my previous boat, but the blades hit the strut in reverse. I discovered this problem while the boat was still on the hard, fortunately. The rep said this was no problem, all I needed was to install a shaft saver. I came up with a better solution and returned the autoprop, after which I installed a Flexofold. Liked it so much that I went straight to flexofold on the next boat.

Well this is the best post for me so far since Bash's last boat is the same as the boat I'm getting. Now I can just rule out an Autoprop!
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Old 01-01-2011, 14:55   #25
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Well a couple of days extra research can turn up lots of things. I orginally was going to go the feathering prop route due to the claims of less reverse prop walk and reverse performance.

Now after finding some more info I think folding props make more sense. Better forward power, almost to and as good far as reverse prop walk, less expensive (will see once alll qoutes come back), less complex. Not as powerful in reverse but I never have needed that.

Had high hopes for the Kiwi prop for a while as the price was good. But it doesn't seem to do anything well other than be low drag under sail and when I'm running the engine I want that prop to perform.
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Old 01-01-2011, 15:57   #26
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Don,

I can't recall where I saw it but one Kiwi prop owner ended going away from his kiwiprop to another brand. Found it

KIWI Prop - Multihulls4us Forums

Good luck with your decision. I think i will be going with the seahawk when time comes.
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Old 24-01-2011, 10:43   #27
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Hi. I have had a 20" Autostream on a 75hp yanmar on a Nimble Wanderer. Frankly, it rescued the boat for me. It now sails so well I now and them surprise what should be faster boats under sail. I agree I lost a bit of speed under power but nothing like I gained under sail. It has worked well for nearly 12 years now and looks like new.
And I have a pair of 16" KIwi's on 25hp yanmars on a 34ft Catalac catamamaran. I love them. They are realatively cheap. I have banged them about, got rope in them etc etc. They have been on since 2005. Last summer we did a quick bottom job, relubed them and tweeked the adjustment. Dispite the abuse they looked fine and are back in the water. Cheers. Lloyd
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Old 31-01-2011, 12:46   #28
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I have always used Maxprops as their service and availability of parts were worth the extra. Maxprops must have the most history with feathering props as well,I believe its all probably changing now but Im still sold on their service. I bought my current boat last year and the blades on the 3 blade maxprop were wobbly and in need of rebuild. (prop was circa 1985) I contacted PYI about rebuilding and they were very professional and I will be sending it to them. They estimated a full rebuild to be a few hundred dollars.
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Old 31-01-2011, 16:49   #29
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I know it isn't strictly a feathering propeller, but we recently fitted a Flexofold 3-blade folding prop, and are very happy with the performance. FWIW, this was repacing a very old, worn-out, 2-blade Autostream feathering prop.
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Old 31-01-2011, 17:00   #30
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Quote:
Originally Posted by CarlF View Post
Nigel Calder did an exhaustive review of folding and feathering props about a year ago in Professional Boatbuilder magazine as part of his hybrid boat project. Lots of graphs and such. I can't find my copy. Hopefully someone will correct any faulty memory:

The props looked surprisingly close (at least to me). The autoprop was a bit of an outlier. It had substantially better efficiency under power but also substantially more drag.

Carl
We have used Bruton Autoprops both on our previous boat (for 10 years) and on our present boat.

I think Carl sums it up nicely. The Autoprop has more drag than other feathering props because the blades are ungeared (the blades change their pitch according to balance between hydrodynamic pressure and centrifugal force by a very clever and very simple mechanism) and one of them always droops down into the water stream.

But their unique, and in my opinion killer advantage, is that they are not only feathering, they are self pitching. So unlike, say, a Maxprop, which has a fixed pitch which can be changed only by mechanical adjustment, the Autoprop changes pitch continuously and automatically. So it is like an automatic transmission shifting gears as required, compared to a single-speed drive like other props. This is fantastic for motoring efficiency, especially in cases where (a) you are bashing into strong weather and need more torque (lower gear); or (b) you are motoring downwind or are motor-sailing and need less power, a higher gear, and lower RPM's. In all situations where you need less than normal power, you can just throttle way back and the Autoprop goes into overdrive. This benefits not only fuel consumption but also noise.

It is also dead simple without any gears, which to my mind is elegant engineering. The blades are simply mounted with ball bearings to the hub and swing freely.

So I like it very much indeed and can highly recommend it to anyone who (a) can tolerate the outrageous cost; and (b) can tolerate the loss of sailing performance.
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