2 Vs 3 blade folding prop

[Robin]

Well I was joking a little about the need for the spare blade! /forums/images/icons/smile.gif

There is no doubt getting the right diameter/pitch is really important and over the years I've had several props altered, either the diameter or the pitch even both. In my case all of them were originally oversized preventing full revs under load and therefore preventing the full engine output from being obtained. The prop on our old W33 I had checked and each blade of the 3 was a different pitch! We reduced the diameter by 1" and the pitch was set the same on each blade and the performance was much better. Later we re-engined and fortunately got the calculations right first time for the new prop needed.



<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[Rob_Webb]

kiwiprop

Living in kiwiland I am surrounded by kiwiprop users (don't have one myself) and they all rate them. Seem good value too. Typical feedback for the 3 blade feathering prop is that they 'bite' as strongly in reverse as ahead, hence response is suprisingly fast - sometimes too fast unless you are used to 'putting the brakes on'!

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[grama]

Pat Manley of PBO has much info on all this. The extensive screed is awaiting PBO's editor to publish........apply pressure to PBO to get it in print! Pat has been waiting a while. You should differentiate between cruising and racing.........ie a cruiser would be more interested in the yachts motoring efficiency and the racers in the folded lack of drag.

 

[Bish]

I had VP 2 blade folder on HR31, OK in flat water, NG in chop or at all in reverse.

Fitted VP 3 blade folder in summer, extra 1 knot ahead, miles better in chop, and the bloody thing goes or stops when in reverse. No noticable difference to sailing.

Best £800 spent this year, even got 15% discount on VP price as prepared to wait 2 weeks for special order at Volspec.

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Hi Stork, I assume by VP you mean Volvo Penta? And when you say “extra 1 knot ahead” is that under sail or power please?

 

[Mr Cassandra]

Nice old thread.
I have a M prop and notice no difference when towing the dinghy.

 

[Daydream believer]

If Santa is really in a generous mood, have you considered a Brunton Autoprop? They adjust pitch to suit load so that they are efficient over a much wider range of RPM, and the blades flip in reverse giving you great stopping power. Drag when sailing is also much lower than a 3-blade fixed prop.

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Pick up weed easily, no good in choppy water, use more fuel, and manouvering in marinas is difficult until you get the hang of them, stopping power is NOT as good as a fixed blade, quite a lot of propwash which is noticeable mid season if the boat starts to get some weed or film on it ( which mine does as i have coppercoat)
excellent if you want to motorsail though
and that is from a user who is so fed up with it that he may change it at the end of the season if pennies are available

 

[langstonelayabout]

I've had two similar boats that I've fitted folding props to.

1: Well worth the money I ended up sailing faster and for a wider range of wind speeds.
2: I bought a 2 blade Flexofold from the UK distributor. It cost a little more and the money was well spent as I had a non-standard taper on my propshaft and they re-tapered the prop before I received it. With their instructions it took me 10 minutes to fit the propellor once ashore.
3: The new 2 blade Gori prop I had fitted was nice and shiny and worked fine. It was fitted by someone else and seemed to need a funny spanner.
4: My choice? I'd buy another Flexofold as first choice. Not only did it work beautifully and was sized correctly, it was so smooth in motion and a item of great (engineering) beauty. It seemed a shame to fit it to the boat and get it wet...

 

[mainsail1]

Pick up weed easily, no good in choppy water, use more fuel, and manouvering in marinas is difficult until you get the hang of them, stopping power is NOT as good as a fixed blade, quite a lot of propwash which is noticeable mid season if the boat starts to get some weed or film on it ( which mine does as i have coppercoat)
excellent if you want to motorsail though
and that is from a user who is so fed up with it that he may change it at the end of the season if pennies are available

I am surprised!
I have had an Autoprop for 15 years on my boat. I find it adds 3/4 knot to speed when sailing. When under power it stops the boat well and goes astern pretty much in a straight line. In ahead you get more push for less revs.
The only annoying thing is that it gets through two anodes a year which is a pain.

 

[BelleSerene]

Anything which came with a 'free' spare blade would worry me, it must mean they think it is necessary or why increase your material costs by 25%!

They do, and it is.

When I had a Kiwiprop one of its 3 blades fell off. Presumably hit by a log. They’re some sophisticated plastic rather than metal.

The dealer told me that was impossible (that’ll make it a miracle then; we must be on the wrong thread.) But they sent me a replacement blade which I fitted.

They now advertise that the blades are ‘sacrificial’, protecting your stern gear. Thus turning a bug into a feature. Accordingly, they give you a ‘spare blade’!

I was very happy with it, FWIW - well, until it turned into a nastily vibrating 2-bladed prop with a 240 degree angle between the blades! But I was pleased to replace it with a Featherstream.

 

[Slowtack]

I have used both a VP 3 blade folder and a fixed two blade prop with the same engine. The two props have the same diameter and pitch. The folder is obviously better when sailing. I have found that the fixed twin blade is somewhat more efficient when motoring (boatspeed vs engine revs) but the three blade folder is better for accelerating from a standing start and for slowing/stopping under engine.

 

[kacecar]

I know it's a resurrected thread but it triggered my memory (an increasingly rare event these days). YM did a fairly extensive test on folding and feathering props way back in 2009, comparing them with each other and with the standard 3-bladed fixed prop - all on an Oceanis 323.

Without giving too much away (I suspect the publishers would prefer an interested punter to buy a reprint) the principal conclusions were that, in general (there were exceptions in almost every case): a folding/feathering prop significantly reduces drag and, therefore, increases sailing speed; with most types one gets less prop walk than with the fixed 3-blade; in general the folders appear to give more forward speed and pull than the featherers, but a bit less pull than the standard fixed 3-bladed prop; going astern the featherers gave more pull than the folders and so produced better emergency stop times (here the difference between the strongest and weakest examples appeared significant, the strongest producing almost twice as much pull in astern as the weakest).

Well, that's what they said at the time.

 

[BelleSerene]

http://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

 

[Roberto]

also, from 2004 youtube has been collecting very explicit underwater videos or pitiful performance of 3-blade *folding* propellers in rear, some of them not even keeping the blades half opened whenever used at less than full revolutions; sorry I do not remember the exact brands but a quick search would show many examples; the very very limited increase in drag under sail of a 3blade feathering compared to a 3blade folding imho is not worth the loss in rear gear performance

 

[Tranona]

also, from 2004 youtube has been collecting very explicit underwater videos or pitiful performance of 3-blade *folding* propellers in rear, some of them not even keeping the blades half opened whenever used at less than full revolutions; sorry I do not remember the exact brands but a quick search would show many examples; the very very limited increase in drag under sail of a 3blade feathering compared to a 3blade folding imho is not worth the loss in rear gear performance

I don't know what props they used in the videos (although could guess!), but that is not true of all folding props. The reverse performance of my FlexoFold is at least as good if not better than the fixed prop it replaced. Agree that feathering propellers are inherently more predictable in reverse (I have had one of those as well) poor reverse performance of folding are design specific and not generic.

 

[geem]

also, from 2004 youtube has been collecting very explicit underwater videos or pitiful performance of 3-blade *folding* propellers in rear, some of them not even keeping the blades half opened whenever used at less than full revolutions; sorry I do not remember the exact brands but a quick search would show many examples; the very very limited increase in drag under sail of a 3blade feathering compared to a 3blade folding imho is not worth the loss in rear gear performance

Except a folded prop does not collect a rope. A feathering prop will. We can stop our boat surprisingly well with our folding Brunton Variofold prop. We never had the opportunity to compare the performance of this prop with a fixed three blade as it was already on the boat but the previous owner reported that it out performed the previous fixed prop

 

[Bish]

I know it's a resurrected thread but it triggered my memory (an increasingly rare event these days). YM did a fairly extensive test on folding and feathering props way back in 2009, comparing them with each other and with the standard 3-bladed fixed prop - all on an Oceanis 323.

Without giving too much away (I suspect the publishers would prefer an interested punter to buy a reprint) the principal conclusions were that, in general (there were exceptions in almost every case): a folding/feathering prop significantly reduces drag and, therefore, increases sailing speed; with most types one gets less prop walk than with the fixed 3-blade; in general the folders appear to give more forward speed and pull than the featherers, but a bit less pull than the standard fixed 3-bladed prop; going astern the featherers gave more pull than the folders and so produced better emergency stop times (here the difference between the strongest and weakest examples appeared significant, the strongest producing almost twice as much pull in astern as the weakest).

Well, that's what they said at the time.

Yes that’s correct, I’ve read that test a few times as it’s available online (someone has linked above). It’s well thought out and executed I think. The glaring omission in the test was that there are no Volvo Penta props for comparison (didn’t make it in time according to the authors). Volvo Penta are major manufacturers worldwide of engines and props, the numbers of these props in the market place must be enormous. The decision to not add them in at a later date is very disappointing. I think they missed an opportunity to turn a good test into an excellent one.

 

[Daydream believer]

I recall a magazine test of props some years ago. May have been the same one mentioned above. It fell down in one particular way. it did not give a proper sea trial.
I know that this is difficult but the performance of some props in a chop leaves much to be desired. In spite of what the manufacturers say my Brunton autoprop is not as efficient in self pitching as it should be. In a chop it starts to drive then hits a wave and stops. The prop then appears to spin with hardly any pitch, ie it feathers, then as it regains its pitch it starts to push the boat forward again. However, by the time it does this it hits another wave and stops again.

The result of this is that quite often in a 1 metre chop I can only get 2-3 kts instead of the 6kts+ i get in flat water. Plus I have to rev the engine really hard and fuel consumption goes up by .5 litres per hour at least.

Looking over the stern one can see that the prop is sort of " pulsing" as a great surge of water pushes out the back then nothing then another great surge.
Some other props are poor in chop, as a friend of mine observed in a 40 ft jeneau & had the same problem with a folding prop.
Anyone who did Dieppe to Boulogne last week in wind against tide will know the conditions that I am talking about

My old fixed blade prop did not do this, yet did not perform so well in flat water. It was, however, more economical on fuel than the autoprop in most conditions.(1.7 litre per hour over 1000 hours against 2 litre per hour over 3000 hours in conditions ranging from rough seas to Dutch canals for both props). It showed up poorly in the test.

The magazine test did not show sea trials in its test- it could not- but effectively gave miss information to readers about the actual performance IN USE of the props

 

[Tranona]

Yes that’s correct, I’ve read that test a few times as it’s available online (someone has linked above). It’s well thought out and executed I think. The glaring omission in the test was that there are no Volvo Penta props for comparison (didn’t make it in time according to the authors). Volvo Penta are major manufacturers worldwide of engines and props, the numbers of these props in the market place must be enormous. The decision to not add them in at a later date is very disappointing. I think they missed an opportunity to turn a good test into an excellent one.

Also missing from the latest guide to props in Sailing Today. Volvo do not actually make props (nor the small HP engines they sell) but just market them. Their folding props have a mixed reputation.

 

[Quandary]

Remarkable fact that all the boats that I have owned since 1975 (except the Nimbus) have had Volvo folding props, mostly two blade which were durable if you were prepared to bore and replace the pins, our Finngulf had the three blade version which was excellent both ahead and astern, my only niggle with it was the short lived anodes. So last winter when I decided to replace the Volvo two blade on our Moody with three I went for a Flexofold, less sophisticated blade shape than the Volvo but a big hub anode which was also available in aluminium, something Volvo did not do. It was interesting that the matching Volvo despite its sophisticated design and the company's reputation would have been almost £500 cheaper to buy. Also interesting that none of the two blade props had anodes or seemed to need them.
Still being assessed but I think the Flexofold is probably as good as the Volvo and the boat should be able to stay afloat for a year if I want it to.