neil1967
Well-Known Member
I know the physical difference between folding and feathering props, but, on a yacht what are the practical advantages and disadvantages of one over the other?
Thanks
Neil
Thanks
Neil
Folding versus feathering props
- Thread starter neil1967
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sailorman
Well-Known Member
Feathering ( ie my Maxprop ) is same drive forward & astern + no drag
bedouin
Well-Known Member
There are many different types of both folding and feathering props.
On average folding props will be cheaper than feathering and give less drag when folded. Most also have the benefit of being a lot simpler so less complex / expensive mechanisms to maintain or go wrong.
Cheap two bladed props have substantially less drive in forward or reverse than most feathering props. Some designs also take a little time to deploy so need more revs to get them to grip, particularly astern.
The very best folding props are very good indeed, they can have as good drive forwards as a fixed prop and better in reverse. However they are expensive and complicated.
On average folding props will be cheaper than feathering and give less drag when folded. Most also have the benefit of being a lot simpler so less complex / expensive mechanisms to maintain or go wrong.
Cheap two bladed props have substantially less drive in forward or reverse than most feathering props. Some designs also take a little time to deploy so need more revs to get them to grip, particularly astern.
The very best folding props are very good indeed, they can have as good drive forwards as a fixed prop and better in reverse. However they are expensive and complicated.
earlybird
Well-Known Member
Astern thrust of most folders usually leaves something to be desired IMO.
When I looked at some feathering props at LIBS a few years ago, I came to the conclusion that, although better in that respect, maximum forward thrust was probably less than a good folder, due to the uncambered blades, at least on the ones I looked at.
Since my engine power is on the low side, I saved my money and stuck with my Flex-o -Fold, which seems to be good in ahead, and put up with the poor stopping power.
When I looked at some feathering props at LIBS a few years ago, I came to the conclusion that, although better in that respect, maximum forward thrust was probably less than a good folder, due to the uncambered blades, at least on the ones I looked at.
Since my engine power is on the low side, I saved my money and stuck with my Flex-o -Fold, which seems to be good in ahead, and put up with the poor stopping power.
westernman
Well-Known Member
At the Paris boat show last year there were curves showing that feathering props have less drag than folding props when sailing.
It might be biased. It was on the stand of a manufacturer of feathering props.
It might be biased. It was on the stand of a manufacturer of feathering props.
zarathustra
Well-Known Member
Which ones do you consider to be the very best folding props?
Koeketiene
Well-Known Member
Ditto my Darglow Featherstream - pleasantly surprised by the price too (compared with Maxprop).
bedouin
Well-Known Member
When I went through the same exercise a few years ago I went for the Gori 3 blade folding prop in preference to the feathering ones. it is a very clever design that opens in different directions in forwards and reverse so as always to present a properly profiled blade. That makes it theoretically more efficient than a fixed blade prop in reverse - and I certainly find its performance excellent. I replaced the 2 blade fixed prop on my boat because the handling astern was problematic - the Gori 3 blade is a vast improvement in that department.
In price and complexity it is rather more like a feathering prop than a folding. It has the downside that it seems to lose efficiency when dirty, more than a fixed would, and it requires anodes and stops replacing on a regular basis that adds to the cost over the lifetime of the propellor.
I think the flex-o-fold is also pretty good, although doesn't have the same benefits as the Gori in reverse (still probably good enough in most cases). I think there is at least one other prop of very similar characteristics to the Gori but I can't remember its name.
Dockhead
Well-Known Member
T'aint no propellor in the world which has no drag. Any folding or feathering prop will have a lot less drag than a fixed prop. Folders tend to be better than featherers, where drag is concerned. Folders tend to be better than featherers where drive in ahead is concerned. Featherers tend to have more drive in astern than folders, however.
A rough rule of thumb. I use a featherer which besides feathering, is also self-pitching -- a nice bonus. It's an Autoprop. It has the highest drag of any non-fixed prop, however, which is the main negative.
Seajet
...
Feathering props simply MUST create more drag than folders; they are also much more vulnerable to collecting lines, nets, general flotsam.
On the plus side, generally more efficient at driving the boat under engine - forwards and backwards - than folding jobs.
It's a rare problem now, but if faced with a folding prop', do make sure the blades are linked by cogged teeth; I met someone who had a boat with independently hinged prop blades, sometimes only 1 would come out resulting in a lot of vibration and 'interesting' motive power...
Tranona
Well-Known Member
Really depends what you are looking for over a fixed prop. Folding props generally have less drag when folded, but most are two blade and perhaps not so good for motoring - so mostly chosen by those who want to improve sailing performance particularly in light airs. However, some of the recent designs, particularly 3 blade folders are both low drag and good for motoring.
Feathering props are usually chosen for cruising where good motoring or motorsailing performance is required, and for installations where there is no space for a folding prop. They are usually more complicated and therefore more expensive and need more maintenance. Some designs are variable pitch and many allow a different pitch in forward and reverse to improve reverse performance at low speeds (and to compensate for flat blade shapes).
YM carried out a review and real life tests of a range of props a couple of years ago, which gives good information of the merits of different designs. However does not give any firm recommendations because different boats and different usage patterns usually determine different props!
richardsnowstar
Well-Known Member
I am fairly certain there was a recent test of a variety of folding and feathering props. Sorry but can't remember if it was PBO, YM or ST.
charles_reed
Well-Known Member
Generalisations are dangerous - many feathering props do not have flat blades - though the Maxprop (to which you are probably referring) does.
In fact, work done at the Wolfson tank in Southampton, shows some feathering props (notably the Maxprop) produce less drag than most comparable folders and a 3-bladed folding prop will, usually, produce more thrust than 2 fixed-blades.
In the end one tends to get what one pays for - the OP's question was disingenuous - as there are feathering props, self-pitching props, and folders, all in at least two categories viz two or 3 bladed and all have different strengths and waeknesses.
The greatest benefit of a self-pitching prop, is the ability to motor-sail at low revs and obtain full thrust, something impossible with any other type of prop - the increase in speed due to reduced drag is incidental (and a good folder will always cause less drag than the self-pitching prop).
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charles_reed
Well-Known Member
At the risk of seeming pretentious, the question you've asked is far larger than the replies you've had.
A brief historical resumé, will illustrate part of the complexity of the question.
There are as you have said 2 main categories - folding propellers and variable pitch propellers. Both originated in Denmark, the earliest being the Hundestedt variable pitch in about 1924 and the Gori folding propellor in 1975.
The Hundstedt, now only produced for commercial vessels, was seized upon by various enterprising Yachties in the 1950's because it was possible to change pitch to fore and aft and reduce sailing drag.
Alteration of pitch was by a rod down the centre of the shaft, ending in a worm-drive which allowed the operator to change the pitch to accommodate load variations. It was widely fitted to Scandanavian FVs, because it also saved money by dispensing with a forward-reverse gearbox. Bringing one of those vessels alongside was a challenge that most yachties would fail.
The Gori folding prop was first marketed in the mid-70s, followed very shortly after by the US Max-Prop. This latter relied upon water-pressure to vary the pitch of the blades to a pre-determined point.
Unlike the folding propeller, or a fixed propeller, it was as effective in reverse as in forward gear and private tank tests showed that a 3-bladed version caused slightly less turbulence at 10 knots than a similar sized folding prop.
Most feathering propellers such as the Kiwi are based upon similar principles, though many have a "shape" to improve drive over the flat-bladed Max-Prop at the expense of slightly more drag when feathered.
Finally, in the late '80s, a UK engineer designed the Brunton Autoprop which is a self-pitching propeller, adjusting the pitch to whatever load was on it - coarsening the pitch when under low-load, such as motor-sailing, and reducing it when plugging into a head sea.
So a summary:- Fixed props are cheapest - high drag - inferior performance in reverse.
Folding props are more expensive, in 2-blade form inefficient in forward, lowest drag and worst of all formats in reverse (though with high-revving shafts less of a problem).
Next in cost (with the possible exception of the plastic Kiwi) are the automatic variable pitch propellers, equally effective in reverse and forward and, in 3-blade form, some cause less drag than a 3-blade folder.
Finally the most expensive - self-pitching props, the most effective in forward and reverse, never (if properly matched) causing the engine to be over-propped, with similar drag to the less-slippery variable-pitch props and giving the most economic fuel consumption (but the difference in first cost would take about 18 years to recover over a fixed propeller).
I hope that answers the question?
PS It's possibly significant that Brunton's now offer a folding 4-bladed propeller.
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Ric
Well-Known Member
One important factor not mentioned by anybody so far is that two-blade folding props fold at much lower boat speed than feathering props can feather. In light winds, when the advantages of a low-drag prop are most apparent, some feathering props don't feather. The otherwise excellent three blade Gori folder also suffers a little in this respect - it only folds at about 3 knots.
Regarding drag of self-pitching props, you're a bit too generous. Segel magazine found that the Brunton had about 10% of the drag of a fixed prop, which was significantly more than feathering props which had ratios of around 2%. The drag of the Gori two-blade folder was so small it was immeasurable.
Finally and pedantically, MaxProps are not a US invention - they were invented by Massimilio Bianchi in 1975 in Milano.
bedouin
Well-Known Member
Not actually 100% true - the Gori 3 blade prop does have a mechanism that can also achieve this - whether it is of any practical benefit is a different matter
Ex-SolentBoy
Well-Known Member
Is this a theoretical question or do you have a particular boat and type of sailing in mind?
brianhumber
Well-Known Member
Not actually 100% true - the Gori 3 blade prop does have a mechanism that can also achieve this - whether it is of any practical benefit is a different matter
Had a Gori 3 blade dual pitch prop since late 1990s when original 2 blade folder on Ronhilda lost a blade.
Regarding the benefit, difference in performance was dramatic, the different pitch astern gave me lots of bite and using this pitch in ahead rotation ( by going astern to ahead without letting the blades fold ) gives me lower revs, better fuel consumption. Over the years this must have saved a lot of fuel and cost which is now becoming of greater importance. Should I want the original design finer pitch power/thrust in heavy weather then I simply let the blades rotate by taking the revs off but in practice I have only used the finer pitch ahead on half a dozen occasions as usuallly sailing in heavier winds.
Very simple, yes the Anode does want replacing but the stops seem to last years for me. The engineering is impressive and it takes but 30 mins to undo the cone and have the prop hub/blades off. As another poster has said you gets what you pay for.
Will be having the gearbox out this winter so will see if the shocks of going from ahead to astern has marked the teeth etc but the PRM delta has not complained as yet. Blades seem to fold at around 2/3 knots and get rid of /let weed pass over the folded blades etc well. Only trouble I have over the years since 1997 is when I have caught pot lines ( once) a floating fleece ( once ) and a fertilizer bag ( once) all three times its was the cutlass bearing that was damaged.
Brian
charles_reed
Well-Known Member
thanks for your corrections - I do have to dispute Segel's findings - my own experience and that of many other Brunton users is that one obtains a 20% increase in speeds in low to medium windspeeds, compared to a fixed prop (in my case a 2-blader).
It is true that some well designed 2-blade folding props, in clean and well-maintained condition, fold at about 2 knots boatspeed (depending on boat underwater configuration), but a feathering prop in equally good nick feathers at about 3 knots on the same hull configuration.
However in terms of efficiency in converting torque into boatspeed and hp into drive 2-bladed props are a non-event and not really for serious cruising, great for getting in and out of the marina in regatta conditions but utterly useless in trying to get up the Needles Channel on an ebb in the teeth of a brisk NE.
Tranona
Well-Known Member
You are falling into your own trap of sweeping generalisations. Motoring performance with my Flexofold 2 blade is virtually identical to the fixed prop it replaced, but probably not as good as a 3 blade. However the boat was never specified with a 3 blade, so don't have comparisons. You can get folders to fold easily at very low speed by putting the engine in Forward after you have switched off - and then back into neutral if you wish.
