Propeller Poll

Do you have a non standard propeller ? i.e. folding/feathering etc exc O/Boards

  • Yes

    Votes: 65 65.7%

  • No

    Votes: 34 34.3%
  • Total voters
    99
flaming said:
On your boat I'd quite agree.

My Dad's old Dufour 40 came with a fixed prop. In the first season that boat was seriously broach happy under sail. At the end of the 1st season I finally persuaded him to fit a 3 blade folding prop and the transformation to the feel in the helm, and the amount of grip it had, without the disturbed flow from the fixed prop when sailing at speed was incredible. I'd never have believed it if I hadn't sailed the boat before and after the change.

The 3 blade folding prop was also way better than the fixed 2 blade thing for actually powering the boat too... First trip out with the new prop I carefully backed it out of the slip, spun the wheel and applied the amount of forward thrust I was used to - and promptly fell over as the boat shot forward. Motorsailing into a bit of chop was transformed too.
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In regards to improving flow over the rudder I quite agree. A common observation when changing up from a fixed prop, as is a beneficial effect on weatherhelm.

My estimations are based on measured resistances of various props from a variety of tests (French, German, Brit and US) and the resistance values I have calculated for my boat. Voile Magazine also did a number of comparative tests, including sailing several identical boats against one another with different props. Compared to folders feathering types still have higher resistance values and a spinning prop reduces resistance by at least 40%. As some said here: they gain 0.5 kts; 50% of which is near enough to my estimate.

To be sure, a sailing boat prop is always a compromise, usually due to low blade area, so as to have the least impact on sailing performance. In this instance a feathering type can be an improvement.

Also, a folder/feathering prop has the most impact at slow speeds when prop resistance makes out to be a greater proportion of overall resistance. Accordingly, perhaps my boat is unnaturally fast in light going (SA/D 18).

I have nothing against reducing my boat's resistance in light airs, but I'd like to have some assurance of a measurable benefit, before I claw back some of my kids' college funds, apocryphal statements of enhanced pub times to the contrary. I have considered taking the prop off between tides to accurately evaluate impact.
 
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geem said:
A friend with a Bav 46 reckoned he got close to a knot of extra boat speed when he fitted a folder.
Our boat came with a Brunton folder so nothing to compare against but it is vibration free and we can punch into big seas and still do very surprising boat speed. The fuel economy is astonishingly good as well. I can't imagine dragging a 22 inch fixed prop along
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You amaze me. My 2 blade Brunton is useless in 1-1.5 metre chop with a bit of wind behind it. From a cruising 6kts at 2100 RPM I go down to as little as 2.5kts at 2900 RPM (max RPM) Plus at normal cruising speed the fuel consumption is about .2 litre MORE. -5 litre as I rev harder. Then there is the much higher prop wash. Handy in my marina because the direction I am berthed. Handy in some locks if I can berth on the Stbd as it will push the stern over hard when stopping if I come in a bit quick & then rev hard in reverse. But a pig if parking with the dock on the port side. When I reverse out of our fuel berth I have to be careful, because going from 1 -1.5 kts astern to forward I can sometimes rotate 150 degrees before actually going forward. It does take getting used to.
 
I didn't know Brunton made 2-bladers. OTOH, that could explain the poor performance of DD's Brunton ;)

Certainly, the Brunton on a friend's Starlight was brilliant. There was an article about whether to get a spinnaker or a cruising chute on a cruising boat in one of the yottie comics several years ago. The conclusion was to get neither, but spend the money on a good folding/feathering prop, because that will help whenever you're under sail, while the sail only helps when the wind's behind you.
 
Daydream believer said:
You amaze me. My 2 blade Brunton is useless in 1-1.5 metre chop with a bit of wind behind it. From a cruising 6kts at 2100 RPM I go down to as little as 2.5kts at 2900 RPM (max RPM) Plus at normal cruising speed the fuel consumption is about .2 litre MORE. -5 litre as I rev harder. Then there is the much higher prop wash. Handy in my marina because the direction I am berthed. Handy in some locks if I can berth on the Stbd as it will push the stern over hard when stopping if I come in a bit quick & then rev hard in reverse. But a pig if parking with the dock on the port side. When I reverse out of our fuel berth I have to be careful, because going from 1 -1.5 kts astern to forward I can sometimes rotate 150 degrees before actually going forward. It does take getting used to.
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We don't have a two blade prop. Ours is three blade folder. The blades have huge area. Imagine Mickey Mouse's ears.
Our fuel economy at 6 kts boat speed is 3.3 l/hr. Not bad for a 19t boat. We do this speed at 1200rpm.
In 2m chop with plenty of revs we can push over 7kts if you are prepared to accept the fuel bill. Handy if you need it but we normally throttle back to 1400/1500rpm and do 5-6 kts.
It does sound like your prop is a lemon. Couldn't be happier with mine
 
Daydream believer said:
You amaze me. My 2 blade Brunton is useless in 1-1.5 metre chop with a bit of wind behind it. From a cruising 6kts at 2100 RPM I go down to as little as 2.5kts at 2900 RPM (max RPM) Plus at normal cruising speed the fuel consumption is about .2 litre MORE. -5 litre as I rev harder. Then there is the much higher prop wash. Handy in my marina because the direction I am berthed. Handy in some locks if I can berth on the Stbd as it will push the stern over hard when stopping if I come in a bit quick & then rev hard in reverse. But a pig if parking with the dock on the port side. When I reverse out of our fuel berth I have to be careful, because going from 1 -1.5 kts astern to forward I can sometimes rotate 150 degrees before actually going forward. It does take getting used to.
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Not all props are suitable for all boats. Bruntons are best for heavy boats with large engines like geems (and my mates Nauticat 33). You rarely see them on light boats with small hp engines, particularly saildrives. In this sort of application 2 bladed Flexofolds or Volvo folding props are far more suitable and common. Suspect all your problems would go away if you changed to a Flexofold such as I had on my 2 Bavarias with saildrives.
 
All of these props have their uses and, as usual, their drawbacks. They represent another point of failure, are costly and introduce an extra maintenance item to the list. So I am not so keen, nor I am totally happy with talk of miraculous performance improvements; reports are very mixed.

They are highly desirable on a flat bottomed boat where a sail drive is hangs below the hull in open water, hence their popularity with newer boats. It's another example of Layering Technology, where problematic technical fixes are introduced to cover up basic design problems and are then marketed as exciting, must have, developments.

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They are highly desirable on a flat bottomed boat where a sail drive is hangs below the hull in open water, hence their popularity with newer boats. It's another example of Layering Technology, where problematic technical fixes are introduced to cover up basic design problems and are then marketed as exciting, must have, developments.

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My boat couldn't be more different from what you describe. We have a deep fin and skeg hull with no flat sections on the hull but the prop performs extremely well using conventional shaft drive. Can you imagine the drag imposed by a three blade 22" fixed prop? Why would you do that?
 
Tranona said:
Not all props are suitable for all boats. Bruntons are best for heavy boats with large engines like geems (and my mates Nauticat 33). You rarely see them on light boats with small hp engines, particularly saildrives. In this sort of application 2 bladed Flexofolds or Volvo folding props are far more suitable and common. Suspect all your problems would go away if you changed to a Flexofold such as I had on my 2 Bavarias with saildrives.
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That's good to know. (y)
 
geem said:
They are highly desirable on a flat bottomed boat where a sail drive is hangs below the hull in open water, hence their popularity with newer boats. It's another example of Layering Technology, where problematic technical fixes are introduced to cover up basic design problems and are then marketed as exciting, must have, developments.

.
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My boat couldn't be more different from what you describe. We have a deep fin and skeg hull with no flat sections on the hull but the prop performs extremely well using conventional shaft drive. Can you imagine the drag imposed by a three blade 22" fixed prop? Why would you do that?
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Exactly! It is far too easy to dismiss the value of non fixed blade props just because they might be seen as an unnecessary expensive attempt to deal with an imagined design failing. The basic conflict between the requirements to propel a boat by a motor and propel it by sails are there, whatever the configuration of the drive train or hull shape. A good propeller is broadly one that is the largest diameter consistent with the space and the power available but this in turns creates the largest amount of drag when sailing.

In reality with a saildrive it is much easier to resolve some of this because the prop operates in clean water and often a simple small 2 blade prop works well, and for a further reduction in drag a simple folding 2 blade even better. A long keel boat with an aperture is a different kettle of fish as the prop is behind a keel and part of the blades do nothing. The 2 boats I currently have illustrate this. They are both the same displacement and have nominally the same hp, but the Bavaria has a simple 16" 2 blade whereas the GH needs a 17" 3 blade with the largest blade area possible - as you say, imagine the drag! Needless to say I shall be fitting a 3 blade Featherstream. I did exactly the same on my earlier Eventide, moving from a 13" 2 blade then to 14" fixed 3 blade (with a larger reduction ratio box) to eventually a 15" JF feathering. The difference in both sailing and motoring with the same Yanmar 1GM was remarkable. Added to the feathering facility the other big benefit of some feathering props is the ability to fine tune pitch and in particular have different pitch forward and reverse which is exactly what we did with the JF - takes a lot to stop 3.5 tons of boat with a 1GM unless you have a steeper reverse pitch.

A huge amount of work has gone into designing non fixed blade props over the last 20 years or so to the extent that most outperform fixed blade props when motoring and give a permanent reduction in drag when sailing. However they are not all the same and it is really important to match the type of prop to the boat and the way the boat is used. Problem for many boat owners is that it is difficult to get unbiased information, although the YM comparative test a few years ago got close. It would be good to do this again as there have been further developments since then, but I fear it is too difficult and expensive for our stripped down magazines to contemplate.
 
Tranona said:
Problem for many boat owners is that it is difficult to get unbiased information, although the YM comparative test a few years ago got close. It would be good to do this again as there have been further developments since then, but I fear it is too difficult and expensive for our stripped down magazines to contemplate.
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Thanks to Long Keeler for raising the issue - though it turns out, unsurprisingly, to be much more complicated.

As an aside

There is a lot of subjective comment in the thread, For an owner to make a choice they need unbiased data, ideally focuses at their particular requirements, sail drive, shaft drive, long keel, short keel, 2 bladed, 3 bladed and that's just to start. Many decisions for yachts are based on unqualified comment on the internet, which totally lacks data, lacks any serious attempt at comparison based on data - and is thus useless. Some of the comments on the internet are totally wrong - but with constant repetition become fact and the author becomes a new Guru. Much work is never peer reviewed - how many experts do we have on prop design here? Some comment on the internet is based on sensible data, looks impressive - but might have no relation to the particular needs of the individual - but the danger of applicability to the wrong application are seldom underlined. One reason being - people have a poor attention span and complain when a post is too long AND its the internet - no-one is paying for hard won data).

The current batch of props available all work - otherwise the manufacturer would have folded :) - but they are basically all different (just look at them)- - they are different). They thus are not ideal for every situation. Extolling the virtues of one's choice is only one side of the equation - defining the downsides needs consideration. There is also little point in defining how effective a prop might be omitting to mention details of the yacht, the prop installation and the conditions under which the data is derived (some have made serious attempts but so much is also omitted).

The over reliance on data from the internet (its on the internet it must be true), including YBW, means subscriptions for the printed media is decimated and the ability of printed media to fund further work is simple impossible.

Props are expensive (and I suspect - profitable) they merit serious, unbiased review.

The answer is in our hands - but I don't see the environment changing.

Apologies for the winge

Jonathan
 
To illustrate the problem I outline

For me to have data for our yacht:

We have 2 engines. We need 2 props from each of the manufacturers, sized by the manufacturers. We should take independent advise as to whether the manufacturers recommendation is correct, maybe from the yacht designer, and if the recommendations are different - test both.

We now need to instal each of the pair of props, we could beach and change but that is tide dependent - or we could slip - imagine the simple cost of changing. Slipping means we could complete the trial quite quickly, but changing a 3 bladed Volvo prop is quite time consuming as you need to take the prop completely apart.

Now we need to conduct a bollard test, we need a load cell, for each pair of props at different engine revs 2 x 20hp Volvos in both forward and reverse with no tide or current. Ideally we should derive some data motoring into a bit of chop and wind. Some propellors can have variable pitch, we should throw that into the mix.

If there is a prop expert (and I have no expertise at all) - they might suggest modifications (and I shudder - additions) to my protocol

Now this would be invaluable to me, except actually it is of no use to me - I'm not changing 2 very expensive 3 bladed folding Volvo props - and its not of much use to most other people as they don't sail a cat - but this will be true of any test yacht chosen - not necessarily relevant to the owner of a long keeled yacht if our test yacht is a Benny. But someone with expertise in props might be able to make some projections on how the data derived will be useful for other yachts.

My guess is this would best be conducted by at least 2 people, preferably 3. But we also need the temporary time of a prop expert. We also need to have someone to lift the cat, it is unlikely my 2 or 3 can operate a travel hoist.

Who is going to pay for all of this? Historically it was completed, as Tranona mentions, but today - with dwindling subscriptions.....

And I don't have the answers.

Jonathan
 
You are describing exactly the sort of testing I was involved with using my old Bavaria 37. Even with expert technicians, deep water access slip for the hoist and a measured half mile run just outside the marina the best we managed including the bollard pulls was 4 props in a full day. The YM test I referred to earlier did the same tests in a different location with one boat and covered around 15 props in 4 days. That worked because of the support from the prop suppliers who fitted the props but still a massive logistical challenge.
 
One of the best prop tests I have seen, was the one in Voile magazine. However, it is impossible to account for all the variables in actual boat for boat application.
Even in standard prop design, choice and sizing is difficult at best to get it right and it is said that if the prop of your choice falls into the 50% efficiency bracket, you are already in the ball park. For a displacement hull, 70% is as good as it gets. Unless a prop is of variable pitch, it will reach this efficiency only within a very narrow range.

For pure motoring efficiency, within the space constraints under a hull, a three bladed fixed prop is still the benchmark. Flat bladed feathering props are simply not as efficient a profile for going forward, though some, especially with a coarser reverse pitch, may be better in reverse.

For reduced drag under sail, folders are unbeatable and, if some of the tests are to be believed, can, at least in their 3-bladed version, be as efficient as a feathering type. That said, I'm not at all sure they have sufficient blade area to move a heavy boat effectively, within a given diametre and RPM.

As some have pointed out here: The degree of gain in sailing speed is highly subjective. After spending a considerable amount of cash for a new prop, I am quite sure that there is a certain pressure to justify the expense and interpret the results accordingly. One statement I read, was that the gains made were between 0.5 and 1.5 kts. I think the operative word here is "between" with 0.8 kts being the generally accepted number over a fixed & locked three blade. If we accept that as fact, though that in itself is hugely variable depending on the individual boat, then having a fixed prop left to spin will reduce this by some 50% to 0.4 kts.
This is at slower speeds only, as when the boat approaches hull speed, this margin is even further reduced by the overall increase in resistance.

It could be argued that lighter boats benefit more from a folder/featherer. However, engine HP and blade area is a function of displacement and a lighter boat will likely have a smaller prop and, consequently, less resistance in the first place. To this point: a heavy boat with a high SA/D value will, in light conditions, have an abundance of power to overcome the resistance due to a larger prop (compared to a lighter boat with an equal SA/D ratio).

Considering that even the professionals have a hard time getting a prop right, I have an equally hard time to ante up the better part of 2500 Brit Pounds to participate in what, to a degree, amounts to a bit of a lottery, even if some of the props allow you to tinker with the pitch to get it "more" right after the fact.
 
Tranona said:
You are describing exactly the sort of testing I was involved with using my old Bavaria 37. Even with expert technicians, deep water access slip for the hoist and a measured half mile run just outside the marina the best we managed including the bollard pulls was 4 props in a full day. The YM test I referred to earlier did the same tests in a different location with one boat and covered around 15 props in 4 days. That worked because of the support from the prop suppliers who fitted the props but still a massive logistical challenge.
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Its actually a bigger logistical exercise than I thought as I had imagined you might do better than 4 props in a day. I imagine (fondly, naively) that all props have their strong points and having the prop suppliers on board is the way to go as whatever those good points are - they will come out in the wash (and hopefully the downsides will also be mentioned). If the prop suppliers are providing some of the labour then the costs for media come down - but do not disappear :( . Someone has to pay for the slipping (and lunch :) ).

Propellors are one of those topics that are ideal for a magazine, which might be a reason both Voile and YM have made group tests. A well defined range of products, a decent cross section of design ideas and the results are important to the reader - and I really cannot think how anyone could complete a group test without the support of a magazine. Other group tests, windlass (for example) - have exactly the same issues (and for windlass - very similar protocols).

We can still rely on the historic group tests - but as Tranona points out, even those tests are already dated (propellors have changed (hopefully improved) but longer term I do wonder where out data, on which we rely to make informed decisions, will come from.

Maybe YM/PBO/Voile/Segeln can get together........

Jonathan
 
Laminar Flow said:
For pure motoring efficiency, within the space constraints under a hull, a three bladed fixed prop is still the benchmark. Flat bladed feathering props are simply not as efficient a profile for going forward, though some, especially with a coarser reverse pitch, may be better in reverse.

For reduced drag under sail, folders are unbeatable and, if some of the tests are to be believed, can, at least in their 3-bladed version, be as efficient as a feathering type. That said, I'm not at all sure they have sufficient blade area to move a heavy boat effectively, within a given diametre and RPM.

Considering that even the professionals have a hard time getting a prop right, I have an equally hard time to ante up the better part of 2500 Brit Pounds to participate in what, to a degree, amounts to a bit of a lottery, even if some of the props allow you to tinker with the pitch to get it "more" right after the fact.
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Not all feathering or indeed folding props have flat blades and some designs such as the Bruntons are specifically designed for heavy boats like yours - you would really notice the difference if you fitted one of those. You only have to look at the newer designs to see that a lot of work has gone into improving motoring performance - as reported by a number of posters on this thread. There is now very little difference between the best folders and featherers in terms of motoring performance and the existence of both types is related to the different types of boats around as I explained above - some boats are better suited (or can only fit) feathering props and others, particularly saildrives are suited to folders.

It is not so difficult to get size right (or at least optimum) now because most boats have more than enough power to achieve hull speed and good suppliers have enough experience now to mostly get it right first time. Of course there are always outliers, particularly in a boat that is underpowered like my old Eventide. We had 3 goes at getting the best compromise.

As to whether these props are good value their increasing popularity suggests they are. Unlike other expenditure on performance improvements what you get with these is a fairly known improvement that does not decay over time. My Featherstream costs much the same as the new mainsail and will last the life of the boat. Individuals make their own choices, and of course buyers often suffer from confirmation bias, but the science and reported benefits are real.
 
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