Kiwi prop or alternatives

[charles_reed]

Well, I'm afraid that I'm going to be the flex-o-fold dissenter.

Our boat was fitted with a two-blade flex-o-fold when we bought her three years ago. Whilst the prop works very well when sailing and quite well when motoring in flat water, the performance drops off as it gets rougher. Where we get worried is when we're going from forward to reverse. It usually works eventually, but often with some cavitation first (lots of noise, but with no 'bite'), but from time to time we get no braking effect at all. As we usualy sail two up, this can necessitate some nifty footwork on the pontoon.

We've only just gone back into the water (three weeks ago), and the prop was free to open and close - no friction or sticking. It was also lightly greased. We've tried lots of strategies - high revs, low revs, combinations, but the unpredictability makes our berthing interesting. We also always check that it'll open in reverse long before we get near our berth, and this is usually (9/10 time) successful. Anyone with similar flex-o-fold issues?

I'm afraid you're illustrating the the common failing of any a) 2-bladed & b) folding prop, rather than anything inherent in the Flex-o-Fold.

There is a world of difference between folding, feathering and self-pitching propellers though people do, in confusion, lump them all together.
All have strengths and all have weaknesses.
The subject does deserve a rather more authoritative study than that provided by this thread.

 

[grievesie]

Kiwi-prop

Another vote for Flexofold. You need to look to see how poorly Kiwi performed in the YM tests a couple of years ago.

This oft quoted YM report was a bit erroneous in my opinion. All the manufacturers were asked to spec their props to achieve max continuous revs of the boat used (Bene 323) - Kiwi-prop complied with this but some of the other manufacturers didn't. Instead they used a higher pitch to give a higher speed in flat water (you only have to look at the range of pitches to see that). The other info missing from YM review was revs achieved for each prop - that would have shown that some were over-pitched.

Alan Pollard of Vecta Marine the UK agent for Kiwi-prop was not pleased about this as you might imagine. If you compare the results for the Kiwi-prop in a April 2009 French 'Voile' magazine review it did much better - that review was more detailed than YM test and more props tested (also included engine rev data). Also it was done in a non-tidal harbour to give consistent results (YM test was done in my home port of Lymington).

All props are a compromise but the Kiwi-prop ticks more boxes than most and at a reasonable price.

 

[RobbieW]

My Brunton Autoprop, now 21 years old requires neither annual greasing and never a new blade.
I would suggest you do not make wild assertions on a subject of which your grasp is obviously flimsy.
Apart from misleading posters, you are leaving ybw.com open to legal action.

Then it is concievable that the spec or design have changed. In the Users Manual for my H5 Autoprop, fitted by the PO in about 2006, it explicitly says '...re-greased once every year...'

 

[cmedsailor]

This oft quoted If you compare the results for the Kiwi-prop in a April 2009 French 'Voile' magazine review it did much better - that review was more detailed than YM test and more props tested (also included engine rev data). Also it was done in a non-tidal harbour to give consistent results (YM test was done in my home .

is this test available somewhere in the web? In English hopefully.

 

[Sans Bateau]

Alan Pollard of Vecta Marine the UK agent for Kiwi-prop was not pleased about this as you might imagine. If you compare the results for the Kiwi-prop in a April 2009 French 'Voile' magazine review it did much better - that review was more detailed than YM test and more props tested (also included engine rev data). Also it was done in a non-tidal harbour to give consistent results (YM test was done in my home port of Lymington).

When I was buying a prop two years ago, I asked someone (Alan Pollard?) on the Kiwi stand at SIBS about the poor results. His answer was that because there were so many boats being tested, by the time they got their turn, there was a tide running. What he suggested was that speed through the water when motoring into the tide was going to be slower than when there is no tide. Isnt speed through the water, just what it says? I went on to ask him about the bollard pull figures, again he called foul, claiming that as the tide was near full ebb the prop was kicking up so much silt it reduced the grip.

I was not impressed with the response from the chap on the Kiwi stand, it sounded like sour grapes with a smattering of BS!

I understand that the only supplier to send along an engineer to that test was Darglow engineering, (Flexofold etc). If the other manufactures were so concerned with results, and certainly Kiwi as their prop could have had the pitch altered, should have done the same.

 

[Halo]

The Kiwi would have been a vast improvement on my old fixed 3 balder and I am sure it is a good product BUT look at it closely. It has blades with squarish ends and which are relatively thick in section. You dont need to be a professor of engineering to deduce that a thinner section with rounder ends is going to be more efficient in use.
All designs/products tend to be a compromise between operating efficiency and purchase cost. The Kiwi seems to be towards one end of the spectrum.
"Yer makes yer choice and pays yer money."

 

[snooks]

A few more details about the test......

Most of the props tested had someone from the company there to fit the props, even if it was just the UK agent, they fitted the propellers to ensure they were fitted correctly in accordance with their guidelines.

Every manufacturer was given the same data: boat dimensions, gearbox ratio etc YM asked then to bring along/supply a suitable prop for that boat/engine combination.

The runs in the river were done in both directions using GPS (averaged) and boat's log. the bollard pulls were performed at Lymington Yacht Haven's fuel pontoon.

The start of the Kiwi installation was at 15:52 24/02/09 and the next prop was fitted at 17:01. So it's fair to assume the Kiwi was tested during that time. LW at Portsmouth was 16:38 0.9m (3 days before springs, 5 days after neaps) LW at Lymington occurs -20 mins so the test of the Kiwi happened at the hour of LW.

Revs were recorded, but not all printed. there were mentioned in the copy when they didn't reach full revs.

The YM test report is available to download from Flexofold's website

 

[rotrax]

A precis of this is that feathering props- what the OP enquired about- vary in construction, materials and design. They also vary in price,quite dramaticaly. The simplicity of the Kiwi and the ability to re-pitch and change blades easily and inexpensivly may be a plus for some, as it was for me. If money was not an issue a self pitching feathering prop would be high on the list. Cash is usually laid out after checking what is available and at what price and then getting the best deal for the money. Our Kiwi was the best price by a long way and so far-two long seasons, 350 plus engine hours-has done exactly what it said on the box. Well pleased.

 

[grievesie]

When I was buying a prop two years ago, I asked someone (Alan Pollard?) on the Kiwi stand at SIBS about the poor results. His answer was that because there were so many boats being tested, by the time they got their turn, there was a tide running. What he suggested was that speed through the water when motoring into the tide was going to be slower than when there is no tide. Isnt speed through the water, just what it says? I went on to ask him about the bollard pull figures, again he called foul, claiming that as the tide was near full ebb the prop was kicking up so much silt it reduced the grip.

I was not impressed with the response from the chap on the Kiwi stand, it sounded like sour grapes with a smattering of BS!

I understand that the only supplier to send along an engineer to that test was Darglow engineering, (Flexofold etc). If the other manufactures were so concerned with results, and certainly Kiwi as their prop could have had the pitch altered, should have done the same.

Just to confirm what I was told by Alan Pollard at the 2010 SIBS here is a quote from him posted by another customer on the S&S Swan Association forum in May 2010:

"I was present at one day of the two day YM tests and was frankly very unhappy with their methods and location. We were asked to make a prop which would enable the engine to run at 3600 rpm and we did so, though we would have preferred to increase the pitch to a setting for best performance as we would for a customer. Then we would have seen better power performance all round from our prop. The stop tests were done in Lymington harbour using a stop watch, but how they decided when a boat had stopped in the ever changing tidal flows I do not know. Very hit and miss. The bollard pulls were done tied to a marina finger, and for our slot at the bottom of the tide there was so little water below the prop it was moving clouds of mud. With sixteen props to test, so sixteen lift outs and relaunch and some tedious installation times, it all took 2 days and so many competitors had better conditions for their tests. They also managed to quote the wrong pitch and the wrong price, and yet ignored externally adjustable pitch. The French sailing magazine VOILE , tested 12 props in a 13 colour page article in their April 2009 edition . The French Tests were in non tidal waters. Our Kiwiprop came out with one of two five star ratings. The summary says “it is a very innovative propeller with high performance and an unbeatable quality-price combination”.

That's exactly what I heard from him too - doesn't sound BS to me. The lack of engine rev data in the YM test makes it a flawed in my opinion. Their whole methodolgy can only be considered simplistic with regards to fairly comparing props - a difficult task even in ideal conditions. The Voile magazine test was conducted within Ouistreham's locked harbour - a far better location for a consistent comparison than Lymington Yacht Haven and the Lymington River.

Addendum: Posted this a bit further on in the thread but for those who don't get that far - found a link to a Dutch web site that has the April 2009 Voiles prop test as a download: http://www.bomarine.net/index.php/autoprop/bekijk-categorie.html
Also some other info/downloads on props on the site as these folk are Autoprop dealers.

 

[snooks]

"The stop tests were done in Lymington harbour using a stop watch, but how they decided when a boat had stopped in the ever changing tidal flows I do not know. Very hit and miss."

The way we decided the boat was stopped was to look over the side at the water. When the water stopped moving past the hull and was stationary, so were we This was done 3 or 5 times (it was over 4 years ago so I forget which) in each direction for each prop. The times were remarkably consistent and were averaged out.

So far from being "hit and miss"

And it was 17 lift outs because we had to put the original prop back on

 

[DaveS]

Just to confirm what I was told by Alan Pollard at the 2010 SIBS here is a quote from him posted by another customer on the S&S Swan Association forum in May 2010:

"I was present at one day of the two day YM tests and was frankly very unhappy with their methods and location. We were asked to make a prop which would enable the engine to run at 3600 rpm and we did so, though we would have preferred to increase the pitch to a setting for best performance as we would for a customer. Then we would have seen better power performance all round from our prop. The stop tests were done in Lymington harbour using a stop watch, but how they decided when a boat had stopped in the ever changing tidal flows I do not know. Very hit and miss. The bollard pulls were done tied to a marina finger, and for our slot at the bottom of the tide there was so little water below the prop it was moving clouds of mud. With sixteen props to test, so sixteen lift outs and relaunch and some tedious installation times, it all took 2 days and so many competitors had better conditions for their tests. They also managed to quote the wrong pitch and the wrong price, and yet ignored externally adjustable pitch. The French sailing magazine VOILE , tested 12 props in a 13 colour page article in their April 2009 edition . The French Tests were in non tidal waters. Our Kiwiprop came out with one of two five star ratings. The summary says “it is a very innovative propeller with high performance and an unbeatable quality-price combination”.

That's exactly what I heard from him too - doesn't sound BS to me. The lack of engine rev data in the YM test makes it a flawed in my opinion. Their whole methodolgy can only be considered simplistic with regards to fairly comparing props - a difficult task even in ideal conditions. The Voile magazine test was conducted within Ouistreham's locked harbour - a far better location for a consistent comparison than Lymington Yacht Haven and the Lymington River. The table of results from the Voile magazine is attached but will be difficult to read as its a small jpg - but it's all I can find on the web at the moment (I'm working abroad at present). Anyone who wants a pdf of the original test can PM me with their e-mail - I'll send it when I get home late next week.

PM sent.

When this was discussed a couple of years ago I made the point about a lack of revs information, and a certain poster not a million miles away from here said he would look into getting the omitted YM test data posted here... I also drew attention to YM's completely incorrect description of how the Kiwi works in reverse: the writer had obviously totally misunderstood.

I have experimented with altering the blade angle of my Kiwi and by reducing the pitch to 17 degrees achieved full rated engine speed, but there were significant disadvantages: higher revs needed for a given boat speed, poorer fuel consumption, and less "bite" when motoring into rough conditions. (This last point surprised me, since I had always assumed that, using the "screw" analogy, a lower pitch was equivalent to engaging a lower gear ratio. The answer is, apparently, that for a displacement craft the pitch should be such that max throttle coincides with max torque not max power.) I now have the prop set back at 20 degrees as supplied by Vectra who clearly know what they're doing.

 

[cliff]

Have a look at the Autostream ticks the boxes for me and easily adjustable pitch both ahead and astern.


So many choices - what to do?, what to do?.........

 

[Sans Bateau]

What does not sit easy with me, that some others seem to accept is the statement, and what was said to me, from Kiwi. Firstly if Kiwi thought their prop would perform better with a pitch as they would set it for a customer, why didnt they? All the other prop suppliers presumably had the same information, some could not alter the pitch. Someone will have to explain to me, Kiwi claimed that their bollard pull figures were poor because of shallow water, since when and how does shallow water affect a props performance?

According to the tidal information in an earlier post, the Kiwi prop would have been tested at near enough LW, so any current flowing may/could have been slack, other props would have been tested in full eeb or full flood.

I dont claim to be any authority on props, but this does all appear to be sour grapes by Kiwi, not the result they wanted. Did any other of the manufacturers complain that they were tested in unfavorable conditions? Because if the tests went over 2 days, chances are someone else would have been tested in similar conditions, have they complained?

 

[snooks]

PM sent.

When this was discussed a couple of years ago I made the point about a lack of revs information, and a certain poster not a million miles away from here said he would look into getting the omitted YM test data posted here...

Hint taken, I did ask the writer for the info, but he didn't send it and I forgot to chase him, so my fault. Sorry, I'll try again and see what I can find out for you. Feel free to PM me a nudge some time next week and I'll chase it up.

 

[DaveS]

What does not sit easy with me, that some others seem to accept is the statement, and what was said to me, from Kiwi. Firstly if Kiwi thought their prop would perform better with a pitch as they would set it for a customer, why didnt they? All the other prop suppliers presumably had the same information, some could not alter the pitch. Someone will have to explain to me, Kiwi claimed that their bollard pull figures were poor because of shallow water, since when and how does shallow water affect a props performance?

According to the tidal information in an earlier post, the Kiwi prop would have been tested at near enough LW, so any current flowing may/could have been slack, other props would have been tested in full eeb or full flood.

I dont claim to be any authority on props, but this does all appear to be sour grapes by Kiwi, not the result they wanted. Did any other of the manufacturers complain that they were tested in unfavorable conditions? Because if the tests went over 2 days, chances are someone else would have been tested in similar conditions, have they complained?

Having now seen the Voile test report (thanks grievesie!) with all the numbers, the Kiwi comes out very well, and the reported numbers tally well with my experience. So, as a Kiwi owner it's quite gratifying.

The Kiwi was not the best on test, however. The Brunton Autoprop gave better fuel consumption and it's had many commendations here and elsewhere on its advantages for motor-sailing (not covered by either YM or Voile), but of course it's dearer than the Kiwi. The 31% fuel saving (Autoprop v. Kiwi, from the Voile test) would certainly usefully improve my range, and with my current consumption of about 100 l per year would save about £40. The capital cost difference of c. £500 would give a 12 year payback at current fuel prices. While I won't be changing any time soon, I've mentally bookmarked the Brunton for future reference.

 

[Tranona]

That reinforces the importance of understanding what you want to get out of a "fancy" prop. For most people who just use the engine for short periods then the only justification is the reduction in drag when sailing. The Bruntons always gets good reports from people who do a lot of motor sailing - cruising long distance round the Med, for example.

Reduction in drag is very similar on most types, but motoring performance varies, as does maintence requirements, and of course some types do not fit some boats.

So it is important to decide what you are looking for and choose a prop that delivers that, taking into account the wide price range! Explains why you get good reports on many different types.

 

[grievesie]

Voiles Prop Test

For those who may be interested I've found a copy of the April 2009 Voiles Prop test on a Dutch web site: http://www.bomarine.net/index.php/autoprop/bekijk-categorie.html A number of other interesting prop info/downloads on the same site as these folk are
Autoprop dealers.

Perhaps YM should take a look and see how much more thoroughly the French mags do their testing - applies to boat tests too.

 

[TiggerToo]

The way we decided the boat was stopped was to look over the side at the water. When the water stopped moving past the hull and was stationary, so were we This was done 3 or 5 times (it was over 4 years ago so I forget which) in each direction for each prop. The times were remarkably consistent and were averaged out.

So far from being "hit and miss"

And it was 17 lift outs because we had to put the original prop back on

sorry Snook,
but on this one YM really did come out amateurish.

 

[njsail]

I'll toss my 2cents into the hat. I just bought a kiwi prop and it should arrive today. I made my choice the old fashion way. I talked to everyone I knew that uses one and it was an overwhelming recommendation. just for comparison I had many positive recommendations for numerous other brands as well but the kiwi price point was very attractive. The common sentiment amongst kiwi owners is it's a monster in reverse. It really bites in and provides great reverse thrust. Determining how much drag is reduced while sailing is more interpretive than reverse but they believed they gained enough to make it worth it. It all depends on the type of sailing you do. It's the sailing that either makes it worth the cost or not. If you're a day saillor it might not be worth the cost but if you are going to sail distance then a little extra speed can make a difference.

The kiwi blades are removable and changable in the water and the cost of a couple extra blades was next to nothing. I carry a couple spare fixed props just in case they are ever needed as well. The kiwi price point and all positive recommendations are what pryed my wallet out. That isn't an easy task to do. I'm shall we say....frugal. I'll let you know my thoughts in a month or two when I get some personal experience with it. Good luck.

 

[Plevier]

My only real complaint with the Kiwiprop is the reverse. It is so coarse pitch that I can only get 2000rpm at full throttle (VP MD2020, should be set for 3200-3600). Yes it gives good initial bite but I have to go astern for about 100 yds every time I leave my mooring and can really feel the limited power available.
I'm about to relaunch and have put temporary packing on the blades to hold reverse pitch to just a fraction more than forward. If this works I shall make new reverse stop rollers, bigger diameter. I think Kiwi should offer a choice of 2 or 3 sizes of these to cover this problem.