ianj99
Well-Known Member
I believe the differences would show up in terms of the efficiency. But the low price, the adjustability of the Kiwi plus the increased pitch going astern are all benefits which outweigh a small increase in fuel consumption.
Kiwi props - any advantage?
- Thread starter NPMR
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I believe the differences would show up in terms of the efficiency. But the low price, the adjustability of the Kiwi plus the increased pitch going astern are all benefits which outweigh a small increase in fuel consumption.
KAM
Well-Known Member
While all this talk about engine performance is interesting, I get almost 3/4 Kt better sailing performance with a 3 blade KiwiProp. (Was fixed 2 blade originally).
I find that more attractive than engine behaviour.
Motoring appears perfectly acceptable as well
I was wondering at what sailing speed you get the 3/4 kt i
mprovement.
Sailfree
Well-Known Member
You are correct the most efficient prop going forwards is a properly sizes fixed prop. I suspect many of the claims of lower revs at a given speed simply means the pitch has been adjusted to be over pitched assuming original fixed prop was correctly sized. Personally I adjust my feathering prop to be over pitched but at higher revs it will strain the engine, can cause overheating but this is not a problem for me as I don't use the high revs that gives me 10 kts and am happy at 7kts!
A feathering prop has advantages in less resistance sailing and maximum power going astern. I loved my feathering Variprop and if I had a low power engine would give serious consideration to a Kiwi prop. However the Kiwi is a cheap feathering prop which in itself may be an attraction for many ( for my 75HP engine I bought the better 4 blade 19" metal Variprop - kiwi cannot handle that size of engine). The economies in the Kiwis cost reflect in no adjustment of pitch in astern and non metal blades.
I just get a bit fed up with postings that unreasonably make claims for it that just cannot be true and do wonder about the validity of the posts as it must help sales.
All props are a compromise see my post above for a summary.
While my feathering prop has now done 3800hrs I am seriously considering getting it refurbished and refitting it over the new £3000 4 bladed feathering prop I fitted last year as I am really missing the stopping power of a feathering prop.
To summarise the Kiwi prop is a cheap feathering prop but it is not a miracle prop that defeats the science of prop design!
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nimbusgb
Well-Known Member
Kiwi prop blades are far from flat. They are hyrodynamically profiled.
Plastic blades are an advantage not a dissadvantage! Marine growth battles to stick to them and they dont get as dinged anditted as bronze ones. They dont suffer dezincification or electrolosys!
The ability to replace one blade, in the water if necessary is an attraction.
At 1/2 to 2/3 the price of a metal prop Kiwi's are a great idea for up to 50 hp powered yachts.
Plastic blades are an advantage not a dissadvantage! Marine growth battles to stick to them and they dont get as dinged anditted as bronze ones. They dont suffer dezincification or electrolosys!
The ability to replace one blade, in the water if necessary is an attraction.
At 1/2 to 2/3 the price of a metal prop Kiwi's are a great idea for up to 50 hp powered yachts.
Sailfree
Well-Known Member
Are you saying they are curved in the shape of a screw to be efficient at forward propulsion or just that the outside blade edges edges of the flat blades are not squared off!!!
It may be news to kiwi prop owners but you can't have it all ways.
Its the very fact that feathering prop blades are flat that give it the much better power astern as prop blades that are shaped for max forward power are inefficient when going astern.
Whether metal "flat" blades are better than the nylon/plastic is a matter of opinion. The fact that they cannot handle more than 50HP demonstrates that they will deform or break easier than a metal blade that can be used for the greater power.
I am constantly surprised by how Kiwi prop owners will allow no criticism of there product and insist its a miracle product that better in all respects and now I am told they have shaped blades - Hollocks
ianj99
Well-Known Member
You are confusing customer satisfaction with blind faith.
The Kiwi prop would not be popular regardless of the low price if it did not deliver good results and even though my 17" version looks like a toy on my 36' 10ton long keel motor sailer, it has improved the low speed handling and astern performance as well reducing the cruising rpm by 10%, apart from any sailing benefit.
For larger engines, there is a 4 blade 100bhp version available.
Sailfree
Well-Known Member
I have no problem with people stating the advantages of a feathering prop of which the Kiwi is a cost effective type. I have owned 3 new boats and had them on the charter market and at various times I have used all the three types of propellers whose advantages and disadvantages I describe in my post #14, (four if you include the Bruntons variable pitch prop).
My problem is the incorrect and exaggerated claims that a number of Kiwi prop owners claim.
Personally I prefer the feathering prop accepting its disadvantages as being a minor compromise. Of the feathering props there are various types again each with its advantages/disadvantages. One of the earliest designs is the Darglow which is metal but the pitch is built into the hub. For heavy charter use they recommend an expensive larger hub. Then there are those where the pitch can be adjusted from outside I would mention the Variprop and the thinner profile stainless steel sea stream, on both these both the astern and forward pitch can be adjusted. Then there is the Kiwi with plastic/nylon blades, my understanding is that only the forward pitch can be adjusted from outside, the astern pitch is very high and fixed. I note that there have been posts in the past stating that the very high fixed astern pitch has caused them problems including for some stalling the engine at low revs.
Thanks for pointing out that Kiwi currently have a 4 bladed prop under test and are commencing production but not sure whether it is available yet. Not sure about the statement that the blades are mounted on stainless steel means whether that is just the hub or a inner blade to reinforce the plastic blade. Nor does it mention whether astern pitch is adjustable.
I am pleased that you and many others are satisfied customers with a Kiwi prop but as I previously stated all types of props have advantages and disadvantages and even within the feathering type of prop the Kiwi has its own advantantages ( esp. Cost) but it also has its disadvantages and it is unfortunate when people post misleading advice.
Currently I have a four bladed folding prop that is best for sailing, and as it folds is less likely to pick up fishing nets/ ropes ( one year I picked up four and charterers a few more with a feathering prop!) , the blades are shaped for better forward power ( but not as much as a fixed prop) but I hate the lack of stopping power of a folding prop.
I will give it another season and if I decide the best set of compromises for me is a feathering prop I will get an estimate to refurbish my Variprop and will even investigate the new four bladed Kiwi prop if it is then available!
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charles_reed
Well-Known Member
It all depends on your criteria and comparison benchmark.
As a long term owner of an Autoprop I'd say the Kiwi was nowhere near as good a performer (I'm talking of two engines and 23 years in use). having just paid out £990 for replacement (due to wear) blades it's certainly cheaper and causes less drag than the 2-blade fixed with which the boat came.
But I don't kid myself - the Autoprop is not the most drag-reducing prop, or the one that gives the most immediate response in tight manoeuvre situations, or the one that will produce the most thrust in a tethered pull.
But there is nothing that approaches it for effective motor-sailing which in the Med is a major benefit.
As a long term owner of an Autoprop I'd say the Kiwi was nowhere near as good a performer (I'm talking of two engines and 23 years in use). having just paid out £990 for replacement (due to wear) blades it's certainly cheaper and causes less drag than the 2-blade fixed with which the boat came.
But I don't kid myself - the Autoprop is not the most drag-reducing prop, or the one that gives the most immediate response in tight manoeuvre situations, or the one that will produce the most thrust in a tethered pull.
But there is nothing that approaches it for effective motor-sailing which in the Med is a major benefit.
Sailfree
Well-Known Member
I investigated the Bruntons auto prop but I was advised the hesitation in going astern and time to develop astern power could be a problem for charterers on a strange boat and hence for charter use I decided that a feathering prop was best. I do agree that the auto prop is the best prop for motors sailing. It's just a pity that others can't describe their choice in a balanced way like you - kiwi owners talk about their props almost in a religious way!
KAM
Well-Known Member
I have long suspected that there was a great deal of myth being perpetrated about the sailing performance benefits of folding or feathering props. I was contemplating going back to fixed and did some calculations on my boat/prop combination at various speeds. Due to the way drag increases rapidly on approaching hull speed and with increasing heel angle the benefit of a folding prop starts to become negligable. The best savings were at lower speeds around 2 kts. A speed at which many yachts start motoring. I decided to stick with the folder as I think there is a big benefit in the reduction in likelyhood of fouling debris when sailing with it folded. This advantage is unavailable on a feathering prop where any blade root undercut may well make it worse than a fixed prop. I have seen drag measurment tests carried out by various magazines but would be interested to see some real data from yachts sailing.
pagoda
Well-Known Member
I would say mid range - our boat was fairly quick for her size anyway, but in the 4 to 6 Kt range she is appreciably quicker. Also sails well at the low end (<3Kt) which we do sometimes if not pressed for time.
The effect on sailing speed will depend on your boat and the drag which the original prop generated.
charles_reed
Well-Known Member
I'd tend to agree with the point about charterers not being able to handle the delay in drive from forward to reverse - when I first had mine I had crew tossed off the foredeck after panicking when reverse apparently didn't work and gave it a big reverse burst. The irony was that the Autoprop is as efficient in reverse as in forward and possibly the most efficient prop there is, in reverse.
I bought mine at the 1991 Soton Boatshow, a very cut price to start them moving - it would be difficult to cost-justify the prop at it's current price. The Featherstream (though not a genuine self pitching prop) appears to be well-made and well-designed and would probably be my choice today.
Round the Med, on an easy driven hull of 9.22m LWL, I'm returning 1.0-1.2 litres/hr with a maximum, flat water speed of 7.7kts from a 3YM20.
I'd agree with KAM that none of the feathering props will reduce drag as much as a good folder.
Unfortunately yachties are all highly subjective - few are natural scientists - so one's unlikly to get "reproducible reported results".
Sailfree
Well-Known Member
Once my boat was no longer going to be chartered and the advantages of the greater astern power was not as important I changed to a folding propeller assured that modern ones have improved astern power. I agree they give the least resistance both to sailing speed and chance of picking up debris, ropes etc but I really am missing the great astern power of a feathering prop.
The real trigger for many to changing from a fixed prop was the modern gearbox on my 2005 Yanmar 75HP engine which locks up the selector if astern is engaged to stop prop noise and wear on cutlass bearing when sailing. I was also told by Jeanneau and Yanmar that locking up the prop when sailing by engaging astern WILL damage these new type of gearboxs.
It is difficult to quantify the greater sailing speed a folder gives over a feathering and both over a fixed as conditions are never exactly the same when a prop is changed but common sense indicates a better performance. Likewise I am not sure that lower revs when motoring at any given speed with an feathering prop adjusted to be overpitched is any more economical as engine is still doing the same amount of work (in energy terms) for any given speed. Obviously from Kiwi owners replies this one type of feathering prop defeats all scientific laws. The argument may have merit if the engine characteristic give a better power to consumption ratio at that given speed.
This year while cruising to and from the Morbihan I had the luxury of taking my time as I had retired from work and I was surprised how low the consumption was if I kept the revs just lower than 2000 (max on my engine is 3800). Still not sure whether it was the use of lower revs or the shaped blades of the new folding prop (over the flat less efficient blades of a feathering prop) that made the biggest difference. My inclination is that its the shaped blades but I do miss the stopping power of the feathering prop esp. when berthing in a strong crosswind when I want to use speed!
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ianj99
Well-Known Member
The OP asked about a Kiwi prop and the replies of positivity and enthusiasm for the prop from those who actually have one speaks volumes. Unlike those who criticise the prop and its proponents, we aren't having a dig at the owners of the other brands.
As regards the fuel consumption, I don't recall personally claiming its better with the Kiwi prop, but generally, a lightly loaded diesel is less fuel efficient (specific fuel consumption in gms/hp/hr) so increasing the pitch and having the engine work a bit harder but at lower rpm means better efficiency, which is not the same as saying the fuel consumption is less. (the extra load is also noticeable in less engine noise & smoother running)
Tranona
Well-Known Member
There is little doubt that the Kiwi is superior to a fixed prop in terms of drag and should be at least equal under power, excepting the well known limitations in reverse, particularly with low powered engines.
However, that was not the OPs question. He was asking whether the Kiwi would be an improvement over his current prop. Based on the way he described his current prop the answer is almost certainly no. He already has a prop that is superior to both a fixed prop or a Kiwi. Any shortfall in motoring performance is more likely due to either fouling or incorrect size.
As I pointed out right at the beginning without some hard at it is just guesswork. It is not difficult to construct a revs vs speed graph, and if indeed it is not performing as expected to contact the manufacturer to get advice on remedial action.
ianj99
Well-Known Member
I'm sure you are right about his existing prop not being correct for his engine/vessel/requirements.
I was offered a Featherstream at a good discount but I was put off by the lack of ease in adjusting the pitch, compared to the Kiwi.
Tranona
Well-Known Member
If you get it right in the first place, which Darglow usually do, there is no need to adjust it. Even if the initial pitch is wrong it is a one off job to correct. Pity you did not accept the good deal you were offered as I am sure you would be just as enthusiastic about your choice.
ianj99
Well-Known Member
I've just noticed that Darglow now provide instructions for diy pitch adjustment by replacing the pitch stop. This wasn't an option when I was looking into feathering props 3 years ago.
So this limitation, plus the cost of having the shaft turned down from 1.5" to 30mm and the taper changed from SAE to metric (for either prop) meant the Kiwi was the only affordable option.
milford
New Member
milfordonsunstar
I have a 3 blade kiwi prop on my sun oddysea 40,56hp yanmar 4jh3.There are 3 identical boats in my marina but i am the only one with Kiwi Prop,others are flexifold and bruntons.I get best economy and equivalent forward performance and best steerable stern drive at half the price:encouragement:
I have a 3 blade kiwi prop on my sun oddysea 40,56hp yanmar 4jh3.There are 3 identical boats in my marina but i am the only one with Kiwi Prop,others are flexifold and bruntons.I get best economy and equivalent forward performance and best steerable stern drive at half the price:encouragement: