Kiwi props - any advantage?

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NPMR

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We have a three blade folding prop supplied with the boat from new - a Jeanneau S.O.33i, with a standard Yanmar 3YM20 engine.

It does not have massive boat speed under engine and it feels as though you have to rev it past the most economical diesel usage point to get to 5kts.

Kiwi Props claim their offering is better.

Does anyone have any experience, one way or another?
 
NPMR said:
We have a three blade folding prop supplied with the boat from new - a Jeanneau S.O.33i, with a standard Yanmar 3YM20 engine.

It does not have massive boat speed under engine and it feels as though you have to rev it past the most economical diesel usage point to get to 5kts.

Kiwi Props claim their offering is better.

Does anyone have any experience, one way or another?
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This suggests your prop is the wrong size. You should be able to get 5 knots at just over 2000 rpm and a maximum of close to 6.5 at about 3400. Before you do anything carry out a series of runs measuring accurately speed through water at different rpm. If you cannot get max revs the prop is too big, but if it easily runs up to maximum without achieving maximum speed it is underpropped. As a Rule of thumb with your boat engine combination a cruising speed of 5.5 knots at around 2400 should be achievable. Find out what make of prop it is, probably a FlexoFold and get a size recommendation from the manufacturer or distributor.

A Kiwi would be a retrograde step in my view. Speed against revs is largely a function of prop size not design. The Kiwi has its features, one of which is low cost, but unlike your present proper the blades do not positively change angle, relying just on waterflow or spring pressure for reverse.
 
When I bought my present boat, I did a test sail in a similar boat fitted with a two bladed folded prop. The boat's performance under power, ahead and astern, was the one area where I was disappointed. I bought a Kiwi prop for my boat and it transformed it - at least 7 knots ahead and nearly 6 kts astern if you want to go that fast, which you don't! I have had it for 8 and a half years now and love it to bits. Talk to Alan Pollard at Vecta Marine and he will spec the right size, pitch etc for your boat.
 
Bruntons do great folding props and they are mechanically so much simpler.....yes more pricey, but the materials used do that. Had a Kiwi, liked it, but not as much as the Bruntons.
 
Some years ago. YM tested 15 different props, mainly folding and feathering. The boat was a 32 ft Beneteau with a 21 hp Yanmar; ie v. similar to the OP's. The props were as recommended by the suppliers.
The best forward speed, 7.6 knots, was with the 3B Flexofold. The Kiwi came bottom of the heap, and was also mediocre on tests in astern.
 
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 :)
 
About 2800 for normal passage making. She's not heavily laden but not stripped out for racing either. I think that peak torque comes in about 2600 and fuel consumption goes up quite steeply above this figure. We seem to be able to keep the hull pretty clean through the Summer.
 
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2800 is a bit on the high side for cruising. You need to do the systematic get I suggested earlier otherwise you are just guessing.
 
Cant comment on fuel consumption as we run the heater from the same tank. We do find that around 3000 to 3200 we have less vibration. Spoke to french marine when we picked the boat up and their advice was not to run under 3000 rpm for long periods and to vary the revs. Glazing/exhaust elbow issues if the engine was not run at good temp was the reason.

I believe I get more than 5knts at 2800 though. Will be a couple of weeks before we can check though.
 
Best prop for going forwards is a standard fixed shaped prop assuming it is sized correctly for the engine/boat.

Best prop for motorsailing is an Brunton autoprop as pitch adjusts to work required but it hesitates most before going astern. Has greater drag than folding and feathering.

Best prop for minimum resistance when sailing is a folding prop. Modern designs improve astern performance but still "weakest" of all for astern power. Folders have least likelihood of picking up a rope when sailing

Best prop for going astern is a feathering prop as blades completely reverse in direction. Has next minimum drag after a folding prop but flat blades mean it cannot be 100% as efficient going forwards. Kiwi prop is cheapest but astern pitch cannot be adjusted and limited in power handling ability.

On charter boats heavy use soon reveals any weakness in the design/materials. Had 2 Volvo folding props on my Volvo 2030 in 1st year (1998) before Volvo gave me my money back with tacit admission not suitable for heavy use 500hrs/yr! I would now only go for Varifold or the Variprop. Had a Variprop on last 2 boats and consider it the best compromise for my requirements. My current one is a 4 blade Varifold, its can handle 75HP and now done over 3800hrs on my charter boat. Its almost as good going forwards as the original 3 blade fixed prop, in fact have found no discernable difference (does 10kts), Pitch both forwards and astern can be adjusted from outside prop for maximum efficiency for engine/hull characteristics (maxiprop you set pitch only during assembly). Best feature for me is the maximum power astern - can stop boat from 6kts in own length and maximum power to get off the putty or get out of jail card when misjudging a berthing - an real asset on a charter boat. One boat on our fleet tried a Kiwi prop and gave up but others with light use like them. I get the impression that owners of 30hp engine and less are happiest with Kiwis.

As others have said all boats and all propellers are a compromise. I have difficulty believing advice from people that say Prop "A " is best in all respects - it cant be and just reflects brand loyalty or self delusion that the individuals purchasing judgement was good!

EDIT -the above is something I have posted before as this question frequently comes up esp. wrt Kiwi as frequently Kiwi purchasers make claims that are unsupportable and if true just proves that their original fixed prop was wrongly sized. Last year a blade of the feathering prop fouled the buoy chain on a almost submerged buoy outside Cowes and a couple of blades got bent. To avoid delays I bought a 4 bladed varifold folding prop as I had read reports that the latest folding props with shaped blades have much improved astern power. Sailing performance is better and going forwards under power appears slightly better than feathering prop (flat blades) but going astern power is still very poor. I need to really rev the engine to get any astern grip. It is so poor I have completely changed my berthing to going in astern as I have no confidence in the astern stopping power.

If your new wonder prop is better than a shaped fixed prop when motoring then you either have an incorrectly sized fixed prop or you are kidding yourself!

One good reason for changing from a fixed prop is that latest gearboxes are damaged if you stop prop turning by engaging astern ( to stop cutlass bearing wear when sailing - and noise!). On these gearboxes the selector mechanism also jams up when sailing and prop has been locked by engaging astern and you have to start engine in astern and v quickly go to neutral once engine starts.
 
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I have had my Kiwiprop for seven seasons now on a Moody31 with a 28HP Volvo 2003 engine.I am more than satisfied with the performance.The sailing performance has improved by in my estimation by about half a knot.The biggest improvement is motoring in reverse.The stopping power is amazing.I also reverse out of my berth and down the alley in tickover.It does need to be greased each year and I use hard antifoul on the blades and lanolin type grease as well over the antifoul.
The support and service from Vecta Marine has been first class.No relationship just a happy customer.
I previously had a Maxprop on another boat and the Kiwi is just as good.
 
NPMR said:
We have a three blade folding prop supplied with the boat from new - a Jeanneau S.O.33i, with a standard Yanmar 3YM20 engine.

It does not have massive boat speed under engine and it feels as though you have to rev it past the most economical diesel usage point to get to 5kts.

Kiwi Props claim their offering is better.

Does anyone have any experience, one way or another?
Click to expand...

I have one on my 36' long keel steel ketch and its a vast improvement on the fixed blade. I fitted it because the heavy old girl takes some stopping and the Kiwi's pitch increases when going astern which helps massively and when going ahead with the old prop, you'd think the gearbox clutch plates were slipping - loads of revs and not a lot of acceleration. This has all changed you can feel the prop 'bite' and it is adjusted for quiet economical cruising at 5.5-6kts at 2000rpm instead of 2200rpm

It is easy to adjust (you could do it afloat) by means of a 4mm hex screw near the root of each blade, so you can adjust the pitch for the results you want very easily, unlike other feathering or folding props. This feature in my view is a big advantage over other designs.

So I echo Ditchcrawlers comments entirely, including the service from Vecta marine and I've yet to hear from anyone with a negative experience.
 
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I had a Kiwi Prop for two years and it is very light and beautifully balanced so the engine was very smooth. However I eventually replaced it with a Flexifold two bladed folding prop because the Kiwi prop is high maintenance requiring servicing and greasing regularly. So its performance was excellent and the boat was faster than with the replacement and the replacement is not as smooth. If you are the sort of chap who does all his own maintenance and can dry out for a mid season service then the Kiwi prop is not a bad choice. The agent in the UK is a really nice guy and his service is excellent, but it was not the right prop for me.
 
Obviously someone must educate prop designers as there are so many on here that know better eg the flat blades of a Kiwi prop perform better than shaped blades.

FYI the Variprop pitch is also adjusted from outside and I believe the SS seastream also is.
 
Sailfree said:
Obviously someone must educate prop designers as there are so many on here that know better eg the flat blades of a Kiwi prop perform better than shaped blades.

FYI the Variprop pitch is also adjusted from outside and I believe the SS seastream also is.
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Changing from a fixed prop to a Kiwi will almost certainly be an improvement. However, as you say there are much better solutions on the market albeit at a significantly higher price. The OP seems already to have one of the better props, so if indeed he has poor motoring performance it is a question of size, probably pitch that is the problem, not the design of the prop.

However all guesswork without hard data.
 
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