Kiwiprop problems in astern

One of the things that a ship designer has to take into account is that the propellor disc (the circle that the prop operates in) sees different flow rates because of the ship's presence upstream of it. This may well be of sufficient concern to prompt a re-design of the local hull form.

Why? Well, because a severe variance in the flow will cause the prop to try and bend. Which it doesn't really. What it does do is bend the shaft, causing vibration.

Could it be that your more efficient prop is reacting to uneven flow from something upstream of it?
 
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Why? Well, because a severe variance in the flow will cause the prop to try and bend. Which it doesn't really. What it does do is bend the shaft, causing vibration.


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Interesting comment - accounts for some of the varying vibrations I get depending on manoeuvre
 
Unfortunately there has been a lot of crap posted on here about the mavelous Kiwi prop with people claiming increased power forwards. They are a cheap feathering prop with plastic blades and for low powered engines offer good value for money except the lack of astern power.

With regard to foward power all feathering props have flat blades so against a fixed prop with shaped blades it cannot perform as well unless the manufacturer fitted the wrong size prop.

Power astern is a known problem with Kiwi props but they are cheap!!

To me one of the biggest advantages of a "proper"feathering prop is the increased power it gives astern as the blades completely reverse. Its great for the odd occassion when you put the keel into the putty or you need to stop quickly. On my boat I can stop from 6kts within a boat length.

There are 3 good feathering props.
1. Seastream that is Australian and made in SS so no incompatibilities in the metals but it is the most expensive. Can adjust pitch both forwards and astern from outside the prop.
2. Maxiprop (Darglow) been around for years but you set the pitch when assembling the hub and for heavy use (charter boats) they recommend a larger hub.
3. Variprop - German made quality product and the cheapest one where you can adjust pitch both forwards and astern from outside the prop. For higher HP you can also get a 4 bladed variprop feathering prop.

On my last 2 charter boats I have fitted Variprops and on the current 75HP engine I have a 4 blade one that also reduces noise and vibration but fantastic power astern and not much difference in forwards power between the 3 bladed fixed and 4 bladed feathering.
 
Thanks for that posting Sailfree..

I havnt ordered one yet so its good to hear another point of view. Although most of the comments I have seen so far contradict your point about lack of thrust in reverse.

But as you say they cost a lot less than the competition and they are good value for money especially with low powered engines (I have an 18 HP Volvopenta 2002).

As I understand it with the Kiwiprop I can expect :-

* Similar performance forwards to what I got from my old 3 bladed fixed prop
* Improved performance under sail
* Improved performance in reverse under power.

Am I correct ?
Thanks

PS .. I have only just come across this forum and think its fantastic for researching products before you buy !
 
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Thanks for that posting Sailfree..

As I understand it with the Kiwiprop I can expect :-

* Similar performance forwards to what I got from my old 3 bladed fixed prop
* Improved performance under sail
* Improved performance in reverse under power.


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My two pennies: had a KIWI prop for two seasons, and although I had the 2GM20F engine, the engine didn't stall, and had plenty of power in reverse. Well engineered product, and very easy maneuvering in the marina. The pitch was spot on (I had installed a shaft RPM meter to assess speed ), but performance in forward -in terms of power- was less, and fuel consumption higher than my old Radice two-bladed folder!
Also, due to fine silt ingress on the muddy rivers, the reverse mechanism packed up mid season (each August), although I had it serviced by the dealer. I've now sold it on, and bought an ordinary two-bladed prop. Peace of mind and all that...
 
Ref your questions.

1. A fixed prop has shaped blades to maximise forward thrust. No flat bladed prop can equate to that providing the fixed prop is correctly sized. I respect balanced information but have read a number of reports on the Kiwi prop stating vastly improving power forwards that I have to seriously question the persons objectiveness/judgement as I repeat a correctly sized fixed prop with shaped blades is designed for maximum thrust.

2. For improved performance under sail a folding prop is best followed by a feathering prop followed by a "locked" fixed prop and worse drag is a rotating fixed prop. Another advantage which I find important in the Channel is the likelyhood of picking up ropes and stray fishing nets! Again a folding prop is best followed by a feathering IMHO.

3. The 3 feathering props I mentioned have vastly improved performance astern but I have read quite a few reports on problems astern with the Kiwi that vary from stalling the engine unless you wack it in astern and apply full power to not much. Note on both the Seastream and Variprop you can adjust/tune the pitch from outside the prop for both forwards and astern. The Kiwi prop is a set non adjustible pitch astern.

When you have a 10 ton charter boat with variable qualities of skippers the maximum power astern of a "proper " feathering prop is an advantage when they cock up but even that did not prevent my boat being stuck on the putty at Lymington a few months ago when a Professional Yachtmaster mistook the wrong channel buoy - now why do I bother to put the latest Raymarine chartplotter/radar on board with a helm repeater??
 
tsadpt said:
Hi Everyone! I am doing some racing this season (fastnet etc) in my Bavaria 36 (dont laugh!) /forums/images/graemlins/laugh.gif, so I splashed out on a kiwiprop, that we fitted in March. THrough April, we had weird broblems in astern: the revs would not go more than about 1200... so, off it came, and on went the old prop (reverse revs now bask to normal).

Kiwi had the prop back, tested it and pronounced it as okay, but moved the stops slightly.

We put it back on this morning, and although it is "better", the revs still top out at 1500 /forums/images/graemlins/confused.gif. Kiwi suggested tickover needs to be higher (currently at 600) so that the blades land on their stops efficiently, so I have tried raising the revs ever so slowly. again, by the time the throttle is fully open, the engine is only doing 1600. this then builds slowly over the next minute or so, but will make stopping in a berth a little "interesting"!!

ANyone ever heared of this problem?

thanks

David
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I've had this problem with their newer style blades and tri rollers. The original blades never do. Now, in reverse, it lugs the engine and puts out a lot of black smoke. I had a diver just check that the blades are swivelling easily, there's now fouling issues, the hub rotates with little hand force ( I set the drag on the hub at 2 lbs, as advised by kiwiprop) , he greased it again, and it still lugs down. I suspect that the blades are hanging up on the tips of the tri rollers as the diver did observe that the blades, while rotating back against the rollers, appeared to be almost flat, with extreme pitch.
 
Welcome to the forum.

Long time since there has been a thread on Kiwiprops, maybe because they have fallen out of favour somewhat since 2007. As suggested they have many desirable features such as simplicity and cheapness, but performance is very variable. The biggest weakness is the unreliable performance in reverse because of the fixed pitch and uncertainty of blades actually engaging in reverse - just as reported by many here. Other propellers avoid these issues by positive blade feathering and crucially the ability to set a different pitch in reverse, either to make reverse more progressive or because many gearboxes like TMC and Yanmar have different reduction ratios in reverse. Even if the ratio is the same as on my PRM there is value in having a finer pitch in reverse, not a greater pitch as often happens with a Kiwi.
yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

This may help understand a bit more about the subject. As you see the Kiwi comes out near the bottom on most performance measures compared with both folding and feathering propellers. Overpropping in reverse is not good for the engine and also leads to all or nothing - that is a high load at low revs if the blades do engage but no speed which is a hindrance if, for example you have to reverse down a run in a marina.

You don't say what boat and engine you have and it may be the prop is just not suited. In general at the price point for most smaller boat a good 2 blade folder is a better buy. As you can see from the test they perform as well as many feathering types, and the 2 blade are simple and reliable.
 
It's on a Cascade 36, fin keel, spade rudder, Yanmar 3GM30F.
I think it was a pre 2007 originally and it performed flawlessly. In reverse itny was over propped but would spool up to about 2500 rpm or so but, it did reverse. With the new style blades it is lucky to get up to 1800 rpm and smokes like hell at anything above idle and just doesn't drive. Kiwiprop told me to engage reverse with some forward speed but this is not practical in a lot of situations.
 
I have the original bladed kiwiprop, and a yanmar 3gm30, on a 31ft boat. The vital thing with these props is lubrication. I would say at least twice a season or three times a year you need to get a grease gun to the various grease ports. Bit of a faff but if you’re coming out for a scrub it’s a quick and easy task. It’s a very simple prop really, and whilst not as efficient in forward as other three bladed folders/featherers due to blade shape, the stopping power in reverse is amazing, and its a good bit cheaper.
 
korucaptain said:
. In reverse itny was over propped but would spool up to about 2500 rpm or so but, it did reverse. With the new style blades it is lucky to get up to 1800 rpm and smokes like hell at anything above idle and just doesn't drive.
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I had exactly the same problem. It was caused by blades not turning smoothly on their bosses. Lubricating sorted this for me, but as Kiwi Prop say, if you knock it into forward momentarily before reverse it’ll behave itself.
 
fredrussell said:
I have the original bladed kiwiprop, and a yanmar 3gm30, on a 31ft boat. The vital thing with these props is lubrication. I would say at least twice a season or three times a year you need to get a grease gun to the various grease ports. Bit of a faff but if you’re coming out for a scrub it’s a quick and easy task. It’s a very simple prop really, and whilst not as efficient in forward as other three bladed folders/featherers due to blade shape, the stopping power in reverse is amazing, and its a good bit cheaper.
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My experience exactly, Fred. The original blades never missed a beat
The new style, with triangular rollers, have been nothing but trouble. My first discovery was that the screws that the rollers near against, we're not flush with the surface. 0nce that was rectified, I thought I'd fixed it. But no, it's erratic. I'm considering switching back to the original style rollers using later blades.
 
I have a newer style Kiwiprop on a VP2003 engine and it causes me no end of issues going into reverse. I have to rev the engine to around 1500 rpm then slam the lever into reverse before the engine speed slows to the even have a chance of the prop engaging correctly. If I don't, the vibration effectively locks up the gearbox and throttle and I have to stop the engine to get back to neutral, restart and try again. Makes for interesting marina berthing! I have tried all sorts and blades swing freely but I am now considering fitting the original 2-bladed prop in its place.
 
MartinR34 said:
I have a newer style Kiwiprop on a VP2003 engine and it causes me no end of issues going into reverse. I have to rev the engine to around 1500 rpm then slam the lever into reverse before the engine speed slows to the even have a chance of the prop engaging correctly. If I don't, the vibration effectively locks up the gearbox and throttle and I have to stop the engine to get back to neutral, restart and try again. Makes for interesting marina berthing! I have tried all sorts and blades swing freely but I am now considering fitting the original 2-bladed prop in its place.
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When did you last lubricate the prop hub Martin? Not the blades, the hub grease ports. I had left mine for too long and had same issues as you. It’s vital to keep the hub lubed too.
 
Thanks. I lubricated it on Friday and it seems to be working fine again! However, I noticed that one reverse roller has sheared off and another is loose. I'm guessing it will need to be returned to KiwiProp for repairs. It's 17 years old.
 
Any decent engineering firm will be able to remove the snapped off reverse roller. I had the same problem a couple of years ago. Use red (not blue!) loctite on reverse roller threads.
 
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