Kiwiprop problems in astern

tsadpt

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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
 

JonJon

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Sounds as tho the prop is too big or too much angle on the blades for the engine power ie not allowing the engine to develop full revs and thus full power. Is this only in reverse? Not that I know a lot about it but have been thinking of buying one meself so interested in the comments.
 

savageseadog

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We have. The pitch in reverse on our unit is far too high and the engine overloads. I hadn't got to grips with sorting this out yet and anyway racing sailors never go backwards /forums/images/graemlins/grin.gif
 

savageseadog

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[ QUOTE ]
Savageseadog, have you played around with you idle speed to see if this makes a difference?

[/ QUOTE ]As you know idle speed is a trade off between smooth, steady low viration running and the need for the lowest possible power and speed in slow ahead or reverse.
 

homer

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We have had reversing problems with our Kiwi (on a Volvo 2002). The underlying cause is, of course the high (fixed) pitch in reverse. Increasing the tickover to 1000rpm has pretty well sorted it although by the end of the season when the blades start to get a little sticky, it can recur.
However, we have a bigger problem - a lot of vibration over about 2000 (engine) rpm. This does not occur with the old, fixed prop and the Kiwi has been thoroughly checked for balance, pitch etc. Has anyone else experienced bad vibration?
 

npf1

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Sure you need to stop but I can't recall a siutation where I've ever needed more than 1500 rpm to stop. Close quartering stuff is normally done so slow that tickover on reverse, or a short burst slightly above tickover, is all that's required.

If you were full ahead and for some reason suddenly needed to stop, well ... yes ... I partially see a potential issue, but 1500 would stop most boats pretty quickly.

All that being said, although it's an issue that you can probably get by with, I fully agree that it's not an ideal situation or one I'd regard as normal or be happy with.
 

Sans Bateau

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If I can interrupt here. On occasions when the wind is coming from astern in largish chunks, I may have no forward revs at all, but need huge amounts of reverse to arrest the forward motion before I have another gel coat job to do on the stem! I would not like a situation where reverse revs have a restriction.
 

TiggerToo

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excuse my naiveity here...
but if the revs are restricted by the combination of pitch/powerof the engine: will your prop not be generating enough backwards thrust at low revs?

Having said that, our Kiwi is regulated to give excellent performance in reverse (and no vibration), so I would not know.
 

JonJon

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You may have a point but the problem is the engine cant develop its full power if it cant rev. A bit like trying to pedal up a steep hill in top gear on a bike - it would be easy to hold you back!
 

mobeydick

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I have seen several complaints of this problem on the Cruisers forum (I think), in some cases stalling the engine in reverse. No solution that I have seen. The list of possible causes on the Kiwiprop website shows there is a problem (MUCH better than denying it ever hapens though....) but also lots of happy customers.
 

davidbains

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I think the problem is that the coarser pitch in reverse is best suited to a gearbox with a much higher ratio in reverse. I find my Yanmar 2GM20 with a 2.62/3.1 gearbox, the reverse power and manouevrability is great. The prop did stop the engine in fwds till the idling speed was raised but now I'm very pleased with the installation.
Be interested to hear the gearbox ratios in those boats with problems.
 

Andy_H

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I have exactly the same situation with the Kiwiprop on my Maxi. I'm told this is normal for this prop and is caused by the coarse pitch in reverse. Whilst it seems a bit odd at first, there is plenty of stopping power in reverse even with the low revs and with the coarse pitch, there is plenty of power at tickover or just over for 'normal' reversing.
 

DaveS

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I would concur. Full throttle in reverse (which I've only tried once as a test) gives me only 1500 rpm, but a reverse boat speed more than I'd ever need or want. A securely locked tiller is absolutely essential IMHO before trying this! For normal manoevering I use little more than tickover astern, and can easily stop the boat within its length.

I've reduced my forward pitch to get nearer to rated max engine revs (c. 3000) at full throttle so as to get full engine power in difficult conditions, but this does of course give reduced speed at lower revs. I find the lower speed at tickover simplifies manoevering. I'm also hoping for improved l/hr figures, but too early yet to tell.
 
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