Kiwi prop or alternatives

[ianj99]

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.

My 4108 will only do 1500rpm astern with my 17" kiwi. This is more than adequate because
a) the bite is excellent and
b) 1500rpm with the pitch at maximum would be about 6kts astern.
c) Going astern to slow down now actually works, hitherto, it felt like the gearbox clutch plates were slipping, ditto when you opened the throttle goaing ahead.

Ahead, the max rpm is 2200rpm which actually gives hull speed of about 7kts and relaxed cruising of around 6kts at about 1800rpm. This compares with the previous fixed prop which gave 5.5kts at 1800rpm and max rpm of 2600.

If you have plenty of power to spare, then go for more pitch. Ie if you don't need the full engine power at full rpm, then why not simply adjust the pitch to achieve hull speed at some lesser rpm.

The argument for not doing this is that your power reserve is limited but in practice I'm not bothered about trying to maintain speed punching into a heavy sea and would rather have a quiet, relaxed cruising speed which is now .5kts more than with the fixed prop.

 

[Sybaris]

The Featherstream can have one pitch ahead and another astern. This was great for us because our Yanmar 66hp's have a different gear ratio in reverse.

 

[njsail]

I just received my new kiwi prop in the mail today from New Zealand and can't wait to install it. It looks like a very well made piece of machinery. It also looks very simple in design to maintain. I'll provide my own review when we launch in a couple weeks.

 

[Plevier]

My 4108 will only do 1500rpm astern with my 17" kiwi. This is more than adequate because
a) the bite is excellent and
b) 1500rpm with the pitch at maximum would be about 6kts astern.
c) Going astern to slow down now actually works, hitherto, it felt like the gearbox clutch plates were slipping, ditto when you opened the throttle goaing ahead.

Ahead, the max rpm is 2200rpm which actually gives hull speed of about 7kts and relaxed cruising of around 6kts at about 1800rpm. This compares with the previous fixed prop which gave 5.5kts at 1800rpm and max rpm of 2600.

If you have plenty of power to spare, then go for more pitch. Ie if you don't need the full engine power at full rpm, then why not simply adjust the pitch to achieve hull speed at some lesser rpm.

The argument for not doing this is that your power reserve is limited but in practice I'm not bothered about trying to maintain speed punching into a heavy sea and would rather have a quiet, relaxed cruising speed which is now .5kts more than with the fixed prop.

But that's a much bigger lower revving engine isn't it?
The VP2020 feels unhappy straining to provide enough power at very low revs with this very high pitch. It's way off the intended operating curve.

 

[ianj99]

But that's a much bigger lower revving engine isn't it?
The VP2020 feels unhappy straining to provide enough power at very low revs with this very high pitch. It's way off the intended operating curve.

The 4108 is not particularly low revving (36bhp at 3000rpm continuous rating), but the torque curve is near enough flat from 1800 to 3200rpm. So, like a car with a 6th gear you can use the surplus torque to reduce engine rpm for a more relaxed and economical cruising speed.

At least with the Kiwi its easy to adjust the pitch (if not cheap due to the cost of a haul out!)