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Old 12 August 2005, 15:33   #1
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From 19" to 21". Too much?

Just considering increasing the pitch on my Suz DF90 prop. It's currently 14 x 19" which at WOT gives 6,100 rpm. This is a bit high so I was going to go up one inch in pitch hoping to drop revs by about 250. However, the next size up is 14 x 21" in the Suz range.

Does anyone have any experience of changing 2"? Will it be too much?

Keith
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Old 12 August 2005, 17:05   #2
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That must be a very efficent hull you have there Keith! My BWM with Merc 90 will Rev to 5700 with a 17" and only 5300 with a 19" pitched prop.
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Old 13 August 2005, 04:02   #3
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Well, you will drop your RPM by about 500 and increase you top end speed. But Decrese your pick up speed. Yuo dont have to use Suzuki props though. Lots of people make good props that will fit. Streamline props are very good.
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Old 13 August 2005, 06:15   #4
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The other option is to go stainless - the suzuki 14" props go up in odd numbers on the ali props and even numbers on the stainless ones.

Although you may find that because a stainless prop is more efficient because of the thinner blades that the 1" increase though will certainly increase your speed may not drop the revs down at all.
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Old 14 August 2005, 04:52   #5
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I went from a 19" too a 21" (alloy)on a 5.7 metre humber assault with a yam f100 4 stroke,before the change I could get 41 knots at 6100 rpm befor chine riding.After the change,the revs had dropped around 400rpm throughout the range,top speed was down too 37 knots before I bottled due to chine riding,but the engine was slightly more economical overall.
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Old 14 August 2005, 16:59   #6
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Might try a 21" then and hope for a drop in revs but no loss of top speed. Hadn't really considered stainless, but then it's quite an expensive option for an uncertain outcome.

Keith
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Old 09 October 2005, 08:38   #7
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Well after waiting about 2 weeks for something less than a F4, I'm now in a position to tell those of you that are interested the outcome. My trial run (which involved brekky in France) confirms that revs are now maxing at about 5,700 and top speed has gone up by about 2 knots. Might be more, but then the hull does need a little bit fo a clean

Now cruises at 30/31 kts at 5,000 rpm and does something like 5.5 mpg according to the Navman Fuel.

End result =

Keith
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Old 09 October 2005, 10:08   #8
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I would say perfect and money well spent and you have a spare prop
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