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Old 06 January 2011, 06:41   #11
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I'm hitting about 5,200 lightly loaded with my 16 x 23 and getting 46ish kts. I would have thought a 14.75 x 23 x 3 would be a tad small but may be worth a try. A 4 blade would be interesting. Engine is rated between 5,000 and 6,000rpm
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Old 06 January 2011, 07:02   #12
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I would have thought a 14.75 x 23 x 3 would be a tad small
So if I told you I reckon a 21" would be about right, you probably wouldn't believe me

I guess we'll find out soon

If you're seeing 5200 with a light load then there's certainly improvements to be had
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Old 06 January 2011, 07:18   #13
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So if dropping from 23" to 21" raises the rpm by about 500 for the same size diameter, what does reducing the diameter from 16" to 14.75" do as well.
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Old 06 January 2011, 07:22   #14
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Thanks for that Aquatec. I did speak to Steel Dev at the end of last year, but as I'm sure youknow all aftermarket props are a smaller diameter, so it's not just a straightforward matter of choosing the next size pitch down. I currently run a 16 x 23, and was looking for a 16 x 21.5. If I go for a Solas 14.75 diameter, what pitch would I need?? Here endeth the calculations and starteth the art
Another thought just occurred to me, yes bit quiet at work today

Pitch is the displacement of the prop, ie a 21" pitch prop would move forward a theoretical 21" through a solid mass (no slip).

Therefore any DIAMETER prop of a certain pitch would be comparable to another of equal pitch, they'll both move through a solid mass the same distance per revolution. Obviously discounting all the other variables, surface area, cupping, etc.

Or am I talking sh*t again?
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Old 06 January 2011, 07:32   #15
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I purchased 2 S/S Suzuki props from Brownspoint Marine in USA without any problems. They are also great for Suzuki spares etc. However, having purchased a new 21in pitch to replace the 19in one I was very disappointed with the results. In the end a 4-bladed 19in prop provided the best solution. The moral is.......... borrow and try before you buy!!
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Old 06 January 2011, 07:34   #16
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I think you've been thinking too hard . Your theory would be fine in a solid (e.g driving a screw into a plank of wood) but useless in a liquid. Slip and hydraulic action all comes into play somewhere.

Try seeing how fast you go with one engine only on Martini II. Second engine doesn't add anything to the overall movement through the effects of pitch alone, it just doubles the surface area of blade in contact with the water.
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Old 06 January 2011, 07:59   #17
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I was wrong once before, long time ago but it has happened

My old Crompton would make a good comparison, 6.7m, single 200hp, topped out at around 47/48 knots. That was swinging a 21" mirage iirc, or may have been a laser II. Might have been a tad small but given your slightly lower top speed this would balance out.

I'll get you a price for the hub kit
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Old 06 January 2011, 08:54   #18
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I'll get you a price for the hub kit
Cheers
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Old 06 January 2011, 11:40   #19
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So if dropping from 23" to 21" raises the rpm by about 500 for the same size diameter, what does reducing the diameter from 16" to 14.75" do as well.
I've always heard approx. 100 rpm per 1/4" of pitch. General rule, rather than written in stone, of course; I have never bothered to verify or discount the rule of thumb.

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Old 06 January 2011, 16:16   #20
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I was wrong once before, long time ago but it has happened
Is this what you are referring to.... joining Ribnet and not bolting your engine on properly

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Hi to everyone, I've just come across this forum recently and thought I would introduce myself to you all!

My name is Matt, im 31 and have owned my 6.7m Crompton for the last 8 years. It has been out of action for the last 2 years as the oil pump failed on my Ficht 150 and didnt bother to tell me! 2 years previous to that the original motor, an Evinrude intruder 150 fell of the back at 45 knots! So I've just bought a '99 Mariner 200 carb model and am rigging it at the moment so fingers crossed will be back in the water very soon!

Looking forward to being an active member of this interesting and informative site,

Matt
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