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prop problem

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Old 12-03-2007, 04:11 PM
  #11
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My Boats: 1972 Cigarette 36 race
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The boat obviously liked the blade area as it was downhill as you went to less. I agree that you should try 4 blades at the least. I don't understand why the RPM did not increase with the change from the 28 to the 25, are you sure the engine is making power? Good fuel flow? Plug your numbers in here:

http://go-fast.com/Prop_Slip_Calculator.htm
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Old 12-03-2007, 05:31 PM
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thanks a million you guys on this forum is so helpfull compared to the
**** british forums. but as props are so expensive and almost unheard of in this neck of the woods it makes it very difficult to try different props would you guys have any props that i could barrow or buy i would pay all the shipping costs
hull:27ft
beam:8ft
waterline:23ft
weight: 2.2ton
hp:440
fuel:diesel
max rpm:3300
shaft angle:fixed 7%
ratio:1-1

thanks again i really appreciate the help
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Old 12-11-2007, 08:16 PM
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i sent both props off to be cut down in dia and relieve some cupping when the props were scanned the 25 had a cup equal to 6inches and the 28 was 3 inches cup witch left both props 31 how much cup is normal
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Old 12-22-2007, 02:45 PM
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i got my 28 3 blade cou down to 16 dia took out some of the cupping and thinned the blade it came up 300rpm and went down 5mph in speed and then i tried my first rolla 17x28 62mph at 2700 rpm i think if i had a 17 or 16 24 rolla it would be good has anyone got one they would sell or lend or advice to give

cheers gerard
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