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Thread: Thrust measurements

  1. #11
    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by Fastjeff57 View Post
    No wonder I was such a bad engineer! I dropped a decimal place in my calculations: It should be 460 plus pounds of force from a 50 hp motor going 40 mph.

    Sorry!

    Jeff
    Its catching it 1st that counts.

  2. #12
    Team Member david bryan's Avatar
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    Quote Originally Posted by Fastjeff57 View Post
    No wonder I was such a bad engineer! I dropped a decimal place in my calculations: It should be 460 plus pounds of force from a 50 hp motor going 40 mph.

    Sorry!

    Jeff
    its amassing to me how guys get screwed up on propeller slip I2 inches of pitch at 5200 rpm = a mile minuet less slip i think that is no way to describe how a prop works please conceder this. the queen marry at long beach ca has about a 18 inch diameter prop shaft and turns 175 rpms a min. the boat goes about 30 miles a hour. now how much pitch do we need to do that
    David Bryan

  3. #13
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    My calculator doesn't go over 17 inches. Sorry!

    Jeff

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    Quote Originally Posted by Fastjeff57 View Post
    My calculator doesn't go over 17 inches. Sorry!

    Jeff
    Jeff you mist the point you can not get enough pitch to go 30 mph @175 RPM but the queen marry dose luck it up on google
    David Bryan

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    Quote Originally Posted by david bryan View Post
    Jeff you mist the point you can not get enough pitch to go 30 mph @175 RPM but the queen marry dose luck it up on google
    Last time i seen that boat in long beach it didn't move much, but i'm following.

  6. #16
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    Quote Originally Posted by david bryan View Post
    Jeff you mist the point you can not get enough pitch to go 30 mph @175 RPM but the queen marry dose luck it up on google
    Somethings wrong there Dave it works out to 1.9mph. Variables in the realm of possible would be a small pecentage of 1.9 so not even close. Either the RPMs are the wrong # or theres a ratio being overlooked.. [2700Rs x 12P would be potential speed.] Besides there being a mistake Im missing the point too.

  7. #17
    Team Member david bryan's Avatar
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    what i am trying to prove is that a propeller dose not screw it self through the water but is a pump that produces thrust like a jet and i have broken world records and won national championships to prove it
    David Bryan

  8. #18
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    Quote Originally Posted by david bryan View Post
    what i am trying to prove is that a propeller dose not screw it self through the water but is a pump that produces thrust like a jet and i have broken world records and won national championships to prove it
    My limited experience has it that more blades -can- equal more speed per RPM at the same pitch. So does it have multiple blades? Progressive pitch? Just asking how.

  9. #19
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    Quote Originally Posted by david bryan View Post
    Jeff you mist the point you can not get enough pitch to go 30 mph @175 RPM but the queen marry dose luck it up on google
    At 175 rpm it takes a pitch of around 15 to 16 feet to yield 30mph. Pretty normal looking prop other than being about 20 feet in diameter.

  10. #20
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    Looking at pictures of those props the pitch looks more than 16 foot & the stuff I read said maximum revs 200.
    What was the hull speed?

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