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20-10-2004, 10:20 AM
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#1
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Registered User
Country: US
Location: Virginia
Interests: Quiet desperation
Boat name: A Little Noisy
Boat make: Excalibur 24
Engines: Express Racing 525
Cruising area: Mobjack Bay (where?)
Join Date: Mar 2004
Location: Virginia
Posts: 1,974
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Prop/Speed calculator
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20-10-2004, 04:54 PM
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#2
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Registered User
Country: Ireland
Location: Dublin
Occupation: Boatbuilder
Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
Engines: 300Hp Mercury 2.4, 130 Yamaha, Bridgeport EFI, XR6, Merc 200.
Cruising area: Malahide, Dublin
Join Date: May 2004
Location: Dublin
Posts: 1,803
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I like this one,
This is a downloadable prop slippage calculator that is designed to easily calculate changes to speed and slip by changing variables such as engine rpm, horsepower, and prop pitch.
http://www.hydrostream.org/Prop.htm
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20-10-2004, 06:16 PM
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#3
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Registered User
Join Date: Mar 2004
Posts: 1,016
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I tried the prop calc and it told me that it "thought I was a lying bastard and to get me GPS checked"....
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“Never try to wrestle a pig” ™ The Sparkler Prefect
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20-10-2004, 06:51 PM
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#4
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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Quote:
Originally posted by Jono
I tried the prop calc and it told me that it "thought I was a lying bastard and to get me GPS checked"....
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How long have you owned a Falcon?
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20-10-2004, 07:35 PM
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#5
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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dont understand that entered all the info and with my laser it said i had 0.08 slip. but with the chopper it said it was impossible as the slip was a minus
explain that please boffins
speed was gps'd over quite a distance
pitch of props measured by prop reveloutions
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20-10-2004, 07:41 PM
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#6
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numbskull
Country: United Kingdom
Location: South
Occupation: none
Interests: none
Boat name: Leviathan
Boat make: Phantom 28
Cruising area: South Coast
Join Date: Mar 2004
Location: South
Posts: 15,959
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was the gps speed taken in one direction only?
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"I Agree with everything you say really!" - John Cooke to Jon Fuller - 26-01-2013
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20-10-2004, 07:44 PM
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#7
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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was in boat on my own, did 2 or 3 runs then looked at max speed.
does that mean that i havent actually done 76mph then
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20-10-2004, 07:46 PM
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#8
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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look
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20-10-2004, 08:02 PM
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#9
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hello
Join Date: Mar 2004
Posts: 2,739
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My boat had negative prop slip too. Cye must be one amazing genius boat rigging dude
Your GPS seemed pretty much bang on next to your mondeo (shiney and new, but it is a ford) speedo when we tried it out if you remember. And that was in all sorts of dierctions and at lots of speeds ranging from bugger all to over a ton.
hmmm go figure
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20-10-2004, 08:03 PM
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#10
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hello
Join Date: Mar 2004
Posts: 2,739
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The tide moves pretty fast at weston
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20-10-2004, 08:06 PM
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#11
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numbskull
Country: United Kingdom
Location: South
Occupation: none
Interests: none
Boat name: Leviathan
Boat make: Phantom 28
Cruising area: South Coast
Join Date: Mar 2004
Location: South
Posts: 15,959
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I'm not trying to belittle your speed, Just pointing out that your 'max' speed would have been the highest 'speed over ground' that you attained, this would have been your actual water speed, plus the speed of the tidal flow you were traveling in, which could be 4 or 5 mph, depending on where you are and point in the lunar cycle it was (tide height etc)
However, a P20 with a 2.5 efi ought to do circa 75-80, mebbe more, you should'a gone to windermere, you might be going even quicker than 75!
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"I Agree with everything you say really!" - John Cooke to Jon Fuller - 26-01-2013
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20-10-2004, 08:08 PM
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#12
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numbskull
Country: United Kingdom
Location: South
Occupation: none
Interests: none
Boat name: Leviathan
Boat make: Phantom 28
Cruising area: South Coast
Join Date: Mar 2004
Location: South
Posts: 15,959
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Quote:
Originally posted by Johnny Boat Dude
The tide moves pretty fast at weston
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but that's unlikely to affect the speedo in your mundane-o
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20-10-2004, 08:08 PM
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#13
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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that was my old sharpe havent tried my P20 yet
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20-10-2004, 08:09 PM
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#14
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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it affected it for a while didnt it johnny
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20-10-2004, 08:10 PM
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#15
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numbskull
Country: United Kingdom
Location: South
Occupation: none
Interests: none
Boat name: Leviathan
Boat make: Phantom 28
Cruising area: South Coast
Join Date: Mar 2004
Location: South
Posts: 15,959
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Quote:
Originally posted by Burty
that was my old sharpe havent tried my P20 yet
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Ah!
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20-10-2004, 08:13 PM
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#16
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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even if i take 7mph off speed it still only says 0.8 whats that 8%?
what would you expect prop slip to be Mr F?
6" setback
20" mid
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20-10-2004, 08:17 PM
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#17
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hello
Join Date: Mar 2004
Posts: 2,739
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That 76 was in his sharp 19 with a mildly tuned 200 merc probably about 210hp at the prop. Enigine was on a 5.5" setback plate running a worked 26" chopper (mine but I'm to scared to use it) which we were told is now 24" by prop revolutions. It was a lovely flat day and he came past me on one of his runs. It looked awesome that chopper picked the whole boat up, it was running with only a palm sized contact point between the hull and the water, big rooster tail too. Looked well twitchy though, most excelent
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20-10-2004, 08:26 PM
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#18
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hello
Join Date: Mar 2004
Posts: 2,739
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Quote:
Originally posted by Burty
it affected it for a while didnt it johnny
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erm
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23-10-2004, 02:44 PM
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#19
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Registered User
Country: Ireland
Location: Dublin
Occupation: Boatbuilder
Boat make: Hydrostream V-king, 650SS OCR ,Ring 21, Ring 18, Phantom 18.
Engines: 300Hp Mercury 2.4, 130 Yamaha, Bridgeport EFI, XR6, Merc 200.
Cruising area: Malahide, Dublin
Join Date: May 2004
Location: Dublin
Posts: 1,803
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slip
Quote:
Originally posted by Burty
dont understand that entered all the info and with my laser it said i had 0.08 slip. but with the chopper it said it was impossible as the slip was a minus
explain that please boffins
speed was gps'd over quite a distance
pitch of props measured by prop reveloutions
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Thats good slip no's, should be around 8-12% if set up right, you need slip, without it you have no thrust. Without thrust youre stopped!
Is your chopper a diferent pitch to the laser? Whats the pitch of the two props? Did you change the speed when you put in the pitch of the chopper?
Whats the pitch of both props and the speed with each?
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23-10-2004, 03:00 PM
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#20
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Registered User
Country: UK
Location: Weston Super Mare
Occupation: Electrical Engineer
Join Date: Mar 2004
Location: Weston Super Mare
Posts: 6,351
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Re: slip
Is your chopper a diferent pitch to the laser?
Yes
Whats the pitch of the two props?
chopper is a 24 laser is a 22.75
Did you change the speed when you put in the pitch of the chopper?
yes
Whats the pitch of both props and the speed with each?
chopper 76mph @ 6200rpm
laser 72mph @ 6800rpm
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