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23-02-2008, 09:23 PM
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#1
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Registered User
Location: teignmouth,devon
Occupation: self employed courier
Interests: banger racing, powerboat,and the missus
Boat name: Badbouys A24
Boat make: Phantom 19
Engines: Yamaha 130
Cruising area: teignmouth,exmouth,south west
Join Date: Feb 2008
Location: teignmouth,devon
Posts: 11
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could anyone help me please
im trying to work out how to turn 57rpm in mph on what scale is it done i got a yam 130 on a phantom 19 in which im starting ocr this season hopfully
thanks wayne
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23-02-2008, 09:38 PM
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#2
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Registered User
Country: Gibraltar
Location: Gibraltar
Occupation: None for the moment, living the Dream
Interests: powerboating,smoking and sleeping
Boat name: used to be The Rock
Boat make: used to be Phantom 19
Engines: Used to be Yamaha 130
Join Date: Mar 2006
Location: Gibraltar
Posts: 33
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Hi Wayne, nice to see you will be joining us in the fleet. Who are you racing with? I will get Mark to answer your question. See you soon mate.
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El MandY
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24-02-2008, 01:53 PM
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#3
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Senior Member
Country: UK
Location: Devon
Occupation: Garage Proprietor
Interests: PowerBoat Racing
Boat name: If Only
Boat make: Bernico F3 OCR, Bernico Prototype Inboard, and some Ribs
Engines: Yamaha Pro V 115
Cruising area: UK, France
Join Date: Jan 2005
Location: Devon
Posts: 3,095
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Quote:
Originally Posted by badbouy
im trying to work out how to turn 57rpm in mph on what scale is it done i got a yam 130 on a phantom 19 in which im starting ocr this season hopfully
thanks wayne
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57mph near as damn it !! and a speedo wont help !!
and its 5700 rpm . i can email you the prop calc spreadsheet if you want.
Bob
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If Only
National Outboard Immersed Propeller Mono Record 103mph
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24-02-2008, 06:27 PM
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#4
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BananaShark Member
Country: UK
Location: Salcombe South Devon
Occupation: Racer and builder
Interests: Winning races
Boat name: BananaShark
Boat make: BananaShark 34' Race
Engines: Twin Yanmar BY 260's
Join Date: Mar 2004
Location: Salcombe South Devon
Posts: 4,638
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Type "prop calc" into Google and take your pick of web based programs - Bob will tell you what your gearbox ratio is if you don't know.
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Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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24-02-2008, 09:15 PM
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#5
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Registered Ozone AbUser
Occupation: Marine Engineer
Join Date: Dec 2006
Posts: 389
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Testing
Quote:
Originally Posted by Cookee
Type "prop calc" into Google and take your pick of web based programs - Bob will tell you what your gearbox ratio is if you don't know.
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Its 2:1 and with the yam 24 overhub you are running,
revs and speed are almost equal as bob says, A speedo is helpful to help you get used to where the boats fastest trim is for acceleration and top end as over trimming can make it seem faster when it actually makes it slower.
You need a trim gauge aswell
Also the revs/speed equation is not an exact science, Different props,ride height and conditions all cause variables.
Make a log of what you do so you can look back to see what actually improves as well as disproves!!
Most of all TEST and lots of it, I have racked up over 10 hours in the new cat in 5 weeks and still learning hugely
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24-02-2008, 10:29 PM
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#6
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Registered User
Country: UK
Location: Bucks
Join Date: Dec 2007
Location: Bucks
Posts: 586
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Out of interest I just used this site;
http://www.go-fast.com/Prop_Slip_Calculator.htm
Using an Argo Cat with a 90 hp yam, running a 29" pitch prop we managed 83 mph (one way) on Windermere (timed not GPS).
The site gave me 77 mph with zero slip, so I guess not an exact science.
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24-02-2008, 10:52 PM
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#7
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BananaShark Member
Country: UK
Location: Salcombe South Devon
Occupation: Racer and builder
Interests: Winning races
Boat name: BananaShark
Boat make: BananaShark 34' Race
Engines: Twin Yanmar BY 260's
Join Date: Mar 2004
Location: Salcombe South Devon
Posts: 4,638
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Quote:
Originally Posted by ciao!
Out of interest I just used this site;
http://www.go-fast.com/Prop_Slip_Calculator.htm
Using an Argo Cat with a 90 hp yam, running a 29" pitch prop we managed 83 mph (one way) on Windermere (timed not GPS).
The site gave me 77 mph with zero slip, so I guess not an exact science.
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Don't forget that props have a variable pitch, so it's that part that is not exact - especially if it's been worked or had its diameter reduced.
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Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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24-02-2008, 11:50 PM
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#8
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Registered Ozone AbUser
Occupation: Marine Engineer
Join Date: Dec 2006
Posts: 389
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Quote:
Originally Posted by Cookee
Don't forget that props have a variable pitch, so it's that part that is not exact - especially if it's been worked or had its diameter reduced.
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I speak from experience with a P19 and yam 24 they are pretty in line..Strange thing is today i ran 7600RPM @76MPH must be a strange coincidence. mind you that's with a Standard 23P old style pre laserII Quicksilver out of the box, cast with dinosours around...
Every boat/prop/set up varies
Trying bunny eared cleaver tues dawn!....excited
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25-02-2008, 02:07 AM
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#9
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Registered User
Country: UK
Location: Bucks
Join Date: Dec 2007
Location: Bucks
Posts: 586
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Quote:
Originally Posted by A30
I speak from experience with a P19 and yam 24 they are pretty in line..Strange thing is today i ran 7600RPM @76MPH must be a strange coincidence. mind you that's with a Standard 23P old style pre laserII Quicksilver out of the box, cast with dinosours around...
Every boat/prop/set up varies
Trying bunny eared cleaver tues dawn!....excited
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Surely at 7600RPM you are well out of the "powerband" ?
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25-02-2008, 02:18 AM
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#10
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Registered User
Country: UK
Location: Bucks
Join Date: Dec 2007
Location: Bucks
Posts: 586
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We managed in my 21' Campbell Cat in 1988 at Windermere with one of the first XR2's - 75.8 mph (I know that because the certificate is hanging up on my wall in the office here!!)
That was running running a very worked on QSS 26"
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25-02-2008, 02:26 AM
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#11
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Registered User
Country: UK
Location: Bucks
Join Date: Dec 2007
Location: Bucks
Posts: 586
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As BluFin on this forum has said many times average race speeds have not dramatically increased over the last 25 years, because Hotboats and Argos go quick now, is no different than Robert Cook doing over the ton in 1980 in a 3D boat.
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25-02-2008, 08:31 AM
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#12
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BananaShark Member
Country: UK
Location: Salcombe South Devon
Occupation: Racer and builder
Interests: Winning races
Boat name: BananaShark
Boat make: BananaShark 34' Race
Engines: Twin Yanmar BY 260's
Join Date: Mar 2004
Location: Salcombe South Devon
Posts: 4,638
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Quote:
Originally Posted by A30
Strange thing is today i ran 7600RPM @76MPH must be a strange coincidence.
Trying bunny eared cleaver tues dawn!....excited
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I wouldn't spend to long at those RPMs with an XR2 - get a bigger prop!
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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25-02-2008, 09:07 AM
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#13
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Registered User
Country: Sweden
Boat make: Argo 18
Engines: Yamaha
Join Date: Nov 2005
Posts: 50
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Quote:
Originally Posted by ciao!
Out of interest I just used this site;
http://www.go-fast.com/Prop_Slip_Calculator.htm
Using an Argo Cat with a 90 hp yam, running a 29" pitch prop we managed 83 mph (one way) on Windermere (timed not GPS).
The site gave me 77 mph with zero slip, so I guess not an exact science.
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I guess that your Tach showed wrong !!! You must have turned more than 5600 rpm more like 6400rpm and 6% slip (usually the the slip on a Argo flat out) to reach 83mph with a 29 !
I guess that Harri F was pleased with that speed !
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25-02-2008, 09:09 AM
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#14
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Registered User
Country: Sweden
Boat make: Argo 18
Engines: Yamaha
Join Date: Nov 2005
Posts: 50
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Quote:
Originally Posted by Cookee
Don't forget that props have a variable pitch, so it's that part that is not exact - especially if it's been worked or had its diameter reduced.
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What has the diameter to do with his actual speed ?
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25-02-2008, 10:12 AM
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#15
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Registered Ozone AbUser
Occupation: Marine Engineer
Join Date: Dec 2006
Posts: 389
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Don't worry cookee i realize it was overrevving!
Was just one quick squirt, That was with a standard 23. The next test is with the 26 Bunny. Also the last test was the first outing having gone from 1:87 to 2:1 dramatically increasing the revs
Thanks for concern anyways
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25-02-2008, 06:28 PM
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#16
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BananaShark Member
Country: UK
Location: Salcombe South Devon
Occupation: Racer and builder
Interests: Winning races
Boat name: BananaShark
Boat make: BananaShark 34' Race
Engines: Twin Yanmar BY 260's
Join Date: Mar 2004
Location: Salcombe South Devon
Posts: 4,638
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Quote:
Originally Posted by 24Maniac
What has the diameter to do with his actual speed ?
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Reducing the diameter will increase the RPM therefore changing the ratio of RPM/Speed/slip
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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26-02-2008, 12:06 AM
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#17
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Registered User
Country: UK
Location: Bucks
Join Date: Dec 2007
Location: Bucks
Posts: 586
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How do you calculate slip?
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26-02-2008, 09:16 AM
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#18
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BananaShark Member
Country: UK
Location: Salcombe South Devon
Occupation: Racer and builder
Interests: Winning races
Boat name: BananaShark
Boat make: BananaShark 34' Race
Engines: Twin Yanmar BY 260's
Join Date: Mar 2004
Location: Salcombe South Devon
Posts: 4,638
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Quote:
Originally Posted by ciao!
How do you calculate slip?
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It's a bit of a chicken and egg thing really - if you put pitch, gear ratio, and speed into a prop calc programme then it will give you slip - the trouble is that even factory pitch measurements are only an average of pitch over the whole blade, and once you reduce the diameter a bit or tweak it slightly it will be some other pitch entirely, and at higher speeds it could make quite a difference to the slip.
http://www.go-fast.com/Prop_Slip_Calculator.htm
__________________
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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