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24-03-2005, 07:00 PM
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#1
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Registered User
Country: United kingdom
Location: West Sussex
Occupation: Grease Monkey
Interests: Makin my boat faster!
Boat name: S.B Racing
Boat make: Ocke mannerfelt canopied B23 / Zapcat
Engines: Merc 200XS Gen 2 / Tohatsu 50
Cruising area: littlehampton/Southampton
Join Date: Jan 2005
Location: West Sussex
Posts: 2,656
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cleaver question!
my boats a bit of a handful when at speed and always wants to push the nose down? a few people have said to me that its my prop lifting the back up? is this right about a cleaver?
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Class 3C Mono EPA National speed record holder 95.35 mph Avg!
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24-03-2005, 07:03 PM
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#2
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Registered User
Location: GOLDEN MILE
Boat name: LILY THE PINK AND TERMINATOR 11
Boat make: PHANTOM 21 AND 20
Engines: 2.5 EFI X 2
Join Date: Mar 2004
Location: GOLDEN MILE
Posts: 2,475
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cleaver gives stern lift , chopper gives bow lift, imho of course.
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PLEASE DON'T STEAL...THE GOVERNMENT DON'T LIKE THE COMPETITION
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24-03-2005, 07:11 PM
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#3
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Registered User
Country: United kingdom
Location: West Sussex
Occupation: Grease Monkey
Interests: Makin my boat faster!
Boat name: S.B Racing
Boat make: Ocke mannerfelt canopied B23 / Zapcat
Engines: Merc 200XS Gen 2 / Tohatsu 50
Cruising area: littlehampton/Southampton
Join Date: Jan 2005
Location: West Sussex
Posts: 2,656
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maybe i ought to get a chopper then! are' these abit snatchy when re entering the water though?
__________________
Class 3C Mono EPA National speed record holder 95.35 mph Avg!
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30-03-2005, 04:06 PM
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#4
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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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Quote:
Originally posted by scottyboy
maybe i ought to get a chopper then! are' these abit snatchy when re entering the water though?
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i found it fine even when surface piercing that is until you back off a bit sharpish and it tries to throw you out the boat sideways
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30-03-2005, 04:26 PM
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#5
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Quote:
Originally posted by scottyboy
maybe i ought to get a chopper then! are' these abit snatchy when re entering the water though?
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Work the prop & take out some of the cup. See the link http://www.mazcoprops.com/products.htm under the RE4
4 blade chopper slightly better than the 3 but it's the same effect.
see clever link also as to how it carries the boat
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30-03-2005, 04:28 PM
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#6
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Typically, monohulls respond better to a bow lifting (chopper style) prop than a cleaver, since they need the bow lift to carry the bow to air the boat out. Cats typically respond to stern lifting (cleaver style) since they are already generating stacks of aerodynamic lift raising the bow.
There are exceptions of course, a very fast mono might get enough aerodynamic lift to not benefit, but that's the guideline, IMHO.
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30-03-2005, 04:29 PM
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#7
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Is it correct that a 4+ blade surfacing prop is loads easier on the gearbox and steering?
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30-03-2005, 04:29 PM
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#8
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Just checked the clever link & it's been amended recently & removed the wording aft lift & used the Mazco Offshore Cleaver is the only way to fly instead, but it did state it
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30-03-2005, 04:35 PM
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#9
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Quote:
Originally posted by Matt
Is it correct that a 4+ blade surfacing prop is loads easier on the gearbox and steering?
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Yes In Theory,
"Do F ask how to prove it, coz I cant find the Book/Article at the Moment"
But in theory the fastest prop in surface applications will have two blades ??????.
All a trade off
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30-03-2005, 04:40 PM
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#10
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Registered User
Location: Scotland
Interests: Hole maker
Boat make: Humber Ocean Offshore
Engines: KAD 300/DPX
Join Date: Mar 2004
Location: Scotland
Posts: 958
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an' a big lump of lead.
Edit: WTF happened to your 1 blade post, Matt?
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JW.
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31-03-2005, 08:44 AM
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#11
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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 Matt
Typically, monohulls respond better to a bow lifting (chopper style) prop than a cleaver, since they need the bow lift to carry the bow to air the boat out. Cats typically respond to stern lifting (cleaver style) since they are already generating stacks of aerodynamic lift raising the bow.
There are exceptions of course, a very fast mono might get enough aerodynamic lift to not benefit, but that's the guideline, IMHO.
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Batboats are also the exception (the 2 litre ones anyway), they all run sternlifting props.
And 1 bladed props are meant to be the most efficient - just got to keep them on the propshaft!
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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31-03-2005, 08:57 AM
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#12
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Here we go !!!!!
Now, How about Screw Threads ( Joke)
Edit: those 1 blade fekers are a bugger to balance ?
Seriously
how about posting some high performance prop links, I know I could enjoy a good nose around those sites
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31-03-2005, 09:00 AM
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#13
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Yeh, I removed it cos when I thought about it, for all effective purposes a surfacing 2 blade prop is a 1 blade - only 1 blade in the water at a time.
Quote:
Originally posted by jw.
an' a big lump of lead.
Edit: WTF happened to your 1 blade post, Matt?
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31-03-2005, 09:05 AM
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#14
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Yeh, I suppose I should have said a 'traditional' non stepped hull, but then some smartarse would have said steps are traditional because they were invented back in the 30's or something, or they would have found some non stepped hull that didn't respond to bow lift. Or noted that underpowered planing hulls don't want bow lift. Etc etc etc.
Quote:
Originally posted by Cookee
Batboats are also the exception (the 2 litre ones anyway), they all run sternlifting props.
And 1 bladed props are meant to be the most efficient - just got to keep them on the propshaft!
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31-03-2005, 09:13 AM
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#15
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Mercury's prop pages are OK:
http://www.mercurymarine.com/chapter...y__development
http://www.mercurymarine.com/chapter...opeller_parts2
http://www.mercurymarine.com/chapter...ropellers_work
http://www.mercurymarine.com/chapter...ler_technology
Wasn't turbinia one of the first high speed propeller applications.
Just did a google, here we go:
Quote:
Parsons had difficulty in choosing the correct propulsion configuration and went through seven different propeller designs, including three screws on one shaft. Because the turbine turned the shaft faster than an expansion engine would, the screws were not as efficient as predicted due to cavitation. This phenomenon, the result of a vacuum forming around a screw turning at high speed, was first observed during tests on Turbinia. When the vessel failed to attain her design speed, Parsons replaced the single shaft with three separate shafts (initially, there were three screws on each shaft) and at the same time replaced the radial-flow turbine with a more efficient parallel-flow turbine. The results were spectacular, and in supervised trials Turbinia attained speeds of thirty-four knots.
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Quote:
Originally posted by BluFin
Here we go !!!!!
Now, How about Screw Threads ( Joke)
Edit: those 1 blade fekers are a bugger to balance ?
Seriously
how about posting some high performance prop links, I know I could enjoy a good nose around those sites
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31-03-2005, 09:15 AM
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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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Actually the BananaShark has some similarities to the Batboat and hates sternlift, although we've made some changes and going to try our "batboat prop" again!
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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31-03-2005, 09:33 AM
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#17
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Yeah, but if you think about it, under ideal conditions a perfectly balanced stepped hull should be best with a very neutral prop. Adding bow lift (which is really stern drop) or stern left is only ever fighting against the hull, that's the whole point of it.
Although, thinking about it some more I reckon you could have 2 classifications of stepped hulls. a) Those that are designed to run on the tip of the steps, effectively with only 2 (or more depending on the design) points of contact on the water. b) Those that use the steps to aerate the water aiming to lower friction. The former would probably be the b23 style where the steps are inclined at a noticeable angle, the latter would be where the step is more of a notch in the hull.
Not sure if this makes sense or not - I'm just thinking out loud.
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31-03-2005, 09:53 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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Matt, the way I understand it (maybe not the right way!) is most hulls are "a" - the steps are inclined to suck air at lower speeds to stop the steps "sucking" and making it harder to get the hull to release and get on the plane quicker. The amount of aeriation (sp?) and the good it does is questionable I believe (been wrong before though!)
__________________
Cookee
British Champions! RIB Formula 1 2005
National Speed Record Holder at 90.15 (still)
www.bananasharkracing.com
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31-03-2005, 10:49 AM
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#19
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Traveling
Country: UK
Location: Alderholt
Occupation: Aerospace
Boat name: T/T D2S
Boat make: Midas 27' Cat, Argo 16 Cat. Avon Rib Thingy
Engines: Merc 280-ROS -JSRE,65Xs, 75 Stinger, Yam 60
Cruising area: Any Seedy Bar
Join Date: Sep 2004
Location: Alderholt
Posts: 4,225
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Don't ya just love theroy.
But us boaters go a bugger it all up by wanting to do things
like turn, accelerate, pull skiers, calm water rough water, ect, ect,ect.
I alwyas had a two prop set up one calm & 1 rough the rough one was cut down by a 1/4 & de pitched by a 1/2", pick up was a lot better but it it flattened off I was feked.
Edit: looked at the Merc link: ok on props but there theroy of Flight F******* Sucks Fig 4.23. Not going to go off of theory of fligt as well props are enough
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31-03-2005, 10:51 AM
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#20
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Why did you drop the diameter?
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