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11-10-2007, 02:16 PM
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#1
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Registered User
Location: Chislehurst
Occupation: Bar/Restaurant manager at Esporta
Interests: Racing, rugby, gym
Boat name: Phoenix
Boat make: Phantom 18
Engines: XR2
Join Date: Feb 2006
Location: Chislehurst
Posts: 6
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Gearbox Advice
Hey all, i'm doing a 3rd yr dissertation project on gearbox shape and ratio and how they affect performance, basing it on the XR2 gearbox. Any help, advice or other information you could help me with would be greatly appreciated.
Cheers
Alex
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11-10-2007, 02:49 PM
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#2
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Just out of interest, who's your lecturer and are you based in the fitzroy building?
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11-10-2007, 03:00 PM
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#3
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Registered User
Location: Chislehurst
Occupation: Bar/Restaurant manager at Esporta
Interests: Racing, rugby, gym
Boat name: Phoenix
Boat make: Phantom 18
Engines: XR2
Join Date: Feb 2006
Location: Chislehurst
Posts: 6
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Not based in fitzroy, as am in the faculty of technology in smeaton. Module leader is Peter Dyson, but i've got Ming Dai as my supervisor
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11-10-2007, 03:11 PM
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#4
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Ah! Yong Ming Dai! Please send him regards from Matt Yorke (doubt he'll remember me though).
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11-10-2007, 03:29 PM
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#5
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Fwiw, here's my 2 penneth worth.
Gearbox flow is almost as difficult to model as surface piercing propellers because it is running in a similarly turbulent flow.
Not quite as bad as props though.
But, if you make a number of baseline assumptions based on ideal scenarios, you could get some interesting results.
Consider the gearbox running with the waterline exactly level with the leading point, and 0 degrees angle of attack in a laminar flow, and also
At that point, the fastest gearbox will be the shortest one that that doesn't blow out. So technically, I reckon blow out speed is going to be a largely a function of length vs width & speed. A blow out is nothing more than high speed stall, same as cavitation is. IIRC a CLE is known to be faster than a SM.
You can exceed the blow out speed of a box by lifting it higher. This effectively reduces the AOA at the contact point with the surface of the water.
The blow out ring is also always contraversial. The idea is that the ridge creates a high pressure zone at the trailing end of the box helping to reduce the likehood of the box blowing out - but of course it also adds drag.
Possibly an easy way to model it would be by looking at it as a finite thickness trailing edge aerofoil. This means you could reasonably model flow over it in 2d to start with.
The skeg also plays an important role since in an ideal world you wouldn't have one. On a single engine boat, the fin is rarely running straight ahead, so creating pretty turbulent flow onto the prop.
If you start running the box at angles of attack other than 0, a more needle nosed box will drop if in terms of performance very quickly, wherease a rounder nosed one will have the varying angles of attack better.
The lift generated from the box runnig high makes a significant contribution to the handling of the boat.
Prop tip speeds seem to be fairly consistent. Myself and Jon have dome a few fag packet calculations and Fwiw, here's my 2 penneth worth.
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11-10-2007, 04:23 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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You dunarf make some good posts!
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"I Agree with everything you say really!" - John Cooke to Jon Fuller - 26-01-2013
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11-10-2007, 04:24 PM
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#7
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Registered User
Join Date: Mar 2004
Posts: 6,891
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11-10-2007, 04:34 PM
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#8
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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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Read your (whole) post again.
Then....I'll graciously accept your apology.
BTW, just been on the blower with Graham.
He has a couple a thousand more stills for ya!
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"I Agree with everything you say really!" - John Cooke to Jon Fuller - 26-01-2013
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11-10-2007, 04:44 PM
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#9
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Cool, get him to send em over.
Quote:
Originally Posted by Jon Fuller
BTW, just been on the blower with Graham.
He has a couple a thousand more stills for ya!
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11-10-2007, 04:49 PM
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#10
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Registered User
Join Date: Mar 2004
Posts: 6,891
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Fixed.
Quote:
Originally Posted by Jon Fuller
Read your (whole) post again.
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12-10-2007, 07:53 AM
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#11
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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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I could bore you on the stuff ive discovered on g.box's and testing.
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