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Old 07-09-2005, 10:48 PM   #21
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Join Date: Mar 2004
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There's 3 benefits of a bullet style gearbox :

a) There is a limit to how fast a normal style box can run before it blows out, which I think ispretty much the same as a high speed stall on aeroplane. ie the fluid can't bend around the curves fast enough so it lets go! A longer more gradual curve makes this less likely to happen, or raises the speed at which it will happen
b) The 'bullet' shape can (but not always) be more efficient
c) Low water pickups mean ya can run higher propshaft heights

A newer style bravos is pretty well documented from not benefitting from a nosecone - it's well enough designed that the standard box is actually pretty good.
There is a small amount of evidence that a nosecone on an old, short, bravo can have a positive effect on top speed.

The down side of a bullet box is as, as Jon says. The flow over a bullet box is great at neutral trim, but as soon as you deviate significantly away from this, the flow is worse than over a normal box. Different boxes and nosecones respond differently to this - but I would say the more pointy and long it is, the more of a negative effect positive trim would have.
(FWIW I think hydromotive make some fairly rounded nosecones that work OK with positive trim)

Also, at ultra high propshaft heights, you can get a massive amount of lift off the box itself as it's end up more or less like a mini planing hull itself.
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