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Old 03-05-2006, 05:16 PM   #1
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pro's n con's?

ok whats the pro's n con's of 2:1 ratio gearboxes?
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Old 03-05-2006, 05:52 PM   #2
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How much of a hydrodynamicist are you?
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Old 03-05-2006, 05:54 PM   #3
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How much of a hydrodynamicist are you?
dunno, but i know how to answer my phone!!
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Old 03-05-2006, 06:11 PM   #4
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IMVHO, 2 factors influence gearbox ratio selection.
a) Availability of prop sizes/styles for given propshaft rpm & boat speed
b) Prop tip speed (efficiency) vs paddle wheel (handling)
And then you need to start factoring in prop dia, no of blades, and loads of other bollocks.
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Old 03-05-2006, 07:13 PM   #5
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I'd look into hull weight as well. Inshore racers are close to 1:1 & 2.5:1 is considered "big foot" for heavy loads.
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Old 03-05-2006, 09:06 PM   #6
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I have the choice of either a 1.87 box or a 2.1
Are they any benefits of having a 2.1 box? I know that people like scottyboy run a 2.1 so any thoughts please would be welcome!

Cheers.
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Old 03-05-2006, 10:28 PM   #7
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Quote:
Originally posted by MrRob
I have the choice of either a 1.87 box or a 2.1
Are they any benefits of having a 2.1 box? I know that people like scottyboy run a 2.1 so any thoughts please would be welcome!

Cheers.
I think we mostly run 2:1 ratios because we only run 2litre engines that dont really have the same amount of torque as a 2.5 200 etc and we need to swing large diameter and fairly tall pitched props at a fairly good high rev on the engine!
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Old 03-05-2006, 10:39 PM   #8
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Yes there are differences thats why people play with 1:62, 1.87, 2:1 & othe oddballs some have even had gears cut in the past.

Jimboats book covers well but what works for one doesnt work for another Every setup is different and is personal preference obviously there is a optimium but that may be undrivable to one and not another. Its a long hard slog and costs a bloody fortune to find not to mention the time. Jim does the software as well if you set it up and put in all the bells and whistles has proven very accurate in it's forcasts & you can do it on your PC.

IMHO the fastest is to have 1- 1 1/2 blades in the water turning about 200 RPM below max limit on the tallest Box ratio. with a trim of no greater than about +1 from neutral. I say -200 to allow for fuel burn weight changes. But that would not be the best for a rough day. A slower turning larger pitch prop is more efficent that an egg wisk, but sometimes thats not what you want it's all about trade offs and balance.
You can play with boxes but time in the seat will show a good cost effective return as well as giving a better overall idea of the direction to take rather than a knee jerk reply. get as many props as you can and run em, keep a log book as to how each performs, used a measured distance and keep using the same one, that will give you a better feel as how it effects the boat. Changing you place can give a totally different feel just from the geography.

Am I waffling or what !!!!!! Sorry went off on one...
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Old 03-05-2006, 10:42 PM   #9
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dunno, but i know how to answer my phone!!
yeh but you cant dial can you
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Old 03-05-2006, 10:44 PM   #10
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Quote:
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yeh but you cant dial can you
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