PDA

View Full Version : Alpha question



CDMA
06-12-2001, 04:40 PM
Does the alpha ratio change in the upper housing or the lower. For example are the lower units from a 1.5 and a 1.65 drive ratio the same or are the upper units the same....or heck are neither the same.

Thanks again

Chris


or if I had the money....

http://www.donzi.net/hull/451/DONZI4.jpg


[This message has been edited by CDMA (edited 06-12-2001).]

Donzitester
06-12-2001, 08:13 PM
The uppers are different,
the lowers are the same.
Its easy to change the ratio's in the uppers however, just a simple gear swap.
Dont eat your heart out over a blackhawk,
allmost all of them break after they are launched 3 or 4 times.

CDMA
06-13-2001, 10:18 AM
I just am fascinated with the concept. I study surface drives at school and the idea of a surface drive duo prop is very interesting hydrodynamically to me. Some day when I am old I would like ot try to build something like an duo prop arneson. You retain the holeshot usually lacking in surface drives and get some wild effincy numbers. The problem I have from a theoretical viewpoint with the blackhawk is that it is a surface drive trucked way close to the boat in primarily turbulent flow ( lots of air). If you could get a blackhawk in cleaner water, lets say 4 feet behind the boat with the duo prop you could potentially be looking at effinecy number higher than anything we have ever dealt with. We always talk about propellor slip but this is very different than complete transfer of power to the water. I am not to sure about the Donzi's but I know in terms of ships we are talking int he area of 30-40%. I think we could get close to 70% with a counter rotaing surface drive way the heck behind the boat.

Chris