drive gear help needed 1:36 vs 1:50
#21
Platinum Member
Platinum Member
I always thought that numerically-higher gear ratios were used in outboards to give adequate life to the shift dogs. Outboards and Alpha-style drives have typically used higher ratios thru the years.
It wasn't until the advent of upper-gearset clutch shifting (volvo/bravo) that "taller" or numerically lower ratios were feasible.
If 2:1 or 3:1 ratios were inherently "better" we would be seeing more of them.
There HAS to be a point where a prop has "too much" pitch to be efficient. If we look at extremes, it is easy to see that a 100" pitch propellor COULDN'T work very well. On the flip side, a 1/2" pitch propellor would be wasting energy just churning water with very little usefulness.
Any thoughts?
It wasn't until the advent of upper-gearset clutch shifting (volvo/bravo) that "taller" or numerically lower ratios were feasible.
If 2:1 or 3:1 ratios were inherently "better" we would be seeing more of them.
There HAS to be a point where a prop has "too much" pitch to be efficient. If we look at extremes, it is easy to see that a 100" pitch propellor COULDN'T work very well. On the flip side, a 1/2" pitch propellor would be wasting energy just churning water with very little usefulness.
Any thoughts?
#22
Exactally. I've heard props in the 26-28" range are the most efficient. Ask SteveDavid- they can set their trans to any ratio and set it up for a ? 26" prop. No, don't have any efficiency curves to back this up.
#23
Platinum Member
Platinum Member
Join Date: Apr 2001
Location: Beautiful Fort Lauderdale www.cheetahcat.com
Posts: 10,833
Likes: 0
Received 6 Likes
on
6 Posts
The outboard gear ratios are for the simple fact that the little 2 strokes do not have much useful torque to begin with Unless you have a very very light boat then numerically high ratios are needed IE 2:1 1.75:1 1.86:1
As the propellers go beyond the 30 inch pitch range and the “helix” angle approaches 45 degrees ! Efficiency starts its march into the amazing and wonderful world of diminishing return.
Oh by the way on the propellers since the US is not a signatory to the ISO 484/2 classification system look out (there are standards 1-3 and a fourth “S” being the finest) in a class 3 propeller there can be as much as 1.5” of drift in the Pitch !! between a pair, If your shop does not have Prop Scan or something equivalent, Run ! Pitch blocks and Hammers LOL for stone masons or the village blacksmith but not my propellers.
Best Regards
As the propellers go beyond the 30 inch pitch range and the “helix” angle approaches 45 degrees ! Efficiency starts its march into the amazing and wonderful world of diminishing return.
Oh by the way on the propellers since the US is not a signatory to the ISO 484/2 classification system look out (there are standards 1-3 and a fourth “S” being the finest) in a class 3 propeller there can be as much as 1.5” of drift in the Pitch !! between a pair, If your shop does not have Prop Scan or something equivalent, Run ! Pitch blocks and Hammers LOL for stone masons or the village blacksmith but not my propellers.
Best Regards
Last edited by Steve 1; 06-15-2002 at 07:42 AM.
Thread
Thread Starter
Forum
Replies
Last Post
Ms PatriYacht
General Racing Discussion
41
11-09-2004 12:26 PM