Drive ratios and efficiency
 

My 271 Formula Fastech Bravo 1 has a 1.65:1 drive ratio. I began to consider the possibility that a lower numerical drive ratio would be more efficient since most powerboaters seem to run 1.50:1 or 1.36:1. A search took me to the BAM website where I found the following quote:


"In my experience, a boat will run the fastest with a higher numerical drive ratio assuming you can find a prop with enough pitch to limit the engine to the desired RPM at full throttle. This does not take into account any handling or bow/stern lift issues.
The theory is that the faster a prop rotates the more power it takes just to turn it in the water. A slower turning prop with more pitch is more efficient than a faster turning prop with less pitch even though the calculation for theoretical speed is the same for both."

If this is true, why are more manufacturers using the 1.65:1 ratio from the factory and why isn't the 1.65:1 more popular? Especially since props are widely available to 32"+.
Anyone have an opinion on this?

Re: Drive ratios and efficiency
 

Torque multiblication and the possibility of broken propshafts?
Also, props around 30" dont have very good planing or low speed characteristics.
Gary

Re: Drive ratios and efficiency
 

I know some of the Fountains now come with the 1:1.65 ratio. They also have a much higher x-dimension than in the past. The result if a higher top end - makes great advertising! They don't tell you about how long it takes to get on plane or how long it takes to achieve their top speed.

Re: Drive ratios and efficiency
 

Most of the performance boats with 165-1 that i have seen also have to high X dem. causing lots of slip. To keep the motors off the rev limiter they use high pitch props ,causing poor low & mid range performance, the 165 / 1 ratio helps low end. Space your drives back down and use a lower pitch prop. Do you have a 30 or 32 on there now ? check your slip !