Re: Performance on a 20cc with a 200 Yamaha ox66
 

http://www.go-fast.com/Prop_Slip_Calculator.htm

2.38ratio
20 pitch prop
5000 rpm

= 40mph with no slip

Re: Performance on a 20cc with a 200 Yamaha ox66
 

Thanks for the prop calculator, and keeping me honest.

I miss spoke on my early post. I meant 5500 rpm.

I know the number still don't match, but I remember my GPS hitting 47 Kts (I always keep my GPS set to knots). Of course, that was 6 years ago, and I'm doing this from memory .

My boat was very light, I was still putting in back together, no windshield, no bench seat, and very little fuel.

With that 20P Powertech Prop, it was slow to get on plane, and at WOT, I had the motor trimmed way up. I only stayed at that speed for about 5 secs because the squirliness I felt made me uneasy. I made another run at WOT, and had the same result. I definitely remember thinking that this hull was not meant to go that fast :eek:

I traded the 20P for a 19P the next day, still didn't like the hole shot, and ended up with the 18P I run now.

That's my story, amd I'm sticking to it :D

Lloyd

Re: Performance on a 20cc with a 200 Yamaha ox66
 

Mercury site has a calculator too...

http://appcenter.mercurymarine.com/propSelector/home.do

Re: Performance on a 20cc with a 200 Yamaha ox66
 

6000 (rpm) 18 (pitch)
----- X -------- X (1-10%) (avg.slip) = 38.7 mph
2.38 (ratio) 1056 (constant)

Re: Performance on a 20cc with a 200 Yamaha ox66
 

I think your gear ratio is too low - I think my Merc is 1.87/1

Re: Performance on a 20cc with a 200 Yamaha ox66
 

new 140 Zukes are 2.59:1
older 140 zukes were 2.38:1

Merc 175/200 v6 fishing motor are 1:87
Some Merc sportmaster lowers came with 1.62 gears

I believe I read somewhere that Merc 3:0L gears will fit into a 2.5L case, but I never tried it.

Re: Performance on a 20cc with a 200 Yamaha ox66
 

The GLM catalog lists aftermarket Mercury outboard gears available in 1.5, 1.62, 1.65, 1.75, 1.84, 1.87, 1.92, 1.98, 2.0, 2.06, and 2.3:1, with the 1.5 available only for large 4.75" gearcases, and the 2.3 available only for the 4"/4.25" gearcase. These are not, however, the gears available for the Sportmaster. Those are different gear types. I didn't look at those. The GLM catalog doesn't list prices, just part numbers.

Mercury sells gears for the 4.75" gearcase in 1.5, 1.62, 1.65, 1.75, 1.87, and 1.98:1 ratios,

and for the 4"/4.25" gearcase all of those up to 1.65:1, plus the 2.06:1 and 2.3:1 gearsets, according to my Mercury parts DVD. (And WOW are they expensive from Mercury at about $1000 for a complete set!!!!)

Re: Performance on a 20cc with a 200 Yamaha ox66
 

Did you guys go off on a Merc tangent for some reason when I was sleeping? I'm running a Yami, but will raise the engine a notch this week and will run this w/e, will let you know the results.

Re: Performance on a 20cc with a 200 Yamaha ox66
 

Nah. That was about gear ratios, regardless of make.

Re: Performance on a 20cc with a 200 Yamaha ox66
 

Well you know the old saying...
Once you go black... :eek:..agh, never mind. :rolleyes:

See ya, Ken