Performance on a 20cc with a 200 Yamaha ox66

[Fr. Frank]

My 200 merc runs 5600 and 48 with a 19 and a T Top...

Dixon, are you really running 48 knots (55 mph) with a T-top? Man, that's haulin' !! Maybe I'm ignorant, but I'd be afraid of breaking my top at that speed.

Like Dr. Suess said, "Go Dog, Go!"

[Bigshrimpin]

Frank - I think he's 48/49mph with the 19 pitch. I seem to remember a discussion about the 50mph barrier being tough to crack.

5600 with a 19p and a 1.87 is in that ball park 48/49mph. 5800/6000 is breaking 50mph with a 19p mirage plus.

[Fr. Frank]

Frank - I think he's 48/49mph with the 19 pitch.

Yeah, that sounds right. If I'd engaged my brain first I'd have remembered that.

I seem to remember a discussion about the 50mph barrier being tough to crack.

You're right about how difficult it is to break the 50 barrier. I got my Seafari over 50 mph a couple of times (when I had the Mercury 2.4L), but the weather, loading, chop and everything else had to be just about perfect. My best ever was an indicated 47 knots on the GPS. More normally, I topped out at 42-43 knots. And for some reason, I always pushed the boat to WOT at least for a little while, just to see...

I had 1.62 gears (I think, or maybe they were 1.65), with a 15.25"D x 16.5"P custom PowerTech OFS prop, turning 6100 rpms, lightly loaded, with a nose cone, low-water pickup, cavitation plate 2.25" above the keel, running the prop just barely surfacing. With a strong cross-wind, it could get a bit squirrelly at top speed. It was fun, though.

[CaptLloyd]

When I first seatrial my 20cc w/ DF140 Suzuki after putting on the bracket, I was running a 20" pitch Power Tech prop and hit 47 kts- 54 mph. Light load with two people, and it was chine walking The hole shot sucked, and only turning 5000 rpm. I now run a 18P prop because I wanted a decent hole shot with heavy loads (30 gal bait well, or full load of scuba gear/tanks). Tops out at 40 mph @ 6000 rpm. I may be a little under proped, but for Sebastian Inlet, I really wanted some low end "get up and go".

Lloyd

[Caymanboy]

well, after reading the pros veiws, I'll raise the engine a notch, see what that does, if it helps, great, if not, I'm done, she was a little squirrly in the ocean, not going that fast all the times anyways.

[Bigshrimpin]

When I first seatrial my 20cc w/ DF140 Suzuki after putting on the bracket, I was running a 20" pitch Power Tech prop and hit 47 kts- 54 mph. Light load with two people, and it was chine walking The hole shot sucked, and only turning 5000 rpm. I now run a 18P prop because I wanted a decent hole shot with heavy loads (30 gal bait well, or full load of scuba gear/tanks). Tops out at 40 mph @ 6000 rpm. I may be a little under proped, but for Sebastian Inlet, I really wanted some low end "get up and go".

Lloyd

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

2.38ratio
20 pitch prop
5000 rpm

= 40mph with no slip

[CaptLloyd]

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

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

Lloyd

[clb33fyxj]

Mercury site has a calculator too...

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

[Fr. Frank]

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