Need help from Ron Hill!!

[omcstratos]

Ive been testing my 11.25 x 18 Yamaha style cleaver and have had a little difficulty. I don't know how low is too low for this style prop to run but I am having a pretty rough time getting the prop to grab the water. First off, Looking at some of these pictures, I am worried that I am getting some exhaust to come around the thru hub and ventilating in the blades. My past experience with thru hub surfacing props are that they don't slip until the boat is about to break over and plane off. This one seems to slip immediately like an over the hub prop when throttle is added.

Secondly, this may be due to me not spending quite enough time playing around with setup but I don't feel like I have gotten 100% hook up from the prop when on plane. I can be cruising along for a while and back off the throttle and the prop finally bites in. I'll ease back on the throttle and immediately lose bite, and do this back and forth all day.

I've tried this with the prop completely submerged and the cav plate 2.5 in out of the water. I get slip and can't plane off at all with the prop submerged and with it raised it only improves a little.

I know cleavers like running high, but I thought it was odd that I couldn't plane off at all with the prop submerged. Any help???

[Ron Hill]

Sounds like too small of a prop in both pitch and diameter.

What is the horsepower of your motor?

This prop usually planes easy!

[omcstratos]

50hp OMC. I know I thought this prop wouldn't have much problems planneing!

[Ron Hill]

See if you can figure out the gear ratio. Some of those Nitro gearcases can swing 12 1/4 X 20-24.....

This is the 12 1/4 diameter....

[omcstratos]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

[omcstratos]

apparently the gear ratio for this motor is 2.42

[Ron Hill]

Keep the hub kit, I'll send you a 12 1/4 by 22.

[Nason]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

I got the same prop,except it was tried on a 40 Mercury,42 mph was the fastest it would go. Slapped on a 3 blade power tec 10-3/8 x 15p fishing prop 45.2, slapped on a 10-3/8 x 18p mercury chopper 49.3

[zul8tr]

After running it today my best numbers was 18pitch prop turning at 6200rpm and I only could get 34mph out of it. I don't know what the ratio is but its the small gearcase for the 2cyls

For the 18" pitch, 6200 rpm, 2.42 gear ratio, and 34 mph that is about 22% slip which is very excessive especially if a light rig, this indicates probably more pitch needed for your rig. Do you know the total weight of the rig running?

With the 22" Ron is sending if you keep the same rpm(?) and slip in the 8% range the expected speed is about 49 mph.

Although not the last word like testing is I find this reasonable for estimates:

http://continuouswave.com/cgi-bin/propcalc.pl

[Ron Hill]

For the 18" pitch, 6200 rpm, 2.42 gear ratio, and 34 mph that is about 22% slip which is very excessive especially if a light rig, this indicates probably more pitch needed for your rig. Do you know the total weight of the rig running?

With the 22" Ron is sending if you keep the same rpm(?) and slip in the 8% range the expected speed is about 49 mph.

Although not the last word like testing is I find this reasonable for estimates:

http://continuouswave.com/cgi-bin/propcalc.pl

That prop chart is excellent, I just forget about it most of the time.

zul8tr, what peed to you think this boat should go? I can't quite see it. I know you've run a bunch of these boats.

Is this a 2 cylinder 50 or is this the three cylinder? I just don't recall this gearcases water pick ups.