Another Prop Question...

Hey guys,

My skiff is finally the way I want it... all that's left is the prop.

First off, I'm running a 1965DLX with a F50 Yamaha (4 stroke).

I'm currently runnin.g a 10.5x12 stainless prop. Topped out I can only get about 5,000 RPM, maybe a little more. And I hit about 27-29mph. Now, to my understanding ideally I should have 6,000 rpm at full throttle right? (this is my first 4 stroke). So I'm thinking I should be going with a 7 or 8 pitch?

The only problem is that when look for props online and enter my engine info the only diameters that are available are 11.5, 12, or 12.5. There's plenty of room for a bigger prop, but I have no idea what pitch to get if I increase the diameter...

What do ya'll think?

I would love for a little more top speed, but I'm mainly just trying to get the most out of my little motor.

Thanks in advance,
Austin

Re: Another Prop Question...

Tell us more about the 1965DLX,seems like a lot of boat for a 50.
Is your speed by gps?
It does appear a 7" wopuld add a up to as much as 1000 rpm but would knock the heck out of the speedat about 19 mph.
How is the present hole shot?
I do wonder if the tach may be off a little low as the slip is only about 5% at 29. Possible but not likely with an under powered boat.
Don't worry too much about diameter with the extreme pitch reduction.Its fairly common for diameter to increase as pitch goes down. If your rpm was actually ,say, 5200 a 2" decrease may put you at about 5600.Acceptable if your running at your typical weight.

Re: Another Prop Question...

It is a lot of boat for the motor... but it's what came with the boat. It's a 19' flat bottom skiff center console with minimal extras. Pretty much just a front and a rear deck with a console.

The speed is per GPS so that's accurate. RPM's are off the stock in dash tach. So I suppose it could be off, it seems to be right on at idle though.

My hole shot isn't great, but it doesn't have any trouble getting on plane.

I suppose my next step would be to confirm my RPM's before I got any further.

Thanks,
Austin

Re: Another Prop Question...

Knowing 29 mph is accurate Using 10% slip 1.85 ratio 12" prop rpm could be about 5246. Slip could very well be higher making the rpm a little higher still.Would be good to verify the tach for a more accurate prop selection.
Look for a switch on the back of the tach note the position and operate it a few times to clean the contacts.
Might solve your problem. Also be sure all all connections are clean and tight.

Re: Another Prop Question...

Your Yamaha F-50 is 50 HP @ 5500 rpm; with a full throttle operating range of 5000-6000 rpm.

Your 10.5 X 12 Performance Series prop is the "smallest" size in that family that fits your motor. It is apparently too much pitch if you are only getting 5000 rpm.

I suggest you look in the prop section and pick out a 10 pitch Solas or TP aluminum prop to get your rpm up to about 5400- 5500 rpm.