Correct prop

[mohill]

Have a 1984 35 hp johnson and it has a SS prop. Prop was on it when i bought the motor and is 10.5 x 11. I think the motor should be moving my boat (14' monark) faster, gps says 28 mph. Should I get a prop with a higher pitch or just leave it alone. I know higher pitch will raise rpm's at full throttle but I have no clue what rpm I am running now at full. Any input would be great.

[dixiedeerslaya]

higher pitch will reduce rpms but reduce acceleration.... the lower pitch will give you more torque out the hole but raise rpms at WOT and loose top end speed

[mohill]

Yeah, you are right, thought about that wrong. It sounds like I am at pretty high rpms when running full throttle and I think I should be going faster, and I think a new hgiher pitch prop will solve this. Didn't know if anyone had toyed with this stuff.
I don't know what to change it to though.

[Phone Man]

do the same thing i'm doing, order a tiny tach and put it on the motor. Then ask a dealer what your recommended WOT shout be for that motor. Then beg steal or swap props til your rpms get there. Luckily some guys on here have some props that will fit my rig and are gracious enough to let me try em before i go fork out 300 bucks for a new one.

[mohill]

Where and how much are these tiny tachometers. My thoughts exactly about trying different props before purchasing one for good.

[Phone Man]

tinytach.com I called today, told her what kinda motor and she sent it.

[Phone Man]

about 40 bucks

[Redleg Camo]

mohill, how well does the boat come out of the hole? Where is the cavitation plate in relation to the bottom of the boat? even, 1/2 higher, 1/2 lower? Does it porpous any?

[mohill]

pops right out and planes off. cavitation plate is right about even. no porpoise action to speak of.

[dixiedeerslaya]

do you have alot of weight in your boat normally?

if not, i would try a 13 pitch... that should give you a few more mph on top end but you wont get out the hole as fast.

[Redleg Camo]

I like to trim my boat to where it ""just" starts porpoising then hook the hull until it stops. If you get about 3 degrees of positive trim you will pick up speed and RPM's. Motor height sounds ok. If you can get it higher, do it. it will help also. jack it up 1/4" at a time. i would try to get it set up right before you get a prop.

[Palmetto Duck]

higher pitch will reduce rpms but reduce acceleration.... the lower pitch will give you more torque out the hole but raise rpms at WOT and loose top end speed

That right? I thought a lower pitch prop provided more torque thus out of hole better but would not let you achieve recommended rpms for WOT thus you don't attain the max speed. Thought higher the pitch the less bite on the water, thus out of hole a little slower, but once on plane attains higher rpms and thus higher WOT speed. Someone tell me if I've got this right or wrong. I'm doing the same thing with a Tiny Tach now while tinkering on my boat.

[dixiedeerslaya]

That right? I thought a lower pitch prop provided more torque thus out of hole better but would not let you achieve recommended rpms for WOT thus you don't attain the max speed. Thought higher the pitch the less bite on the water, thus out of hole a little slower, but once on plane attains higher rpms and thus higher WOT speed. Someone tell me if I've got this right or wrong. I'm doing the same thing with a Tiny Tach now while tinkering on my boat.

the lower the pitch on the prop the less water it turns per revolution... there for the motor can turn the prop easier... once it gets up on plane, it will run at higher rpms because its easier for the motor to turn the prop... now if you go up in pitch, the prop moves more water per revolution.... therefore the motor has to work harder to turn the prop, reducing acceleration, but increasing topend speed...

[dixiedeerslaya]

the only thing stopping your motor from over revving is the resistance of the water on the blades....

think about it like a ten speed bicycle... when the back chain is around the smaller sprocket you can peddle like hell and only be goin a few mph... but the larger the back sprocket the harder it is to peddle but the faster you go.....

[dixiedeerslaya]

on a boat motor you have to find that balance.... like on a bicycle, you cant start off in high gear because its too hard to pedal, but you cant go very fast in low gear, even though its easier to turn, because you will be worn out with all the peddling...

[Civil-Cock]

Northern tool and die has tiny tachs. Order one. Every pitch increase will reduce RPM's about 300. Props are different some run better highly trimmed out the water others run better submerged. If you have electric tilt and trim look for a prop which runs higher without cavitating.

Make a run at or about normal weight, mark the rpm then base your prop change + / - 300 rpms until reach normal req from the manufacture. Done deal....Of course get a stainless prop.