Prop size

I have a 1996 johnson 175 with

I have a 1996 johnson 175 with a 15x17 viper prop. It maxes out at 5500-5600 rpm. It is pushing a Seaswirl 2100 at a top end of about 43mph. What can I expect performance wise if a put on a 14 3/4 x 19 viper prop?

"Vincent, you seem to be a lit

"Vincent, you seem to be a little "under propped" with your current 17 pitch. Your optimum wide open throttle (OWOT) is about 5200-5300 rpm.

That is the rpm where your motor will produce maximum horsepower without over-revving. Your max rpm on that motor is 5500.

The 19 pitch should move your top rpms down to about 5200 and the 1/4" less in diameter may add 50 or so back which should put you bang on the mark where you want to be with that motor.

When you ask about performance I suspect you are looking for what kind of "speed" increase you might see. correct??

Just doing some rough calculations you may see 2 more mph under ideal conditions. However, more importantly, your motor will be running where it was designed to which will add years to it's life.

Your prop must match the motor and the boat that it is placed on. You should change your prop because your numbers show that you have the wrong prop. Don't consider say going to a 21 pitch because "some guy" says it will be faster. Thats non-sense. In pure theory a 21 pitch will move further through the water in the same period of time compared to a 17 pitch. However, you are limited by the rpms at the propshaft for any given motor. You could put a 21 pitch on but your rpms would drop making you slower than with the correct pitch...."

"Thanks for your advice. As f

"Thanks for your advice. As for performance I inquired about, I was curious about hole shot since my teens like water sports."

"Vincent, if you are looking f

"Vincent, if you are looking for a great hole shot, quicker to plane and hold plane at lower speed you may want to consider a 4 blade prop.

It will do all that for you. The flip side is however, you shave 2 or 3 mph off your top end.

A 4 blade will also take an extra 100 rpms or so off your WOT compared to a 3 blade.

On your rig you could still easily run a 4 blade 19 pitch with good results. Alternately, you could run an 18 pitch but that may be difficult to find - most props tend to come in odd numbered pitch sizes.

There is a couple of "variable" pitch props out there. The idea is not new and some are good, others are outright bad designs.

Last year I acquired a 4 blade variable. The brand is ProPulse (a scandinavian company makes it - WestMarine sells it). It's a replacable blade type composite design so if you happen to hit some rocks you can replace a single blade quite easily. On my particular model you can vary the pitch between 15-19 simply by fiddling around with it. So far I have been fairly impressed with how it has worked.

The one nice thing about the variable is, as the summer progresses motors tend to work harder and lose rpms as the air gets more dense/humid. You can lower your pitch by 1 or 2 and get the motor running at peak again. This system saves having a "second prop" of a different pitch for that purpose. Additionally, if you have that time where you have a boatload of guests, you can lower the pitch and save some gas...

Piranha propellers are similar to the one I'm running and you could check out their website (www.piranha.com) if interested."