do I need a different prop?

[jwilkey84]

I have a boat that is 14' long, and weighs 570lbs. by itself. It has a 1983 johnson 50 hp motor on it. My buddy and I were in it (300lbs. total) and we were cruising at 29 mph on the GPS. Other weight would have been 6 gal. of gas and a battery. The prop is labeled 12-1/2x13. Are we getting the maximum speed out of the 50hp, or would a different prop help. It seems like we have a lot of power out of the hole, just wondering if we could sacrifice some of that for a little more speed.

 

[steelespike]

Re: do I need a different prop?

Really can't make any judgement without a max rpm and speed.You could get a tiny tach ,easy install, reasonable price can use it on any similar motor without regard to poles.Your speed is certainly in the ball park for your setup.28-33 is typical.Be sure the motor is in good tune,throttle opens all the way.
bottom is clean prop good.
Optimize your setup.Motor vertical height raise it to a point just before venting becomes a problem.Be sure it pumps water.If you can gain 1 inch you could get 2 to 3 mph depending on your setup now.

 

[jwilkey84]

Re: do I need a different prop?

the bottom of the boat is clean, as the boat was just painted. The throttle is opening all the way, and the prop isn't in terrible shape. I am unsure how to install a tach. As for the height of the motor, where is the best location. Isn't the cavitation plate supposed to be even with the bottom of the boat?

 

[steelespike]

Re: do I need a different prop?

Antivent plate even with the bottom is considered a starting point.
Ideal could be lower but 99% of the time it is higher.
The tiny tach is cake to install you might check their site.
I don't know the details just that it is simple using spark pulse to measure rpm.Don't know if there is a phone but pretty sure they have a faqs section.
I'm on the same spot and hope to be getting a tach and doing a prop change
if necessary.
A prop change without a max rpm reading is a crap shoot at best and motor suicide at worst.You may be able to get a tech go with you or borrow a tach
to check your rpm.