Need advise for prop!

[noob-boater]

Hey guys,

spring is coming! so I gotta get my boat ready.I screwed up 2 of my props last year. So I have to replace it with a new one.
My boat is a 1992 Javelin 353B 15.25ft...it's got a 1992 70hp Johnson at the back. The prop that was on is a 13 1/4 x 17 pitch OMC prop. I was getting Max 5500 RPM and top speed 37mph...loaded with 2 persons and fishing gears
Now I just bought a 12 3/4 x 21 pitch prop...wondering what will happen with that? Will it increase top speed, slower hole shot, low RPM? or better hole shot, slower top speed, and higher RPM?? or neither? OR should I just stick with 13x17? or even 13x19?
Any input would be greatly appreciated!

Cheers,
Jackie

 

[steelespike]

Re: Need advise for prop!

A prop shop can probably repair your props.
The 21 was probably not the best choice.My info says the max rpm is 6,000.
So at 5500 you were actually a little low.Your speed was probably pretty close.
The 21 will likely lower your rpm 6 to 800.Not good.It will slow your hole shot.
Likely lower your speed though it might increase slightly .
You will be lugging your motor which could cause premature failure.
Give it a try;then I would go back to the 17 and fine tune your setup.
Raise the motor on the transom to a point just before venting(cavitation) becomes a preoblem.
Be sure the throttle opens all the way and it is in excellent tune.
Adjust trim carefully for the best speed.