Please Help!

[Jackie]

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 motor is a 1992 70hp Johnson. The prop that was on is a 13 1/4 x 17 pitch OMC prop. I was getting Max 5500 RPM and top speed 39mph...

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

[mike rousseau]

Probably won't do much...

 

If your looking for top end... Stay with the 13 inch and increase your inches of travel up from 17....

 

I uped my diameter by an inch and travel by an inch or two and gained 5 mph...

 

Take off wasn't effected enough to bother me either...

[SlowPoke]

In therory the new prop should give you better hole shot and better top end provided you have the horses to propell it. My instinct tells me your hole shot will stay about the same and you might drop a few RPM at WOT.

I'd be inclined to stay with what you had provided you were happy with the hole shot. Your RPM is good and 39mph from a 70hp is pretty good on any hull.

[moosehead]

I am thinking the new prop might be too much pitch for that motor, i had a similar problem when my motor did not have enough hp to turn it fast enough to get the boat on plane and when it did eventually get on plane the rpm's were way below the max. They say that for every inch you go up in pitch your max. rpm's drop by about 150-200

[mrpike]

I have just the thing for you . a 13 3/8 x 17 SST prop . it came off my 90 hp johnson . mint shape you can have it for $125. 00 . I payed over $ 500.00 back 1985 for it. or you can just try it out and see if it does the job for you. keith.

[Jackie]

Thanks for all the advise guys! I will give it a try sometime next week. If the RPM doesn't go too low, and there is some top speed gain, then i will probably stick with it. If not I will probably exchange it with a 17pitch.

 

Hey mrpike, I will pm you if this prop doesn't fit me. Thanks!

[NANUK]

With that prop you'll get slightly better hole shot, lower RPM and lower top speed.

[lplp]

21 pitch is for high speed ,, will not get you out of the hole fast ,for instance if you are taking someone waterskiing ,and with the hp of engine. stay with a 17 pitch for that engine ,it is not like you are going to break any water speed records. and you can get your old props fixed for around 80 ,but that 125 prop would be a deal..