another prop question,Maco...,RAP...

[phester]

what i've seen the last few months in this forum,Macojoe and RAP seem to have the most prop expierence, but anyone else in the know, feel free to respond.My 1993 Johnson 150 oceanrunner spins a 15 1/2 x 15 pitch 3 blade aluminium. Based on my tach, my comfort/speed cruise is about 3900 rpm's at approx 29-30 mph[no speedometer or gps just a good est.] My wot, tach reads 5100 at approx 36-37 mph. I cant say for sure how accurate the tach is but at cruise speed the motor "sounds" perfect for how fast it's moving,however, I think the rpm's should be a bit lower...maybe 35-3600???? Now, I should have a redline of 5500, shy of standing on the throttle with both feet, I get no more than 5100,and the motor is just purring [well maybe more than purring]but I know it has more.Now, I'm not trying to fly to the moon ,or chase Havis across the Gulf, but maybe a smaller diameter and a 17 pitch may get me where I wanna be.Do these numbers sound correct???I'd like to see a slightly lower rpm at cruise and a bit more on the top end.Whatta ya think??

[chumbucket]

I think you're on the right track. My 150 Yammi spun a bit smaller diameter with a 17 pitch and topped out right where you're looking to be. You're close and not in danger of over/under working your motor. Just need to tweak it a bit, then use that current prop for a spare. ;)

[reelapeelin]

I like CB on the PITCH(17), but my experience tells me these boats perform better w/a larger diameter prop...mine is 15 1/4 x 17 and I'll betcha that's gonna get the numbers you're lookin' for...15 1/2 will probably work as well, but the 17 pitch I'm sure of... ;) ;D...

[macojoe]

well I have had 3 different props on my V20, When it was a I/O it had a 15 3/4 X 15 and was pretty perfect!

Then Iconverted to a 175 yamaha and I put a 14 1/4 X 17, even though it was a good prop, I never was able to get to my 5500 RPM, but I got 30 to 33 for curz and toped about 38 or so with a 5100 rpm
I was also getting some spin when takeing off.

I just called a local prop shop and had a long talk about were I wanted to be. I now have a 15 1/4 X 15
I get 5500 RPM now and I get outn the hoe fast!! with no planing time!
I have lost about 5 mph off the top end. But this thing performs great now and I am happy as $hit!!!!

As for you I bet you will be good with what most run which is a 14 1/4 X 17

when you go from 17 to 15 you will get more RPM on the top end.
when you go 15 to 17 you get less RPM on the top end

good luck!! Call a local prop shop tell them what you have and what you want, They will help you match your prop with in one size, and if you get from them they will let you use it to try, and if you want different they will trade, as long as you no bang it up like CB did to mine!!

I just had to!! ;)

[chumbucket]

::) Let it go..............your inner self will thank you.














So will I. ;D

[phester]

thanks for the reply fellas.I do like my current 15 1/2x 15 outta the hole,she gets on plane real nice. I think i'm goi ng to try the 17 and see what happens

[reelapeelin]

Phester, I think you'll like the 17... ;D...keep us posted...







CB, he just ain't gonna let it go... ::)...

[phester]

I understand about pitch and its cause and effect,but what about the diameter? The15-1/2 dia. I have now is the largest dia. I could get on that motor,the blades are about 1/2 maybe 3/4 of an inch away from the cavatation plate, so I am not really looking for more diameter. What cause and effect does a smaller dia. have?....MJ,spare yourself and let it go....you'll be a better person.....trust me