got a speed and an rpm....which way now?

[bob johnson]

i took my boat out with the new to me 115 johnson. the prop I used came off my 90 ocean pro it is a 14x17.

my tach now works( must have been an issue in the 90 hp I had)

I used my gps to mark speed. I got up to 37 mph in my Ultra Roughneck MV turning at 5300 rpms.

from talking around this rig should be in the 40 with a 115 hp on it.

it looks like I have clearance for a larger dian prop..almost an inch between the prop now and the cav plate..

so I figure I could go to 15-15.5" dia.

I would have figured I needed to go down in pitch to get this 115 hp ocean runner( 60 degree V4) up to the rpm range to run the most efficient.

wil the dia change effect the pitch I need to go to.....how much pitch change do I need to get to 5700-5800 rpms?\\boat has a 13 degree deadrise floats very shallow..it has floatation pods welded on the back and gerts on plane in seconds

the total weight my run to about 1200-1400 lbs

I have a jack plate and I adjusted it , but the highest setting before cavitation on down to standard( cavitation even with keel) there is no change in speed, but playing with trim, I gained a mile or two per hour

thanks

bob


thanks

 

[Bifflefan]

Re: got a speed and an rpm....which way now?

sorry, got kinda lost in the reading.
What was the question????

 

[bob johnson]

Re: got a speed and an rpm....which way now?

sorry, got kinda lost in the reading.
What was the question????

it is in the title...which way do i go to try the next prop???

they always say give all the info of the boat -use-motor-combo

so that repliers can get the whole picture

bob

 

[Bifflefan]

Re: got a speed and an rpm....which way now?

Basic:
To go faster move up in pitch,
To pull harder or come out of the hole faster, go down in pitch.
Diameter usually is set my the manufacturer. It make very little difference, Although I have a 14d and a 13d, the bigger one has a little more tourque steer than the smaller one.
Usually 2"p is is a good change, with out being to big. I cant remember exactly what RPM change it is, 300 rpms I think.

 

[bob johnson]

Re: got a speed and an rpm....which way now?

my first goal i was thinking was to get the rpms in the range they are supposed to be....so i am looking to get about 5800 rpms at WOT.

I thought the only way to do that was to adjust the pitch.

I cant remember if the change to move the rpms up higher is a pitch change of less pitch , or more pitch.

I read the Iboats prop offerings and it appears I have a pre 1195 prop, because the the offerings for 1195 and later are 15 to 15.5" mostly. Which it appears i have room for.

I have a ton of torque steer now..I adjusted the tab all the way and it lessned it a lot, not not all of it. When I had the 1997 90 evinrude on the boat I didnt have any torque steer...

right now the if i turn the steering wheel to the right it turns easy, if i turn it to the left it is way harder to tuen.

bob