Question about prop

[rme hunter]

I have a 17 ft Ranger R70 sport. The boat has a 125 horse Mariner on the back with a 22 pitch prop. I can only go about 40 miles at best. Does anyone know how fast this boat should go or what kind of size prop I need to get better performance. Also the boat is a 1995 model if any of you have one like this how fast can you go?

[stevec]

sounds a little slow..you should be in the mid 40's..maybe 50..how is the holeshot on the boat..are you running a ss prop..or aluminum..are your speeds from seedo or GPS ?

[rme hunter]

The prop is ss the hole shot is OK and the mph is off of GPS.

[DaveR]

seems like a pretty big prop. Are your RPMs atrated range, 5500-5700 I believe is what you want (double check that). My 92 330V with a 115 Merc had a 19" prop and speedo read 52 mph. Speedo is only good to see if you are going faster or slower than before, it won't be accurate on actual speed. GPS will give you accurate top speed reading. Things like loading and weight distribution in the boat will affect things too. There is a theoretical speed calculation formula that you can get by searching for theoretical speed on http://www.wmi.org/bassfish/bassboard/boats_motors/index.html

[rme hunter]

I think the prop is the problem as well. When I bought the boat it had a 24 pitch on it. I down sized to the 22 that I have now and I am about to go down again. Could the plugs have anything to do with it? The motor isn't missing but I am just not a mechanic.

[ttwigg]

I had the same boat, Mine had a 115 johnson and I got 58.8mph on a gps. You need to try several props. You have a great boat, I wish I still had mine at times. On the speed thing, you might have too much junk in your boat. I took 60% of the crap out of my new boat and the performance was much better. Good luck........

[rme hunter]

Do you remeber what prop you had on yours?

[DaveR]

what RPM's are you getting now at wide open throttle? Got to thinking, engine height could affect speed, but not by 10 mph. A jackplate is an investment, but would allow you to tweak the rig with the right prop and improve driveability and will typically get you 1-2 mph increase.
The plugs shouldn't be affecting the speed unless they aren't firing and you aren't running on all cylinders. call the Ranger factory and get ahold of the rigging department, they can tell you what prop they rigged that model boat with for a 125hp typically and that is a great place to start. Until you get close to the right prop, hard to tell if engine is running right. Good Luck.

[VMAXX]

RPM's needed,without them no one can give you a straight answer

[rme hunter]

Last night I was running 5100 RPM's that is about 150 short of what I need.