Prop size and pitch

[Tormented96]

I've been getting my 90 sea Ray 160 bow rider with a 70 hp force ready for its first outing and since the boat is underpowered slightly I'm having trouble figuring out prop size and pitch to help it get out of the hole and on to plain. I havnt looked to see what prop is on it now because it junk and the pitch and size for my needs are probably wrong anyway. I was told by a longtime outboard tech that I should get the lowest prop pitch is this true?
Please help point me in the right direction

 

[SkiDad]

if you haven't' taken it out yet don't assume it is under powered - we had a 65 horse on a similar size boat when I was a kid and we could pull skiers with it.

when you get out in the water, take a pen and paper and note what the max RPM is and at what speed - if you have a phone download a free GPS app to get the correct speed.

 

[Frank Acampora]

No, not true. Probably not underpowered for general recreational use and probably would not use the lowest pitch prop available.

The 70 is a very nice running engine and should power your Sea Ray adequately as long as you don't try to slalom ski with 4 people in the boat. Props are nominal 10 inch diameter (Usually 10 3/8) and normal use pitch runs from about 10 to 14 inch (you can find higher pitches but your boat would not use them).. I have worked on a couple on 16 foot boats--true, they were tin boats but performance was good--the engine surprised me.

The engine actually uses a Mercury prop so your choices are unlimited... First try to find some numbers on the back of the hub or between the blades of the existing prop. This will be your starting point. If you can not find any numbers I recommend you go to ebay and find a cheap used prop of about 12-13 inch pitch to start. Engine RPM should be in the 5000-55000 range. From there you can see what prop you would need as a "permanent" prop.

 

[scout-j-m]

I have a 1994 70HP Force on a 17' aluminum bass boat. I think I have a 13" pitch prop. My tach doesn't work so I'm not sure what exact rpm's I'm turning, but at WOT with a reasonable load and calm conditions, I see about 39-40 MPH on GPS. I think starting with 12 pitch 3 blade prop is the best way to go for you.

 

[jerryjerry05]

I think there is a prop forum here someplace .
You can try Michigan Propeller.
You'll need all the specs for the boat and motor.
Trying to figure it out without a working tach is impossible.

I have 17p on my motors.
I wanted MORE!!!
I changed to 19p.
I got MORE.
3mph more. and the motors used 20-25% more fuel.

My boat isn't fast 32mph. with twins at 5200 rpms
But it's dependable.

But I still have towing insurance.

 

[Tormented96]

Sorry for the late reply but the number on my prop is 48-73132-a40-10p
Now I know the pitch is 10 but is that to low for my size and weight of a boat to just get the same prop