Which Prop would give me top speed

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eavdic

Seaman Apprentice
Joined
Aug 2, 2010
Messages
48
Hi I have a 1991 Force outboard with 75 HP , I have a prop on there now the boat gets me about 32 MPH I want more out of it. Tried to research but can not find anything , found one that says if I buy this 11-3/4x17 prop it would go 40-46 mph, is this right and what would you guys suggest.

thank you
 
W

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: Which Prop would give me top speed

Realistic expectations would be to gain 3-4mph working the set-up.
Boat, (hull design) prop type, among other things will be a factor in the available gain.
 
Frank Acampora

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: Which Prop would give me top speed

Without knowing the boat length, weight, and hull style, and without knowing the pitch prop on the engine now, it is impossible to predict speed with your engine.

However, while the 75 is a nice engine, it is still only a 75. The 17 pitch prop is used for light loads or smaller hulls. It may cause you to lose top speed if used on a larger or heavily loaded hull by loading the engine down out of its rated operating RPM range.

Nothing is "etched in stone" but if your boat is larger than 15 feet long, most likely the only way you will get more speed is with a bigger engine.
 
E

eavdic

Seaman Apprentice
Joined
Aug 2, 2010
Messages
48
Re: Which Prop would give me top speed

Frank Acampora said:
Without knowing the boat length, weight, and hull style, and without knowing the pitch prop on the engine now, it is impossible to predict speed with your engine.

However, while the 75 is a nice engine, it is still only a 75. The 17 pitch prop is used for light loads or smaller hulls. It may cause you to lose top speed if used on a larger or heavily loaded hull by loading the engine down out of its rated operating RPM range.

Nothing is "etched in stone" but if your boat is larger than 15 feet long, most likely the only way you will get more speed is with a bigger engine.
Click to expand...

What I have right now is 10.38x14 pitch prop, boat is 16ft 7inches bayliner capri bowrider with force 75HP motor. Top speed is 32MPH with just me on the boat and the RPM are 4900 where the RPM should be 5500 I am thinking of reducing the pitch of the prop but not sure by how many inches heard that every inch is worth 200 RPM thinking of going to 10.38x12 pitch prop. Any suggestions.
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Which Prop would give me top speed

Before making a prop change be sure the Carbs are opening all the way.
The antivent plate,just above the prop should be visable on plane.
In the extreme raising the motor could result in 2 to three mph.with additional rpm.
Does the boat respond to up trim?
Is the bottom clean and smooth?Motor in excellent tune?
With a boat that is likely refered to as a 17; I think 12" prop would be a good start.
if these other things check out.
 
E

eavdic

Seaman Apprentice
Joined
Aug 2, 2010
Messages
48
Re: Which Prop would give me top speed

steelespike said:
Before making a prop change be sure the Carbs are opening all the way.
The antivent plate,just above the prop should be visable on plane.
In the extreme raising the motor could result in 2 to three mph.with additional rpm.
Does the boat respond to up trim?
Is the bottom clean and smooth?Motor in excellent tune?
With a boat that is likely refered to as a 17; I think 12" prop would be a good start.
if these other things check out.
Click to expand...

No the motor does not respond to trim, but the hull does :) I have it in the middle of the trim I have never paid attention to the antivent plate being visible during plane. The bottom is clean but lot of scratches and chipps and dings needs some fixing and maybe painting. which I am thinking of doing myself in the spring.
 
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