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| Author |
Message |
    
dvan
Member
Username: dannyvan
Post Number: 45
Registered: 08-2008
| | Posted on Friday, July 03, 2009 - 08:42 pm: | 
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have a 1994 landau pontoon that came with a 40 hp and would run around 14mph. I changed over to a 85hp johnson and changed the prop to a 14x9. My question is "why will my pontoon only go 20mph wot at 5200rpm's"? Are there such things as a boat will only go so fast per its design? Planes out good, motor runs good, good compression (115 psi). Any suggestions? |
Dcramer
Advanced Member
Username: dcramer
Post Number: 135
Registered: 05-2008
| | Posted on Friday, July 03, 2009 - 10:06 pm: |
|
Hi dvan,
The limiting factor is the "square law". Basically put, to go twice as fast, you need the square of that, or 4 times the power. You got 43% more speed from the power increase. The square law puts you at about 46% more speed. The relative strength of the motors, plus the extra weight probably make up the difference. |
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