haffiman37
Silver Medal Contributor
"Propeller calculations are no
"Propeller calculations are not that difficult. The mix of metric and inches, mph/kmh/knots messes it a bit up, but here is a general formula.
rpm x pitch" x 0.0254 x 60
-------------------------- = speed (theoretical)
gear ratio x factor
The factor is:
knots: 1852
mph: 1650
kmh: 1000
This will then give you the theoretical boat speed, no slippage.
Then deduct about 10 - 15% slippage, and you should get close to your real speed.
If your slippage on a planning hull gets above 15%, you are most likely either under powered or running wrong prop type. Normally too little blade area/too small dia.
But be sure you get the recommended rpm!"
"Propeller calculations are not that difficult. The mix of metric and inches, mph/kmh/knots messes it a bit up, but here is a general formula.
rpm x pitch" x 0.0254 x 60
-------------------------- = speed (theoretical)
gear ratio x factor
The factor is:
knots: 1852
mph: 1650
kmh: 1000
This will then give you the theoretical boat speed, no slippage.
Then deduct about 10 - 15% slippage, and you should get close to your real speed.
If your slippage on a planning hull gets above 15%, you are most likely either under powered or running wrong prop type. Normally too little blade area/too small dia.
But be sure you get the recommended rpm!"