Data Input |
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| Waterline length in feet: | feet |
| Beam at the waterline in feet: | feet |
| Hull draft in feet (excluding keel): | feet |
| Vessel weight in pounds: | lbs |
| Engine Horsepower: | HP |
| Number of engines: | |
| Total Engine Horsepower: | 0 HP |
| Engine R.P.M. (max): | RPM |
| Gear Ratio: | :1 |
| Shaft R.P.M. (max): | NaN RPM |
| Number of shaft bearings (per shaft): | |
| Hull Constant: | |
| Desired speed in Knots: | knots |
Horsepower Calculations |
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| This will calculate the maximum horsepower and torque available at the prop(s). | |
| Total available horsepower at the engine(s): | 0 HP |
| Total available torque ft/lbs at the engine(s): | NaN ft/lbs |
| Horsepower loss of 3% per gearbox: | - 0.0 HP |
| Horsepower loss of 1.5% per shaft bearing: | - 0.0 HP |
| Total horsepower available at the propeller(s): | 0.0 HP |
| Total torque ft/lbs available at the propeller(s): | NaN ft/lbs |
Speed & Power Calculations |
|
| Calculations based on desired speed and available HP | |
| HP required at propeller(s) for desired knots speed: | NaN HP |
| Estimated speed with existing 0 horsepower: This is the speed we will use for the propeller size. | NaN Knots |
| At this point it is important to note that all of the calculations above are based on full RPM and HP. Most engines are rated to run at a percentage of thier full RPM. This is what will determine your maximum cruising speed. The propeller sizing calculations below are based on 90% of full RPM, which allows the engine to develop it's maximum power without overloading. The chart below shows typical engine ratings, you can find this information in your engine specifications. | |
| Recomended RPM for continuous operation | |
| Type of engine | % of max RPM |
| Light-duty gasoline and diesel automotive conversions | 70 - 80% |
| Light-duty or high output marine diesels | 80 - 85% |
| Intermittent-duty marine diesels | 88 - 92% |
| Continuous-duty heavy marine diesels | 98 - 100% |
Propeller Size |
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| Number of blades | Diameter (inches) | Pitch (inches) | |
| 2 Blade | NaN | X | NaN |
| 3 Blade | NaN | X | NaN |
| 4 Blade | NaN | X | NaN |
| The propeller sizes shown above do not contain calculations for cavitation or blade loading. If you find that the recommended propeller is too large to fit your vessel, you can try increasing the shaft speed. Failing this, you can reduce the diameter and increase the pitch at the expense of your propeller efficiency. The rule of thumb is 1 inch of diameter is equal to 1 1/2 to 2 inches of pitch. | |||
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Intructions This calculator is free to use
as often as you wish.
The calculations and results are based on imperical data and formulas. The results are only as acurate as the data you enter. The calculated propeller sizes are based on standard propeller designs; 2 blade = 30% blade area ratio 3 blade = 50% blade area ratio 4 blade = 69% blade area ratio |
Calculate a propeller size based
on the data you enter
No calculations for cavitation |