*note* that this calculator is using a sigmoid function ( return min(($a * $HULLMAXSPEED) * tanh($b * $x ), $HULLMAXSPEED); a=2 and b=0.01 where x = value to change from linear to tan curve ) to change a linear result to a slightly more real result that the real world would produce. This is entirely an estimated result that attempts to take into consideration… see Other Considerations below.
V (Velocity) is the speed at which the boat is traveling (mph, knots, kph),
RPM (Rotations per Minute) is the crankcase speed (rpm),
GR (Gear Ratio) is the number of revolutions the crankshaft needs to produce one revolution of the prop shaft e.i. a 2 would mean that 2 rotations of the motor would rotate the propeller once,
PP (Propeller Pitch) is the blade pitch of propeller (inches),
PS (Propeller Size) is the index of propeller performance (as a percentage),
C is the constant to convert inches-per-minute of revolution to boat speed V;
V (in mph), C = 1056;
V (in knots), C = 1215.2;
V (in kph), C = 656.
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Other Considerations
Thrust Distribution: The number of blades can affect how thrust is distributed across the propeller. For a given RPM, a 3-blade propeller may generate more thrust than a 2-blade propeller, assuming other factors like blade pitch are constant.
Efficiency: The efficiency of a propeller can be influenced by the number of blades. Some propeller designs with a specific number of blades may be more efficient at converting engine power into thrust.
Caveats for this calculator and why results WILL NOT match the real world
The results of the formulas used here to calculate boat speed or motor RPM can be influenced by a variety of external factors and conditions. These factors should be taken into account for accurate modeling and real-world applications. Here are some external factors that can impact the results:
Load and Resistance: The resistance experienced by the boat in the water or the load on the electric motor can significantly affect the actual RPM or boat speed. Changes in load due to varying water conditions, cargo, or towing can influence performance.
Environmental Conditions: External factors such as wind, waves, and current can impact a boat’s speed. In the case of electric motors, temperature and humidity can influence motor efficiency and performance.
Maintenance and Wear: The condition of the boat’s hull, propeller, and motor components can affect performance. Proper maintenance and wear and tear over time can impact the efficiency of the system.
Battery Voltage and State of Charge: For electric motors, the voltage supplied by the battery and its state of charge can affect the power output and, consequently, the motor’s RPM. Lower battery voltage or depleted batteries may reduce performance.
Motor Controller Efficiency: Electric motors often require controllers to regulate power. The efficiency and performance of the motor controller can influence the motor’s behavior.
Propeller Design: The specific design of the boat’s propeller, including blade shape, size, and pitch, can affect how efficiently it converts power into thrust.
Hull Design: The shape and design of the boat’s hull play a critical role in how it interacts with the water. Different hull designs can yield varying speeds for the same power input.
Operational Practices: The way a boat is operated, including throttle control and navigation techniques, can impact speed and efficiency.
Water Conditions: Calm water conditions provide less resistance than rough seas. Water temperature and salinity can also affect water density, which can influence boat performance.
Altitude (for Land-Based Electric Motors): Electric motors used at high altitudes may experience reduced air density, which can affect cooling and motor performance.
Additional Equipment: The presence of additional equipment, such as stabilizers or towing gear, can change the overall resistance and performance characteristics of a boat.
To obtain accurate results, especially for critical applications, it is essential to consider these external factors, gather relevant data, and potentially conduct real-world testing and simulations. DO NOT RELY ON THIS CALCULATOR as real world results WILL BE different.
If you need to be sure, then consulting with experts in boat design, motor engineering, or specific applications can provide much more valuable insights into how these factors may impact the results of the formulas.
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