Resistance and Powering Design

How big to make the engine?  That innocent question reveals a complex field of study.  Resistance and powering require multiple methods of calculation to obtain an accurate prediction for engine size.

 

 

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To predict the engine size, we handle the propeller and the hull separately.  This typically consists of two stages:

  1. Resistance estimate
  2. Propulsion design

The resistance estimate determines the total thrust required for each speed.  This produces a curve of thrust and power requirements, accounting for water, wind, waves, fouling, and several other factors.  DMS has multiple methods available for a range of accuracy and budget needs.  

Next, the propeller must develop that required thrust by converting the power of a spinning shaft.  Most propellers vary from 50% – 70% efficiency, which profoundly impacts your fuel bill.  This is where DMS focuses intensely on selecting the right propeller.

The best propeller requires DMS to specify several variables.  Diameter, blade pitch, blade area, and other geometry features.  The ultimate goal is peak efficiency, but the engineer must also consider cavitation, vibration and noise, operational profile, engine matching, and several other factors.  It becomes a balancing act.

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