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Calculating Speed Of Advance (S.O.A)

You are turning 90 RPM with a propeller pitch of 20 feet and an estimated slip of +4%. What is the speed of advance?

Given:

RPM = 90
Pitch = 20 ft
  Slip = +4%

What is asked?

 Speed of advance

Solution:

1. We are going to solve first for the efficiency. This is the formula for getting efficiency:

    Efficiency  = 100 - Slip  
                            100
                     = 100 - (+4)
                            100
                     = 100 - 4  
                            100
                     = 96 
                       100 
                Eff = 0.96

2. We can now then proceed to solve for the speed of advance. This is the formula for speed of advance.

           S.O.A = RPM x P x 60 x Eff   
                                   6080
                      = 90 x 20 x 60 x 0.96 
                                   6080
                      = 103680 
                           6080
                      = 17.05 knots is the speed of advance

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