BOAT HULL DESIGN 2-15 



By considering v , the effective relative velocity of the water perpendicular to the struck 

 surface of the boat, composed of the vertical and horizontal components of boat velocity and 

 orbital velocity of the water particle in the wave, and relating these values to the forward 

 speed and size of the boat the following equation may be derived: 



Pi 



= AV 2 + B WT + C L (2. 2) 



p T = maximum local impact pressure in pounds per square inch to be 

 expected when the boat is driven in waves at the 

 maximum possible speed 



V = the forward speed of the boat in miles per hour 



L = waterline length of the boat in the at-rest position 



D = 1 = llih.f>5j a constant including water density 



and dimension conversion factors 



p x 1 ft 2 

 2 x lUh in 2 



A, B and C are constants expressing the relationships between wave height, wavelength, 

 boat size and conversion from feet per second to miles per hour. These have been evaluated 

 from the experimental data obtained during tests made on a PT boat (13). 



A = 2.151 B = 1.267 C = 16.884 



The nomograph presented as Fig. 2-14 provides a ready means for evaluating this 

 equation. To use this nomograph proceed as follows: 



Place a straight edge on the graph so that it passes through the appropriate 

 speed on scale A, and the appropriate length on scale C. 



Mark the point at which the straight edge crosses the line located between 

 scales A and B. 



Compute V x Vh. 



Rotate the straight edge so that it passes through the previously marked 

 point on the line between scales A and B and the computed value of V xVL 

 on scale D. 



Read the pressure at the point at which the straight edge crosses scale B. 

 A detailed example is indicated on Fig. 2-14. 



The pressure obtained from the procedure given above represents the maximum bottom 

 impact pressure which will be present over a small area of the bottom, for short periods of 



