Velocity 
Predictions
( Double Hard Chine vs True Round Hull)

The following Velocity Predictions compare two steel versions of 'Thunder Cloud'.   

The 'Velocity Predictions Charts' 

  • Results are given  in 'Seconds per Nautical mile - (Sec/NM).
  • The BTW is the Track angle with respect to the true wind direction.
  • Six True Wind  speeds are listed (Knots)
  • Boat A is the True Round version of the hull.
  • Boat B is the Double Hard Chine version of the hull.

Example One:

What would be the speed in  (Sec/NM)for the True Round version - Boat-A, in a ten (10) knot True Wind Speed, at a BTW of 45-degrees?

897.82 = (Sec/NM)

Example Two:

What would be the speed in  (Sec/NM) for the Hard Chine version - Boat-B, in a ten (10) knot True Wind Speed, at a BTW of 45-degrees)?

(879.82 - 11.18) = 868.64 (Sec/NM)


Looks like the Hard Chine hull is a bit faster than the True Round version at a 45-degree Btw in a ten knot wind speed.

True Round vs Hard Chine

(Speed Comparison Cart

Looking at the above Cases, this is what I see:

  •  There is no real difference the Double Hard Chine and the True Round hull as far as speed is concerned.·        
  •  From a Stability point of view the Double Hard Chine hull is a bit more tender than the True Rounds hull.·         
  • The true round hull has a bit more maximum stability than the Double hard Chine hull.·         
  • The Double hard Chine hull has a higher Angle of Vanishing Stability at, 127-degree then the True Round hull at 122-degrees.·        
  •  The only meaningful difference and probably the most important to most sailors is:  One is True Round and the other is not.

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