Finding the Apparent Floatation Pivot Point (AFPP)

1. Definition of AFPP:

   • The AFPP is the point on the original waterline around which the ship appears to pivot as it trims down by the head due to flooding.
   • It differs from the Longitudinal Center of Floatation (LCF), which is the geometric center of the current waterplane.

2. Calculation of AFPP:

   • The AFPP can be determined using the ship’s draft forward and aft.
   • The formula involves the length between perpendiculars (L), changes in draft forward (ΔDf), and changes in draft aft (ΔDa).

3. Example Calculation:

   • Using data from Hackett & Bedford’s work, the AFPP for Titanic in a flooded condition (C3) was calculated to be approximately 580.9 feet aft of the Forward Perpendicular (FP).

4. Behavior of AFPP:

   • For small angles of trim (less than 10°), the AFPP remains approximately in the same location as more water enters the ship.
   • The trim angle increases in direct proportion to the volume of floodwater.

5. Graphical Representation:

   • The document includes diagrams and calculations showing the relationship between the trim angle and the volume of floodwater.
   • The AFPP’s location is shown to remain relatively stable even as the ship’s trim angle increases.

6. Summary and Conclusions:

   • The AFPP provides a useful reference point for understanding the ship’s behavior as it floods.
   • The analysis shows that the ship appears to rotate around this point, which remains relatively constant for small angles of trim.

Halpern's article provides a detailed technical analysis of the AFPP and its significance in the context of the Titanic’s sinking.