Uncertainties in the wind-heel analysis of traditional sailing vessels: The challenges it presents for forensic analysis of sailing vessel incidents

There are many uncertainties in the interpretation of full-scale sailing vessel data taken under dynamic conditions, and even more uncertainties when forensic analysis is attempted based only on survivor's recollections. Frequently, the analysis is based on static equilibrium assumptions, sometimes modified to steady-state motions of the wind and heeling response of the vessel. Dynamic conditions are generally non-deterministic and statistical methods must be used. Even more complicated is the non-stationary random process nature of most accidents. In the wind-heel research carried out on Pride II, it has been shown that wave action frequently adds uncertainty to the correct attribution of contributions to establishing the cause of the resulting heeling action. The best data are found in steady 10 to 20 knot wind strengths in minimum waves found in the lee of a shoreline. This criteria can be interpreted as minimizing the uncertainties in characterizing the wind-heel performance of a given sail combination at normal angles of heel. Examples of quasi steady-state response are presented in the paper as characterized by the Wind Heel Stiffness Ratio (WHSR), which is equal to the square of the apparent wind velocity in knots divided by the resulting heel angle in degrees. WHSR is not non-dimensional but is independent of the system of units, (SI vs. EG). The WHSR for each sail combination is most easily established by a maneuver the crew of Pride II has deemed "The Crazy Ivan." However, it is uncertain whether this concept can make useful predictions at heel angles higher than those beyond GZ_max in the absence of any good data taken during these conditions. CFD studies of various sail combinations provide very good agreement between the recorded wind-heel responses of the vessel up to deck edge submergence. The corresponding CFD predictions provide a method of predicting the normal wind heel responses of a traditional sailing vessel during the design process. The paper discusses operational guidance uncertainties that appear as a "fork in the road" decision, with bearing away as one path and heading up as the other. The paper examines the tradeoffs in the decision making process relative to the type of vessel involved and the observable wind and sea conditions at the time. Recent attempts to re-analyze the dismasting of Pride II in 2005 and the sinking of the SV Concordia off Brazil in 2010 are also included. Lastly, the possible downward lift force involving square sails at high angles of heel needs to be investigated in wind tunnels since full scale testing of this concept is virtually impossible.