Abstract
Amateur keel boat racing has becoming more and more popular on coastal regions with an old sailing tradition, such as in Adriatic. Although the traditional experience is transmitted to new generations of skippers and crews that compete on national and international regattas with open class boat, the material limits of the boat are often measured subjectively, by sail or mast failure, and transmitted by a story. Most sailors know why some component failed, but often they don’t know what force was needed for the particular failure. Forces acting on a boat are usually estimated with CFD and towing tank experiment for relevant sailing conditions, but full scale data in seaway are rarely taken. Here we wanted to show a low budget method to get a rough estimate of aerodynamic and hydrodynamic forces acting on a keel sailboat using a kinematic sensor. Some approximations are taken into account to construct a simplified mathematical sailboat model, which allow to relate kinematic data to forces acting on sail, hull, keel and rudder. Some data as the geometry and mass distribution of the boat has to be known, other parameters such as water resistance instead has to be experimentally measured. Results of a series of measurements are presented and discussed. Looking on the limitations of such a method, a proposal for a new sensor is made.
Highlights
An inverse dynamic approach was attempted to evaluate the forces and moments acting on a sailboat while underway
The body coordinate system is fixed to the sailboat: the origin coincides with the boat’s center of gravity (CG), axis 1 is toward bow parallel to the design water plane, axis 2 is toward port side parallel to the design water plane, and axis 3 completes the right-hand system
The linear and angular acceleration and velocities were measured by the motion tracking device (MT) that was fixed off the body CG
Summary
An inverse dynamic approach was attempted to evaluate the forces and moments acting on a sailboat while underway. The input data to the model has been later taken measuring kinematic and rudder position. In controlled conditions repeated experiments will give different measurements. In such an approach, there are many kinds of errors to take into account when working out the solution. The inertial system is fixed: the origin coincides with the first measured position on the water level, axis 4 is toward north, 5 is toward west, and 6 completes the right-hand system toward zenith (up). The body coordinate system is fixed to the sailboat: the origin coincides with the boat’s center of gravity (CG), axis 1 is toward bow parallel to the design water plane, axis 2 is toward port side parallel to the design water plane, and axis 3 completes the right-hand system. Second index 1 axis Body-x Body-y Body-z Inertial-North Inertial-West Inertial-Up
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