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In small sailboats, the bodyweight of the sailor is proportionately
large enough to induce significant unsteady dynamics
of the boat and sail. Sailors use a variety of techniques
to create sail dynamics which can provide an increment
in driving force, increasing the boatspeed. In this
study, we experimentally investigate the unsteady aerodynamics
associated with one such technique, called “sail
flicking”. We employ a two-part approach...

Towards a Νew Mathematical Model for Investigating Course Stability and Maneuvering Motions of Sailing Yachts

In order to create capability for analyzing course
instabilities of sailing yachts in waves, the authors are at an
advanced stage of development of a mathematical model
comprised of two major components: an aerodynamic,
focused on the calculation of the forces on the sails, taking
into account the variation of their shape under wind flow;
and a hydrodynamic one, handling the motion of the hull
with its appendages in water.
Regarding the first part, sails provide the aerodynamic
force necessary for propulsion. But being very thin, they
have their shape adapted according to the locally
developing pressures. Thus, the flying shape of a sail in real
sailing conditions differs from its design shape and it is
basically unknown. The authors have tackled the fluidstructure
interaction problem of the sails using a 3d
approach where the aerodynamic component of the model
involves the application of the steady form of the Lifting
Surface Theory, in order to obtain the force and moment
coefficients, while the deformed shape of each sail is
obtained using a relatively simple Shell Finite Element
formulation. The hydrodynamic part consists of modeling
hull reaction, hydrostatic and wave forces.
A Potential Flow Boundary Element Method is used to
calculate the Side Forces and Added Mass of the hull and
its appendages. The Side Forces are then incorporated into
an approximation method to calculate Hull Reaction terms.
The calculation of resistance is performed using a
formulation available in the literature. The wave excitation
is limited to the calculation of Froude - Krylov forces.

The Influence of Sailor Position and Motion on the Performance Prediction of Racing Dinghies

The time-varying influence of a sailor’s position is
typically neglected in dinghy velocity prediction programs
(VPPs). When applied to the assessment of dinghy race
performance, the position and motions of the crew become
significant but are practically hard to measure as they
interact with the motions of the sailboat. As an initial stage
in developing a time accurate dinghy VPP this work
develops an on-water system capably of measuring the
applied hiking moment due to the sailor’s pose and
compares this with the resultant dinghy motion. The
sailor’s kinematics are captured using a network of inertial
motion sensors (IMS) synchronised to a video camera and
dinghy motion sensor. The hiking moment is analysed
using a ‘stick man’ body representation with the mass and
inertial terms associated with the main body segments
appropriately scaled for the representative sailor. The
accuracy of the pose captured is validated using laboratory
based pose measurements. The completed work will
provide a platform to model how sailor generated forces
interact with the sailboat to affect boat speed. This will be
used alongside realistic modelling of the wind and wave
loadings to extend an existing time-domain dynamic
velocity prediction program (DVPP). The results are
demonstrated using a single handed Laser and demonstrate
an acceptable level of accuracy.

Bifilar Suspension Measurement of Boat Inertia Parameters

Measurements of the inertia parameters (Gregory, 2006) of a keelboat hull using a bifilar suspension (Newman and Searle, 1951) are described. Bifilar yaw moment measurement normally entails accurate measurement of the length l and spacing 2d of the suspension, and of Ty the period of pure yaw oscillation (Miller, 1930). The primary difficulty with a bifilar suspension is avoiding unwanted modes of oscillation, specifically sway when measuring yaw. However, for an athwartships suspension, the sway motion is that of a simple pendulum of period Ts and observation of the combined motion allows the yaw gyradius ky ≡ kzz to be determined as ky = (Ty/Ts)d. Thus only the ratio of the periods and the suspension spacing need to be measured. Measurements of the normal mode periods of the double pendulum motion (Rafat, Wheatland et al., 2009) when the hull is displaced in surge allow for the pitch gyradius kp ≡ kyy and the height l2 of the center of mass to be determined. The latter can be confirmed by measuring the incline angle of the hull when a weight is suspended from the stern and/or the bow. Repeating yaw measurements with the hull tilted, and then with the bifilar suspension fore and aft to measure the roll gyradius, kr ≡ kxx, allows for the angle ψ of the inertia ellipsoid (Wells 1967) principal x axis to the hull x axis to be calculated. Although the present keelboat measurements were made using ultrasonics (Daedalon, 1991) and photogates (Pasco, 2000), such measurements can now be more easily made using MEMs gyros, such as that in the iPhone (xSensor, 2010). This is illustrated by the measurements on a model keelboat.

Tacking Simulation of Sailing Yachts with New Model of Aerodynamic Force Cariation During Tacking Maneuver

A mathematical model for the tacking maneuver of a sailing yacht is presented as an extension of research by the same authors. The authors have proposed the equations of motion for the tacking maneuver expressed in the horizontal body axis system. The calculation method was applied to a 34-foot sailing cruiser and the simulated result showed good agreement with the measured data from full-scale tests; however, the modeling of aerodynamic force variation during tacking was insufficient due to lack of information about the sail forces. In this report, the authors performed full-scale measurement of sail forces during tacking maneuvers using a sail dynamometer boat Fujin. The Fujin is a 34-foot sailing cruiser which has a measurement system to obtain simultaneously sail forces, sail shapes, and boat attitude. Based on the results of full-scale measurements, a new model of aerodynamic force variation for the tacking maneuver was proposed. The equations of motion were also simplified to more easily perform the numerical simulation. Using this calculation method, the tacking simulations were performed and compared with the measured data from three full-scale boats. The simulated results showed good agreement with the measured data. This simulation method provides an effective means for assessment of tacking performance of general sailing yachts.