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A relatively new phenomenon within the sailing world is the use of hydrofoils to boost sailing performance. This technique is applied to a wide range of boats, from dinghies to ocean racers. An interesting question is whether one of the slowest racing boats in the world, the Optimist dinghy, can foil, and if so, at what minimum wind speed. The present paper presents a comprehensive design campaign to answer the two questions. The campaign includes a newly developed Velocity Prediction Program (VPP) for foiling/non-foiling conditions, a wind tunnel test of sail aerodynamics, a towing tank test of hull hydrodynamics and a large number of numerical predictions of foil characteristics. An optimum foil configuration is developed and towing tank tested with satisfactory results. The final proof of the concept is a successful on the water test with stable foiling at a speed of 12 knots.
Full Scale Pressure Measurements From SYL Navigation: An Upwind Case Study
The present work discusses an upwind case study about full scale measurements gathered during navigation on the Politecnico di Milano Sailing Yacht Laboratory (SYL). SYL is a 10m sailing boat, consisting in standard instrumentation, integrated dynamometer, a 3D flying shape detection system and distributed pressure sensors on sails. Particular attention was devoted to pressure measurements: full scale results are analysed and compared with wind tunnel test. The comparison of full scale/wind tunnel pressure distributions holds consistently, with the highest differences observed in the regions close to the leading edge. Critical aspects related to performing full scale measurements are also discussed.
Pressure Measurements on Yacht Sails: Development of a New System for Wind Tunnel and Full Scale Testing
The paper presents an overview of a joint project
developed among Politecnico di Milano, CSEM and North
Sails, aiming at developing a new sail pressure measurement
system based on MEMS sensors (an excellent compromise
between size, performance, costs and operational
conditions) and pressure strips and pads technology. These
devices were designed and produced to give differential
measurement between the leeward and windward side of the
sails. The project has been developed within the Lecco
Innovation Hub Sailing Yacht Lab, a 10 m length sailing
dynamometer which intend to be the reference
contemporary full scale measurement device in the sailing
yacht engineering research field, to enhance the insight of
sail steady and unsteady aerodynamics [1].
The pressure system is described in details as well as the
data acquisition process and system metrological validation
is provided; furthermore, some results obtained during a
wind tunnel campaign carried out at Politecnico di Milano
Wind Tunnel, as a benchmark of the whole measuring
system for future full scale application, are reported and
discussed in details.
Moreover, the system configuration for full scale testing,
which is still under development, is also described.
Modal Analysis of Pressures on a Full-Scale Spinnaker
While sailing offwind, the trimmer typically adjusts the
downwind sail "on the verge of luffing", letting occasionally
the luff of the sail flapping. Due to the unsteadiness
of the spinnaker itself, maintaining the luff on the verge of
luffing needs continual adjustments. The propulsive force
generated by the offwind sail depends on this trimming and
is highly fluctuating. During a flapping sequence, the aerodynamic
load can fluctuate by 50% of the average load.
On a J/80 class yacht, we simultaneously measured timeresolved
pressures on the spinnaker, aerodynamic loads,
boat and wind data. Significant spatio-temporal patterns
are detected in the pressure distribution. In this paper we
present averages and main fluctuations of pressure distributions
and of load coefficients for different apparent wind angles
as well as a refined analysis of pressure fluctuations, using
the Proper Orthogonal Decomposition (POD) method.
POD shows that pressure fluctuations due to luffing of the
spinnaker can be well represented by only one proper mode
related to a unique spatial pressure pattern and a dynamic
behavior evolving with the Apparent Wind Angles. The
time evolution of this proper mode is highly correlated with
load fluctuations.
Moreover, POD can be employed to filter the measured pressures
more efficiently than basic filters. The reconstruction
using the first few modes allows to restrict to the most energetic
part of the signal and remove insignificant variations
and noises. This might be helpful for comparison with other
measurements and numerical simulations.
An Investigation of the Dynamic Behaviour of Asymmetric Spinnakers at Full-Scale
This paper presents new results obtained from analysing on-the-water pressure, shape, force, speed and direction data that
were obtained from experiments in the Hauraki Gulf in Auckland, New Zealand in April 2014. A fully instrumented Stewart 34 Class
yacht sailing downwind was used for the tests. Details of the analysis of the results from simultaneous time-resolved measurements of
pressure, sail shape and loads are presented. The dynamic behaviour of the fluid-structure system made up of a light sail cloth and
highly curved flow is investigated. Aerodynamic forces on the asymmetric spinnaker are determined from the combination of point
pressure measurements across the sail with simultaneous shape measurements. Simultaneous time histories show a strong correlation
between the variations of pressure distributions, flapping sail shape and the forces at the corners. Periodic curling and filling of the
spinnaker luff influences suctions, in particular at the leading edge, and forces, which can dynamically change on the order of 40-
50%. The results are similar to, and extend, those that were presented by the authors at the 2013 Innov’sail Conference in Lorient,
France. It is expected that the results from this work will give reliable benchmark data which may be used to validate unsteady fluidstructure
interaction numerical simulations of downwind sails.