Experimental validation and accuracy assessment of Velocity Prediction Program for a high-performance sailing boat

The present study describes the verification methods and accuracy assessment procedures, provided by ASME guide, of sailing yacht performance prediction program useful in order to the develop better and more efficient racing sailboat. To this end the numerical results of the Velocity Prediction Program (VPP) are compared with the feedback provided by the instruments used for the experimental data acquisition, which come from the sensors installed on a skiff designed and built by Polito Sailing Team. The goal is to determine how close is the simulation output with the real one. The main output of a VPP is a performance diagram (polar plot) that states the boats optimal target speed as a function of the sailing conditions. From this it is possible to evaluate the best sailing condition for a given design and it is also possible to give the sailor an advantage in knowing the strength and weaknesses of the boat. Validation procedure consists of an assessment of the simulation errors, associated with physical model’s assumptions, input data and numerical solutions and then compared with the experimental results and with possible errors associated. The difference between the two models will confirm or not the consistency of the theoretical VPP’s model. The estimation of a range within which the simulation modelling error lies, for specified validation variables at a specified set of conditions, is a primary objective of the validation process. The data are processed by calculation software to obtain outputs comparable with the values simulated by the VPP, where were excluded the values that deviate excessively from the average of the data population and those that were acquired in conditions other than those foreseen in the VPP's design phase, i.e. sailboat at top speed regime with constant wind. To consider the VPP’s constraint that the heeling moment may not exceed the maximum available righting moment given by weight of the sailors, it was calculated the distance from the sailboat centre of gravity and that one of the two sailors in the maximum speed regime, which is another VPP output. This aims to assess the value of the heeling moment generated by the wind and balanced by the weight of the sailors. From the comparison carried out with the points representing certain sailing referring to certain values of beta angles, which in turn are specific for a single wind speed, an average error was found for each output variable and it is caused by multiple error sources. The sum of these errors is the difference between the value of the measurement determined in the experiment and the true value of the variable. The uncertainty of the results is expressed as a standard deviation to establishing if the error entities are constant, so would be useful to know the possible error offset and to be able to correct it. Even so, the steady-state way conditions envisaged in the VPP’s design phase have not been found in reality. Therefore, it is not possible to affirm for all the ranges of values that the VPP reproduces reality correctly, because, due to the lack of accurate data, it was not possible to have reliable feedback values. So, the accuracy of the results should be investigated and improved in the future by acquiring further data in order to confirm, with a sufficient number of values, whether these error entities are constant or if they vary between the various sailing conditions.