Science Of Sailing

Download link here Polar A polar table can be constructed by entering the TWAs listed in the blue cells as the TWA. BS, VMG, Leeway will be collected automatically and the polar is drawn for this Camber and TWS. Note this is dynamic and will be overwritten whenever a TWA is entered out of order. This is a limitation of writing for Excel Online. Data can be saved or expanded by duplicating the worksheet and having 1 sheet for each TWS, for example. Or copying the table to another sheet or workbook. But I'm leaving this up to you. Similarly Camber and Board Length can be explored: Depending on TWS, it is better to flatten the sail before maximum hiking is reached. This is reducing the sail profile drag by more than the lift is reduced, I guess. Feel free to contact on accuracy, errors, questions, improvements, requests.

A previous post outlined the  basic forces  on a yacht - Righting Moment, Heeling Moment, sideforce, friction drag, induced drag. It is an essential introduction to the work here. Download or run online  "VPP Laser & dinghy v2c.xlsx" To calculate the speed of a yacht is both simple and complex. Simply find the speed where the forward thrust from the sails is equal to the aftwards drag of the yacht. When these two forces are balanced the yacht is at a steady speed. At the same time, find the heel angle or hiking position or sail twist/flatness where the Righting Moment balances the Heeling Moment. The first Velocity Prediction Program VPP was written in about 1970 by Kerwin. The link above is a VPP spreadsheet that can be run online without Excel and links the forces and moments together to calculate speed. The process of balancing them is precise. However, modelling the forces is less exact and is simplified in various ways: Thrust The forward thru