Velocity Prediction for Sailing Ships

Discussion in 'Boat Design' started by rbraithwaite, Oct 15, 2009.

  1. rbraithwaite
    Joined: Oct 2009
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    rbraithwaite Richard Braithwaite

    I have recently produced a basic velocity prediction spreadsheet for ship rigged sailing ships. A previous project involved reconstructing drawings of an 18th century British frigate, HMS Southampton, from a variety of contemporary and modern sources (using 18th century drawing practices as far as possible, albeit in CAD!). Data from this reconstruction was used to produce a weight estimate, stability analysis and as the inputs for the velocity prediction spreadsheet.

    The spreadsheet itself balances thrust, side force and heeling moments for a given wind force/direction and sail setting. The outputs are speed, heel angle and leeway. There is an option to also balance yaw moments by adjusting sails (combination set and bracing angle) and rudder angle. But this relies on some fairly dodgy assumptions on CLR and rudder effectiveness.

    The spreadsheet is very manual to operate (no automatic generation of polars etc.) and relies on the user playing around with sail combinations, bracing angles and rudder angles to find the optimum set up for each condition.

    Unable to access any tank test data for 18th century frigate hull forms and wind tunnel data for square sails, I have had to make some fairly basic assumptions (e.g. use of Delft polynomials for wavemaking resistance). Despite this, the results of the analysis for HMS Southampton align reasonably well with contemporary sea trial reports of the vessel.
    The spreadsheet is available for download at the following link, together with a report covering the assumptions and results of the analysis.

    The web page also has links to the drawings and notes on the reconstruction together with a report on the weight estimate and stability analysis.

    I would welcome any comments on the assumptions behind my spreadsheet, particularly if anyone knows/has access to tank test/ wind tunnel data for this kind of vessel.
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