Comparing the Performance of Boats
Often it’s interesting to see just how one boat does against another. Usually this is done using weight or displacement, speed, and required power. Of course the tricky bit is comparing like with like, and getting accurate data. Don’t use the published weight, find out the real weight from an accurate scale or travell lift. Don’t believe published HP, calculate power required from fuel use. Luckily there are some published norms, two are included above.
The blue graph is from Professional Boatbuilder and includes curves for speed/length ratio or speed in knots, against pounds of displacement per HP. Speed/length is the vertical axis and pounds/HP is horizontal. The longer, upper curves cover big ships and semi-planing types, up to planing hulls in the upper lefthand corner. Smaller and faster hulls are covered in the lower curves running up to 100 knots.
The second graph showing transport efficiency is a bit more complex to calculate, but covers a wide range of boats. Et (vertical scale) is calculated as shown using displacement multiplied by speed and divided by HP multiplied by the constant 550. Graphed against the Volume Froude number (horizontal scale) gives an indication of how the boat being compared does against current state-of-the-art hulls from what are now many years ago.
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External Links
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