409 Dive Log Australasia December 24

White Tip Reef shark show how well it can bend its body to literally turn on a dime

One example is our understanding that little notch on the tip of the shark tail. What is it for? It minimises energy waste through the tip of the tail fin. Energy that might be lost by the tip of the tail is utilised by the enlarged tip and converted into forward thrust. With a little knowledge and understanding, we can stand back in awe and marvel at the hidden genius that shark design features for those who have the eyes to see. In short, sharks are brilliant examples of how Mother Nature displays mind blowing design in creatures that give them the survival edge. Let’s take a closer look. Length to diameter ratio of sharks. An interesting observation regarding large sharks is given by the so called ‘ Fineness Ratio ’, commonly used in boat design. This length to diameter ratio has a significant effect on how objects move through water and the dispersal of energy. It is used by ship designers to predict how boats sail. Put in its crudest form, you could compare the energy efficiency of a series of cylinders with various length to diameter ratios, say 3 : 1 or 4 : 1 or 5 : 1. Which is better for hydrodynamics, long and thin or short and thick? It turns out that the optimum dimensions to maximise thrust and minimise drag are 9 to 2 (or 4 ½ to 1.) Large sharks and whales have this body shape. This formula predicts the girth of a nine metre Orca should be 2 metres. Spot on.

A large male Hale’s Ornate Wobbegong has just swum inches over my head from behind. You can see his large Tail fin and his claspers.

DIVE LOG Australasia #409 - December ‘24 85

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