Mark Denny

I'm a science writer, and my books explain how things work.

. (3) Float Your Boat! The evolution and science of sailing

The earliest sailing vessel was a raft with a simple sail attached to a single mast. Over millennia these rafts evolved into the most magnificant of sailing ships: the nineteenth century clippers that raced across the world carrying tea or spices. This evolution is interesting from a technological standpoint because it depended upon several key innovations. The modern sailing yacht takes advantage of all these innovations and more. In this book I look at the physics that underpins sailing technology. The level of presentation fills a yawning gap that I see in the sailing literature (less technical than an Americas Cup boat designer would want; more technical than your average sailing magazine article).

The sail of a modern fore-and-aft rigged sloop is very similar to a bird's wing. This is no coincidence: both are designed to produce aerodynamic lift. Image courtesy of Simona Manca.


"Intelligent and understandable explanations of the physics of sailing . . . If you want to sound smart the next time you try explaining sailing to someone, read this book!"—Latitudes & Attitudes

"...a light-hearted yet informative look at the physics of sailing ships."--Physics World (July 2009)

"Denny's book is an entertaining read for any sailor, or any armchair physicist for that matter." Ocean Navigator 2008-01-00

"An excellent approach for any nautical library." Midwest Book Review 2009-01-00 

For more about the book, see the publisher's website:

Additional material:


The Oseberg ship. I included an old photo of this important Viking longship in my book, but here is a better one (for which I am grateful to Waldemar J. Poerner). Note the clinker hull construction, the low gunwhale to aid rowing, and (clearly of secondary importance) the single mast. This ship was not built especially as a funeral ship (though it has served that purpose since 834 CE) so what we see here are the graceful lines of a true, ocean-going longship, employed as such for many years before being used to convey a Viking queen to the afterlife. 

An Egyptian felucca. Note the long, angled lateen sail--one of the key maritime technology innovations of the first millennium. This rigging permitted boats to sail closer to the wind than the old square-rigged vessels. Europeans added lateen sails to their little ocean-going carracks and caravels during the Age of Exploration. The combination of square and lateen sails took Columbus to the New World. (Thanks again to Waldemar J. Poerner for this photo.)

Do you notice something odd about this dramatic NASA picture of a wingtip vortex? It appears to emanate from the right wing tip, but this cannot be so because the right wing vortex should flow counterclockwise. Why? Air laps around the wing tip from the lower surface to the upper surface due to pressure differences, and this flowing air is shed as a vortex. Such aerodynamics also applies to sails--in fact sail aerodynamics is more complicated than airplane aerodynamics because the sail is not rigid.