Scott Welty - The Why Book of Sailing: The Curious Sailors Guide to the Science of Sailing and Seamanship

Sue Budde, wife and mate, for taking and organizing all the photos; for reading every word; and for asking great questions.

Expert sailor Jeff Dalsin, for reading early drafts of this book. More canvas!

Fellow cruisers Joe and Peg aboard Calcutta who, after just meeting us in Portsmouth, asked me about relativity, thus giving me the idea for a physics book for sailors ... or is this a sailing book for physicists?

And, finally, to my physics teaching partners, John Miller, Jeff Rylander, and Jake Scruggs, for always making me explain it better.

Its interesting to note that the sloop-rigged sailboat has made it into the 21st century from hundreds of years ago with virtually no changes. Oh, sure, we have more modern materials and electronics. Our sails have better shapes and last longer. But you could take an 18th-century sailor and put him on our boat and hed know how to sail it instantly. (The engine would scare him, so we wouldnt turn it on.) This is part of the lure of sailing: connecting old with new, exploring in the old wayslow and steady as she goes.

Staniel Cay, Bahamas, March 2007

REFERENCES

Chapter 1

Web sites

www.mcs.drexel.edu/~crorres/Archimedes/contents.html

A nice collection of miscellany about good old Archimedes.

Chapter 2

Web sites

www.physclips.unsw.edu.au/jw/sailing.html

Good stuff about relative wind and more.

Chapter 3

Web sites

www.aerospaceweb.org/question/aerodynamics/q0215.shtml

A very clear and understandable site about the nature of golf ball dimples.

www.northsailsod.com/articles/getaccess-19php

For you mathy types, a good article by Paul Bogataj at North Sails about design features of sails.

www.boatbuilding-links.de/Jim-Michalak/sail-math-and-thoughts-of.html

More neat math stuff on sail design and also center of gravity by Jim Michalak.

Chapter 4

Web sites

www.sailtexas.com/modernyachtdesignfinalb.html

Great pics and an article about the canting keel design.

Chapter 5

Web sites

www.celestialproducts.com/Products/MPCXX.asp

This is a site selling the popular Miller Planisphere star locater.

http://visibleearth.nasa.gov

One NASA site with beautiful pictures of our home planet.

www.nmm.ac.uk/server/show/conWebDoc.355

A site from the Royal Observatory in England telling the story of solving the longitude problem.

Books

A Field Guide to Stars and Planets (Peterson Field Guides) by Jay M. Pasachoff and Wil Tirion. Houghton Mifflin; 4th edition (1999). Every boat should have a star guide on board!

Chapter 6

Web sites

www.chaseday.com/lightning.htm

Fantastic and scary pictures of lightning.

Books

The 12-Volt Bible for Boats by Miner K. Brotherton and Edwin R. Sherman.

International Marine/Ragged Mountain Press; 2nd edition (2002).

Chapter 7

Web sites

www.sailingusa.info/cal__hull_speed.htm__hull_speed.htm

This site includes a hull speed calculator.

Books

Waves and Beaches: The Dynamics of the Ocean Surface by Willard Bascom. Anchor Press; revised and updated (1980). A great old book about the physics of waves and their effects.

Chapter 8

Web sites

http://polarization.com/water/water.html

Cool pictures of the effect of polarized sunglasses.

www.islandnet.com/~see/weather/elements/mirage1.htm

Good site about mirages.

http://mintaka.sdsu.edu/GF

Everything you wanted to know about the green flash, including pictures!

Chapter 9

Web sites

www.azsolarcenter.com/technology/pas-2.html

Some good ideas regarding passive solar heating.

Books on boat design, theory, repair, and maintenance

Boatowner's Mechanical and Electrical Manual by Nigel Calder. Adlard Coles Nautical; third revised edition (2005).

High Performance Sailing by Frank Bethwaite. International Marine/ Ragged Mountain Press; 1st edition (1996).

We begin by launching our boat and hoping that it floats, the way it did last season. Certainly this is the very basic requirement for our sailboat. Its gotta float! A little mental voyage, then, into the subtleties of floating, density, and buoyancy is in order.

Legend has it that Archimedes was given a task by King Hiero II to determine if a crown was pure gold or gold mixed with silver without destroying the crown. A neat trick! Archimedes lowered a chunk of pure gold of equal weight to the crown into a bowl of water filled to the brim. He then took out the gold and lowered the crown into the bowl. If the crown was made of part silver, he reasoned, then it would have more volume than a pure-gold version (silver being less dense than gold); more water would be displaced as a result.* In fact, that was the case: The crown was part silver. There are serious questions as to whether or not Archimedes could have actually used this method in his day with the precision required. No matter. We are still thankful to him for a complete description of the nature of buoyancy.

How come a chunk of steel doesnt float but a steel boat does?

What Archimedes figured out was that an object placed in a fluid is pushed upward by the fluid with a force equal to the weight of the fluid displaced. In simple terms, a 10-ton ship will float when it has pushed aside (displaced) 10 tons of water. Sometimes people mistakenly think that sinking or floating is a property of materials: Wood floats. Steel sinks. But of course while this is true in the case of solid chunks of stuff, it doesnt explain very well why you can make boats out of steel that float. In fact, its a matter of design: You need to shape the hull of the boat so that it will displace its own weight before the decks are awash!

Could you float a 10,000-ton battleship in a gallon of water?

This is an oldie but a goodie! The answer is yes... but not really. Heres a more practical question. When a container ship enters a narrow, shallow lock from the open ocean, does it float higher or lower in the water? The answer, of course, is that it floats the same. Remember, its not how much water is in the ocean, but rather how much of the ocean water has been displacedwhich is the same whether youre in a lock or the ocean! The old question about floating a battleship in a gallon of water is a little too extreme. Look, it takes about 30,000 gallons of paint to touch up the bottom of an old battleship. One gallon of water wouldnt be near enough to cover it. To a reasonable limit, then, the battleship would float the same in the smaller and smaller containers. Thats Archimedes!

What will happen if I sail my boat from fresh to salt water?

First off, it will start to rust like nobodys businessbut thats another story best left for our chapter on electricity... really. Notice that Archimedes principle is completely general and not confined to fresh water alone. When you sail from fresh water to salt, will your boat float higher or lower in the water? Since salt water is denser than fresh, you dont have to displace as great a volume of salt water to match the weight of the boat. Thus your boat will float higher in salt water than in fresh. If youve gone swimming in fresh and salt water, youve definitely noticed the difference, without the rust.