Notes on the Design of a Sailboat

   Everything about the design of a sailboat has to do with the study of how fluids, such as water and air, act when they move, or when things move through them. In our case of sailboats, what happens to make the boat move as it does? In the simplest form, a sailboat moves by the force of the wind pushing on the sail. This has been known for thousands of years and presumably started in the times of ancient Egypt or perhaps before.

Dhow, an ancient Sailboat design used in Persia and Egypt for many centuries

Dhow, an ancient Sailboat design used in Persia and Egypt for many centuries

Viking Ship
In the times of the Vikings, when the wind was right they got a free ride. If not, they rowed.
This image is probably copyrighted from the recent movie 'The 13th Warrior', however the execution of this Viking Ship is so good, I could not leave it out. The craftsmanship and perfection of form make this boat stand out head high. My hats off to the builders.

    During these times, and up through the times of the Square Rigger sailing ships, this was the means of propulsion, and a boat could only move with the wind. This is why the trade routes were established as they were. In the 16th, 17th and 18th centuries. To get from Europe to the Americas, the route was south until the 'Trade Winds' blowing west from Africa pushed you across the Atlantic.

Atlantic Trade Winds

To return you followed the currents North until you found the easterly flow of air, which would carry you back again.

Square Rigger

Gaff Rigged Schooner

     At some time back then they noticed something strange.  They found that if the winds were blowing from the side of the ship, or even from points toward the front of the ship, and the sails were positioned right, the ship would move forward. This is when they discovered that the wind in the sails could pull the ship, as well as push it.

     Shortly after this time the sail patterns on the boats changed. The picture to the left of a gaff rigged schooner is testament to the state of the art of this new technology. The sails are no longer rigged square to the boat, but rigged so that the sails can be turned in an ark around the mast to take advantage of winds from any direction. If the wind is from behind, the sails are set with one sail well out to the one side of the boat, and the other sail on the other side providing a large area of sail for the wind to push.

     But if they needed to go into the wind, they positioned the sails like this, and the wind would pull them along. In this photo, the wind is coming from in front and to the right of the ship.

     Sailboats move into the wind for the same reason that airplanes fly. The air flowing over the wings of airplanes travels faster over the curved surface. This creates a low pressure area above the wing, and the wing is then pulled up unto this low pressure area.

     The only difference between an airplane and a sailboat is that the wing on an airplane is horizontal, and the wing on a sailboat is vertical.

For more info on why this happens, from

The Central Michigan University, Click Here.

Here is the MIT class on the same subject.
Mass. Inst. of Technology
It isn't that tough, listen to this guy.

Pressure diagram air flow over a foil

Video Here

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Sailboat lift diagram

sailboat tack diagram

     If the wind is coming from somewhere in front of the boat, then the sails are set in the manor pictured to take advantage of the low pressure that is made in front of the sail. With the keel and rudder giving directional stability in the water, we could sail into the wind, not directly onto the wind but to within perhaps 30 or 40 degrees of directly into the wind. That meant that by zig zagging into the wind, we could sail anywhere we wanted to go, upwind, downwind or in circles if so desired.

Gaff Rigged Sloop

As we gained more and more knowledge of how the wind can pull is along, our boats changed and got much faster. The shapes of the hulls as well started to transform.

The photo at right of America One shows the trend to make the sails look and act more and more like true wings.

And this trend continues...

America One

Sailboat with a modern wing shaped sail

Escaping Displacement

    In the extreme of our designs for speed today, there are competitors.

Maquaire Innovation at speed

    One is the 'Maquaire Innovation' which was patterned after a similar craft named 'Yellow Pages'. This craft has attained speeds of over 50 nautical miles per hour( 57 mph or 93 kph) using only the wind for power. A main limitation of this design is that it can only sail into the wind. The pilot is on the extreme left in the small round appendage. The pilot is ballast to help balance the torque on the craft caused by the side ways lift of the wing sail. The craft moves almost entirely on the pontoon on the right of the picture.

 See This Boat Run! Click Here.

Finian Maynard World Speed Record Run

One other type of craft is simply a sailboard. In April 2005, Finian Maynard captured the world speed record for wind at a speed of 48.70 nautical miles per hour. (56 mph, or 90 kph)

Click here for a video of his

World Record breaking run.

 Then on October 28, 2010, Rob Douglas became the new world record holder with a speed of 55.56 kts. (64.04 mph or 103 kph.) He did that with a kite board.

 Click Here to see this New World Record run.

Rob Douglas as the only American to ever hold the world sailing speed record reaching  55.65 knots?

Rob Douglas 55.65 knots World Record run

Vestas SailRocket2 65 knot run.VESTAS Sailrocket 2

Nov. 24, 2012 Paul Larsen in the Vestas Sailrocket 2 smashes all world sail speed records with an incredible run of 65.37 knots. (75.23 mph - 121.06 km/h)

The Video is HERE! or click on the image. (19 Megs)

It just keeps getting better!!!

      In other areas of sailing, land sailing, wheeled vehicles powered only by the wind, have attained speeds of 116.7 mph (188 kph ).

Two high speed Land Sailing craft

On the morning of March 26th, 2009 on the 'dry' Lake Ivanpah, The Greenbird - driven by British engineer Richard Jenkins - smashed the world land speed record for wind powered vehicles. The Greenbird clocked 126.1 mph (202.9 km/h), eclipsing the old, American held, record of 116 mph, set by Bob Schumacher in the "Iron Duck" in March 1999 at the same location.

Greenbird land speed record using only the wind

Video Here

     Similar vehicles have been used in the north sailing on ice. The current ice sailing speed record was set in 1938 on Lake Winnebago in Wisconsin (USA) by John D. Buckstaff using a stern steering craft named "Debutante". Buckstaff reached 143 mph (230 km/h), reportedly in a 72 mph (116 km/h) wind.

Twice the speed of the wind in 1938

deburante III ice sailing record

And so we see what is possible using only the wind as power.

Now, if you want something to think about, watch these videos.
These are demonstrations of machines that start with the wind pushing them, and they end up going

  Directly Downwind Faster Than The Wind.
To put that another way, with the wind at their back, and using only the wind for power, they outrun the wind.
Blackbird 2.7 times the speed of the wind
Blackbird - 2.7 times the speed of the wind.

Boats today are designed using computer graphics.
Below are two screen shots of an open source program called "Free!ship". This program is not the ultimate in computer aided design, but it is enough to get someone going if they seriously want to design a boat. The program gives you complete 3D control over the shape of the boat, and like the name says, it is free.
To download Free!ship Click Here.
Freeship Plus ver 3.2  - 30.5 megabites.
The manual is included in the zip file.
Download, unzip and run. Installation is not necessary.

lines plan used for designing boats

Free ship - graphics program used for designing boats
You simply click and drag those points to where you want them to be.

For More Information, Contact me Here -
Escaping Displacement
The Elimination of Ballast
Controlling Heel
Using Water to Fly

The Boats of Tampico
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