Polar plots have an important role in the history of sailing dinghies. A polar plot is a circular graph showing your boat speed on all wind angles around the boat (1, 2). Where and when did they start being used? In 1925, Dr. Manfred Curry published one of the classic texts on sailboat navigation: Yacht Racing and the Aerodynamics of Sails and Racing Tactics. The original volume and later editions up to 1948 do not appear to make any mention of the use of polar plots. The first documented use that we have seen with a graph in polar coordinates for sailboat navigation was by Frank Bethwaite, the designer of the Tasar, 49er and Laser II in Sydney Australia. From the article above:
Frank Bethwaite (a WWII aviator) was using polar plots when designing racing dinghies in the early 1970s, as shown in the three books he published… So before computers and GPS, the use of a polar graph to show boat speeds and the fastest heading upwind (Velocity Made Good) is probably another technology that came out of WWII aviation.
VMG into the Wind (Velocity Made Good into the Wind) is still a handy concept for racers on the upwind-downwind leg. (Although unless otherwise specified, VMG on GPS chartplotters is VMG to the Mark
, which does not work correctly with sailboat tacking.) Fortunately on all points of sail, the SailTimer tacking app
is a quick and easy way to see your optimal tacks and precise laylines. It uses your tacking distances and polar plots for rapid trigonometry calculations as your heading, wind and GPS location change. The details are broken down in this case study
from our June 2018 newsletter.
The "Sailor's Dilemma" is a central issue for sailboat navigation: whether to sail farther off the wind to get more speed (but at the expense of longer distance), or to pinch closer upwind to reduce the tacking distances (but with less speed). Being off by just a few degrees in your estimate can substantially increase your arrival time. With a Bluetooth Wind Instrument onboard, the SailTimer app
can give a quick and easy display of your optimal tacks and Tacking Time to Destination, even in a sailing dinghy.