Page 26: of Marine Technology Magazine (November 2017)

DVLs downward in different directions. to move along its track. Yet wind also forward motion.

Echoes are returned due to scattering causes motion across the vessel’s head- Minimizing sideslip due to winds and off the seabed. Because the DVL sonar ing. This downwind motion is called currents is a critical advantage in com- is aboard a moving vehicle, returning leeway. It can be seen by a sensor that petitive sailing. Measuring leeway can echoes carry a change in pitch; this is is looking at the water. The effect of lee- provide key information for winning. the Doppler Effect. way can be seen when the vessel’s wake A rapid and accurate system to measure

Generally, a different frequency shift is angled away from straight astern. leeway gives a navigator direct and im- is heard along each beam. Combining To counter leeway, sailboats with mediate feedback after course changes these readings tells how fast the vehicle multi-hull designs use adjustable dag- or daggerboard adjustments. This infor- is moving and in what direction. gerboards. These are retractable keels mation helps in tuning the boat’s use of that slide vertically through a slot in the wind power to move most ef