Raymarine ALPHA Operating Instructions Manual page 72

Term Meaning
Time To Burn (TTB) The time remaining during race start countdown
before the boat needs to start moving towards the
start line at full speed.
Time to Tack Time to tack is the duration left until you need to
tack.
True Wind The actual wind flow; it is the wind flow you feel, on
the water, when stationary. True wind is calculated
from Apparent wind data from a wind transducer
and STW (Speed Through Water) from a speed
transducer.
True Wind Angle The angle of the wind over water, relative to boat's
(TWA) bow, observed when stationary.
True Wind Direction The direction of the wind relative to north. This is
(TWD) the actual direction the wind is blowing.
In addition to STW, Heading is also required to
calculate TWD.
True Wind Speed The wind speed observed when stationary, on the
(TWS) water. TWS is the actual speed the wind is blowing
over water.
Upwind Moving in the opposite direction from which the
wind is blowing.
Velocity Made Good Sailing term related to the component of a sail
(VMG) vessel's velocity vector that is in the direction of
true wind.
Wind shift The amount of variation in True Wind Direction
(TWD) over time.
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