Racing Functions; Some Definitions And Terminology; Improving Race Performance With The Race Master - Raymarine Race Master User Manual

Race Master
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Racing Functions

3.1

Some definitions and terminology

True Wind Direction (TWD), the current actual direction of the wind
over the water, expressed as a compass heading. If the boat is head to
wind, the TWD is the same as the heading of the boat.
Mean Wind Direction (MWD), the average of the True Wind Direction
over a sufficiently long period to even out any regular periodic changes
in the wind direction.
Tack Angle (TAK), the angle through which the boat turns when going
from close hauled on one tack to close hauled on the other. Typically this
is about 90 degrees.
Line Bias, the angle between the heading of the start line and a line at
right angles to the wind.
3.2

Improving Race Performance with the Race Master

Racing and Wind Shifts
Like most things in sailing, the wind does not remain constant in either
strength or direction.
The crew tend to react naturally to gusts but find wind shifts more
difficult to detect. However the wind does tend to shift in regular
patterns, oscillating from one side of the Mean Wind Direction (MWD) to
the other. Every shift in the wind requires the boat to alter its heading in
order to maintain a close hauled course. A shift that allows the boat to
change its heading closer to the Mean Wind Direction (MWD) is called a
"lift"; a shift that forces the boat to change course away from the Mean
Wind Direction (MWD) is known as a "header".
In an oscillating wind, a boat that
regularly tacks when headed will spend
more of its time sailing a lifted course
and will sail a shorter distance to the
windward mark than a boat that regularly
sails a headed course. This gives the
boat sailing in the lifts a considerable
advantage.
In the diagram, the boat on the right sails
a shorter course by tacking when
headed and thereby sailing mostly in
lifts.
The opposite is true sailing down wind. A boat that gybes to sail in the
"headers" will sail a shorter course to the leeward mark than a boat that
sails a "lifted" course.
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