Page 41 - Race

8.9 Tidal Compensation

Fortunately many venues do not have this problem.
However, it is essential that ROs understand the issues
created by tidal currents within the course area. The
guidance offered here is very much a rough guide, a ‘rule
of thumb’, to adjusting the course to compensate for a
tidal current. The reason why it is only a rough guide is
that no two venues are the same. Sometimes the start
can be in an area with very little current but the windward
mark may be exactly opposite with anything up to 4 or 5
knots of current.

In some areas trying to work out the compensation is
extremely difficult. For winds of 10 knots or more with a
0
1 knot tide at 90 to the wind, set the windward mark
o
downtide by approximately 15 . With winds of 8 knots
0
or less then the offset should be 20 or more. As far as
the leeward mark is concerned, the offset for all winds
is approximately 5°. For tides diagonal to the wind,
halve the allowance and for tide of 2 knots double the
offset.

8.10 Assessing the Tide and the 'Sailing Wind'

There are methods to assess the tide which influences the 'Ground Wind' and produces the 'Sailing
Wind'. Ground Wind is that experience by an object that is fixed to the earth, such as an anchored
committee vessel. Sailing Wind is the wind experienced by a free-floating object or boat. Apart from
'guesstimating' the sailing wind it can be more accurately assessed by:

1. the wind as measured by a RIB that is completely stationary in the water (engine off) but floating
with the tide.

2. observe boats sailing close hauled upwind of the start line and assess the wind angle they sail
in - they are sailing to the Sailing Wind. This is a method that requires experience and practice.

3. Send a RIB, at the speed the boats are sailing at, along the bearing of the ground wind and this
will give the overall angle of the Sailing Wind for that leg (as the drift will usually vary over its
length).

8.11 Compromise for Tide

Unfortunately, when there is a cross-course current, it is impossible to set perfect beats and runs
when only using two marks on a windward-leeward course. The RO has to make compromises:

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