TRS (Tropical Revolving Storms) Plotting Calculation

TRS Plotting Calculation

A TRS is moving at 305° T at 16 knots and is estimated to be 160°T at 200′ from a ship with a speed of 10 knots in the present conditions. Find:

  • The course to steer to pass at maximum distance from the storm center
  • The minimum distance the ship will pass storm on this course

TRS Plotting Calculation

Plot the TRS at 160°T x 200′ (point X scale 40:1)
Plot speed vector of the TRS WA 305°T @16 Knots (scale 2:1)
On the side away from TRS, draw a 10 kt arc to contain O (scale 2:1)

Draw a tangent from A to the arc – OA is the relative approach between the ship and TRS.
Join W to 0. This is the course to steer 356°T at 10 knots speed.
From X, draw a line parallel to OA.
From W, draw a perpendicular to reach the line from X at Y.
Distance WY is the nearest approach: 191.9′
The ratio of XY to OA on a common scale can provide the
time to the nearest approach.

Considering the information available and its analysis, the course of action should be decided. There should be an attempt to remain outside a distance of 250′ from the storm center. If this is not possible, every effort should be made to pass the storm at a distance of at least 80′. Where the ship is already at a safe distance from the storm, the course to steer can be determined by plotting.