Seamanship_Secrets_185_Tips_-_Techniques_for_Better_Navigation-_Cruise_Planning-_and_Boat_Handling_Under_Power_or_Sail_(Re)_e..

110 seamanship secrets

5. Multiply the 50-90-100 Rule factors by the maximum current and
   place these next to the appropriate times. For instance, if the maximum
   current is 2 knots at 1212, the current at 1004 will be 50% × 2 or 1 knot.
   At 1108, it will be 90% × 2 or 1.8 knots.
   Let’s apply the 50-90-100 Rule to our graph of Charleston Harbor tidal currents,
   covering all times and velocities for Charleston Harbor on September 20, 2008. For
   more accuracy, calculate time intervals for each half-cycle. It looks like this:
   Time Intervals
   Flood cycle runs from 0632 to 1306
   First half of cycle: 0632 (slack) to 0919 (max flood)
   2 h 47 m (167 minutes) ÷ 3 = 56 minutes
   0632 + 56 m = 0728
   0728 + 56 m = 0824
   Repeat the process for the last half of cycle: 0919 (max flood) to 1306 (slack)
   3 h 47 m (227 minutes) ÷ 3 = 76 minutes
   0919 + 1 h 16 m = 1035
   1035 + 1 h 16 m = 1151
   Repeat this method for the remaining cycles.
   Current velocity (round results to closest tenth)
   Maximum flood = 1.9 knots
   0728 velocity = 50% × 1.9 = 1 knot
   0824 velocity = 90% × 1.9 = 1.8 knots
   0919 velocity = maximum flood = 1.9 knots
   1035 velocity = 90% × 1.9 = 1.8 knots
   1151 velocity = 50% × 1.9 = 1 knot
   1306 velocity = slack
   Repeat this method for the remaining cycles.

HOUR 3

100% Maximum Speed

HOUR 1

50% Speed

HOUR 2

90% Speed

HOUR 4

90% Speed

HOUR 5

50% Speed

HOUR 6

0 = Slack

HOUR 0
Cycle Begins
Th e 50-90-100 Rule during a 6-hour fl ood.