Chapter 8: Tides and Tidal Currents

1. Navigation Study Guide Chapter 8: Tides and Tidal Currents Instructor: Forrest Meiere All Questions are important for exam PowerPoint Presentation by Forrest Meiere

2. Navigation Study Guide S8-1. Tides and currents arise from the same forces and, although related, are distinct terms. Tide refers to the .motion of the water, tidal current to the ._________ flow of the water. vertical horizontal S8-2. The term high water denotes ______________ the maximum height reached by each rising tide; and low water denotes the minimum height reached by each falling tide

3. Navigation Study Guide difference between consecutive high and low waters . S8-3. Tidal range is defined as the _________________ S8-4. There are three principal daily patterns observed for tides: _______,____________ and ______. DiurnalSemidiurnalmixed

4. Navigation Study Guide S8-5. In addition to the daily tide patterns, there are more subtle patterns with a longer period. Tides have decreased range when the moon is in ________ and increased range when the moon is in ________. Apogee Perigee S8-6. When the moon and the sun are "pulling together," larger tidal ranges, termed ____________, occur. Spring Tides

5. Navigation Study Guide S8- 7. Alternatively, when the gravitational force of the sun and the moon are at right angles, tides with smaller range, termed __________, occur. Neap tides S8-8. In the United States and certain other parts of the world, the vertical reference plane or datum is what is termed _____________________________. mean lower low water (MLLW)

6. Navigation Study Guide S8-9. Locations for which tidal predictions can be made with the aid of the Tide Tables are subdivided into two classes: _______________ and ___________________. reference stationssubordinate stations difference in height between mean high water and mean low water. S8-10. The mean range is defined as the _____________

7. Navigation Study Guide average semidiurnal range occurring semi-monthly as a result of the moon’s being new or full. S8-11. The spring range is defined as _______________ S8-12. The mean tide level (also termed half-tide level) is defined as __________________________________ a plane midway between mean low water and mean high water, measured from chart datum.

8. Navigation Study Guide S8-13. Three common errors made by students in tide height calculations are: _________________________ a. neglecting to convert from daylight to standard time, b. not being alert to date changes when calculating tides for subordinate stations, and c. applying high water time differences to low water or converse. S8-14. Three methods for estimating tidal currents include: _____________________________________ a. observed directly from the movement of the water around stationary objects, b. calculated as you go using the methods of current sailing, and c. estimated or calculated from various published aids.

9. Navigation Study Guide S8-15. Data given in the Tidal Current Tables for reference stations include ______________________ the time of all slacks, the time and strength of ebbs and floods and the direction of the ebb and flood. a tidal current which flows alternately in approximately opposite directions with a slack water at each reversal of direction. S8-16. A reversing current is defined as _____________

10. Navigation Study Guide a tidal current that flows continually with the direction of flow changing through all points of the compass during the tidal period. S8-17. A rotary current is defined as ________________ S8-18. The most important use of the Tidal Current Diagrams is to determine ______________________ the most advantageous time of departure to maximize fair currents over the intended voyage route.