Costal Navigation (3) Past Paper PDF

Dpartment of Navigation -1- Costal Navigation (3) Chapter( 1) Tide (18 hours) WK Objectives I.M.O No No...

Dpartment of Navigation -1- Costal Navigation (3) Chapter( 1) Tide (18 hours) WK Objectives I.M.O No No Chapter( 1) 1.1.2.11 Tide 1 -Introduction ------------ 2 - explains the basic theory of tides 1.1.2.11-1 3,4 - defines 'spring tides', 'neap tides', 1.1.2.11-2 'height of tide' 'high water' and 'low water', 'mean high water springs', 'mean high water neaps', 'mean low water springs', 'mean low water neaps', 'range', 'chart datum' 5 - calculates the spring and neap ranges 1.1.2.11-3 for standard and secondary ports 6,7,8 - finds the predicted time and height of 1.1.2.11-4 high and low water at standard and secondary ports. 6 *Exercise (1) ------------ Dpartment of Navigation -2- Costal Navigation (3) Dpartment of Navigation -3- Costal Navigation (3) 5-*Explains the basic theory of tides: In any consideration of tidal theory, it is convenient to start with a spherical earth uniformly covered with water. It is also convenient to consider se- parately the effects of the moon and the sun, following this with a consideration of the combined effects of both bodies. Tides are caused by the effects of gravity in the earth-moon-sun system, and the movement of those three bodies within the system 5-1-The effect of the moon: The earth, and especially the oceans on it, are affected by the gravitational attraction between the earth and the moon, and by the centrifugal forces resulting from their revolution around a common center, a point located within the earth about 810 miles (1500 km) beneath the surface. The gravitational and centrifugal forces are in balance, and as a result, the earth and moon neither collide nor fly away from each other in space. Although the earth-moon system as a whole is in equilibrium, individual particles on the earth are not the centrifugal force is the same everywhere, since all points on the earth's surface describe the same motion around the common canter of mass; these forces are all parallel to each other and to a line joining the canter of the earth and moon. On the other hand, the gravitational force is not everywhere the same; particles nearer the moon feel a greater attraction force than those on the far side of the earth; those forces are not parallel, each being in the direction from that particle to the canter of the moon. The combination of these forces, much exaggerated for emphasis, is shown in (Figure 7). Figure (7) Gravitational and centrifugal forces Dpartment of Navigation -4- Costal Navigation (3) Note that there are a series of resultant forces that will cause the surface water to flow toward the points on the earth's surface that are then nearest and farthest from the moon. This flow causes higher than normal levels of water at these points, and lower than normal levels of water at these points, and lower than normal levels at the areas from which the flow comes. Although at the nearest and farthest points there is an indicated outward force, this is very slight and not nearly enough to cause an appreciable tide the true tide results from the near-horizontal forces causing the flow described above. As the earth rotates daily around its axis, the line of direction toward the moon changes, and so each point has two highs and two lows. As result of the tilt of the earth's axis, the highs and lows are not normal of equal levels. 5-2-The effect of the sun: This overly simplified explanation must now be complicated by the presence of the sun, a body of immensely greater mass than the moon by relatively so much more distant that its effect is less (about 46 percent as great). The tides that occur on earth are the result of the lunar and solar influences. Figure (8) figure ( 8) Gravitational and centrifugal forces. Dpartment of Navigation -5- Costal Navigation (3) 5-3- *Defines Spring and Neap Tides A-Spring Tides: The maximum raising force occurs when the moon and sun are almost on the observer's meridian. At new moon, (Fig. 9) the forces of the moon and sun are combined and give rise to a spring tide; the same occurs again about 14.5 days later at the period of full moon, when moon and sun are in opposition and the forces are again in the same straight line. Figure (9) Full Moon, New Moon, Spring Tide B-Neap tides: occur about seven days after spring tides when the moon is in quadrate (Fig. 10), then the H.W. due to M2 coincides with the L.W. due to S2 and the result is a tide having a smaller range. The range at neaps is expressed as (M2 - S2 ). They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another Figure (10) Dpartment of Navigation -6- Costal Navigation (3) Suppose the moon alone produced a tide having a range of 14 units-say 14 meters (to get something tangible) and the sun alone a range of 6 units, or 6 meters, then: at springs (M2 + S2) = (14 + 6) = 20 meters. at neaps (M2 - S2) = (14 - 6) = 8 meters. A difference of 12 meters, and this difference would be termed the phase Inequality of Heights as it would be due to the phase of the moon. The mean lunar day is about 50 minutes longer than the solar day, so that normally, an interval of about 24 hrs. 50 minutes. Separates the high water of one day from the corresponding high water and the next low water is therefore, about 6 hrs. 12 minutes. High water and the next low water is therefore, about 6hrs. 12 minutes. Dpartment of Navigation -7- Costal Navigation (3) Exercise (2) Put (T) for True answer and (F) for False answer: 1-The mean lunar day is about 50 minutes longer than the solar day, ( ) 2- The mean lunar day is about 50 minutes less than the solar day, ( ) 3-Spring Tides: Is the maximum raising force occurs when the moon and sun are almost on the observer's meridian ( ) 4-When moon and sun are in opposition and the forces are again in the same straight line. ( ) 5-The maximum raising force occurs. At new moon, full moon ( ) 6-Neap tides: occur about 14 days after spring tides ( ) 7-Neap tides: occur about seven days after spring tides ( ) 8-Neap tides when the moon is in quadrate ( ) 9-Neap tides when the moon is full ( ) 10-Neap tides: occur about seven days after spring tides ( ) 11-Spring Tides occur when the gravitational forces of the Moon and the Sun are perpendicular to one another ( ) Fill in space with suitable number: (1)Spring Tide (2)Neap tides ( ) ( ) ( ) ( ) Dpartment of Navigation -8- Costal Navigation (3) Multiple Choice 1-Neap tides: occur about A- 7 days after spring tides B- 14 days after spring tides C-A.B correct answer 2-The maximum raising force occurs A- At new moon, B- Full moon C-A.B correct answer 3-Neap tides: A-Occur about seven days after spring tides B- Occur when the gravitational forces of the Moon and the Sun are perpendicular to one another C-A.B correct answer 4-Spring Tides: A-Occurs when the moon and sun are almost on the observer's meridian. At new moon, B- Occur when the gravitational forces of the Moon and the Sun are perpendicular to one another C- A,B correct answer 5-Spring Tides: A-Occurs again about 14.5 days later at the period of full moon, B-Occurs When moon and sun are in opposition and the forces are again in the same straight line C- A,B correct answer 6-The mean lunar day is about : A-50 minutes longer than the solar day, B-An interval of about 24 hrs. 50 minutes. C- A,B correct answer