Bowditch - Ch. 35 Tides & Currents

Question 1

This is the periodic motion of the waters of the sea due to changes in the attractive forces of the moon and sun upon the rotating earth.

Answer 1

Tides
Bowditch - Pg.561

Question 2

The horizontal movement that accompanies the rise and fall of the tide is called what?

Answer 2

The tidal current

Bowditch - Pg.561

Question 3

The mariner is concerned with the _________ and ________ of the tide as it effects access to shallow ports. When it comes to the current he/she is concerned with the ________ , __________ and _________ as it will effect position, ETA and Course.

Answer 3

1. Amount
2. Time
3. Time
4. Speed
5. Direction

Bowditch - Pg.561

Question 4

The principal tidal forces are generated by the ________ and the _________. Of the two the ________ effects tide the most.

Answer 4

1. Moon
2. Sun
3. Moon

Bowditch - Pg.561

Question 5

Using this law it is found that the orbits of two point masses are conic sections about the Barycenter of the two masses.
A. Law of relativity
B. Law of gravitation
C. Newton’s first law of physics
D. Law of quadrodynamics

Answer 5

B. Law of gravitation

Bowditch - Pg.561

Question 6

This has two interactive but distinct components: One is the tide, generating forces are differential forces between the gravitational attraction of the bodies (earth-sun and earth - moon). The other is the centrifugal forces on the earth produced by the earth’s orbit around the sun and the moons orbit around the earth.
A. The fundamental tide-generating force
B. The fundamental current generating force
C. The Gravitaitonal force of the sun
D. None of the above

Answer 6

A. The fundamental tide-generating force

Bowditch - Pg.561

Question 7

True / False: The tide generating force of the sun is 46 / 100 of the tide generating force of the moon.

Answer 7

True
Bowditch - Pg.362

Question 8

The point on the moons that is directly below the moon is called the ________. The point on earth exactly opposite is known as as the _________.
A. Antipode
B. Sub Lunar Point
C. Point of Apogee
D. Nodal Point

Answer 8

1. B. Sub Lunar Point
2. A. Antipode

Bowditch - Pg. 362

Question 9

the horizontal components parallel to the earth’s surface have the effect of moving the water toward the _________ and _________ points until an equilibrium is reached.

Answer 9

1. Sublunar
2. Antipodal

Bowditch - Pg. 362

Question 10

The horizontal components which are the principle tide generating forces are knows as _______ forces and are zero at the sublunar and antipodal points and ______________.

Answer 10

1. Tractive forces
2. Along the great circle halfway between these two points.

Bowditch - Pg. 362

Question 11

Equilibrium will be reached when a bulge of water has formed at the _________ and _________ such that the tractive forces due to the moon differential gravitational forces on the mass of water covering the surface of the earth are just balanced by the Earth’s gravitational attraction.

Answer 11

1. Sublunar Points
2. Antipodal Points

Bowditch - Pg. 363

Question 12

How long does it take the moon to transit around the earth?

Answer 12

24 hrs 50 mins

Bowditch - Pg. 363

Question 13

If an observer is standing at the equator how many high tides (or bulges of water will the observer experience) in a 25 hour period?

Answer 13

2, one when the moon is directly overhead at sublunar point and one when the moon is at antipode.

Bowditch - Pg. 363

Question 14

True / False: in theory the heights of the tides are equal at the equator and as the observer moves North and South the tides are not as great.

Answer 14

True

Bowditch - Pg. 362

Question 15

The effects of declination are shown in three cases in the diagram what are they?

Answer 15

1. when the moon is on the plane of the equator, the forces are equal in magnitude at the two points on the same parallel of latitude and 180º part on longitude.
2. When the moon has north or south declination, the forces are unequal at such points and tend to cause an inequality in the two high waters and the two low waters each day.
3. Observers at points X, Y, and Z experience one high tide when the moon is on their meridian then another high tide 12 hours and 25 mins later when at X, Y, and Z. The Second high tide is the same for X’ as at X. High tides at Y’ and Z’ are lower than high tides at Y and Z.
   See the second diagram for some more explanation.

Bowditch - Pg. 363

Question 16

True / False: Tides will also vary according to the Sun’s declination and its varying distance from the Earth.

Answer 16

True

Bowditch - Pg. 363

Question 17

The theoretical tide at any place represents the combination of the effects of both the ________ and the _______.

Answer 17

Moon and Sun

Bowditch - Pg. 363

Question 18

What is the period at high or low water during which there is no apparent change of level is called?
A. Slack Water
B. Stand
C. High Tide and Low Tide
D. Sub Lunar Point

Answer 18

B. Stand

Bowditch - Pg. 363

Question 19

what is the difference in height between consecutive high and low waters called?

Answer 19

Range

Bowditch - Pg. 363

Question 20

What is it called when there are two highs and two low waters in a tidal day? when there is a single high and low water in a tidal day what is it called?

Answer 20

1. Semidiurnal tide
2. Diurnal tide

Bowditch - Pg. 364

Question 21

This is characterized by a large inequality in the high water heights and low waters heights or both.
A. Stand of the tide
B. Diurnal Tide
C. Semi-Diurnal Tide
D. Mixed tide

Answer 21

D. Mixed tide
Bowditch - Pg. 365

Question 22

The advance of a low water trough that is so shallow the crest of the rising tide overtakes the low and advances upstream is called a tidal ________.
A. Wave
B. Crest
C. Bore
D. Rogue

Answer 22

C. Bore
Bowditch - Pg. 565

A tidal bore occurs when a rising tide pushes into a narrow estuary or river, creating a sudden and strong surge of water that can travel upstream.

Question 23

What kind of tides result from the Earth, Moon and Sun lying approximately on the same line when the tractive forces of the Sun are acting in the same direction as the moon’s?
A. Neap Tides
B. Spring Tides
C. Tropic Tides
D. Perigean Tides

Answer 23

B. Spring Tides
The ranges are much greater than average.

Bowditch - Pg. 566

Question 24

When the tractive forces of the sun are acting at approximately right angles to the moon’s what types of tides are these?
A. Spring Tides
B. Neap Tides
C. Apogean Tides
D. Perigean Tides

Answer 24

B. Neap Tides
These ranges are less than average.

Bowditch - Pg. 566

Question 25

With the moon in positions between quadrature and new or full the effect of the sun is to cause the tidal bulge to either lag or precede the moon which is called ______ and ______ the tides.

Answer 25

1. Priming 2. Lagging Bowditch - Pg. 566 ## Footnote This phenomenon occurs due to the gravitational pull of the sun affecting the tidal forces, resulting in a shift in the timing of the tidal bulge relative to the moon.

Question 26

What is it called when there are moon is at the point in its orbit nearest to the earth?

Answer 26

At perigee Bowditch - Pg. 566

Question 27

When the moon is at the closest point to the earth the lunar semidiurnal range is increased and called what? A. Apogean neap tides B. Tropic Tides C. Perigean Tides D. Equatorial Tides

Answer 27

C. Perigean Tide Bowditch - Pg. 566 ## Footnote Perigean tides occur when the moon is closest to Earth, resulting in higher tidal ranges due to the increased gravitational pull.

Question 28

What is it called when the moon is farthest away from the earth?

Answer 28

At Apogee. Bowditch - Pg. 567

Question 29

When the phenomena with the moon at Perigee and the moon and sun in line pulling together what is this called?

Answer 29

Perigean Spring Tides Bowditch - Pg. 566

Question 30

When the Phenomena of the Moon being at apogee and the Moon and Sun opposing each other as at quadratures what is this called?

Answer 30

Apogean neap tides Bowditch - Pg. 566

Question 31

what happens when there are moon tides are priming and lagging?

Answer 31

When moon tides are priming, they are at their maximum effect, causing higher high tides and lower low tides. Conversely, when they are lagging, the tidal effects are diminished, resulting in lower high tides and higher low tides. ## Footnote This phenomenon is influenced by the gravitational pull of the moon and the alignment of the sun, affecting the overall tidal range.

Question 32

What is diurnal effect when it comes to tides?

Answer 32

The diurnal effect refers to the variation in tidal patterns that occur within a 24-hour cycle, typically resulting in two high tides and two low tides each day. ## Footnote This effect is influenced by the gravitational pull of the moon and the rotation of the Earth, leading to differences in tidal heights throughout the day.

Question 33

When the moon is at its maximum semi-monthly declination these kinds of tides occur in which the diurnal effect is at a maximum? How does this affect the tides?

Answer 33

1. Tropic tides occur 2. These tides are characterized by higher high tides and lower low tides, influenced by the gravitational pull of the moon at its closest point to the Earth. Bowditch - Pg. 566

Question 34

When the is the diurnal effect at a minimum and what kind of tides are these?

Answer 34

1. When the moon is at its minimum declination. 2.equatorial tides. ## Footnote Equatorial tides occur when the moon is positioned directly above the equator, resulting in minimal diurnal variation in tidal heights.

Question 35

When is there more water available at low tide and less water available at high tide? when is there more water available at high tide and less water available at low tide?

Answer 35

1. Neap Tides 2. Spring Tides Bowditch - Pg. 566

Question 36

What is a synodical month (lunar month)? How many days is it?

Answer 36

1. When the moon revolves around the earth with respect to the sun. 2. 29 1/2 days Bowditch - Pg. 568

Question 37

When the moon revolves around the earth with respect to the sun what does this mean?

Answer 37

The moon's revolution around the Earth with respect to the sun refers to its orbit, which affects the phases of the moon as it changes position relative to the Earth and the sun. ## Footnote This revolution takes approximately 29.5 days, leading to the lunar cycle that influences tides and various cultural calendars.

Question 38

This is 18.6 years and is the period of time it takes for the moon to do a complete cycle of the sun and the moon appearing at precisely the same relative positions in the sky.

Answer 38

Nodal Period Bowditch - Pg. 568

Question 39

What is the tidal day also known as? How long is it?

Answer 39

1. The lunar day 2. 24 hours 50 mins Bowditch - Pg. 568

Question 40

This is the interval between the moon’s meridian transit and a particular phase of tide which is fairly constant thought out the month?

Answer 40

Lunitidal interval Bowditch - Pg. 568

Question 41

True / False: Caution should be used in inferring the time of tide at a place from tidal data for nearby places.

Answer 41

True. The tide enters from sea and is usually sent upstream as a progressive wave so the tide occurs progressively later at various places upstream. Bowditch - Pg. 569

Question 42

True / False: Another name for the tidal datum is the vertical geodetic datum.

Answer 42

False Bowditch - Pg. 569 ## Footnote The vertical geodetic datum is a reference surface used for measuring elevations, while the tidal datum specifically refers to the average level of tides at a location.

Question 43

The most important level of reference when it comes to the tides is the __________ datum this is also known as the _________ plane to distinguish it from the vertical geodetic datum.

Answer 43

1. Sounding datum 2. Reference plane Bowditch - Pg. 569

Question 44

By international agreement the level used as chart datum should be low enough that ___________. A. The low waters never fall below them B. The low waters seldom fall below them C. The low waters may only fall 25% below them D. The low waters do not fall very far below them

Answer 44

D. The low waters do not fall very far below them Bowditch - Pg. 569

Question 45

At most places how do they determine the tidal datum.

Answer 45

It’s taken from the mean number of low waters (usually over 19 years) . Bowditch - Pg. 569

Question 46

This is the average height of all low waters at a given place. (Half of the low waters fall below it and half fall above it)

Answer 46

Mean Low Water (MLW) Bowditch - Pg. 569

Question 47

This is the average level of the low waters that occur at the times of spring tides.

Answer 47

Mean low water springs (MLWS) Bowditch - Pg. 569

Question 48

This is the average height of the lower low waters of each tidal day.

Answer 48

Mean lower low water (MLLW) Bowditch - Pg. 569

Question 49

This is the average height of the lower low waters (or of the single daily low waters if the tide becomes diurnal) that occur when the moon is near maximum declination and the diurnal effect is most pronounced.

Answer 49

Tropic lower low water (TeLLW) Bowditch - Pg. 569

Question 50

This tidal datum includes the spring effect of the semi-diurnal portion of the tide and the tropic effect of the diurnal portion of the tide and the tropic effect of the diurnal portion.

Answer 50

Indian spring low water (ISLW), Indian tide plan or harmonic tide plane. Bowditch - Pg. 569

Question 51

This is the average level of the lower of the two low waters on the days of spring tides.

Answer 51

Mean lower low water springs (MLLWS) Bowditch - Pg. 569

Question 52

This is the average height of monthly lowest low waters discarding any tides disturbed by storms.

Answer 52

Lowest Normal Low Water Bowditch - Pg. 569

Question 53

This is the an extremely low datum. It conforms generally to the lowest tide observed or even somewhat lower.

Answer 53

Lowest low water Bowditch - Pg. 569

Question 54

True / False: Heights of terrestrial features are usually referred on the nautical charts to a low water datum.

Answer 54

False. They are referred to as a high water datum. Bowditch - Pg. 570

Question 55

What Datum is generally used on charts of the United States, its territories and possessions for terrestrial features.

Answer 55

Mean High Water (MHW) Bowditch - Pg. 570

Question 56

What is the datum that is the average level of the high waters that occur at the times of spring tides.

Answer 56

Mean High Water Springs (MHWS) Bowditch - Pg. 571

Question 57

What is the tidal datum for terrestrial features that is the average height of the higher high waters of each tidal day.

Answer 57

Mean Higher High Water (MHHW) Bowditch - Pg. 571

Question 58

This is a datum used for terrestrial features that is the average height of the higher high waters (or the single daily high waters if the tide becomes diurnal) that occur when the moon is near maximum declination and the diurnal effect is most pronounced.

Answer 58

Tropic Higher High Water (TcHHW) Bowditch - Pg. 571

Question 59

What is all currents not due to the tidal movement.

Answer 59

Nontidal Current Bowditch - Pg. 571

Question 60

Tidal current offshore is rotary and flows continuously it is caused by the earths rotation in the Northern Hemisphere the current flows ____________ and in the Southern Hemisphere the current flows ___________.

Answer 60

1. Clockwise 2. Counter Clockwise Bowditch - Pg. 571

Question 61

A dipiction of rotary current direction by a series of arrows representing direction and speed of current at each hour is called a __________ .

Answer 61

Current Rose Bowditch - Pg. 571

Question 62

The tides at the two ends of a straight that connects two different tidal basins can experience this current which is generated largely by the continuously changing difference in height of water at the two ends. The speed of the current varies nearly as the square root of the difference in height.

Answer 62

Hydraulic current Bowditch - Pg. 572

Question 63

A currents direction is called ______ and the speed / velocity of the current is called ________.

Answer 63

1. Set 2. Drift Bowditch - Pg. 572

Question 64

In a purely semidiurnal current unaffected by no tidal flow the flood and ebb each last about ___ hrs ___ mins.

Answer 64

6 hrs 13 mins Bowditch - Pg. 572

Question 65

Tidal currents may be either ________, __________, or mixed.

Answer 65

1. Semidiurnal 2. Diurnal Bowditch - Pg. 572

Question 66

Along the Pacific Coast of the U.S. there are generally ____ flood (s) and ____ ebb (s) every day, but one of the floods or ebbs has a greater speed and longer duration than the other the inequality varying with the declination of the _______.

Answer 66

1. Two 2. Two 3. Moon Bowditch - Pg. 572

Question 67

True / False: The flood and ebb of the current always occur at the same time as the rise and fall of the tide.

Answer 67

False Bowditch - Pg. 572 ## Footnote The flood and ebb of the current can occur at different times than the rise and fall of the tide due to various factors such as local geography and tidal patterns.

Question 68

The stronger Spring currents occur near which of the below times. A. During Perigean tides B. During the times of the moon’s perigee C. During New and Full moon D. All of the above

Answer 68

D. All of the above Bowditch - Pg. 572 ## Footnote Spring currents are strongest during perigean tides, at the times of the moon’s perigee, and during the new and full moon phases due to the alignment of the Earth, moon, and sun.

Question 69

The weaker neap currents occur at which of the below times? A. During Apogean tides B. During Perigean Tides C. When the moon is at perigee D. All of the above

Answer 69

A. During Apogean tides Bowditch - Pg. 572

Question 70

This type of current happens with an increase diurnal speeds or with larger diurnal inequalities in speed? During what types of tides do they occur?

Answer 70

1. Tropic currents 2. Tropic Tides Bowditch - Pg. 572

Question 71

These types of currents have minimal diurnal effect what are they? What kind of tides do they generally happen with?

Answer 71

1. Equatorial currents 2. Equatorial tides Bowditch - Pg. 572

Question 72

True / False: When dealing with a non-tidal flow for what ever the reason (drainage, oceanic circulation, wind or other the speed of the current flowing in the direction of the nontidal current is equal to the magnitude of the nontidal current and the speed of the current flowing in the opposite direction is decreased by an equal amount.

Answer 72

True Bowditch - Pg. 573

Question 73

True / False: when dealing with a nontidal current in addition to a tidal current and teh nontidal current exceeds the magnitude of the reversing current the result is a constant flow of current in one direction.

Answer 73

True Bowditch - Pg. 573

Question 74

True / False: Where there is considerable diurnal inequality in tide or current or where the type of current differs from the type of tide, the relationship is not constant and it may be hazardous to try to predict the times of current from the times of tide.

Answer 74

True Bowditch - Pg. 573

Question 75

The belief that slacks occur at local high and low tides and maximum flood and ebb currents occur when the tide is rising or falling most rapidly is mostly true in what areas?

Answer 75

Seaward entrances and in the upper reaches of an inland waterway. It is not true in other parts of inland waterways. Bowditch - Pg. 574

Question 76

True / False: When an inland waterway is extensive or its entrance constricted the slacks in some parts of the waterway often occur midway between the times of high and low tide.

Answer 76

True Bowditch - Pg. 574

Question 77

True / False: The speed of the tidal current is consistent with the range of tide.

Answer 77

False Bowditch - Pg. 574 ## Footnote The speed of tidal currents can vary significantly depending on the geographical features and local conditions, and is not solely determined by the tidal range.

Question 78

In inland tidal estuaries the time of tidal current varies across the channel from shore to shore. On average where does the current change first?

Answer 78

Nearshore Bowditch - Pg. 574

Question 79

The speed of current often varies acrossed the channel when a river or channel is fairly straight where can the most current be found? When the river or channel is winding where can it be found? Where is the current the weakest on winding river or channel?

Answer 79

1. Mid channel or midstream 2. Near the concave shore (or outside corner of the curve). 3. Near the convex shore (or inside corner of the curve) Bowditch - Pg. 574

Question 80

True / False: In tidal rivers the subsurface current acting on the lower portion of the ships hull may be working the opposite direction to the surface current.

Answer 80

True. The Current can also be appreciable subsurface when the surface current is slack. Bowditch - Pg. 574

Question 81

In lower reaches of a tidal estuary where the density of water differs the flood current may start earlier here (subsurface or on the surface) than on the other area. (Subsurface or surface).

Answer 81

may start earlier on the subsurface. Bowditch - Pg. 574

Question 82

True / False: The difference in time of ebb from surface to bottom is normally small and subject to variation with time and location.

Answer 82

True Bowditch - Pg. 574

Question 83

The ebb speed usually ______ (decreases / increases / stays the same) gradually from top to bottom. The speed of the flood at strength often is _________ (stronger / weaker) at the subsurface depths than at the surface.

Answer 83

1. Decreases 2. Stronger Bowditch - Pg. 574

Question 84

True / False: Soundings shown on the largest scale charts are the vertical distances from the selected reference datum to the bottom.

Answer 84

True, this is the vertical geodetic datum Bowditch - Pg. 575 ## Footnote Soundings are measured from a reference datum, typically mean sea level, to the seabed, providing crucial information for navigation and safety.

Question 85

What is the vertical geodetic datum used on charts?

Answer 85

The vertical geodetic datum used on charts is the *Mean Sea Level (MSL)*. ## Footnote MSL serves as a reference point for measuring elevations and depths in nautical charts, ensuring consistency in navigation.

Question 86

When conditions vary greatly predictions for heights of tide may be considerably in error. When the atmospheric pressure is higher than normal or there is a persistent offshore wind height of tides may be ______________ (lower than / higher than) normal.

Answer 86

Lower than Bowditch - Pg. 575

Question 87

True / False: The greater the range in tide the less reliable the predictions for both height and current.

Answer 87

True Bowditch - Pg. 575

Question 88

How is the nature of the tide at any place best be determined? A. By tidal predictions in tide tables B. By the tidal data provided on nautical charts which are based upon detailed observations at specific locations C. By observation D. None of the above

Answer 88

C. By observation Bowditch - Pg. 575

Question 89

During periods of low atmospheric pressure the water level tends to be __________ (higher / lower) than normal.

Answer 89

higher than normal Bowditch - Pg. 575

Question 90

True / False: Where the range of tide is very small, the meteorological effect may sometimes be greater than the normal tide especially in shallow areas the wind has more of an effect on the water level.

Answer 90

True Bowditch - Pg. 575

Question 91

Counter currents and eddies may occur on either side of the main currents of a river or narrow passage and especially occur in what locations?

Answer 91

Locations with obstructions or in bights Bowditch - Pg. 576

Question 92

How can the mariner obtain locally the Mean High Water Lunitidal Interval? How can Low Water be found from this?

Answer 92

1 .The approximate time of high tide can be found by adding the lunicurrent interval to the time of transit of the moon. 2. Low water occurs at approximately 6 hr 12 min before and after high tide. Bowditch - Pg. 576

Question 93

What is the lunicurrent interval?

Answer 93

The interval between the time of the moon's transit over the meridian and the time of the corresponding high or low water. ## Footnote This interval varies based on the location and the phase of the moon, affecting tidal patterns.

Question 94

In the tidal data publication This Table is the table that provides information for finding the approximate height of the tide at any time between high water and low water.

Answer 94

Table 3 Bowditch - Pg. 576

Question 95

In the tidal data publication This Table is the table that contains a complete list of the predicted times and heights of the tide for each day of the year at a number of places designated as reference stations.

Answer 95

Table 1 Bowditch - Pg. 576

Question 96

In the tidal data publication This Table is a sunrise-sunset table at five day intervals for various latitudes from 76º N to 60º S.

Answer 96

Table 4 Bowditch - Pg. 576

Question 97

In the tidal data publication This Table is the table that provides an adjustment to convert the local mean time of Table 4 to zone or standard time.

Answer 97

Table 5 Bowditch - Pg. 576

Question 98

In the tidal data publication This Table is the table that gives tidal differences and ratios which can be used to modify the tidal information for the reference stations to make it applicable to a relatively large number of subordinate stations.

Answer 98

Table 2 Bowditch - Pg. 576

Question 99

How is the time difference applied to the reference stations to find the time of the corresponding tide at the subordinate station in the publications for predicting tides?

Answer 99

The interval is added (+ sign) or subtracted (- sign) to the reference station for the corresponding day and time. Bowditch - Pg. 577

Question 100

What zone time are the results in after applying the subordinate station correction to the reference station in the publications for predicting tide?

Answer 100

The zone time of the meridian shown directly above the difference for the subordinate station. Bowditch - Pg. 577

Question 101

How are height differences in the tides determined from the reference station in the Publications for predicting tides? A. Height differences listed in the subordinate stations are added or subtracted from the height given at the reference station. B. Using ratios given in the subordinate station section multiply the height at the reference station by the ratio to find the height at the subordinate station C. A ratio and height correction is given at the subordinate station multiply the ratio by the reference station and then add / subtract the difference height correction to find the height at the subordinate station D. All of the above

Answer 101

D. All of the above Bowditch - Pg. 577

Question 102

See below reference picture for showing clearance required to clear Obstruction at a particular tide.

Answer 102

Bowditch - Pg. 578

Question 103

In the Publications for Tidal Current Tables this table gives duration of slack, or the number of minutes the current does not exceed stated amounts for various maximum velocities.

Answer 103

Table 4 Bowditch - Pg. 578

Question 104

In the Publications for Tidal Current Tables this table gives differences, ratios and other information related to a relatively large number of subordinate stations.

Answer 104

Table 2 Bowditch - Pg. 578

Question 105

In the Publications for Tidal Current Tables this table contains a complete list of predicted times of maximum currents and slack water, with the velocity of the maximum currents for a number of reference stations.

Answer 105

Table 1 Bowditch - Pg. 578

Question 106

In the Publications for Tidal Current Tables this table provides information to determine the current’s velocity at any time between entries in Table 1 and Table 2.

Answer 106

Table 3 Bowditch - Pg. 578

Question 107

In the Publications for Tidal Current Tables this table gives information on rotary tidal currents.

Answer 107

Table 5 Bowditch - Pg. 578

Question 108

What order are the stations listed in for Table 2?

Answer 108

Geographic Order Bowditch - Pg. 578

Question 109

What kind of type is the reference stations listed in?

Answer 109

Bold type Bowditch - Pg. 578

Question 110

In the Tidal Current Prediction Tables how are times of subordinate stations for slack and max current found from Table 2? Does this provide the correct time for the subordinate station?

Answer 110

1. The times for slack water and max current are added or subtracted based on their signs to the times provided in Table 1 for the Reference Station. 2. The correction time includes the time difference between the reference station and subordinate station so this is the accurate time. Bowditch - Pg. 578

Question 111

In the Tidal Current Prediction Tables how is the correct velocity of current for max current found for the Subordinate Station from the information in Table 2.

Answer 111

The speed of the current is the product of the velocity at the reference station and the ratio provided for the Subordinate Station. Bowditch - Pg. 579

Question 112

How are the maximum and minimum velocities of currents found in the Tidal Current Prediction Tables in Table 2? How is direction found?

Answer 112

1. Minimum and Maximum velocities before flood and ebb are listed for each station 2. True Directions are listed as well Bowditch - Pg. 579

Question 113

What speed of current does slack water list in the Tidal Current Prediction Tables?

Answer 113

The instant of zero velocity Bowditch - Pg. 579

Question 114

In the current diagrams what does an intersection of any vertical line with any horizontal line represent?

Answer 114

Represents a given moment in the current cycle at a given place in the channel Bowditch - Pg. 580

Question 115

In the Current Diagrams what is the shaded area mean and what does the unshaded area mean?

Answer 115

Shaded represents flooding Unshaded represents ebbing Bowditch - Pg. 580

Question 116

What are the two reasons to use the current diagrams?

Answer 116

1. To find the favorable times to pass through the channel 2. To find the average current to be expected during a passage though the channel Bowditch - Pg. 580

Question 117

What can be used to find the current expected to be encountered in a transit using the Current Diagram for that area?

Answer 117

Use a velocity line set for ship speed starting at the correct time and location. Bowditch - Pg. 580

Question 118

In the Current Diagrams what is the current velocity values given? How can an accurate current velocity be achieved?

Answer 118

1. The values are averages 2. To find an accurate velocity use the ratio provided from the subordinate station and multiply it times the value found on the diagram. Bowditch - Pg. 580