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Skipper > Tides / Tidal Streams > Flashcards

Tides / Tidal Streams Flashcards

1
Q

New moon to 1st quarter

A

waxing crescent

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2
Q

springs occur how many days after a full and new moon?

A

2 days

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3
Q

full moon to last quarter

A

waning gibbous

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4
Q

If we can see the moon and stars, is it likely to be high or low pressure?

A

high pressure

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5
Q

what symbol is used in the almanac for a new moon?

A

black filled circle under the date and day of week

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6
Q

last quarter to new moon

A

waning cresent

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7
Q

What is the tide called when you are going from a high to low tide?

A

ebb tide

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8
Q

What are Spring tides?

A

The highest high tides and lowest low tides.

Occurs twice in the orbits of the moon and earth when the moon is between the earth and the sun (new moon) and when the earth is between the moon and sun (full moon).

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9
Q

On average, how many minutes later do tides get each day?

A

50 min

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10
Q

Tidal Diamond table on chart

A

HW -6 thru HW +6
Set in degrees true
Spring tide
Neap tide

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11
Q

If we have low pressure on the south coast of England, what kind of wind is likely and which direction will it come from?

A

Southwesterly wind

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12
Q

What are Neap tides?

A

Lowest high tide and highest low tide.

Occur twice when the moon is at a right angle to the earth and sun. These are the lowest tides.

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13
Q

If it’s overcast or raining, is it likely to be high or low pressure?

A

low pressure

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14
Q

A waning moon has what shape?

A

Letter ‘C’

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15
Q

What do you call a place that has two high tides during a 24 hour period?

A

Semi-diurnal

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16
Q

How do you find the range of the tide?

A

Subtract the low tide from the high tide

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17
Q

A waxing moon has what shape?

A

Letter ‘D’

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18
Q

How to know which tidal curve to use

A

Determine range
HW - LW

Compare this to the Mean HW Springs and Neaps on the tidal curve to determine which you are closest to.

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19
Q

Full moon to new moon

A

waning (reducing)

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20
Q

What do you do if the tidal range is significantly larger or smaller than Springs/Neaps Mean?

A

Range calculated by you / MHWS or MHWN
and then multiply this by the tide you calculated using the tidal curve.

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21
Q

Tidal Stream Atlas

A

Tidal set is indicated by arrows. You can use your chart plotter to figure out the degrees. Align plotter with the arrow closest to where you want.

1st two numbers are for Neaps

2nd 2 numbers are Spring rate

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22
Q

what symbol is used in the almanac for a full moon?

A

unfilled circle under the date and day of week

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23
Q

1st quarter to full moon

A

waxing gibbous

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24
Q

What do you call a place that has only one high tide during a 24 hour period?

A

Diurnal

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25
Q

How long is a lunar month?

A

29.5 days

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26
Q

New moon to full moon

A

Waxing (growing)

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27
Q

For Dayskipper exam, which tides will you have to calculate?

A

Springs, Neaps, or Midway between

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28
Q

What is the tide called when you are going from a low to high tide?

A

flood tide

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29
Q

If we have high pressure on the south coast of England, what kind of wind is likely and which direction will it come from?

A

Light northerly winds

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30
Q

What causes the tides

A

The combined graviational pull of the sun and the moon as the earth rotates on its axis

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31
Q

what causes neap tides

A

for the graviational pull of the sun and moon to be offset by 90 degrees

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32
Q

what causes spring tides

A

for the sun and moon to be in line and pull together

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33
Q

Why is there a tide on the opsiste side of the planet from the moon

A

As the Moon circles the Earth it not only pulls the sea towards it but the land and the Earth itself. It also pulls the centre of gravity of the Earth towards it.

This results in a slightly reduced gravity on the opposite side of the Earth allowing centrifugal force to pull more on the sea causing a second tide.

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34
Q

What is a spring tide

A

a larger tide than average

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35
Q

what is a neap tide

A

a smaller tide than average

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36
Q

How is mean sea level defined

A

the average hight of the ocean taken over 20 years

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37
Q

what does MHWS stand for

A

mean high water springs

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38
Q

what does MLWS stand for

A

mean low water springs

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39
Q

what does MHWN stand for

A

Mean high water neaps

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40
Q

what does MLWN stand for

A

Mean low water neaps

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41
Q

what does HAT stand for

A

highest astronomical tide

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42
Q

what does LAT stand for

A

Lowest astronomical tide

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43
Q

What is a tides range

A

the total difrence between Low water and High water

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44
Q

What are virtical cleareces given as

A

will normaly be given from HAT but not always so check the chart information

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45
Q

what is chart datum

A

the 0 depth of the chart, from where the tide is measured from

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46
Q

what is the hight of tide

A

the level of the tide mesured from chart datum

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47
Q

what is the rise of tide

A

the increase between the previous low water and the next high water

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48
Q

what is the fall of tide

A

the decrease in level between the previous highwater to the next low water

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49
Q

what are charted objects eg lighthouses hight measured from

A

mhws

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50
Q

What limit do depth sounders have

A

100m

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51
Q

as well as checking depth what can depth sounders be used for

A

obtaining a position fix

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52
Q

how should you calibrate the depth sounder

A

doing a manual check with a weight and a line

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53
Q

what positions could the depth sounder be reading from

A

The waterline, the bottom of the keel, or the transducer location

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54
Q

what are the advantages to setting your depth sounder to read from the water line

A

it allows you to use the depth to easily obtain a position fix

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55
Q

what are the advantages of setting your depth sounder to read from the bottom of the keel

A

you know exactly how much water before you run aground.

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56
Q

how do you calculate the depth of water using the tide

A

total depth = charted depth plus hight of tide

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57
Q

when a depth is written with an underline what does it mean

A

that it is a drying hight, and it is the hight above chart datum the land is.

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58
Q

Where can you find average tidal heights for areas

A

on the chart information

59
Q

What are the standard columns in an average tide table

A

place, lat, long, HAT, Mhws, Mhwn, Mlwn, mlws

60
Q

what is a tide table

A

a sheet displaying the tidal heights for every day

61
Q

why are there not always 2 hw and lw a day

A

as the tides advance, sometimes one occurs early in the morning of the next day

62
Q

what do you somtimes have to take into account reading tide tables

A

time zone and DST to allow for time conversions

63
Q

What time are tide tables normaly given in

A

the local timezone

64
Q

where do you find infomation on a tide tables time zone

A

in the top left corner

65
Q

what are tidal gages and what are they used for

A

they are found at harbour entrances and other depth-sensitive areas. they are basically large meter sticks that show the real hight of the water

66
Q

What are 3 things found at the top of a tide table

A

Location, Year and Timezone information

67
Q

What do you need to do to times in the shaded areas of a tide table

A

nothing, they are in gmt already

68
Q

what do you need to do to times in the non-shaded area of the tide table

A

add one hour to convert to BST to allow for DST

69
Q

what does U.T. Stand for

A

universal time

70
Q

what does DST stand for

A

daylight savings time

71
Q

what does GMT stand for

A

grenwich mean time

72
Q

what does BST stand for

A

British summer time

73
Q

What information is listed on a tided table for a given day

A

the date, the day of the week, all hight and low tides, and colouration marking it as a neap or a spring or inbetween

74
Q

what’s the formula for tidal range

A

High water - low water = range

75
Q

what time and hight is the hight tide in the afternoon on Thursday the 27th of June at Dunbarton

A

13.52 dst, 4.1m

76
Q

what is the time and hight of high water at Dunbarton in the morning of the 6th of Feb

A

6:04 UT 3.7m

77
Q

what is the range of tide at victoria? is it springs neaps or mid-range? During the morning/early afternoon of Saturday the 6th of April

A

neaps 2.4m

78
Q

what is the range of tide at victoria? is it springs neaps or mid-range? During the afternoon of Thursday the 3rd of January

A

springs 4.9m

79
Q

what is the range of tide at victoria? is it springs neaps or mid-range? During the afternoon of Monday the 18th of February

A

3.6m, mid-range

80
Q

what is a tidal curve used for

A

working out hight of the tide at a time between high and low water

81
Q

what goes in the row of boxes at the base of a tidal curve

A

the high water time in DST and then the times hours before and after up to the low water before and after the high in question

82
Q

what does the blue dashed line on a tidal curve represent

A

the tidal change during a neap tide

83
Q

what does the red line on the tidal curve represent

A

a spring range tide

84
Q

why should you work out the range of the tide in question before using it on a tidal curve

A

to find out if it is a spring or neap tide

85
Q

where do the tides hights get added to the graph

A

at the scales at the top and bottom on the left side of the graph

86
Q

describe the process of using a tidal curve

A

first, find the tide information for the nearest standard port, and look up the day’s tides in it. Then find the high water time and hight closest to when you are sailing. Next, convert the tide time into DST if necessary and write it in the high water tide time in the bottom of the chart. Next populate the time boxes 1 hour forwards and back of high water time all the way to low water on either side of high water. Next, add the high water and low water heights to the scale bars on the top and bottom of the left section of the tidal curve. Join these up to form the tidal hight line. Now to work out the tidal hight, draw a line vertically up the chart till it intersects the tidal curve. here turn 90 degrees and draw along the chart until the line hits the tidal hight line drawn earlier. lastly, turn 90 degrees upwards until the line reaches the scale bar at the top of the chart. the hight of the tide at the time can then be read off the scale.

87
Q

a skipper anchoring in port Fraser at 1030 wishes to know the hight of the tide when the high tide is 4.2m at 1230DST and the lows are both 0.4m. What is the height of the tide at this time? If the vessel has a draught of 1.2m and the skipper wants a clearance of 1m, what is the minimum depth of water to anchor in at 10:30?

A

the hight of the tide at 10:30 is 3.1m, the minimum depth of water is4.9m

88
Q

why is using the tidal curve important when anchoring?

A

it allows the skipper to calculate the rise in tide from the current depth, allowing it to be added on the reading from the depth sounder, and finding the maximum amount of water and thus chain needed for the precise location

89
Q

What is the height of tide 4 hours after HW in the afternoon of Tuesday 29th January at Namley Harbour?

A

1.4m

90
Q

What is the height of tide 2 hours before HW in the evening of Sunday 9th of June at Port Fraser?

A

3m

91
Q

On Sunday 25th August at Victoria.
7a) What is the time and height of daytime HW and the height of the following LW?
7b) What will be the height of tide at 1545 DST?

A

daytime hight is at 12.45 dst with hight 5.2m
evening low is at 18:45 with a hight of `1.1m
the hight of tide at 15:45 Dst will be 3.1m

92
Q

What is a secondary port

A

a secondary port is a port without a set tidal curve and tide table

93
Q

how are tides calculated in a secondary port

A

by converting from the curve and tide tables for the nearest standard port

94
Q

what direction around the times to the corections move for a secondary port table

A

in an x shape

95
Q

if the tide time is halfway between the tide times on the secondary port correction table what is the difrence

A

halfway between the two corection values

96
Q

What are tides caused by?

A

Gravitational effects of the Earth, moon and the sun

97
Q

Which has a greater effect on tides? The moon or the sun?

A

The moon

98
Q

How many high tides and how many low tides do most places have per day?

A

Most places have two high tides and two low tides per day

99
Q

When do Spring Tides form?

A

When the sun and the moon are aligned

100
Q

When do Neap tides form?

A

When the sun and the moon are not aligned

101
Q

How long does it take for the moon to circle the Earth?

A

27.5 days

102
Q

True or False?
Charts are drawn showing tide level at Chart Datum (CD)

A

True

103
Q

What are depths measured from?

A

Chart Datum (CD)
A chart datum isthe water level surface serving as origin of depths displayed on a nautical chart. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. Common chart datums are lowest astronomical tide (LAT) and mean lower low water (MLLW).

104
Q

What are clearance heights measured from?

A

Highest Astronomical Tides (HAT)

105
Q

What does MHWS stand for?

A

Mean High Water Springs

106
Q

What does MHWN stand for?

A

Mean High Water Neaps

107
Q

What does MLWN stand for?

A

Mean Low Water Neaps

108
Q

What does MLWS stand for?

A

Mean Low Water Springs

109
Q

What are secondary ports?

A

Ports that don’t have very much commercial traffic

110
Q

How often do Spring Tides occur?

A

Every two weeks

111
Q

what is a tidal stream

A

a flow or current of water caused by the tide

112
Q

why does a skipper need the tidal stream to work out an estimated position

A

the current carries the boat with it, causing it to move difrently than on a flat body of water so it needs to be accounted for

113
Q

what 3 things impact the strenght and direction of a tidal stream

A

the location of the vessel, Weather the tide is neaps, springs or midrange, and the time relitive to high water at the refrence port

114
Q

Why do you not want to sail against the tidal stream

A

it will subtract from your speed, causing the voyage to take longer

115
Q

Why do youw ant to sail with the tidal stream

A

it adds tot he vessesl speed, causing the boat to move faster

116
Q

What is the COG

A

Course over ground

117
Q

if a vessel is sailing at 4 knots, and the tide is flowing with the vessel at 4 knots, what is the Sog

A

8 knots

118
Q

if a vessel is sailing at 4 knots and the tide is flowing against the vessel at 4 knots, what is the sog

A

0 knots

119
Q

if the Sog is 0, will the log read 0 if sailing into an aposing current

A

no, as it mesures the speed through the water

120
Q

What is a tidal diamond

A

a mark on a chart that links with a table on the chart to give tidal stream information

121
Q

When using a tidal stream table, where is the refrence port listed

A

at the top of the table

122
Q

Which timeframe does each entry on the tidal stream table refrer to

A

half an hour either side of the time relitive to high water

123
Q

what 3 bits of information are listed in the tidal stream table for a given time and location

A

the tidal set (bearing) and two tidal drift mesurments, one for spring tides which is first and one for neap tides which is second

124
Q

how do you know if it is a neap or spring tide when using the tidal stream table

A

Using the tide table for the reference port, work out the range for the tide, and compare it to the tidal neaps and spring ranges located on the tidal curves to see which it is closer to

125
Q

what is a tidal laddar

A

a way of writing out times to work out which highwater hour to use for a given period at sea

126
Q

What are the steps for constructing a tidal lader

A

work out the closest time of high water to when you are sailing. Convert to BST if nessacary. Then work out half an hour backwards and forwards from the high tide, this is the first time range. Then subtract an hour from this to get hw -1 hour, and repeat to get hw -2 through 6, then add 1 hour to get hw+1 and repeat to get hw +2 through 6, then take the time period which suits the time being sailed

127
Q

What is a tidal stream atlas

A

its a chart of the area sailed with lines added on representing tidal streams

128
Q

why should an atlas be used instead of an atlas

A

there are many more measurements, leading to a more accurate plan to be made

129
Q

when a tidal stream is written as 02.12 what is the neap and spring tidal drift

A

neaps = 0.2 knots
springs = 1.2 knots

130
Q

if an arrow on a tidal stream atlas is curved, how do you get the tidal set

A

take it from the tif of the arrow to the base of the arrow to get the average of the angle

131
Q

Where can you find data on Tidal Streams?

A

Nautical Almanacs, Pilot books and Tidal Atlasses

132
Q

What is direction known as?

A

SET

133
Q

What is rate known as?

A

DRIFT

134
Q

Name one thing which can affect tides?

A

Weather
Storm Surges
High or Low pressure

135
Q

Where can you find the direction of the tide on the Tidal Diamonds table?

A

Next to the time column and at the left of each diamond

136
Q

Where can you find the rate of the tide on the Tidal Diamonds table?

A

The column next to the direction column. There are two numbers, the first is the Spring rate and the second smaller number is the Neap rate

137
Q

True or False?
The ‘tidal hour’ begins from half hour before the time stated and ends half hour after

A

True

138
Q

How can you find the direction of the tide (SET) using a Tidal Atlas?

A

Measure the arrows uses a plotter or protractor

139
Q

What do thicker arrows mean in Tidal Atlases?

A

The tide is stronger

140
Q

What does slack mean?

A

Not moving

141
Q

How do you find the rates in a Tidal Atlas?

A

Two numbers separated by a decimal point, the first smaller number is Neaps and the second is Springs

142
Q

What do you use for Computation of Rates?

A

A Computation of Rates graph

143
Q

What is the first step for course to steer?

A

Draw a line from A through B and beyond

144
Q

True or False?
Course to Steer may cut AB before or after B

A

True

Skipper (22 decks)

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