Tides

Question 1

What causes the tides

Answer 1

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

Question 2

what causes neap tides

Answer 2

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

Question 3

what causes spring tides

Answer 3

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

Question 4

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

Answer 4

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.

Question 5

What is a spring tide

Answer 5

a larger tide than average

Question 6

what is a neap tide

Answer 6

a smaller tide than average

Question 7

How is mean sea level defined

Answer 7

the average hight of the ocean taken over 20 years

Question 8

what does MHWS stand for

Answer 8

mean high water springs

Question 9

what does MLWS stand for

Answer 9

mean low water springs

Question 10

what does MHWN stand for

Answer 10

Mean high water neaps

Question 11

what does MLWN stand for

Answer 11

Mean low water neaps

Question 12

what does HAT stand for

Answer 12

highest astronomical tide

Question 13

what does LAT stand for

Answer 13

Lowest astronomical tide

Question 14

What is a tides range

Answer 14

the total difrence between Low water and High water

Question 15

What are virtical cleareces given as

Answer 15

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

Question 16

what is chart datum

Answer 16

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

Question 17

what is the hight of tide

Answer 17

the level of the tide mesured from chart datum

Question 18

what is the rise of tide

Answer 18

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

Question 19

what is the fall of tide

Answer 19

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

Question 20

what are charted objects eg lighthouses hight measured from

Answer 20

mhws

Question 21

What limit do depth sounders have

Answer 21

100m

Question 22

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

Answer 22

obtaining a position fix

Question 23

how should you calibrate the depth sounder

Answer 23

doing a manual check with a weight and a line

Question 24

what positions could the depth sounder be reading from

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

you know exactly how much water before you run aground.

Question 27

how do you calculate the depth of water using the tide

Answer 27

total depth = charted depth plus hight of tide

Question 28

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

Answer 28

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

Question 29

Where can you find average tidal heights for areas

Answer 29

on the chart information

Question 30

What are the standard columns in an average tide table

Answer 30

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

Question 31

what is a tide table

Answer 31

a sheet displaying the tidal heights for every day

Question 32

why are there not always 2 hw and lw a day

Answer 32

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

Question 33

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

Answer 33

time zone and DST to allow for time conversions

Question 34

What time are tide tables normaly given in

Answer 34

the local timezone

Question 35

where do you find infomation on a tide tables time zone

Answer 35

in the top left corner

Question 36

what are tidal gages and what are they used for

Answer 36

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

Question 37

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

Answer 37

Location, Year and Timezone information

Question 38

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

Answer 38

nothing, they are in gmt already

Question 39

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

Answer 39

add one hour to convert to BST to allow for DST

Question 40

what does U.T. Stand for

Answer 40

universal time

Question 41

what does DST stand for

Answer 41

daylight savings time

Question 42

what does GMT stand for

Answer 42

grenwich mean time

Question 43

what does BST stand for

Answer 43

British summer time

Question 44

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

Answer 44

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

Question 45

what's the formula for tidal range

Answer 45

High water - low water = range

Question 46

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

Answer 46

13.52 dst, 4.1m

Question 47

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

Answer 47

6:04 UT 3.7m

Question 48

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

Answer 48

neaps 2.4m

Question 49

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

Answer 49

springs 4.9m

Question 50

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

Answer 50

3.6m, mid-range

Question 51

what is a tidal curve used for

Answer 51

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

Question 52

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

Answer 52

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

Question 53

what does the blue dashed line on a tidal curve represent

Answer 53

the tidal change during a neap tide

Question 54

what does the red line on the tidal curve represent

Answer 54

a spring range tide

Question 55

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

Answer 55

to find out if it is a spring or neap tide

Question 56

where do the tides hights get added to the graph

Answer 56

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

Question 57

describe the process of using a tidal curve

Answer 57

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.

Question 58

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?

Answer 58

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

Question 59

why is using the tidal curve important when anchoring?

Answer 59

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

Question 60

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

Answer 60

1.4m

Question 61

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

Answer 61

3m

Question 62

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?

Answer 62

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

Question 63

What is a secondary port

Answer 63

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

Question 64

how are tides calculated in a secondary port

Answer 64

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

Question 65

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

Answer 65

in an x shape

Question 66

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

Answer 66

halfway between the two corection values