Positon fixing

Question 1

What is a ships log

Answer 1

any device used for measuring speed through the water and distance travelled

Question 2

What is a logbook

Answer 2

A document documenting the passage of a vessel

Question 3

what information would you find in a log

Answer 3

Time, course, the distance the ship has travelled, depth of water, wind speed and direction, barometer and remarks

Question 4

When on a transit, what 2 options does the skipper have for obtaining a position fix

Answer 4

taking a bearing off the side of the vessel and plotting where that lines up with the transit, or taking the depth, accounting for the height of the tide, and then plotting where the transit crosses a contour.

Question 5

when taking a 3 point fix how far apart should the objects used be

Answer 5

at least 90 degrees

Question 6

which bearings should be taken first when making a 3 point fix

Answer 6

the ones off the bow or stern as they will change the least

Question 7

when noting a fix in the logbook what else should be added

Answer 7

time, boat speed, distance travelled and the course being steered

Question 8

when a 3 point bearing produces a triangle what is this called

Answer 8

a cocked hat

Question 9

when working with a cocked hat, what should you take as the actual position fix from a 3 bearing fix

Answer 9

the centre, unless any dangers are nearby, in which case you should take the part of the triangle closest to the danger as this the worst-case scenario

Question 10

what are the 4 steps to creating a 3 bearing fix

Answer 10

First choose 3 things you can see both outsides and on the chart. these should have a spread of at least 90 degrees. Take bearings from each of them and note them down. Then convert the magnetic bearings to true bearings and plot them on the chart. Lastly, take note of the produced fix and error size and add it to the logbook.

Question 11

When using a hand compass to measure the bearing of an object which way is the bearing pointing

Answer 11

towards the boat

Question 12

when using a GPS to get a bearing, which way is the bearing facing

Answer 12

away from the boat

Question 13

How can you use the compass rose and GPS to obtain a fix?

Answer 13

by setting the centre of a compass rose as a waypoint in the GPS, you can then get range and bearing to that waypoint, allowing you to draw a line from the centre of the compass rose out the range distance and obtain a fix. note that you have to flip the bearing 180 from a gps

Question 14

what is dead reckoning

Answer 14

The position estimated by taking course steered and the log, not taking account of the tide

Question 15

what does dead reckoning not take into account

Answer 15

tidal currents or leeway

Question 16

how do you convert a dead reckoning to an estimated position

Answer 16

you add the tidal speed and set for that period, giving you an estimated position

Question 17

how can you use an estimated position to get speed over ground

Answer 17

take the distance of the ground track, and divide it by the number of hours the estimated position covers

Question 18

how many arrows mark the true course when marking the estimated position

Answer 18

1

Question 19

how many arrows mark the ground track when marking the estimated position

Answer 19

2

Question 20

how many arrows mark the tidal vector when marking the estimated position

Answer 20

3

Question 21

when does a circle of error apply to an estimated position

Answer 21

when in fog or no other way to work out the accuracy of the estimated position

Question 22

when creating a circle of error, what size should it be

Answer 22

10 per cent of the total journey up to that point

Question 23

when first installing a depth gauge, how should it be checked

Answer 23

by comparing it to a reading from a leadline

Question 24

what are good ways to help check the estimated position

Answer 24

depth contours, bearing fixes and gps

Question 25

if sailing for 2 hours how do you account for the tide when calculating the estimated position

Answer 25

draw the two tidal vectors tip to tip and use that as one large tidal vector

Question 26

if sailing for less than an hour how do you take account of the tide when working out the estimated position

Answer 26

divide the tidal set by the fraction of an hour sailed

Question 27

what is a projected estimated position?

Answer 27

a projected estimated position is an estimated position drawn up using anticipated speed and course steered, to work out the course over ground and final position