Chartwork (Fixing Position) Flashcards

1
Q

Range of light from Vertical sextant angle

A

Height of light (from Chart or ALLFS)

Height of light/Tan x (VSA)
Bring to Nm by dividing the result by 1852

1852m is equal to 1NM

OR we use the Range by VSA table in Norries

Range and the Bearing gives you the Fix

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2
Q

What allowances may we have to make for a VSA?

A

Tide: When accounting for tide, add the tidal difference between MHWS and the current state of tide

Index Error on the Sextant

Correction for the HOE (Norries assumes the HOE is 11m) here we make a correction for DIP

ALLFS has a height of the OBJECT, Chart has a height at the centre of the LENS

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3
Q

Horizontal Sextant Angle Pro Forma Method 1: station pointer
(Can be with a compass)
Can be used on the chart with a station pointer

A

Method 1
1. Measure angle from Point A to Point B
2. Measure angle from Point B to Point C
3. Use a station pointer to get your position
When the three limbs line up with the points, put a dot in the middle of the station pointer.

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4
Q

Beam Bearing

A

090 Degrees from Course Steered
Port side of vessel, CoSt - 090
Stbd side of vessel, CoSt + 090

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5
Q

Gyro High

A

Take off to get to T

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6
Q

Gyro Low

A

Add to get to T

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7
Q

Running fix Pro Forma

A
  1. Plot initial LOP
  2. Plot an EP anywhere in safe water on that EP, Time Stamp
  3. Lay off water track for given time interval >
  4. Lay off tidal vector for same time interval&raquo_space;>
  5. Transfer initial LOP through your second EP at the END of the tidal vector
  6. Lay off second bearing off second object, pass it through transferred LOP
  7. This is your FIX

GROUND track length and course is EP to EP
Transfer GT through Fix back to initial LOP to find Initial EP&raquo_space;

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8
Q

Tide experienced Pro Forma

A
  1. Plot initial Fix
  2. Plot water track for given time interval >
  3. Plot second given position Fix
  4. Join W/T to second position Fix&raquo_space;>
  5. Lay off G/T between two points&raquo_space;
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9
Q

Plot a CTS pro forma

A
  1. Plot initial position
  2. Plot end position
  3. Join two positions, this is your GT, COG, CMG&raquo_space;
  4. Lay off Tidal vector from initial position&raquo_space;>
  5. Arc off boat speed for given time interval (WT) >
  6. Add counteraction for Leeway to this track (Off chart) this is your CTS
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10
Q

Plot an EP Pro Forma

A
  1. All calculations first
  2. Plot position
  3. Lay off W/T for given time interval, taking into account the effects of LEEWAY >
  4. Lay off tidal vector for same interval&raquo_space;>
  5. Plot EP with time
  6. Join initial position fix to EP, to give CMG, COG&raquo_space;
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11
Q

Admiralty publications that can be used for passage planning

A

Chart catalogue
Navigational charts
Sailing directions/ pilot books
ALRS
List of lights and fog signals
Tide Tables
Ocean passages for the world
Routeing charts

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12
Q

10 Items of useful information found in Admiralty publications for passage planning

A

VTS stations to call
Radio Information required in report
requirements for pilots
details of navigation lights
Height of tide for port entry
Recommended routes
Radar conspicuous objects for position fixing
Predominant wind for ocean crossing
Port facilities
Location of pilot boarding stations

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13
Q

Sections in the Weekly edition of the Admiralty Notice to Mariners

A

I explanatory notes. Publications list (charts affected this week)
II Updates to Standard Nautical Charts
III Reprints of NAVAREA I Navigational Warnings
IV Updates to ADMIRALTY sailing directions
V Updates to ADMIRALTY list of Lights and Fog Signals
VI Updates to ALRS
VII Updates to miscellaneous ADMIRALTY nautical publications
VIII Updates to ADMIRALTY digital services

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14
Q

Procedure for checking a chart is up to date once receiving the weekly notices

A
  1. Obtain weekly NM from an approved provider
  2. Use section I to update our chart outfit (ensure correct charts on board)
  3. Use section II to see which charts are affected
  4. Gather Equipment for correcting
  5. Np5011 Np 133A Np294
  6. Check bottom left for corrections applied until now
  7. Apply correction
  8. Place correction number at the bottom of the chart
  9. Record this in the chart correction log
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15
Q

Ways of Fixing your position:

A

Primary fix, GPS
Cross checked by:
3 point fix
Radar Range and Bearing
3 Radar Ranges
VSA
Horizontal Sextant Angle
Dipping/Raising Height
Bearing of conspicuous object with a depth contour
Running Fix

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16
Q

How often do we fix our position?

A

Often enough that the ship will not get into danger between fixes. This is heavily depended on the speed of the vessel, SAFE SPEED (rule 6)

17
Q

How do we check our Echo Sounder?

A

Throw a lead line over the side, in line with the transducer.

18
Q

How do we do a dipping height?

A
  1. Find height of object in List of Lights or from Chart
  2. Take bearing of light
    Formula = 2.08 × (√Elevation + √Eye height)
    Or Distance of the sea horizon table in Norries
    Answer to this gives you a range
  3. Bearing + range gives you a fix
19
Q

What is a PI

A

Parallel Index, a way of continuously monitoring a ships cross track tendencies, in relation to a pre determined passage plan

20
Q

What can a PI also do?

A

Back up or confirm a GPS position, NOT A FIX

21
Q

Define Tides:

A

Periodic vertical movements of the water on the Earths Surface
Caused by the gravitational pull by the Sun and the Moon

22
Q

Define Tidal Streams

A

Periodic movements of the water that result from the tides

23
Q

Define Height of the Tide:

A

Vertical distance at any moment between Chart Datum and the current water level

24
Q

Define Tidal Range:

A

Difference between the High and Low Tide

25
Q

Define Spring Tides:

A

Higher highs and lower Lows, Greater range
Full moon and the New moon phase

26
Q

Define Spring Tides

A

Lower highs and higher lows, Less range

1st quarter and the 3rd quarter phase of the sun and moon