General Bridge / Nav Flashcards
**What is variation?
&
What is Deviation?**
Variation:
- The angular difference between true and Magentic North
- Geographical Location - Nothing to do with the vessel itself
Deviation:
- The differerence between Magentic North and Ships Compass North for a given ships heading
- Calcuation is only on the course steered and nothing to do with the bear of an object
What Causes Deviation?
Hard Iron - Permanent Magentism
- Ships construction
- Corrected by athwartship and horizontal magents fore and aft and also vertical magenets, healing bucket
Soft Iron - Induced Magentism
- Ships instructments, electro magnetic equipment, Cargo
- Correced by Flinders Bar and Kevlins Balls, which are made of Soft Iron. They get induced with an equal and opposite effects of what is happening to the Magnetic compass and corrects it.
How often should a magnetic compass be swung or checked?
- After being laid up after a long period of time i.e. dry dock
- On installation
- Any major trauma to the ship - Fire, Collision or Grounding
- Or if the Deviation card is inaccurate
- Period not exceeding two years
Magnetic Compass Information
- SOLAS requires you to keep a fully corrected magnetic compass. It doesn’t say how often it should be corrected though
- Compass Error book that shows that the deviation card is correct, means that it need not be swung or adjusted
- In Heavy seas / hitting bigs waves, if the MC is not accurate any more - Likely cause is that the magnets have been dislodged. On the reverse side of the deviation card should be the location of the magenets. Compass should then be corrected at the next available opportunity.
- If wake is not in a straight line when steering on autopilot, Could be caused by a wondering gyro. Change autopilot to steering by magentic compass and correct for variation / deviation. Service Gyro and next available opportunity. ( A wondering gyro will see the heading move and then come back as the unit attempts to correct itself. Usually casused by bearings wearing out) Average Gyro life is 5 years.
Define Nominal Range, Geographical Range, Luminous Range
Nominal Range = The range of visibilty in 10nm
Geographical Range = The physical range at which you can see an object due to the height of the object and your height of eye
Luminous Range = The power of the light
Where can you find details of:
Lights?
Reporting Points?
Chart symbols?
Admiralty List of Lights:
- Go into the back of the book and look up the name
- It will give you a number
- Go into the front of the book with the number
- Details will be great than what can be printed on the chart
- Greater detail of lights can also be found in Sailing Directions
Reporting Points:
- Details can be found in the Pilot Book ALRS Vol 6.
- *Chart Symbols:** NP5011 (Chart 5011)
- *ECDIS Symbols and Abbreviations:** NP5012
Define:
Source Data
CATZOG
ECDIS Layers
Source Data:
- Who did the survey, when and how + accuracy
- What the realiabily is (through * in triangles)
CATZOG:
- Category zone of confidence - reliability of the source data - position accuracy, depth accuracy and sea floor coverage
- On an ENC you need to go into custom settings and turn the layer on. Do this when passage planning
- A1, A2, B, C, D, U - 6 stars - no stars. A1 =0.5m depth / 5m position accuracy / full search area
ECDIS Layers:
- BASE
- STANDARD
- CUSTOM / ALL OTHER
Chart Corrections
-You can only correct a chart that is the latest edition
-All latest edition charts get corrected from earliest date to present date
-On a weekly basis you download the Weekly Notice to Mariners. If we can’t download it we will get it sent to us.
-All BA Charts from January 2015 have a QR reader code on them. PSC likes to check them -ensures authentic, checks latest edition + NM’s
-Cumulative list of NtM - every 6 months
-AS of NTM - Yearly - All Ts and Ps in force
What are the 8 Parts to the Weekly Notice to Mariners?
- Notes on how to correct Admiralty Publications - New Publications published that week
- Chart Corrections - Pg1 is chart affected by this weekly edition. Also includes T’s & P’s
- Reprints of NAVAREA 1 Navigational Warnings
- Updates to Sailing Directions
- Updates to Admiralty List of Lights and Fog Signals
- Updates to Admiralty List of Radio Signals
- Updates to Miscellaneous Admiratly Publications
- Updates to Admiralty Digital Products and Services
What are temporary and Preliminary Notices (T’s & P’s)?
T = Temporary:
- i.e. A buoy is removed for maintenance and there is no replacement, as it’s near a danger they put a temporary south cardinal telling you to keep south. Once the maintenance is complete and the original buoy is back in place the Temporary Notice is withdrawn
P= Preliminary:
- is a warning that something is going to change. i.e we are going to replace a cardinal mark with an isolated danger at some point in October. Exact date unknown. Once completed it will be issued as a permanent correction
On an annual basis the UKHO issue an Annual Summary Notice to Marines - Reprints of all T’s and P’s current in force from previous years.
What is a Mercator chart?
In a Mercator projection:
- Meridians of longitude are parallel.
- Line of latitude, while still parallel are no long equidistant by further apart the further north or south from the equator. This casues distortion in the shape and size of land and ocean masses as these features are enlarged closer to the poles
- The advantage of Mercator chart is that meridians and parallels cross each other at right angles to form a rectangular grid. This means a straight line course through the water can be plotted as a a straight line on the chart. Something that is not possible on other projections
- Transvere Mercator Chart: Is when the cylinder is turned through 90* degrees. Advantages for countries like Chile, which has a long North / South border but a narrow East / West.
What is a Gnomonic Chart?
- Meridians converge and lines of latitude are curved. It’s like unfolding a Terry’s Chocolate Orange
- For a Gnomonic Projection, imagine placing a screen tangential to the Earths surface and then project the features onto it (done mathematically) This projection can be used in polar regions where a conventional Mercator projection would not work, it is also used for large scale harbour plans and charts for planning ocean crossings.
- Great circle routes are straight lines and rhumb lines are curved.
- A great circle is the longest line that can be drawn around the earth A segement of a great circle is the shortest distance between two points on the earths surface
- When planning ocean passages, small scale gnomonic charts can be used to calculate great circle routes. On longer passages, ships can save fuel by sailing the shorter great circle route.
Traffic Separation Schemes
- When printed on a chart it is important to know if it is adopted by the IMO - If not, Rule 10 does not apply! However any TSS not adopted by the IMO can still be made to comply with Rule 10 of Colregs. This is done by Rule 1 - Colregs. They make a special rule. If as special rule is in place, it will be noted on the chart in magenta.
- UKHO will tell us if its not adopted, but will tell us where to get the information if it is adopted:
- Sailing Directions
- Annual Summary Notice to Mariners (Old Charts)
- Mariners Handbook can provide guidance on TSS adoption - When Passage Planning, all notes on the chart in magenta should be read prior.
What is the annual summary notice to Mariners?
Divided into two parts: NP247(1) & NP247(2)
- A publication issued by admiralty (UKHO) on yearly basis.
- The notices advise mariners on the important matters related to ships navigation, hydrographic information, aids to navigation and changes in shipping channels.
- The current edition supersedes and cancels the previous one
- This annual summary is of prime importance to mariners in keeping navigational chart folios up to date for corrections pertaining to temporary and preliminary notices for ships navigation and sailing directions
- The annual summary serves as a database with details of history of corrections for all the charts and sailing directions published by the British Admiralty or UKHO.
What are the contents of NP247(1)?
Section 1 - Annual Notices to Mariners section 1 - 26
Section 2 - Temporary and Preliminary Notices
- The publication also includes an exhaustive list of traffic separtion schemes and information related to ship routing system shown on admiralty charts
- It contains port state notification issued under the EU Directives and some parts of ship navigation related regulations issued by the United States. The annex provided with the notice contains extracts from the US navigation safety rules.
Parts of a magnetic compass
