ECDIS/GPS

Question 1

How would you confirm your ECDIS is compliant?

Answer 1

• Type apporval certificate
• MED wheel mark stamped on ECDIS
• Cargo Ship Safety Equipment certificate Form E

Question 2

How would you know your ECDIS is up to date?

Answer 2

By checking that the ECDIS displays the latest S-52 Presentation Library, which is 4.0

• Navigate to ECDIS chart 1 at an approximate Lat and Lon
• If it is not up to date, it will not be possible to view the new symbols.

Question 3

How would you calculate safety depth on ECDIS?

Answer 3

Draught + UKC (including squat & safety margin) - Height of Tide

Question 4

What is a Safety Contour and Safety Depth?

Answer 4

Safety Contour:
A specific depth contour set by ECDIS which defines the boundary between safe water and shallow water. It is displayed as a bold line and will give an alarm at a specified time if the ship is going to cross the contour.

Safety Depth:
A value which is set by the mariner which will display depths as black if they are equal to, or shallower than the value, and grey if they are deeper.

Question 5

What are the limitations of ECDIS?

Answer 5

• Over reliance on the information provided
• Lack of training/understanding of the equipment
• Too many layers may cause the ECDIS to become cluttered
• Incorrect safety parameters set
• Incorrect route check parameters set
• Susceptible to tech failures
• Input failures causing false information

Question 6

Carriage requirements of ECDIS

Answer 6

• Passenger ships >500GT
• Cargo ships >3000GT

Question 7

Inputs into ECDIS

Answer 7

• GPS
• Gyro
• Speed log

Question 8

How does GPS work?

Answer 8

• Calculates the distance from the satellite by measuring time/2. This gives a line of position
• Multiple lines of position triangulate position. The more satellites, the more accurate the position
• Needs 24 satellites

Question 9

Errors of GPS

Answer 9

• Ionospheric and tropospheric delay - 6m
• Satellite orbit errors (ephemeris errors) - 3m
• Satellite clock errors - 3m
• Multipath errors (reflect off sea etc) - 0.5m
• Solar flares

Question 10

What is differential GPS

Answer 10

• Satellite will transmit signal to a LES at a known position
• Error in position is calculated and transmitted via MF to DGPS user

Question 11

What is SBAS/EGNOS/WAAS etc?

Answer 11

Satellite based augmented system where it calculates errors in GPS position and relays to the user

Question 12

Mandatory alarms ECDIS

Answer 12

• Crossing safety contour
• Area with special conditions
• Deviation from route
• Positioning system failure
• Input failure
• Approaching critical point
• Different geodetic datum
• Malfunction of ECDIS