navigation nau 102 lesson 36. vessel grounding
TRANSCRIPT
Navigation
NAU 102
Lesson 36
Vessel Grounding
Magnetic Compasses
Disadvantages
Deviation
No digital output
Gyrocompasses
Disadvantages
Expensive
Difficult and expensive maintenance
Requires stable power and backup
Takes a long time to stabilize
New Advances
Flux Gate Magnetic Compass
Ring Laser Gyrocompasss
•No moving parts•Digital output
•Low power requirements•Rapid start-up•Self correcting
Flux Gate Compass
Two harmonic coils wrapped around a magnetic core.
Earth’s magnetic field changes the core’s magnetic induction.
The coils sense the changes.
Electronics calculate the magnetic field necessary to cause the change.
Flux Gate Compass
To minimize deviation, the sensor is placed at the top of the mast.
Residual deviation is automatically calculated as the ship changes course 360°.
It makes its own deviation table!
Deviation is automatically applied.
Flux Gate Compass
Operator can input the variation.
Resulting true direction is sent to digital equipment.
Ring Laser Gyrocompass
Two laser beams travel in opposite directions around a fiber-optic ring.
When the compass (the ship) isn’t turning, the beams are in phase.
When the compass turns, the beams are out of phase.
The quicker the turn, the larger the phase differences.
Ring Laser Gyrocompass
Exam Review!
A ship is proceeding on course 240° at a speed of 18 knots. The apparent wind is from 040° relative at 30 knots. What
is the true wind.
True Wind Calculation
WindStep 1: Plot ship’s course
& speed.
Wind
Step 2: Convert relative direction of apparent wind to true direction, if necessary.
A ship is proceeding on course 240° at a speed of 18 knots. The apparent wind is from 040° relative at 30 knots.
R + S = T
040° R + 240° = 280° T
WindStep 3: Draw the apparent wind from the tip of the
ship’s course & speed vector.
(Remember, draw the direction the wind is blowing towards!)
WindStep 4: Complete the triangle. Result = True wind.
Direction = 315 °T
Speed = 20 knots
Slip
The propeller on a vessel has a diameter of 24.6 feet and a pitch of
26.1 feet. What would be the apparent slip if the vessel cruised 462 miles in a 24 hour day at an average
RPM of 72?
Slip
The propeller on a vessel has a diameter of 24.6 feet and a pitch of 26.1 feet. What would be the apparent slip if the vessel cruised 462 miles in a 24 hour day at
an average RPM of 72?
Distance = Pitch x RPM x Time (in minutes) x Efficiency
6080 feet/nm
Slip
The propeller on a vessel has a diameter of 24.6 feet and a pitch of 26.1 feet. What would be the apparent slip if the vessel cruised 462 miles in a 24 hour day at
an average RPM of 72?
462 nm = 26.1 ft x 72 RPM x (24 hr x 60 min/hr) x Efficiency
6080 feet/nm
Efficiency = 1.038 (103.8%)
Slip
The propeller on a vessel has a diameter of 24.6 feet and a pitch of 26.1 feet. What would be the apparent slip if the vessel cruised 462 miles in a 24 hour day at
an average RPM of 72?
Slip = 100 - 103.8% = -3.8%
Slip = 100% - Efficiency
Fuel Consumption
While steaming at 19.5 knots your vessel burns 297 barrels of fuel per day. What will be the rate of fuel
consumption if you decrease speed to 15 knots?
Fuel Consumption
While steaming at 19.5 knots your vessel burns 297 barrels of fuel per day. What will be the rate of fuel
consumption if you decrease speed to 15 knots?
New Consumption = New Speed3
Old Consumption Old Speed3
Fuel Consumption
While steaming at 19.5 knots your vessel burns 297 barrels of fuel per day. What will be the rate of fuel
consumption if you decrease speed to 15 knots?
New Consumption = 153
297 barrels 19.53
New Consumption = 135 barrels
Fuel Consumption
Your vessel has sufficient fuel to steam 812 nm at 15 knots. At what
speed must you proceed to reach your next port, 928 miles distant?
Fuel Consumption
Your vessel has sufficient fuel to steam 812 nm at 15 knots. At what speed must you proceed to reach your
next port, 928 miles distant?
New Consumption = New Speed2 x New Distance Old Consumption Old Speed2 x Old Distance
Fuel Consumption
Your vessel has sufficient fuel to steam 812 nm at 15 knots. At what speed must you proceed to reach your
next port, 928 miles distant?
x nm = New Speed2 x 928 nm x nm 152 x 812 nm
14.03 kts = New Speed
Introduction to Navigation
Questions?