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?