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Navigation

NAU 102

Lesson 36

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Vessel Grounding

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Magnetic Compasses

Disadvantages

Deviation

No digital output

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Gyrocompasses

Disadvantages

ExpensiveDifficult and expensive maintenance

Requires stable power and backup

Takes a long time to stabilize

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New Advances

Flux Gate Magnetic Compass

Ring Laser Gyrocompasss

No moving parts

Digital output

Low power requirements

Rapid start-up

Self correcting

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FluxGate Compass

Two harmonic coils wrapped around a

magnetic core.

Earths magnetic field changes the coresmagnetic induction.

The coils sense the changes.

Electronics calculate the magnetic field

necessary to cause the change.

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FluxGate 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.

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FluxGate Compass

Operator can input the variation.

Resulting true direction is sent to digital

equipment.

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Ring LaserGyrocompass

Two laser beams travel in opposite

directions around a fiber-optic ring.

When the compass (the ship) isntturning, the beams are in phase.

When the compass turns, the beams are

out of phase.

The quicker the turn, the larger the phase

differences.

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Ring LaserGyrocompass

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Exam Review!

A ship is proceeding on course 240 ata speed of 18 knots. The apparentwind

is from 040 relative at30 knots. What

is the true wind.

True Wind Calculation

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Wind

Step 1: Plot ships course& speed.

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Wind

Step 2: Convert relative direction of

apparent wind to true direction, if necessary.

A ship is proceeding on course 240 ata speed of 18 knots. The

apparentwind is from 040 relative at30 knots.

R + S = T

040 R + 240 = 280 T

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WindStep 3: Draw the apparent wind from the tip of the

ships course & speed vector.

(Remember, draw the direction the wind is blowingtowards!)

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WindStep 4: Complete the triangle. Result = True wind.

Direction = 315 T

Speed = 20 knots

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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 averageRPM of 72?

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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

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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%)

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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

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FuelConsumption

While steaming at 19.5 knots your

vessel burns 297 barrels of fuel perday. What will be the rate of fuel

consumption if you decrease speed to

15 knots?

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FuelConsumption

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

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FuelConsumption

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

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FuelConsumption

Your vessel has sufficient fuel to

steam 812 nm at 15 knots. At whatspeed must you proceed to reach your

next port, 928 miles distant?

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FuelConsumption

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

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FuelConsumption

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

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Introduction to Navigation

Questions?