General
What happens when you go full astern on the vessel?
Transverse thrust will cause heading to deviate
Direction depends on type of propellor
Loss of steerage and speed
Vessel will eventually come astern in direction
What influences stopping distances?
Speed of vessel
Inertia of vessel
Loading condition
Influence from tide and wind
Shallow water effect
How does transverse thrust work on right-handed propellor?
Ahead = clockwise => small creep to starboard
Astern = anti clockwise => large creep to port
What is the ranging and the effect of ranging?
If a vessel is moored with slack lines and a vessel passes
Suction caused by passing vessel may suck vessel away from quay then push back
May result in damage
Moored vessels avoid this by ensuring lines tight
Passing vessels pass at safe distance and slow speed
What can affect the performance of a vessel?
Hull growth
Corrosion
Hull damage
List
Trim
Displacement
How does transverse thrust work on left-handed propeller?
Ahead = > small creep to port
Astern => large creep to starboard
Where does the legal requirement for a passage plan come from?
SOLAS Chapter V
MS Safety of Navigation regulations
IMO Res 893.
How does transverse thrust work?
As propellor moves like a paddle wheel
Causes stern / bow to “walk” to port or starboard
Lower propellor blade has more influence because more pressure
Hence greater transverse thrust when going astern
What is better for twin propeller vessels, inward or outward turning?
Inward turning propellors port = right-handed, starboard = left-handed
For STBD turn,
-STBD Ahead, PORT astern
-Transverse thrust pushes stern to STBD and bow to PORT
-Counters swing
Outward turning propellor would complement during turn
Interaction
What are the main types of interaction?
Vessel to vessel
Shallow water
Canal effect
Drag
How to prevent or reduce vessel to vessel interaction?
Pass wide
Vessels pass at safe low speed
What is the risk of squat?
Touching bottom
Damaging hull, propeller or rudder
What is the shallow water effect?
Increased turning radius
Increased stopping distance
Vessel more difficult to steer
Near shoals -> vessel may shear
May result in vessel vibration
Errors may occur in echo sounder
How can vessel interaction occur?
Head on
Overtaking
Bank cushion
Canal effect
Ranging
What is squat, how does it occur?
hydrodynamic phenomenon by which a vessel moving quickly through shallow water creates an area of lowered pressure that causes the ship to be closer to the seabed than would otherwise be expected
List measures how to reduce effects of squat?
Slow down
Increase UKC
Navigate with caution
Proper voyage planning / deep water routes
Chart accuracy & up to date
Accurate draught
Dock water allowance
What is canal effect?
Vessel in canal type area
Vessel pushes water ahead generates positive pressure field
Low pressure forms at midships
Creates increased velocity of water to fill
Results in squat
Avoid by reducing speed
What happens when two vessels pass?
Each vessel has positive pressure area at bow and stern, negative pressure in middle
Bows deflect
Sterns may attract
Small counter helm required
How does interaction affect the stopping ability of a vessel?
Vessel in shallow water may ‘drag’ water
40% of vessels displacement
Even when vessel slowing to a stop, water continues to move
Pushes vessels and may turn heading
What are the factors of squat?
Speed -> more speed = increased squat
Draught in relation to depth of water -> more prominent in shallow water
Type of bow
Cb value of vessel -> greater the block co-efficient, the greater the influence of squat
Position of LCB -> determines the trim
Maneouvres
What is the pivot point?
Point where vessel rotates
Vessel turns around vertical axis
Said to be 1/3 from vessels bow when go ahead
Causes the stern to swing out
How do you unberth a right-handed propellor, port side alongside?
Keep forward spring (doubled)
Full port rudder, kick ahead (bow in, stern out)
Stern clear
Rudder amidships, come astern
When clear stop engines, starboard rudder, kick ahead
How do you berth with a strong onshore wind?
Stop vessel over ground 1/2 L from berth
Let go offshore anchor
Controlled drift in with ahead on engine to check vessel
Pay out cable as required
When all fast, slack cable
What are the general precautions to take when berthing?
Risk assessment
Manoeuvring plan made
Environmental conditions -> wind, tide and current
Mooring plan made
Equipment in good condition
Sufficient power
Consider use of tugs
Always check safe to manoeuvre -> other vessels
Manoeuvres at walking pace -> 3 knots
How do you berth Right-handed propeller, port side alongside?
Minimal speed
Approach at 30°
Stop Main Engine before berth
Engines astern, rudder to starboard (transverse thrust)
Send forward spring first
How do you unberth a right-handed propeller, starboard alongside?
Single up,
Heave on headline & spring
Brings stern out
Let go, main engine astern
How do you unberth with wind and tide ahead?
Single up,
Slack and release bow
Turn rudder into stream
Tide will separate bow from quay
When bow off, release lines and come ahead
What are the common errors with berthing?
Too fast approach – not enough stopping time
Kicks ahead / astern – too much
Stopping short of berth – blown off, too low speed to correct
Wind – windage factors / container & cruise vessels
Current – reduced speed = more influence
Ropes parting – too much strain
How do you berth Right handed propellor, starboard alongside?
Minimal speed for steerage
Approach at fine angle – 15°
Vessel almost stopped
Rudder to port, kick ahead -> pivot point moves forward very quickly
How do you berth with strong offshore wind?
Approach berth at wide angle
As close to wind as possible
Slow and steady
Pass bow and stern lines together
Dead slow astern
Take in stern slack and pay out bow
Draw vessel alongside
How do you unberth with wind and tide astern?
Single up
Main engine astern
Ease out stern line
Turn rudder into stream
Gradually come astern
Heavy weather & ice
Outline the navigational hazards when entering ice?
Hull damage due to excessive speed
Hull damage due to entering ice at acute angle
Damage to bulbous bow, propellor and rudder at inadequate draft
Blockage of suctions by ice
Fog due to the presence of ice
What are the general precautions to take when berthing?
Risk assessment
Manoeuvring plan made
Environmental conditions -> wind, tide and current
Mooring plan made
Equipment in good condition
Sufficient power
Consider use of tugs
Always check safe to manoeuvre -> other vessels
Manoeuvres at walking pace -> 3 knots
Outline the navigational hazards when manoeuvring in ice?
Damage due to excessive speed
Damage to bulbous bow, propellor and rudder by ice at inadequate draft
Damage to hull when turning due to impacts aft
Variable ice thickness
Ice concentration increasing due to wind effects
Besetment due to inadequate power
Blockage of suctions by ice
Presence of fog caused by ice
What are the general precautions to take when berthing?
Risk assessment
Manoeuvring plan made
Environmental conditions -> wind, tide and current
Mooring plan made
Equipment in good condition
Sufficient power
Consider use of tugs
Always check safe to manoeuvre -> other vessels
Manoeuvres at walking pace -> 3 knots
Outline the navigational hazards when approaching port in ice conditions?
Lights obscured and sectors inaccurate due to icing
Floating marks absent, or displaced by ice
Channels obstructed by ice
Berth obstructed by ice
What are the general precautions to take when berthing?
Risk assessment
Manoeuvring plan made
Environmental conditions -> wind, tide and current
Mooring plan made
Equipment in good condition
Sufficient power
Consider use of tugs
Always check safe to manoeuvre -> other vessels
Manoeuvres at walking pace -> 3 knots