SHIP HANDLING Flashcards
What is the rule of thumb for Shallow Water Effects will be present on a vessel?
Generally, if the water depth is less than twice the draft of the vessel
What happens to the forces on a vessel in shallow water?
There is build up of pressure along the hull on the outside of the turn, aft of the pivot point due to restricted flow under the keel
- The rudder loses efficiency, must overcome a much greater lateral resistance so is considerably less efficient
- At the bow, because of reduced UKC, there is a build up of pressure both ahead of the vessel and port bow (turn to stbd) because of water that would normally pass freely under the vessel with no significant restriction, is now restricted.
This changes fwd momentum and longitudinal resistance, moving Pivot point further aft.
This loss in rudder efficiency can increase the advance by half in shall water & double the transfer.
What Effect would the wind have on a vessel making headway?
It will make the bow seek the wind.
The impact of wind on shiphandling must be considered in conjunction with the pivot point.
The greater the distance the force is from the focal point, the greater the lever & therefore greater the force.
What is Banking Effect?
When a vessel is making headway, an area of High Pressure builds up foward of the pivot point, low pressure then runs the length of the hull.
If a vessel closes a shoal or bank with a sloping bed, the high pressure at the bow pushing the bow away and sucking the stern in towards the bank.
Action to take: often significant helm towards the bank to break its effect.
NOTE: The magnitude of effect varies with the square of the vessels speed/water flow. Imperative that speed is kept low.
Keep the centre of rotation in mind, bigger level aft of ‘P’ to cause suction towards the bank.
What effect would squat have on the Banking Effect?
In shallow water, there will be an added effect of squat, which will reduce the turning lever used to counteract the banking effect.
Likely a poor response to helm orders
What are the difference phases of Ship to Ship interaction when two vessel are meeting head on in confined waters?
Note: A reduction in speed will reduce the effects when meeting another vessel in confined waters
Phase 1: Bows Pushed out
Apply helm towards other vessel just before meeting to counter the HP Areas around the bow
Phase 2: Bows Sucked into Midships
As required, midships wheel & apply helm away from otehr vessel is dangerous amount of sucking in.
Phase 3: Stern Sucked in
Helm in to prevent sterns swinging together (LP)
What Are the Phases of Interation Between vessel when overtaking in confined waters?
OVERTAKING (OUT - IN - OUT)
Phase 1
Overtaking vessels bow sucked in to LP around mid ships
Both vessel apply outward helm
Phase 2
Bows pushed out when vessel bows meet
Inward helm applied by both vessels to counteract
Phase 3
Overtaken vessels bow sucked into midship area
Outward helm applied by both vessels
Important things to note during Interaction Between Vessels
- Vessels should remain in the the centre of the channel to minimise banking effect
- Speed should be kept slow to minimise effects
- Low speed gives vessel option for kicks ahead if required to have more water over rudder
- Smaller vessels will be effected more
- If vessels pass from deep to shallow during manoeuvre, the effects will significantly increase
What is Bernoullis Principal?
When there is a constriction or narrowing in the path or flow of liquid, there is an increase in velocity and consequent decrease of pressure.
Squat on vessel when entering shallow water: an increase in speed of water under the vessel, causing suction to the seabed, or an increase in draft.
What is the formula for squat?
SQUAT = Cb x V^2/ 50 (SHALLOW WATER)
SQUAT = Cb x V^2/ 100 (OPEN WATER)
What was the Crash Stop & Turning Circle of your last vessel?
Crash stop
193m Advance
25m Lateral Deviation
Time: 1 Minute from 14 Knots
Turning Circle
160m Advance at 90 Deg
43m Transfer
Full turn time 1:50s an dmax ROT is 200Deg/Min
Heavy Weather Considerations…
SEVERE WEATHER CHECKLIST
All loose items to be secured/stowed
Cargo Lashings to be increased - Cargo Securing Manual
Lifeboat Gripes and Lashings Checked
Liferafts & Buoys Secured - Include Fire Boxes
Consider Safety Lines
Galley securings
Weathertight & Watertight Closures
Hatch covers
Drain Valves
Pressurise they hydraulic system
Closing down of main deck flaps
Anchors: Additional lashings if requires
Spurling Pipe Watertightness
Hawse Pipe storm plates
SCUPPERS are freely draining
Stability condition - remove slack tanks where possible
Fill DB if not already
Exrta Ballast
Swimming Pools drained if fitted
NOTIFY CREW -
Secure Bridge
Shelter Options - Safe Port
Record all actions in the Deck Log Book
Navigation in Heavy Weather
Maintain safe distance from storm centre
Reduce speed to reduce unnecessary damage to vessel/cargo
Avoid being caught on a lee shore - between system and shore line
Consideration of GM
What is Synchronous & Parametric Rolling?
• Synchronous rolling occurs in beam seas, when the roll period of the vessel matches the wave period. The vessel heels over with
ever larger successive roll angles.
• Parametric rolling occurs due to changes in vessel stability as the vessel moves in waves. It is most common in heavy head seas
but can occur also in following seas. It is a sudden phenomenon with large and rapidly increasing roll angles experienced over a
short period of time.
What are the key environmental factors to be aware of when Synchronous or Parametric Roll conditions are suspected?
KEY TRIGGERING CONDITIONS TO WATCH FOR
• Vessel rolling period (time it takes for the vessel to roll from port, to starboard, then back to port) approximately equal to the wave
encounter period, or twice the wave encounter period.
• A low metacentric height (GM) leading to long rolling period.
• Near following sea conditions or head seas.
The wave encounter period can be measured with a stopwatch as the time between two wave crests. It is close to the vessel pitching
period (time it takes for the vessel to pitch bow down, stern down and back to bow down).
