Bridge Management - Manoeuvring Flashcards
Where is the Pivot Point for a stationary vessel with no wind or tide?
Centre of gravity
Where is the Pivot Point for a vessel starting to make headway with no wind or tide?
Initially P moves right forward however water resistance increases with momentum so P will be about 1/8 of Length
Where is the Pivot Point for a vessel with headway (constant speed) and no wind or tide?
P is 1/4 of Length
Where is the Pivot Point for a vessel starting to make sternway with no wind or tide?
Initially P moves right aft however water resistance increases with momentum so P will be about 1/8 of Length from aft
What is Bank Effect?
Positive forward pressure area will push the bow away from the bank
Negative pressure area along the vessel’s side and stern will draw the vessel’s stern towards the bank
What is Bow Cushion Effect?
The forward pressure area creates a bow cushion
What is Canal Effect?
The forces on each side of the bow will force the vessel into the centre line
What is Squat?
Increased water flow around the vessel creates a low pressure zone, low pressure causes loss of buoyancy so the vessel dips which leads to a loss of UKC
What are the effects of Squat?
Heading is greatly affected
Pivot point moves and so steering lever is affected
If the vessel takes a shear, much more helm required to correct a swing
Burst of power essential to regain control before reducing speed to minimise squat
Describe the three steps of Williamson turn
1 - Helm hard over to the side of the casualty
2 - After the heading has changed by 60 degrees, reverse the helm to hard over the opposite way
3 - When the heading is 20 degrees short of the reciprocal of the original course, helm to midships
What are the three advantages of Williamson turn?
1 - Makes good original track line
2 - Good in reduced visibility
3 - Simple to execute
What are the two disadvantages of Williamson turn?
1 - Takes vessel away from casualty
2 - Relatively slow
