Squat effect
Squat ( engl. of to squat, squat ) is a term from the shipping industry and it is the driving dynamic vertical sinking of a ship on the actual draft out ( drawdown or sunk ), while trimming. The trimming forward or aft is dependent on the block coefficient.
Definition
The decrease can be observed in all vessels, especially sailing in a river or canal, and is dependent on the cross-section of the vessel, the speed, the waterway cross-section and the traffic situation, ie when meeting or overtaking other vessels. The lower the water level, the greater is the squat. During the voyage of the ship caused by the lateral and depth limitation on a return flow from the bow to the stern of the ship. This reverse flow causes a decrease in the water level and therefore the ship. Under extreme conditions the decrease can be so strong that the ship undergoes grounding and the ship's hull or the drive may be damaged.
In rivers it comes inside of curves to silting. Because here but the flow and thus the resistance is at its lowest, go inland vessels for the ride mostly the inner arc. Now comes the ship too close to the silting up, so there is a dynamic draft magnification to recognize the highly becoming stern wave that moves forward. In this case, you must immediately reduce speed, otherwise there is a grounding due to insufficient Flott water. Keel called the safety distance between the fairway and basic ship's bottom. The Schiffsabsunk plus the keel give the keel clearance.
Squat, achieved by high speed driving, can be used to drive under critical low drive-through height under bridges. This happened, for example, the transfer of the " Allure of the Seas ".
Calculation approaches
Calculation approach by Tuck
Ernest O. Tuck identified the following calculation for the drawdown and the trim using the Slender -body theory:
With
- = drawdown
- = Absunkkoeffizient
- = Sunken in water volume of the vessel in cubic meters
- = Length of the vessel ( P / P )
- = Froude depth number
With
- = trim
- = Trimmungskoeffizient
The Absunkkoeffizient and the trim angle coefficient are complex expressions of characteristics of the particular ship.
Calculation approach by Dand
Ian W. Dand determined following equation for the drawdown, and the trim of the viewing this as a vertical force and moment
With
- = drawdown
- = Width of the vessel measured at the waterline at the point x
With
- = trim
Calculation approach by leaders and Roman
The leader of M. and K. Roman calculation approach they developed first using a model an equation for the squat at the critical speed. The critical speed is the limit of the concentrated on by the outflow cross-section the displaced water from the ship is not fully discharged rearward facing backwards. For the squat at the critical velocity is given by:
With
- = Squat at critical speed and Bugtrimmung
- = Block coefficient
- = draft
With
- = Squat at critical speed and Achterntrimmung
Others
The faster the speed over ground, the stronger the drawdown. The cruise liner Queen Elizabeth 2 ran in 1992 on the basis of which a rock at Cuttyhunk Iceland ( Elizabeth Islands ). The drawdown was not considered by the ship's officers and the water depth was gem anyway. Map borderline.