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Factors governing ship squat and how to calculate

Squat is the bodily sinkage of a ship in the water when making headway. This varies from ship to ship. The amount of squat will depend upon several factors but in certain conditions may be as much as two metres. If not factored for appropriately, this could potentially lead to grounding, loss of steering and/or collision.

Squat and Interaction : When navigating in channels or areas with restricted depth, the effect of increased draught due to squat must be taken into account. It must be borne in mind that this effect will increase with speed and is greater when the channel is also restricted in breadth. The handling characteristics of the vessel may appreciably deteriorate when navigating in shallow water, in narrow channels or when navigating in close proximity to other vessels.

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Oil Tanker Safety Guide
Squat can occur with a moored vessel, in an ebb tide, alongside a jetty. Tide speed along the stationary vessel produces components of bodily sinkage and trimming effects. The two combined give ship squat for a stationary vessel. This should be considered when calculating UKC alongside. Particular allowance should also be given to the effects of sea and swell when the vessel is engaged in operations at an offshore mooring such as a SBM.

The UKC calculation record must be shown to the pilot during the Master-Pilot information exchange discussion.

Squat information relevant to the vessel for both loaded and ballast passages should be displayed on the wheelhouse poster compliant with IMO Res. A.601(15) and included on the Ship to Shore Master/Pilot Information Exchange provided to the Pilot.

Factors Governing Ship Squatt

Factors governing the ship squat are: A graph depicting these relationships should be displayed in the wheelhouse.

UKC calculation
Fig: UKC calculation

How to Calculate Ship Squat

The following formulae can be used as a guidance when calculating squat. Note however that every vessel is different and characteristics do change from ship to ship. Answer is in metres, where Cb is the vesselís block co-efficient and V is the ships speed in knots.

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