Ship Squat

Most Deck Officers know about ship squat. Ship Squat is the reduction of the vessels under-keel clearance caused by its relative movement. A vessel tends to squat when making way through the water or riding with the current. How does a ship squat occurs?

A ship, while making way through the water tends to push a mass of water in or on her bow or stern. This water flows back the under and the side of the ship. Thus Ship Squat will cause the vessel to either trim on the bow while moving ahead, or by the aft when moving astern.

In case of a very small ship’s under-keel clearance as featured by tc.gc.ca, let’s say 1.0 or 1.5 meters. Ship Squat should be monitored carefully. At certain speed ship squat could cause the vessel to trim too much either forward or aft depending on the speed of the ship. Which would later on could cause the ship to ground. There are various ways to calculate a ship squat.

Open Waters:

Confined Waters:

Wherein: V = the speed of the vessel through the water in knots; and Cb = the Block Coefficient.

You can calculate the ship squat at different speed, in order to identify the effects of squat on the under-keel clearance of the ship at different speed.

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9 Responses to “Ship Squat”

  1. hernandez joel says:

    more topics on navigation

  2. JACOB says:

    PLEASE TELL ME HOW TO FIND Cb ( BLOCK COEFICIENT ) ASAP!

  3. batur says:

    thanks for info….

  4. marleo says:

    great help..

  5. robert smith says:

    I work on a tug barge unit with an intercon system. We are not rigidly conected as in a composite unit. Pins extend from the tug to the barge which does allow for fore and aft flexation, but the tug and barge act as one regarding rolling period. My problem is this: Squat calculations established for ships (monohull) don’t seem to apply to my vessel. The Block Co-efficient that we have to use is for the barge. The block co-efficient is determined by the length of the vessel. With our tug notched up, there is approximately 100 ft aft of the barge (and the propulsion point “propellers”) that is not accounted for in the equation. Also, the tug is at different levels in relation to the barge when the barge is light or loaded. Also, the tug draft varies as to ballast and fuel. How does this change the dynamics of squat vs a ship and does this render our calculation useless? Thanks, Bob Smith

  6. jonathan v. hulleza says:

    how do i know if the squat is in the forward or aft?

  7. Elvis Bierneza says:

    Asan ko makukuha to?

  8. cesar bartolata says:

    how do I apply the 2/3 on velocity return factor and also on vessels speed(V) which is raised to 2.08? thanks

  9. Mike Schiehl says:

    Does a moored vessel (single point bow center line) “squat” with a broadside wheel wash induced current?
    Are the calculations the same using velocity of water in place of velocity of vessel.?

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