What is Ship Squat Effect?

Motion of a ship on water is a result of several hydro dynamics in play all at same time. Of the several phenomena that occur at once, ship squat effect is a fairly important one. On several occasions, ships have run into extreme situations because of this particular effect. For all mariners and ship lovers, understanding what is ship squat and how it affects the motion of a ship is fairly important.

What is ship squat effect?

To understand this better, consider image of a ship moving through waters. As the ship’s hull cuts through the water’s surface, a volume of water is shoved aside. This water is actually replaced to sides and underside of the ship.


This creates a region of low pressure, causing the ship to dip vertically at points of low pressure. The vertical dip in the ship caused due to low pressure is actually the ship squat effect. This dip is proportional to the speed of the ship.

The major effects of such low pressure conditions are especially felt in shallow water, even more so if the ship is going at a high speed. That is where the relation between ship’s speed and the squat effect comes handy. Altering the speed can greatly help maneuver through the shallow waters easily. Cutting the speed down by half would approximately lower the squat effect by a factor of four.

Why is ship squat important?

A ship’s squat is one of the more important things that help in ensuring a ship’s safety through water. Vessel squat is a combined outcome of ship’s dimensions, weight, water depth, wind draft and several other factors that come into play while a ship is in motion.

Knowing a ship’s squat becomes important then as its loading capacity, speed, its seaworthiness through particular routes would all be affected by its squat value. As mentioned above, vessel squat is proportional to ships’ speed. So it becomes important information for a ship’s pilot that increasing his ship’s speed by a certain factor, he would also be increasing the ship’s squat. Or while loading a ship, say for a 100,000 tons dwt tanker, a load of extra 30 cm could increase the ship squat by 3%.

These become crucial pieces if information to ensure a ship reaches destination safely. Besides, it is always sad when a ship runs aground or is rendered out of service, for any reasons. Certain factors like ship’s speed and load weight can be checked to prevent such incidents. Hence, knowledge of vessel squat could ensure a ship wouldn’t have to face such avoidable circumstances.

Is ship squat good or bad?

There is no straight answer to this question. In certain situations, while traveling in shallow waters, ships have been grounded due to ship squat effect. Grounding of QE2 would be a perfectly good example of that, where the ship ran aground despite of having enough room for its passage. That happened due to additional vertical dip experienced by ship, causing it to brush off against a rock that would otherwise have caused no harm.

Since 1987, more than 113 ships have run aground chiefly because of the squat ships had to experience. On the flipside, this very property has been used in certain occasions to help ships pass through regions otherwise considered unfavorable. Travel of largest ship of the world, Oasis of Sea, through Great Belt Bridge would be a perfectly good example of that.

It can be said now that the total squat ship has to experience plays role in its overall integrity, which is for sure. However, it becomes a matter of captain’s discretion especially upon entering shallow waters that can prevent things from going bad.

References: ship-squat , vht-marine , gobalspec , scg.ulaval

Image Credits: pilotmag, rpmedia


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