DAN Medical Frequently Asked Questions

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Ship's Motions

New Terms
  • Heave
  • Pitch
  • Yaw
  • Surge
  • Roll
  • Sway
  • Before we discuss types of boats, it is important to recognize that a boat is a dynamic environment. While the space you occupy may be small, the force of movement of a floating boat can be great, depending on a variety of factors. As land-based humans, our bodies are not accustomed to functioning easily in this dynamic environment, as such we must take special precautions and do every action with a deliberate intent while on a boat. What we mean by that is every action has an opposite reaction and it is the ship's motions that dictate how things move on a boat.

The ship's motions fall under the six degrees of freedom derived from mechanical terms. They are: heave, the vertical up and down motions; sway, the side to side motions; surge, a front/back movement; pitch, the rotation of a vessel as it moves side to side; roll, the heavy side-to-side moment; and finally yaw, the rotation of a vessel on its vertical axis.

While a boat may be stable, every movement of the boat will cause any unsecured item on that boat to move, slide, or fall to the deck. This is why you will see most items on a boat secured. However, not all of those items are dynamic in nature; the dynamic variable on a boat is you. We will discuss how to move around on a boat later in this DAN On-Board program, but we wanted to put this concept of the ship's motions into your mind early on so you can begin to imagine how a ship's movements affect your time on board.

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