General PQS's Pt.2

Difference between deep-water waves and near shore breaking waves

Deep-water: Deeper water allows for larger swells to be generated. As these swells approach shallow water on the coast, they will loose speed and gain height,Shore breaking: When deepwater waves move into shallow waters, the waves are influenced by the bottom, becoming shallow-water waves.

Characteristics/Causes of various breaker typesa. plungingb. spillingc. surging

a. Plunging breakers are created when a wave encounters a sudden decrease in depth, such as a reef or a steep rise of the ocean floor. The momentum caused by the breaking top of the wave will cause the water to curl.

b. Spilling breakers are created when wave energy encounters a gentle sloping ocean floor. The spilling breakers normally have a crest of white water spreading down the wave face.

c. Surging breakers are created on very steep beaches. The wave builds very quickly and expends its energy on the beach.

State the effects of bottom contour, jetties, islands, and obstructions

a. Bottom contour: Breakers are a result of wave interaction with the bottom contour of the sea, shoal, reef, bar, or inlet. With each of these waves/swells the bottom of the wave slows on the ocean floor, shoal, reef, bar, or inlets while the top of the wave moves ahead of it causing it to break.

b. Wave refraction (Wave refraction occurs when the wave moves into shoaling water, interacts with the bottom and slows down.), cause major changes in the amount and direction of current, Beaching

c. Almost any obstacle can reflect part of a wave, including underwater barriers such as submerged reefs or bars, even though the main waves may seem to pass over them without change. These reflected waves move back towards the incoming waves (Figure 5-4). When the obstacles are vertical or nearly so, the waves may be reflected in their entirety.

Effects of wind on sea conditions

The higher the wind velocity, the larger the area and the longer the wind blows, the greater the opportunity wind waves have to combine and grow. Wind affects the speed of currents. Sustained wind in the same direction as the current increases the speed of the current by a small amount. Wind in the opposite direction slows it down and may create a chop

Effects of current and tidal conditions on breaking seasa. Flood current b. Ebb current c. Slack Current d. Longshore current e. Eddy currents f. Tidal currents

modifying wave steepness, height, and energy:

- FLood current : horizontal motion of water toward the land, caused by a rising tide.

- Ebb current: Ebb current is the horizontal motion away from the land, caused by a falling tide.

- Slack current: . Slack water is the period that occurs while the current is changing direction and has no horizontal motion

- Longshore current: run parallel to the shore and inside the breakers. They are the result of the water transported to the beach by the waves.

- Eddy currents: Eddy currents (eddies) occur at channel bends, near points of land, and at places where the bottom is uneven.

Tidal Current: The horizontal motion of water caused by the vertical rise and fall of the tide.

- Tides effect the currents which effects the type of sea conditions

Define the Following Terms:a. Closeoutb. Windowc. Saddled. Shouldere. Low/High Side

a. "Closeouts" occur when a wave breaks from the ends toward the middle, or two waves break towards each other. The middle may look like a good saddle, but can quickly turn into whitewater. Closeouts should be avoided because they can create more energy than a single break.

b. A window is an area where the waves have momentarily stopped breaking, opening up a safer area of operation for your boat. The window may remain for a long time or may begin breaking again almost immediately.

c. The "saddle" is the lowest part of a wave, bordered on both sides by higher ones. Often it is a small, unbroken section of a wave that is breaking. It is preferable to drive a boat in the saddles if possible, thus avoiding the white water. While saddles are very useful, they must be watched carefully, because they easily turn into "close-outs."

d. The "shoulder" is the edge of a wave. It may be the very edge of the whitewater on a breaker, or the edge of a high peaking wave that is about to break. The shoulder is usually lower in height than the middle of the wave. Driving on the shoulders can be particularly useful in a narrow surf zone because it allows driving very close to a break in relative safety.

e. The "high side" is defined as the section of a wave which carries the most potential energy. The "low side" is where the least potential energy exists and represents the safest direction to turn when facing the wave/swell (Figure 5-11).These high and low sides often change rapidly, and the ability to quickly navigate the high and low sides is a critical skill for surf operations.

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