Sail A Flashcards
(30 cards)
What is apparent wind vs true speed wind?
The true wind is the wind as it blows across the land or water, the wind in the weather forecasts, the wind you feel when you’re standing stationary onshore. However on a boat, you are moving due to wind and current, and so the apparent wind is how much wind you feel when standing on the boat.
how are waves formed?
wind, gravity, tidal waves or earthquakes and tsunamis
what is wind velocity?
the speed of the wind
what is fetch?
the distance over the water that the wind can blow uninterrupted
what is duration?
the amount of time the wind blows over the patch of the water
what three factors affect wave formation?
wind velocity, fetch and duration.
the greater the wind velocity means….
Greater duration, and longer the fetch.
Basically, more energy is converted to waves, and they are large.
if the wind velocity is low then….
waves will be small, regardless of the fetch or duration.
frictional drag occurs when______.
Wind moves across the water surface.
Drag is a force that acts against the relative motion of one fluid with respect to another fluid.
why is drag less over the ocean than on land?
the sea is much smoother than your typical land features.
boundary layer?
portion of troposphere where friction drag is felt.
the thickness of the atmospheric boundary layer depends on….
temperature, water surface and wind
definitions
Crest = Highest point of the wave
Trough = Lowest point of the wave
Wavelength = Distance from one crest/trough to the next (m)
Wave Height = Height from trough to crest (m)
Wave steepness = ratio of wave height to wavelength
Amplitude = distance from the centre of wave to the bottom of the trough (m)
Wave Period = time for one full wavelength to pass a given point (s)
what is a wave train?
when waves settle into groups of different size, and velocity while continuously moving away from the source.
the speed at which a group of waves travels across the water is known as….?
group velocity
the apparent speed of each individual wave in the group is known as…..
phase velocity
what are wind-generated waves?
wind-waves are a result of wind disturbing the ocean surface and displacing water. Different types of waves are named based on their restoring force.
what are capillary waves?
short-wavelength waves. (small ripples that are around a few cm in length)
what are gravity waves?
waves in which gravity acts as the restoring force. (these waves can be up to metres to km long)
what are swells?
Waves formed from distant storms. They are capable of travelling long distances.
-Swell with longer wavelengths tend to have lower wave heights and are less susceptible to decay from surface winds. They also carry more energy, and are more likely to form large breakers once they reach the shore.
what are rogue waves?
very large waves formed due to wave interference.
destructive interference - waves meet and cancel each other out
constructive interference - the waves add up, and resulting waves are bigger
are rogue waves dangerous?
yes they can be
what are tsunamis?
very long wavelength waves resulting from seismic events such as earthquakes, under-water landslides and volcanic eruptions. In the open ocean (away from shore) they travel very fast (the same speed as a jet airliner), but have very small amplitude (cm to a meter or so). Thus, they have very small wave slopes, and you might not even notice it in the deep ocean, because the normal wind-waves would catch your attention instead
when waves break against the shoreline they have impact on….
erosion and how shorelines are shaped
