Extreme Surfing

1
Extreme Surfing
Tow-In Surfing is an ocean based sport that
requires the use of a Personal Watercraft (PWC),
Rescue Sled, Life Vests, Tow Rope/Handle and two
very experienced and passionate big wave surfers.
Drivers utilize a PWC, trailing a 30- 40 rope
and handle, to position their surfer in the right
part of fast moving ocean swells. When the surfer
drops the rope he uses his momentum to catch
waves that are generally un-catchable by paddle
in surfers.
Extreme Surfing World Champion
The surfers life depends on his partners
ability to drive that PWC, assist in pick-ups and
come in for the intense rescue before the next
mountain of water rolls over them. It is not
uncommon for both surfer, driver and PWC get
plowed over by four or five building size walls
of whitewater.
2
Big Wave Tow-in Surfing
On September 1, 2004, the state's Department of
Land and Natural Resources' (DLNR's) Division of
Boating and Ocean Recreation enacted rules
regulating big wave tow-in surfing in Hawaii. It
requires that "thrill craft" operators and tow-in
surfers be certified through an accredited course
on the safe use and operation of thrill craft
in high surf, and that thrill craft be
registered with the DLNR.
This accredited course is entitled "Ocean Safety
Educational Course" and is taught through the
University of Hawaii system by Jim Howe
(Honolulu's Ocean Safety and Lifeguard Services
Operations Chief), Ken Bradshaw (veteran big-wave
tow-in surfer), Brian Keaulana (big wave surfer
and expert in ocean safety risk management), and
Archie Kalepa (Maui County Ocean Safety
Operations Chief), among others. The 10-hour
course spans two days, and has been well
attended, with classes filled to near capacity.
3
Origin of Waves
All ocean waves begin as disturbances caused by
releases of energy
rock tossed into a pond wind movement of
fluids of different densities landslides into
the ocean underwater seafloor movements gravitat
ional pull of the Moon and the Sun on
Earth human activities in the ocean
Waves are created along the interface between two
fluids air/water interface ? ocean
waves air/air interface ? atmospheric
waves water/water interface ? internal waves
4
Internal waves

• Water-water interface

• Associated with pycnocline
• Larger than surface waves
• Caused by tides, turbidity currents, winds, ships
• Possible hazard for submarines
• Wave heights can exceed 100 m

5
Other Waves

• Splash wave
• Coastal landslides, calving icebergs
• Seismic sea wave or tsunami
• Sea floor movement
• Tides
• Gravitational attraction between Moon, Sun, and
  Earth
• Wake
• Ships

6
Waves Energy in Motion
Once initiated, waves transmit energy through
matter by setting up patterns of oscillatory
motion in the particles that make up the
matter. Progressive waves waves travel
without breaking longitudinal (push-pull) BODY
WAVE transverse (side-to-side) BODY
WAVE orbital (longitudinal transverse)
INTERFACE or SURFACE WAVE
7
Wave Characteristics
Wave length (L) horizontal distance from crest to
crest Wave height (H) vertical distance between
crest trough Wave steepness (H/L) ratio of H
to L wave breaks if H/L gt 1/7 Wave period (T)
time for one wavelength to pass a fixed position
(sec) Wave frequency (f) 1/T number of waves
passing a fixed position per unit time (Hertz, Hz
1/sec)
8
Circular Orbital Motion

• Water particles move in circle
• Movement up and down
• Movement back and forth
• The diameter of the orbit at the surface is equal
  to the wave height (H).
• This motion advances the wave form, not the water
  particles themselves. (Wind blowing across a
  field of wheat is similar.)
• Wave drift net mass transport (motion is slower
  in trough than in the crest)

9
Orbital Motion

• Circular orbital motion decreases with depth and
  is negligible at a depth called the wave base
  (L/2) measured from the still water level.
• Hardly any motion below wave base

10
Deep-Water Waves

• Water depth (d) gt wave base (L/2)
• No interference with ocean floor
• All wind-generated waves are deep-water waves.
• Wave speed (S) wavelength (L) / period (T)
  S L / T
• S 1.25 L1/2 (L in meters)
• S 1.56 T (m/s)
• In general, the longer the wavelength, the faster
  the wave.

11
Deep-Water Waves
Ideal relations among L (wavelength), T (period)
and S (speed) for deep-water waves. Red lines
show an example with L 100 m, T 8 sec, S
12.5 m/sec.
12
Shallow-Water Waves

• Water depth (d) lt L/20 (long waves)
• feel bottom ocean floor interferes with
  orbital motion
• Back-and-forth oscillation vertical motion
  decreases with depth
• Wind-generated waves that move into shallow
  water, tsunami, tides
• Wave speed (S) (gd)1/2 , where g 9.8 m/s2
• S 3.13 d1/2 (d in meters)
• In general, the deeper the water, the faster the
  wave.

13
Transitional Waves

• L/20 lt d lt L/2
• Wavelength (L) between 2d and 20 d
• Wave speed (S) depends on water depth (d) and
  wavelength (L)

14
Wave development

• Most ocean waves wind-generated
• Capillary waves (ripples) formed first
• Rounded crests, very small wavelengths (lt1.74 cm)
• Restoring force capillarity
• Increasing energy results in gravity waves
• Symmetrical waves with longer wavelengths
• Restoring force gravity
• Increasing energy results in trochoidal
  waveforms
• Crests pointed, troughs rounded
• Sea area where waves generated by storm

15
Wave development

• Sea area where waves generated by storm
• choppy, waves move in many directions
• H lt 2 m in general H 10 m, T 12 sec
• wind-wave max 18.3 m (60-ft rule)
• USS Ramapo (1935) T 14.8 sec, H 34 m!!!
• whitecaps (open ocean breakers) H/L gt 1/7
• wind speed, wind duration, fetch
• Swell uniform, symmetric waves beyond storm area

16
Fully Developed Sea
Maximum wave height (H), wavelength (L) for
particular fetch, speed, and duration of winds at
equilibrium conditions Energy gained from wind
Energy lost to breaking (whitecaps)
17
Swell

• Uniform, symmetrical waves that travel outward
  from storm area
• Long crests H/L decreases
• Transport energy long distances
• Longer wavelength waves travel faster and
  outdistance other waves, separating from slower,
  shorter wavelength waves
• Sorting of waves by their wavelengths is wave
  dispersion
• Wave train group of waves with similar
  characteristics (H, L, S, T)
• Wave train speed is 1/2 speed of individual wave

18
Wave Trains
The leading wave in a train is drained of energy
(because it must set up the circular motion), but
after the wave train passes, it leaves behind
enough energy to generate a new wave. Wave train
speed 1/2 wave speed
19
Wave Interference
It is inevitable that swells from different
disturbances will meet when this happens, they
will interfere with each other CONSTRUCTIVE
INTERFERENCE Wave trains are in phase (crests
coincide, troughs coincide L1 L2) amplitudes
add larger wave results DESTRUCTIVE
INTERFERENCE Wave trains are out of phase
(crests coincide with troughs L1 L2)
amplitudes subtract smaller wave results MIXED
INTERFERENCE Wave trains are in out of phase
(crests and troughs do not coincide L1 ? L2 H1 ?
H2) complex pattern results surf beat
20
Wave Interference
21
Wave Interference
22
Shoaling Waves

• Shoaling depths interfere with wave base
• Wave speed (S) decreases
• Wavelength (L) decreases
• Wave height (H) increases
• Wave steepness (H/L) increases
• Waves break (H/L gt 1/7) surf
• Depth (d) 1-1/3 H

• Deep-water swell waves shoal (d gt L/2)
• Transitional waves (L/20 lt d lt L/2)
• Shallow-water waves (d lt L/20)

23
Surf Breakers

• Top of wave topples over base because of decrease
  in wave speed due to friction with seafloor
• Wave form not sustained
• Different types of breakers associated with
  different slope of seafloor

24
Surf Breakers

• SPILLING BREAKER
• Water slides down front slope of wave
• Gently sloping seafloor
• Wave energy expended over longer distance

25
Surf Breakers

• PLUNGING BREAKER
• Curling crest
• Moderately steep seafloor
• Wave energy expended over shorter distance
• Best for board surfers

26
Surf Breakers

• SURGING BREAKER
• Breakers on shore
• Steepest seafloor
• Energy spread over shortest distance
• Best for body surfing

27
Wave refraction

• As waves approach shore, they bend so that the
  wave crests are nearly parallel to shore
• Wave speed (S) is proportional to the depth (d)
  of water (shallow-water wave) S gd1/2
• Different segments of the wave crest travel at
  different speeds

28
Wave refraction

• Energy focused on headland
• Headland eroded
• Energy dissipated in bay
• Bay filled up with sediment (deposition)

29
Wave reflection

• Waves and wave energy bounced back from barrier
• Reflected wave can interfere with next incoming
  wave

30
Standing or Stationary Waves

• Two waves with same wavelength moving in opposite
  directions
• Water particles move vertically and horizontally
• Water sloshes back and forth

31
Standing Waves

• Two waves with same wavelength moving in opposite
  directions
• Water particles move vertically and horizontally
• Water sloshes back and forth

32
Tsunami or seismic sea wave

• Sudden changes in seafloor caused by
• Earthquakes, submarine landslides, volcanic
  eruptions
• Long wavelengths (gt 200 km or 125 m)
• Shallow-water wave
• Speed proportional to water depth so very fast in
  open ocean
• Sea level can rise up to 40 m (131 ft) when
  tsunami reaches shore

33
Tsunami or seismic sea wave
Sequence of photos of a 1983 tsunami in northern
Japan that surges toward fleeing spectators in a
harbor. Red arrows show stationary motorcycle.

• Most occur in Pacific Ocean (more earthquakes and
  volcanic eruptions)
• Damaging to coastal areas
• Loss of human lives
• Example, Krakatau eruption (1883) in Indonesia
  created tsunami that killed more than 36,000
  people
• Example, Aura, Japan (1703) tsunami killed
  100,000 people

34
Tsunami or seismic sea wave
Large tsunami since 1990.

• Pacific Tsunami Warming Center
• Seismic waves forecast possible tsunami
• Tsunami watch/Tsunami warning
• Evacuate people from coastal areas and send ships
  from harbors
• Increasing damage to property as more
  infrastructure constructed near shore

35
Wave Power
LIMPET 500 (Islay, Scotland)

• Lots of energy associated with waves
• Mostly with large storm waves
• How to protect power plants
• How to produce power consistently
• Environmental issues
• Building power plants close to shore
• Interfering with life and sediment movement
• Offshore power plants?
• LIMPET Land Installed Marine Powered Energy
  Transformer November 2000 1.6 million

36
Coastal Wave Energy Resources

• More wave energy is available along western
  shores, especially in So. Hemisphere