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Alaska Pilots > Bowditch - Ice Navigation > Flashcards

Bowditch - Ice Navigation Flashcards

1
Q

Bowditch Ice Navigation - glaciers can flow…

A
  • more than 30 m/day, but generally less than that
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2
Q

Bowditch Ice Navigation - iceberg calving

A
  • when parts of an iceberg breaks off forming smaller bergs
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3
Q

Bowditch Ice Navigation - bergy bit

A
  • relatively large iceberg piece
  • 1-5 meters above surface
  • 5-15 meters long at waterline
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4
Q

Bowditch Ice Navigation - growler

A
  • smaller bit of iceberg
  • < 1 meter above surface
  • 5-15 meters along waterline
  • named for noise it makes when bobbing in the sea
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5
Q

Bowditch Ice Navigation - iceberg mass below surface

A
  • 8-9 tenths of mass below surface (pg 515)
  • 60-80% of bulk is submerged (pg 497)
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6
Q

Bowditch Ice Navigation - iceberg drift

A
  • current mostly affects drift because of larger underwater area
  • wind has increasing effect as iceberg deteriorates over time, reduces height to draft ratio
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7
Q

Bowditch Ice Navigation - vessel proximity to icebergs

A
  • dangerous to get close even if it appears stable
  • breaks, rams, capsizing and water displaced by such activity
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8
Q

Bowditch Ice Navigation - iceberg rams

A
  • dangerous underwater extensions
  • melting above surface faster than below
  • also form at ice fronts and ice walls of glaciers
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9
Q

Bowditch Ice Navigation - sea ice %

A
  • freezing salt water
  • accounts for 95% by area of all ice encountered
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10
Q

Bowditch Ice Navigation - pack ice concentrations

A

open water < 0.1
very open pack = 0.1-0.3
open pack = 0.4-0.6
close pack = 0.7-0.8
very close pack = 0.9-1.0
compact or consolidated pack = 100%

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11
Q

Bowditch Ice Navigation - unreinforced vessel can navigate…

A

≤ 0.3 ice concentration

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12
Q

Bowditch Ice Navigation - only occasionally accessed unreinforced vessels…

A

0.3-0.5 ice concentration, depending on wind/current

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13
Q

Bowditch Ice Navigation - 0.5-0.7 ice concentration accessed by…

A
  • only ice strengthened vessels, with ice breaker assistance occasionally
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14
Q

Bowditch Ice Navigation - ice concentrations only accessed by ice breakers…

A

≥ 0.7 ice concentration

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15
Q

Bowditch Ice Navigation - fast ice

A
  • sea ice of any age connected to shore of some kind (ice wall, shoal, ice front, etc.)
  • can be augmented by snow
  • very thick > 2m above surface
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16
Q

Bowditch Ice Navigation - leads

A
  • cracks in ice cover that allow passage of a ship
17
Q

Bowditch Ice Navigation - blind lead

A
  • lead ending in a pressure ridge or other impenetrable barrier
18
Q

Bowditch Ice Navigation - shore lead

A
  • lead between pack ice and shore
  • danger of grounding if closed on
19
Q

Bowditch Ice Navigation - flaw lead

A
  • lead between pack ice and fast ice
  • danger of shear zone if closed on
20
Q

Bowditch Ice Navigation - iceberg detection - clear day

A
  • with excellent visibility, might be sighted at 20 miles
21
Q

Bowditch Ice Navigation - iceberg detection - in dense fog

A
  • sun shining - luminous white object
  • sun not shining - dark, somber mass with narrow black streak at waterline
22
Q

Bowditch Ice Navigation - iceberg detection - blink

A
  • diffusion of light in fog will produce an area of whiteness around iceberg
  • looks bigger
23
Q

Bowditch Ice Navigation - iceberg detection - dark/clear nights

A
  • seen at distance of 1-3 miles
  • smaller growlers more difficult to detect
  • reduce speed/sharp lookout
24
Q

Bowditch Ice Navigation - snow blink

A
  • bright white glare observed above snow surface
  • useful in detecting pack ice
25
Q

Bowditch Ice Navigation - ice blink

A
  • reflection on underside of clouds caused by accumulation of distant ice
  • little less bright than snow blink
26
Q

Bowditch Ice Navigation - water sky

A
  • dark pattern reflected on underside of clouds that are above open water
  • darker pattern than “land sky”
27
Q

Bowditch Ice Navigation - ice detection - radar return strength

A
  • ice presents 1/60 radar return of vessel with same cross sectional area
  • ice reflection coefficient 0.33
28
Q

Bowditch Ice Navigation - iceberg detection - radar ranges

A
  • average iceberg detected at 8-10 miles
  • dangerous size growlers detected at < 4 miles and lost in seas > 4 feet
29
Q

Bowditch Ice Navigation - iceberg/ice pack avoidance

A
  • to windward, if possible, to avoid pieces of ice blown away from main body
30
Q

Bowditch Ice Navigation - sea ice detection - fog

A
  • think bands of fog form over ice edge as moisture condenses from warm air passing over colder ice
31
Q

Bowditch Ice Navigation - iceberg/pack ice drift together

A
  • icebergs among pack ice may be drifting in different direction and speed
  • icebergs = current dependent
  • pack ice = wind dependent
32
Q

Bowditch Ice Navigation - ASIP

A
  • Alaska Sea Ice Program
  • produces ice products for commercial operations
  • support to government and public users

Alaska Pilots (35 decks)

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