underkeel clearance - capt. john hamill

8/14/2019 Underkeel Clearance - Capt. John Hamill

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UNDERKEEL CLEARANCE

SHIP SQUAT & TIDES

BEST NAVIGATION PRACTICES


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DEFINITION OF SQUAT

REDUCTION OF UNDERKEEL CLEARANCE (UKC)

CAUSED BY A SHIPS MOVEMENT THROUGH

THE WATER.

(IT IS NOTAN INCREASE IN DRAFT. RATHER, IT IS

THE BODILY SINKAGE OF A VESSEL WHICH

PLACES IT CLOSER TO THE SEA BOTTOM.)


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STATIC DRAFT + SQUAT


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SQUAT FACTS

C >.7 (bulker) squats by bow. C < .7 squatsby stern

Squat varies directlywith breadth (doublingbreadth doubles squat)

Squat varies by the square of speed (doubling

speed quadruples squat) Squat can be doubledwhen meeting another

ship


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SQUAT FORMULAE


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BEST GENERAL FORMULA

V squared/100= SmetersSpeed=6KTS

36/100=.36 meter squat

Speed=12kts

144/100= 1.44 meter squatDoubling the speed quadruples the squat


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HULL TYPES

BLOCK COEFFICIENT (C )


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LARGE BLOCK HULL

C > .7


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FINER HULL

C < .7


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VARIOUS SQUAT FORMULAE YIELD

SIMILAR CONCLUSIONS


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SQUAT PREDICTIONS


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TIDAL CONSIDERATIONS

ZERO TIDE


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TIDE +4 FEET


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TIDE +8 FEET


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TIDAL CONSIDERATIONSUSING TIDE TO GOOD ADVANTAGE

NOAAS PORTS TOOL ONLINE

LOCAL KNOWLEDGE OF PILOTS

CREDIBLE PREDICTIONS OF METIORILOGICALFACTORS ON TIDES (NOAAS FORECAST

PROGRAM)


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NOAAS OPERATIONAL FORECAST

SYSTEM


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OPERATIONAL FORECAST SYSTEMSCREEN SHOT 7/24/11


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NOAAS PHYSICAL OCEANOGRAPHIC

REAL-TIME SYSTEM (PORTS)SCREEN SHOT 7/24/11


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NOAAS SEARCHABLE STATIONS

www.tidesandcurrents.noaa.gov


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PORTS COMPOSIT PAGE

CHESAPEAKE CITY, MD


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PORTS AIRGAP OBSERVATIONSC&D CANAL


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Association of Maryland Pilots

H FLAG

PILOT ON BOARD

underkeel clearance - capt. john hamill

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