Harbours and Marinas

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Harbours and Marinas
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Siting

• Good land transportation
• Sheltered water
• Natural harbour preferred
• Breakwaters possible
• Waves
• Littoral drift sedimentation
• Tides currents
• Navigation
• Cost

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Waves

• Small entrance
• Big wave reduction
• Difficult approach (esp. in heavy sea)
• Align entrance at small angle to heaviest sea to
  improve ease of entry.
• Wave height reduces with
• Distance from entrance
• Width parallel to shore
• Wave absorbing devices parallel to waves

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Predicting wave height

• Use a model
• Computer simulation
• Physical model (allow for size effects)
• Empirical method (Stevenson formula)
• is the height of the reduced wave at the
  point being considered. H is height at entrance

b
D
B
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Sedimentation occurs as a result of

• Littoral drift direction can change with
  season.
• Heavier particles accumulate on drift side of
  obstacles may extend to inside.
• Fine particles deposited in marina where water
  velocities are lower.
• Tidal movements
• Material enters harbour as tide rises and is
  deposited at turn when water is slack (i.e.
  moving at low speeds).
• Water in marina moves more slowly than out at sea
  carries less sediment.
• Where marina or harbour is at mouth of river
• material carried in river is deposited when
  river water slows down on meeting sea.
• Complicated by differences in density between
  fresh water and salt.

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Navigation

• Channel size depth required depends on
• Boat dimensions
• Water flow parameters
• Waves, velocity etc.
• Boat speeds
• Hydrodynamic effects
• a) bows move apart
• b) bow moves to other ship, stern moves away
• c) stern moves to other ship, bow moves away

Hydrodynamic effects of two ships passing,
travelling in opposite directions
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Oscillatory Waves

• L wavelength
• m.w.l. mean water level
• Pa apparent path of water particle - trochoid
• Pt true path of water particle - circle
• T period of wave or time for particle to
  apparently travel distance L (or to truly travel
  circumference Pt)
• V wave velocity (L/T)
• H wave height

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Translatory Waves

• A wave will always break on a sloping shore when
  the water is shallow enough

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Forces from wave impact -difficult to estimate.

• The pressure, p, that a breaking wave applies to
  a vertical plane is

• Difficult to predict wave velocity.
• No simple relationship between wave velocity and
  wave height.
• Waves break at vertical planes only when water is
  shallow.
• Most waves at vertical planes are usually
  oscillatory, at least at high tide.
• The height of an oscillatory wave at a vertical
  plane will double compared to deep sea.

? is density of water V is velocity of breaking
wave g is acceleration due to gravity
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A Look at Floating Structures

• http//www.shoresidemarinas.com/index.asp
• http//www.shoresidemarinas.com/images/MoreProject
  Richland.jpg
• http//www.shoresidemarinas.com/images/MoreProject
  SpineRd.jpg
• http//www.shoresidemarinas.com/images/USCG_Monter
  ey1.jpg
• http//www.abcpm.co.uk/marina/
• http//www.marinasolutions.com/build.htm
• Video of floating breakwater
• http//www.atlantic-meeco.com/Table_Rock.html

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Motion of Floating Structures

• Six degrees of freedom
• Side to side ( or x)
• Up and down ( or y)
• Forwards and backwards ( or z)
• Rotate about any of 3 axes.

y
x
z
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Significance of pontoon size

• Small compared to Wave

Large compared to Wave
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Bending of Floating Structures Critical Loading
Arrangements
(a) Simply Supported Beam unit supported at
ends only
(b) Double Cantilever unit supported at centre
of gravity only
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Anchorages of floating structures

• Vertical loads carried by the water.
• Horizontal loads transmitted to anchorages.
• Should be designed to permit free vertical
  movement of pontoon.
• Should allow for vertical movement of one end
  relative to the other in response to wave action.
• Must avoid/cater for crabbing.
• Must be inspected and maintained.
• Consider consequences of each failure mode and
  try to ensure that structure is fail safe.

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System must tolerate relative movement (e.g. from
(a) to (b))
(a)
(b)
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Stresses in Floating Structures designed to
permit free vertical movement

• Pressure from wave or vessel impact.
• From units flexing
• (a) Tensile stresses in bottom, compression in
  top of unit maximum at centre of span.
• (b) Tensile stresses in top, compression in
  bottom of unit maximum over crest of wave.
• Unit flexing across width of unit (into page)
• Twisting of unit about vertical axis.
• Combinations of the above
• In anchorages resisting horizontal translation.

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Piles

• A pile is a column that is sunk into the ground.
• It carries vertical load by a combination of
• End bearing
• Friction between the pile sides and the ground
• It carries horizontal loads
• By using raking piles
• Single vertical pile
• By bending and shear within the pile and by
  transmitting the torque and the sliding force
  into the ground the ground must be able to
  resist.
• Remember - ground is weak near the surface.

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Raking Piles most robust solution for piles
carrying horizontal loads
Ship moored at fixed wharf applies horizontal
force that is taken by raking piles.
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Single piles under horizontal loads short rigid
pile ground failure
F
F
Centre of rotation
(a) Free head
(b) Fixed head
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Single piles under horizontal loads long pile
pile failure
F
F
(a) Free head
(b) Fixed head
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Effect of Large Deformation on Bending Moment
Secondary Effects
V
h
H
Deformed Bending Moment Hl Vh
L
l
Undeformed Bending Moment HL
column
Note structural analysis commonly assumes small
deformation.
Fixed Base
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Material Selection

• High Strength/Weight ratio.
• High Strength/Cost ratio.
• High Stiffness/Weight ratio.
• High Stiffness/Cost ratio.
• Durable under working conditions.
• Water
• Salt
• Exposure
• Attractive appearance.
• Surface properties may be significant
• Wear resistance
• Frictional resistance

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Rot or Decay of Timber

• Fungus grows on timber feeding off the cell walls
  and destroying the structure of the timber.
• Damage caused by mycelium, not by fruiting body
  wood looses strength stiffness.
• Rot can be cubical spongy stringy etc.
• Needs moisture to grow (above 20), can remain
  dormant for many months when dry.
• Needs oxygen only grows above low water line.
• Some timber naturally resistant.
• Growth vigorous when warm (above 20oC).

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Weathering of Timber

• Weathering
• Slow disintegration of timber as a result of
  exposure to elements.
• Surface softens under effect of water.
• Rapid drying causes surface splitting.
• Surface forms small cubes sometimes. mistaken
  for dry rot.
• One surface has disintegrated rot often set in.

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Marine Borers and Timber

• Technically not insects.
• Teredo, or ship, worm best known.
• Much more severe in tropical climes than in
  temperate zones.
• Greenheart billian have natural resistance
  (greenheart is poisonous so watch out for
  splinters).
• Preservatives available consider environmental
  effects but casing in Muntz metal (a brass
  copper zinc) or studding with nails probably
  more cost effective.

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Metal choose one developed for a marine
environment

• Mostly alloys of copper, nickel and austenitic
  steel.
• Copper-nickel alloys commonly have 10, (ship
  hulls) 30 (for pipes) 70 nickel (fasteners,
  propeller pump shafts) with traces of other
  metals.
• Austenitic stainless steel contains nickel and
  (especially when used with trace alloys) performs
  well in marine environments
• http//www.stainless-steel-world.net/pdf/10011.pdf
  
• Aluminium is good, and getting cheaper.
  http//www.eaa.net/home.jsp?content/transportatio
  n/marine.htm
• Titanium is good but very expensive.
• Often metals are protected by painting
  (specialist paints available), galvanising, epoxy
  coating etc.

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Concrete

• Need dense, high quality concrete.
• Good curing (control of setting) important.
• Correct moisture content during setting
• Correct temperature
• Control of cracking
• Small diameter, closely spaced reinforcement
• Often pre-cast, pre-stressed concrete provides
  the best solution
• Presence of chlorides and sulphates in sea water
  means you need a special mix.

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Harsh Environment

• The marine environment is very harsh
• Storm dependant loads
• Corrosive atmosphere
• Dangerous working conditions
• Fragile ecosystem
• Many valuable resources yielding high rewards

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Any Questions?