1 mooring of ships - forces course no. 1. 2 purpose of mooring to bring the ship alongside to keep...
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Mooring of ships - forces
Course no. 1
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Purpose of mooring
To bring the ship alongside To keep the ship alongside To assist the ship when un-mooring
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Design criteria of mooring configurations
Based on the forces acting upon the ship Wind Current Waves Swell Other ships passing by (suction effect) Location of the berth – Protected or sea berth Types of ship – size, displacement, draught
etc.
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Example: Mooring of VLCC’s
Often moored outside the harbours along sea berths Forces are so great that no winch is capable of bringing
the ship alongside Tugs are always used when mooring and leaving berth The only criteria is the holding force of the winches The ship must be maintained in position related to the
shore manifold (chiksans)
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Mooring winch with undivided drum
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Mooring winches – Divided drum-polyprop octopus
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Chicksan
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Chicksan
One of the biggest problems with the fixed loading/discharging systems is the restricted liberty of movement of the ship
If one of the limits is breached => ESD-system activated
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Different materials for ropes
Different configurations All steel wire ropes (equipped or not equipped
with tails) All ropes are synthetic Mixed systems (synthetic + steel wire rope) New materials
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Steel wire rope + tail
Purpose of the tail is to add elasticity to account for change in tidal heights
To protect against chafing cover splice of the tail with leather or plastic
The tail is connected to the steel wire rope by means of a Tonsberg shackle or a Mandal shackle
In case of frequent use tails are changed every 18 months
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Tonsberg shackles
Mandal Shackle
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Synthetic mooring Biggest problem is elasticity It can give an important « sway »
(balancer) to the ship (breaking out) 3 mooring ropes – different materials –
same length (50 m), MBL and load Steel wire – 0.3m elongation Polyprop – 5m elongation Nylon – 8 m elongation
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Synthetic mooring
A side effect is sagging The « sag » is function
of: m-n Weight of the
mooring line Tension in the line Water depth (suction
effect)
Shallow Water Effects
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Squat effect
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Mixed mooring systems
Mix of wire ropes and synthetic ropes
Certainly NOT the best configuration but the most common one.
If possible use steel wire rope as springs and breasts and use synthetic ropes as head- and stern line
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New materials
Composite materials
Expensive but excellent mooring system
Kevlar –Aramid ropes are very strong, light and show little sagging. They react fast in case of breaking out of the ship.
Two mooring lines using the same bollard
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Efficient mooring
The efficiency of a mooring rope depends on the The efficiency of a mooring rope depends on the following factorsfollowing factors
Material (steel wire or synthetic – elongation & Material (steel wire or synthetic – elongation & MBL)MBL)
LengthLength
Angles Angles • in the horizontal planein the horizontal plane• in the vertical planein the vertical plane
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Function of the different ropes
Head- and stern lines & the springs are stabilising the ship alongside
Breast line will prevent the ship to break free from the berth
Breast lines must be as perpendicular as possible to the ships longitudinal axis
Springs must be as parallel as possible to the berth
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Recommendations The function of springs and breast lines is clear.
Springs are preventing longitudinal movement, while Breast are opposing transversal movements.
The function of head and the stern lines depends on their angle with the longitudinal axis.
• Great angle => they serve mainly as breast line while
• Small angle => stopping longitudinal movement
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The ideal configuration will rarely be achieved.
To obtain a perfect mooring configuration their must be a perfect harmony between the ships equipment , disposition on board and the configuration ashore
Berthing ships is always a matter of compromises
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Following recommendations have been
published by the OCIMF = Oil Company International Maritime Forum
The recommendations are valid for a tanker moored alongside a T-berth
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Recommendations based on OCIMF – Effective mooring
1. The horizontal angles of head-, stern- and breast lines < 15°
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Mooring Dolphin
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2. The vertical angle with the horizontal plane must be < 25°
The effective force is proportional to the cosine of the angle
If the angle is 25° the line is effective for 91% If the angle is 45° the efficiency is reduced to 71%
=> Springs & breasts must be long enough and not to steep
Recommendations based on OCIMF – Effective mooring
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Springs & Breasts
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3. Breast lines are most effective is on the longitudinal axis.
If is 45° we have to increase the force in the breast line till 141 ton to obtain an effective transversal force of 100 ton
Recommendations based on OCIMF – Effective mooring
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4. Springs offer the greatest holding power in the longitudinal direction. Their length is 60 meters
Recommendations based on OCIMF – Effective mooring
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5. The impact of the head and the stern lines on the total holding power of the mooring configuration is less important than the influence of springs and breasts. This mainly because these lines are too long.
Never the less they are important to compensate the dynamical forces.
Recommendations based on OCIMF – Effective mooring
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6. Very short lines must be avoided. They always take the most important part of the load, especially when the ship is moving
Short length = important vertical angle
Recommendations based on OCIMF – Effective mooring
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Short breast lines
Long breast line: 52ton load is sufficient to obtain an effective holding power of 50 ton
Short breast line: Load has to be increased till 88 ton to obtain same result
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7. All the mooring ropes in the same group (working in the same direction) must have the same tension.
If not, the weakest line will break first. Total load will have to be received by the remaining lines => increased risk of breaking (chain reaction)
Groups are aft spring + head lines, Stern lines + forward spring, breast lines
Recommendations based on OCIMF – Effective mooring
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8. Their must be an equilibrium between the 4 groups: head- and stern lines, springs and breasts.
Optimal mooring configuration is determined after studying the static and dynamical forces for a specific berth.
Recommendations based on OCIMF – Effective mooring
Example: Proposed configuration (Direction of the wind: 110°)4 breast lines (aft) + 1 stern line
3 headlines + 3 breast lines (fore)
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9. The number of lines is function of the size of the ship and the prevailing weather conditions
Recommendations based on OCIMF – Effective mooring
A – Panamax (75.000 dwt) - 12 lines (2 headlines – 4 breasts – 4 springs – 2 stern lines: 2 –2 – 2 fore and aft)
B – VLCC (150.000 dwt) 16 lines (4 headlines – 4 breasts – 4 springs – 4 stern lines: 4 –2 – 2 fore and aft)
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Mooring configurations bulk carriers
Cape Size: 4 –2 – 2 (fore and aft) Panamamax: 4 –1– 1 (fore and aft) Handy Size: 4 –1 (fore and aft) Mini Bulker: 3 –1 (fore and aft) Mini Bulker – moored so it can shift forward and
backwards during loading/discharging
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10. Mooring lines must be passed ashore using the deck fittings (fairleads) because of friction and the curvature relation.
Curvature relation = curvature deck fitting/ mooring line
Recommendations based on OCIMF – Effective mooring
Mooring of ship - TVS 1ste kan 39
Deck fittings
OCIMF equipment:Panamahawse- hole Pedestal Fairleads (Chaumard)
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Info
Suez & Panama Canal
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Suez Canal Total length is 190.25 km Water surface width is 280.345 m Width between the buoys is 195.215 m Canal depth is 22.5 m Maximum ship draught allowed is 62ft Speed allowed for loaded carriers is 13 km/h Speed allowed for unloaded carriers is 14 km/h. Average transit time is 14 hours
Suez Canal
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Panama Canal The Panama Canal is approximately 80 kilometers. The Canal uses a system of locks The locks function as water lifts: they raise ships from
sea level (the Pacific or the Atlantic) to the level of Gatun Lake (26 meters above sea level)
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Panama Canal Each set of locks bears the name of the townsite where
it was built: Gatun (on the Atlantic side), and Pedro Miguel and Miraflores (on the Pacific side).
The maximum dimensions of ships that can transit the Canal are: 32.3 meters in beam; draft 12 meters in Tropical Fresh Water; and 294.1 meters long
The narrowest portion of the Canal is Culebra Cut
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Panama Canal
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Gatun Lock
Gaillard Cut
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Pedro Miguel Locks
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Mira Flores Locks
4-roller fear lead Towing Bracket
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Smit Towing Bracket
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Chocks and buttons
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Bits and Bollards
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Panama chocks
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Roller Chocks
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Roller Fairleads
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Towing pads (point d’attache pour le câble de remorque)
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Mooring alongside a classic berth (quay)
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Mooring alongside a classic berth (quay)
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Mooring alongside a T-berth
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Mooring with 2 anchors
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Ship to ship
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SPM – Single Point Mooring Buoy
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SPM - buoy
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SPM - buoy
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FPSO – single point mooring
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FSO - operations
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STL – Submerged Turret Loading
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STP – Submerged Turret Production
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STP – Submerged Turret Production