[1] Quay walls and jetties are facilities where ships can load or unload their cargo while they are safely moored to the structure. Sometimes the harbour is protected by a breakwater or by natural protection.
[2] Quay walls are continuous structures, combining the unloading and the mooring function. Behind the quay ample space will be available to receive and store the cargo before loading and / or after unloading. Passengers of ships can also be considered as “cargo”, but most times we shall be dealing with containers or bulk cargo.
[3] Jetties are marine structures with a long access road [access trestle] and a separated function of the [un] Loading platform, the Berthing dolphins and the Mooring dolphins. The material transport will be mainly by pipelines [liquids or gases] or conveyor belts [dry bulks].
[4] In all cases fenders will be used to absorb the berthing forces and Bollards [qua walls] or Quick Release Hooks or “QRH’s” [jetties] to moor the ships.
[5] On the jetties a berthing aid system can used to monitor approach velocity, angle and distance of the vessels to the berth and display these to the ships captain.
[6] Navigation aids is a system of illuminated buoys marking the approach channel and the turning circle.
[7] Most requirements are specified in BS 6349 part 4
2 The Mooring process
[1] The ship will be brought under own engine, or assisted by tugs, to a position
approximately 20 to 50 m1 in front of the future berth, more or less parallel to the berthing line.
[2] Small boats will pick up the mooring lines and bring them to the shore or the mooring dolphins. The mooring lines will be fixed to the bollards or QRH’s and the ship can bring itself to the berth by it’s own mooring winches.
[3] The longitudinal position then can be maintained by the ships own engines. Some times the tugboat will help the ship to move into the berthing positions.
[4] Once berthed, the mooring lines will be secured in both directions and be adjusted continuously, taking account of tidal range and degree of loading / unloading.
The mooring lines must not be too tight nor should they be too loose.
3 Fenders
3.1 General
[1] Fenders basically protect the berthing structure against ship impact; they do not protect the ship.
The protection of the ship is secondary importance; if a ship damages her berth, the owner of the ship will be responsible and costs are normally born by the ship’s insurer.
[2] The above is slightly different for a larger tankers, where by the allowable pressure starts playing a role. There fore theories have been developed to calculate the expected berthing energy, resulting from the mass and berthing velocity / angle of the ship.
[3] The following fender systems can be considered:
- Hard fenders by wood or plastic for smaller vessel types below 1,000 DWT
- Soft rubber fenders by rubber only or pneumatic for larger vessels and tankers above 1,000 DWT
- Combination of the above [fender piles] for 1,000 to 3,000 tons DWT
- Mono tubes, combining deflection in the large diameter fender pile and the deformation of the rubber fenders.
3.2 Basics of fender design
[1]Berthing Energy
The berthing energy governs the fender design and depends mainly on:
- The mass of the ship [DWT]
- The berthing velocity of the ship, to vary between 0.10 m1 and 0.20 m1 / second
- The berthing angle, mostly not more then 10 degrees
- The eccentricity of the ship towards the first point of contact with the berth
Note: For quay walls the first contact point will be the bow or the stern bow of the ship.
For jetties this would be ideally on a ¼ of the total ships length, but can vary due to wrong manoeuvring or desired berth lay out.
[2] Quay walls
Fender spacing for quay walls should not be more then 15% of the of the length of the smallest vessel to berth. Besides that, the curvature of the bow and the fender height in depressed shape may cause the maximum spacing to be smaller.
[3] Jetties
For jetties, with independent breasting dolphins, the centre tot centre distance of the outer dolphins should be in the range of 30% to 40% of the largest ship and for the inner breasting dolphins in the range of 30% to 40% of the smallest ship.
[4] The installation level of the fender
This will be again governed by the smallest ships; the freeboard at lowest water should still be able to have proper and adequate contact with the fender. Specially in the case of transportation barges this can have serious effects on the fender design. Sometimes precast fender brackets are used to bring down the installation level of the fender below sea level.
[5] Fender boards [Frontal Frames]
These are steel structure frames in front of fenders and can have 2 functions. The main function is to distribute the fender reaction force over the hull of the ship to achieve a hull pressure below 40 ton per m2 [some specifications require 20 tons per m2]. Secondly the fender board can be rectangular in such away that the underside is just below low waster, thus allowing big barges to be moored on the structure.
They have a low friction surface to avoid rubbing forces in longitudinal as well as vertical direction, due to the movements of the ship direction.
[6] Rubber type fenders and reaction forces
Rubber fenders are available in different rubber qualities. By selecting a softer, but larger sized fender, the fender reaction force can be reduced. Consequently by selecting a more expensive fender, savings can be made in the costs of the dolphin structure; resulting in a total cheaper structure. This wil specially be the case in deeper waters.
[7] Fender piles
Sometimes H-beam [or cy pile is used [driven] in front of the quay, supported by a rubber unit against the quay coping. If protected by hardwood, this solution is often used in harbours with an extreme tidal difference.
The energy is then absorbed by the deflection of the pile as well as the absorbing fender cushion against the quay.
[8] Mono tubes
Another type of a fender pile for large jetties is a so called mono-tube; a single large diameter driven pipe on which the complete fender unit can be places in one go. The berthing energy here is also achieved by deformation [bending] of the pile and the rubber fender on top. Since it is freestanding the constant wave action will cause a regular movement of the pile, possibly causing fatigue cracks in the fender pile.
[9] Safety factors and berthing speed
Both BS 6349 and EAU recommend berthing speed in combination with a maximum safety factor of 2 on the berthing energy for accidental berthing. Be careful, as sometimes the extra energy is already allowed for in the berthing speed. Also when tugboats assist during berthing it can be considered to reduce this safety factor as well.
Anyway this is an item to be reviewed in case of design & construct since a considerable saving can be achieved by reducing this [unnecessary?] safety factor.
3.3 Most Common Fender types
[1] Hard fenders [rubbing fenders]
They normally consist of hardwood[Azobe], but recently synthetic materials become more popular. As already mentioned these are used for small craft [tugs, launches, barges or fishing boats] up to 1,000 tons, whereby the ship will always have his own protection [tires or foam filled bags]
They are also used in combination with access ladders to mooring and breasting dolphins. Wood sizes will mainly be in the 0.25 to 0.35 m2 range.
[2] Rubber cylindrical fenders
The smaller cylindrical fenders [starting from 150 mm OD / 75 mm ID] can be produced in lengths up to 12 m. These fenders, up to 500 mm OD, are also used for the above small craft. The largest cylindrical fender [ up to 2400 mm OD / 1200 mm ID] are available in maximum length of 2 m and have an energy absorption of 85 ton meter [43 tm / m1]. These are often used for large container ships, but unsuitable for tankers, due to the higher hull pressure.
They are fixed to the structure by steel chains, although for the larger sizes a steel bracket is preferred.
In general this is a very economical type of fender in the larger ship sizes. For small craft it is always cheaper to use hard fenders.
[3] Arch or M type fenders
These fenders are normally used for vessels in the 1,000 to 100,000 dwt range. Their height [fender face to quay face] will vary from 300 mm [3.5 m long] to 1,000 mm [2 m long]. Energy absorption then ranges from 10 ton meter to 90 ton meter [45 t m / m1]
They give a relative high hull pressure, but by combining them with Front Panels the hull pressure can be reduced to acceptable levels.
These also are available in different rubber grades; for example for a 2 m long SM 600 H or For SM 800H ‘Bridgestone” fender we can make following comparison:
[4] Cell fenders [Bridge stone]
These consist of large rubber cylinders, placed perpendicular on the quay face, combined with a large front panel. Although smaller units are available their normal range is from 1,000 mm to 3,000 mm, with energy absorption from 20 ton meter to maximum 400 ton meter each. They cater for tankers up to 500,000 DWT [VLCC's].
Bridge stone is the most recognized supplier for these kind of fenders [SUC series] and are available in 5 different rubber grades.
Also here it might be worthwhile to consider a larger, softer and more expensive fender in order to save on the dolphin structure.
[5] Cone fenders [Fentek]
They are similar to Cell Fenders [as above] but the rubber cylinder is tapered. According the supplier, the coned shape gives a better performance during angled berthing [max 10 degr], and assists in self centring.
The largest size is SCN 2,000 [2,000 mm height, which can have an energy absorption between 300 to 500 ton meter depending on the rubber grade].
Typical E / R relation of approx 1.0 [E of 500 ton meter gives a R of approx 500 tons].
[6] Pneumatic Fenders [Floating]
They are normally placed against solid faced quay structures and have following advantages;
- Easy and fast to deploy
- Very low reaction and hull pressure
- Performance adjustable by varying initial pressure
- No problem with large tidal differences
It is not a very common fender.
[7] Element Fender
A modular rubber fender system, consisting of slender rubber units, which can be configured in many ways. The front panel creates a connection at the front, causing the individual units to work together.
[8] Other types of fenders, not further discussed, are:
- Parallel motion fenders
- Foam fenders
- Donut fenders
- Shear Fenders
- Corner or wheel fenders
- D & Square fenders
- Turtle and Pot fenders
3.4 Fender selection summary
Note: DWT divided by 1,000 gives approx nett berthing energy [E]. By adding 50% a safety allowance is [partly] included
3.5 Other Considerations on Fenders
[1] Anchor bolts
The cast-in part of the anchors can be stainless steel [Super bolt], available up to M 76 and by Resin box [Chess anchor], available up to M 36 [for smaller feder sizes.
For the anchor bolt itself, SS 400 galvanized steel bolts are normally used; these have to be replaced regularly. Stainless steel is normally weaker then carbon steel and there fore not usable as anchor bolts for fenders
[2] Chains
Often suppliers offer fenders in combination with [galvanized] chains. These chains will give the fender unit extra longitudinal stability, because the fender unit itself is not strong enough. Although technically acceptable, this is not an ideal solutions. Chains will corrode rapidly [splash zone] and consequently, if not timely replaced, can snap during the ships berthing. This can cause damage to the dolphin [and ship].
[3]Major Fender vendors and manufacturers
- Bridge stone – Japan
- Fentek – Germany / Australia
- Svedala /Trellex – Sweden
- Seibu – Japan
- Sumitomo – Japan
4 Moorings
4.1 General
[1] The proper mooring of a ship not only requires the ship to stay at it’s berth, but also to keep it’s position, within certain limits. Container ships, being [un]loaded with container cranes, will require a better fixation then for example bulk cargo ships being loaded with a conveyor.. On the other hand, liquid tankers will not always have their manifolds at the centre of the ship.
[2] For quay walls the mooring lines will be fixed to bollards, positioned at the front of the face, causing these lines to become more and more inclined, due to the effects of the tide and the unloading.
[3] For jetties, having separate mooring dolphins, the mooring points [mostly Quick release Hooks] will ideally be more then 35 m away from the side of the tanker. This will require access walkways or alternatively mooring launches to man the mooring points.
[4] Following terms are used for the various mooring lines:
- Stern and head lines are the mooring lines at front and stern, to be placed as far away as possible, say 45o angle to the quay
- After and forward breast lines come from the same location on the ship but are more or les perpendicular to the quay
- Spring lines come from the ship at approx quarter length and run more or less parallel to the quay.
4.2 Design aspects
[1] Forces acting on the ship
The major mooring force on ships is caused by wind, coming from land. Normally designs will be made on the basis of maximum winds, but they moastly come from sea. This create a conservative approach.
Normal tankers will have a lower profile then for example gas tankers, resulting in larger mooring forces for gas tankers.
In the literature, also forces created by current, waves and tidal effects will be considered, but to my opinion they play a minor role.
[2] Loads on mooring points.
Most designers will calculate the mooring forces following the recommendations of BS 6349 or the EAU. This will provide the load on a single mooring wire or rope. When applying multi hook Quick Release Hooks, the will assume that one mooring wire will be loaded to it’s maximum allowed load. Consequently for the total load on the dolphin, they will multiply this maximum load by the number of hooks and allow a reduction factor of say 70 %.
The theory of the undersigned is that only one mooring wire will exercise the maximum force and the other lines will not apply forces to the hook or bollard.
Quick Release Hooks certainly, but bollards sometimes should have a load point that the load will be released or the Bollard breaks.
Again an example of over conservative design principals.
[3] Quick reference table according BS 6349 – part 4 ; 1994
4.3 Bollards
[1] Bollards can be made of cast iron [BS1452], graphite cast iron [BS 2789] or cast steel [BS 3100]
For bollards below 25 tons, they can easily be made in our own workshop, using a piece of steel pipe on a base plate, a mild steel cross bar and concrete fill.
Some times the anchor bolts include break-out devices, so the quay is not overloaded by the pulling forces. Specially at upcoming tides the boat’s watchman can forgets to release the mooring lines in time.
[2] Following shapes are common:
- Pillar type
- Tee-head type
- Twin-head type
- A safe working load of 200 tons is the maximum for commercially available Bollards
4.4 Quick Release Hooks [QRH's]
[1] Quick Release Hooks are units with 1 to 4 hooks each, so they are able to receive various mooring lines. They can be released quickly, without releasing the mooring wire tension, in case of emergency. This release can be manual or by remote control.
[2] individual mooring hooks will vary in holding capacity from 60 tons to maximum 200 tons each. The quantity of single hooks per QRH unit can vary from single to sextuple [6 hooks per unit]
Also back to back units are available [combining 2 x 2 hooks].
[3] To handle the [heavy] mooring wires, these QRH’s are mostly combined with an electrical capstan on the back of the assembly. These again are available in different pull loads [2 tons to 10 tons] and pulling speeds [10 to 20 m per minute].
In case of LNG / LPG Jetties the enclosure has to be explosion proof and depending on wave / deck level, water proof. This also means that electrical cables have to be installed along the walkways or through the water if no walkways foreseen.
[4] Most specifications also require remote control and remote load measurement, making the installation quite expensive
[5] QRH’s capacity vs Ship size
5 Other Quay hardware
[1] Ladders
Ladders are normally fixed to the front of quays and to breasting and mooring dolphins, to allow access from small craft.
To protect them, vertical rubbing wood is placed on both sides.
Stainless steel seems to be the preferred material, chosen by designers, but these days GRP or rubber ladders become more popular.
[2] Mooring rings
To fix the above mentioned small craft, mooring rings are to be provided at the quay, but common practice is that these ropes are fixed to the ladders.
6 Berthing Aid Systems
[1] On the jetties a berthing aid system can be used to monitor approach velocity, berthing angle and distance of the vessels and display these to the ships captain.
Radar sensors measure the berthing speed and distance to the berth and display the information as mentioned by large illuminated boards, taking a lot of place.
7 Navigational aids
[1] Navigation aids is a system of [illuminated] buoys marking the approach channel and the turning circle for incoming and out going vessels.
[2] The so called Sentinel Buoy’s can vary in diameter from 1.50 m to 2.5 m, depending on expected waves. They are fitted with a lantern, a battery, solar panel, radar reflector and possibly a day mark.
A system of chains and concrete ballast blocks will keep the buuy in position. Configuration and size of chains will depend on expected currents.
[3] Smaller marking and spar buoys can have day or top marks and reflectors in various types. Configuration and types of day / top marks differ per harbour
[4] Dock obstruction lights are placed on the structure, to indicate the obstruction present.
