Jetty: POL Jetty Loading & Unloading Facility – Part I

Topics covered:

Overview of jetty:

A jetty is termed as a long, narrow structure made of wooden, earth, stone or concrete that protects the coastline against the currents and tides. They stretch from the shore into the water.

Currents and tides in an ocean cause erosion which gradually washes away a beach or other features along the coastline. Strong river currents or waves from a lake can also erode a coastline. Jetties protect the shoreline of a body of water by acting as a barrier against erosion from currents, tides, and waves.

Pier is a type of jetty which is used to connect the land with deep water farther away from shore for the purposes of docking ships and unloading cargo.

Figure 1: Jetty for cargo unloading

Figure 1: Jetty for cargo unloading

Types of Jetties:

On broad basis following are types of jetties.

  1. POL (Petroleum oil) jetty – Petroleum oil products (white oil as well as black oil) are unloaded/ loaded at this jetty.
  2.  COAL jetty: The name itself is self explanatory for its function.
  3. Material handling: Food grains and edible oils are loaded /unloaded @ this jetty.

Selection of POL Jetty

There could be two situations in which unloading facilities need be planned for POL products.

1.1.  Jetties which are constructed for handling the POL products.

1.2.  Conversion of material handling/Coal jetties to POL unloading facilities (partly/ fully).

Check list and Guidelines required for POL Jetty development are listed in the below section ‘Methods of unloading’, however additional points which need be considered for providing POL unloading facilities at the existing material handling/Coal jetties are noted below.

a)  Permission from Port Authorities for proposed conversion.

b)  Feasibility and risk management study.

c)   Fire fighting system of the port has to be reviewed as per guidelines of          OISD –156 (latest revision).

d)   Apply for CCOE approval to convert the existing jetty to POL (partly/ fully). Hazardous area classification drawing also needs to be  submitted during CCOE approval.

e)   Convert all the electrical fittings in hazardous area classification to flame –proof.

f)    Method of unloading requires a higher infrastructure cost   as one has to add a new System without disturbing the existing operation. For e.g. mounting the loading arm on a mobile trolley. During CCOE approval of such system one has to clearly identify the operational sequence in which the equipments for two separate systems (POL and COAL/ MATERIAL handling) are proposed to be operated including their viability. This should cover the proposed parking for the loading/ unloading equipment of one type when the handling operation of the other commodity is in progress.

g)    Providing facility for containment boom.

h)     Providing Water curtain.

i)     Ensure that Vessel size (Parcel) through which unloading is done matches with the dimensions of Berthing Dolphins & Mooring Dolphins.

j)     Quick release couplings automated through control room to ensure that ship is disconnected from berth in case of fire. Developing this Automation involves high cost.  But this could be a requirement in case of new jetty.

Method of unloading

Once selection of jetty is done, next important parameter is method of unloading the planned product. There are three methods broadly used to unload POL product.

A)  Marine loading arm. (MLA): This is the most safe method of unloading POL product and widely used around the world. Installation of MLA is possible only if the jetty is in construction stage or if the owner has left adequate space (base plate) during construction stage. MLA is huge in size (ON-BOARD arm = 10 to12 m and Off-BOARD ARM 10 –12m), it is almost impossible to use this method if initial provision is not made. MLA is located very close to berthing edge and almost at the jetty center. One jetty can have 4 to 5 MLAs (owned by different users) located centrally next to one another.  Central location of MLA is important from berthing of vessel is concerned, as the tie-ropes need to be properly tugged in the Bolards / Quick release couplings located on berthing dolphin and mooring dolphin. It is to be noted that MLA is very costly (approx. 4 crores based of safety features attached) item and very few vendors are available in market who venture in this section. The reason to qualify this as most safe method is that there is a ERS (emergency release system), in event of fire detaches itself from the berthing edge jetty. This system is also useful during Tidal variations.(Refer fig.2)

Based on the Vessel Traffic one can also opt for using the installed MLA on lease basis.

  B)   Hoses: This is very crude way of unloading POL products .The distance between pump discharge manifold installed on vessel and inlet connection point at jetty is approximately 40-50 m. No Manufacturer makes hoses of such long lengths and also it is very difficult to handle hoses of such high lengths. In such event the total length is achieved by connecting multiple hoses of 6.0m each. This develops joints which are points of leakage. Also one must note that once a Parcel berthing takes place it has a limited time frame in which the total unloading has to take place, time extension causes demurrage charges. During the entire operation if any of the joint leaks then the entire operation is upset. In the event of fire this system cannot be easily disconnected and poses a major safety problem. Though this system is extremely cost effective being the cheapest it is not used with due consideration to safety. (Refer fig.3)

C)   Tapp-off from existing manifold: In-case if MLA installation is not feasible (high capital cost or if owner has not provided provision) and hose unloading is not permitted then the only option is to take a Tapp-off from existing manifolds. Generally at the downstream of MLA there are manifolds developed based on class of fluid and users .One can take a Tapp-off based on the class of fluid and agreement one has with the owner of MLA / manifolds.

Jetty head part 2 >>