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be used by the aircraft of convenience or of the permanently installed type. Standard built-in
spraying systems of crop spraying aircraft, widely used in agriculture, can be adapted for the
spraying of dispersants.
Only neat concentrate dispersants are suitable for use with airborne spraying systems.
11.1.1 Airplanes
Crop spraying airplanes are readily available. However, it is advisable to modify the spraying
nozzles because the application rate of dispersants is much higher than that of agrochemical
products. They could not be used far from the shore due to limited tank capacity and
insufficient safety offered by a single engine.
Figure 21: Crop spraying aircraft
Fixed systems for converted
multi-engine aircraft comprise storage for dispersants, a pump
including powerpack spray arms with nozzles and a remote control system.
As an alternative, some independent system (with tank, pump and spray booms), have being
developed which can be clamped under the fuselage as a detachable pod (i.e. instead the
luggage chest); these systems allow to convert quickly regular planes into spraying aircrafts.
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Figure 22: Spraying multi-engine aircraft during Deep Water Incident
(source US Coast Guard)
POD spraying systems for small aircraft; self container spraying system which can be rigged
under a small plane as a POD (luggage trunk). It is quick and easy to convert regular plane
usually devoted to good or passenger transportation into a spraying aircraft. The capacity of
these systems is around 1.5 t of dispersant.
Figure 23: POD spraying aircraft (source French Customs)
Self-contained airborne spraying systems are built to suit large transport airplanes which
have rear cargo doors able to remain open during the flight. Containerized units comprise
tank, power pack, pump and retractable spray arms and can be easily loaded into the cargo
hold.
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Figure 24: Large Self Contained spraying system (20t capacity) on C130 Hercules
11.1.2 Helicopters
Fixed spraying systems for helicopters are mounted under the fuselage and are made up of
the same parts as the units built-in fixed wing aircraft.
Figure 25: Fixed spraying systems for helicopter
Helicopter spray buckets can be used with any helicopter having a cargo hook for under slung
loads. Units are self contained (tank, pump, power pack, spraying arms) and can be remotely
controlled from the cockpit.
Figure 26: Helicopter equipped with independent spraying bucket (source SINTEF)
Aerial application of dispersants depends on the visibility over the slick area and relies on wave
energy for mixing dispersant with spilled oil.
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Aircraft permanently equipped for dispersant spraying are rare due to high costs involved and
the use of under slung helicopter buckets seems to be the most readily available solution. In
addition, the use of helicopters has the advantage of extremely good manoeuvrability but their
carrying capacity decreases very quickly when the distance to be covered increases. The
selection of fixed wing aircraft is limited by the lowest speed at which the aircraft can operate
and which should not exceed 150 knots.
11.2
Boat mounted spraying systems:
Several types of this equipment exist including units fixed on the vessel as well as removable
ones.
11.2.1 Systems for spraying conventional dispersants
Systems for spraying
conventional / 2
nd
generation (hydrocarbon based dispersants) are
rarely used nowadays since these dispersants are sprayed undiluted and due to the 1:1 or
maximum 1:3 dispersant/oil rate, a large amount of dispersant needs to be carried on board.
They comprise a fixed flow rate pump and 2 spraying arms usually with 3 nozzles each; these
units were often stern mounted.
Figure 27: Conventional dispersant spraying system for boat
11.2.2 Systems for spraying concentrate pre-diluted into sea water
The application of dispersant pre-diluted into sea water was invented to apply the concentrate
dispersant (low dispersant/oil dosage) using the equipment originally developed for applying
conventional dispersants (high dispersant/oil dosage). Indeed, the dilution enables an increase
of the flow rate to be sprayed and therefore allow spraying with the same equipment (large
nozzles). These systems are designed to pre-dilute the dispersant generally around 10%
dispersant into sea water.
This goal can be achieved by:
Eductor systems are designed to work with the ship's built-in fire-fighting system. The eductor
connected to the discharge side of the pump, causes a negative pressure at the point of
dispersant intake, thus sucking it in into a discharge line. The diluted dispersant is applied by a
fire monitor or through nozzles mounted on spraying arms attached to the vessel's side.