PILOT PROJECT: REMOVAL OF MARINE LITTER FROM EUROPE'S FOUR REGIONAL SEAS
Toolkit: Derelict Fishing Gear Retrieval, Implementing your project, Technical parameters for the vesselsSee also: Selection of locations | Timing of retrieval operations | Involving fishermen in retrieval | Involving divers in retrieval | Reception of DFG at the port | Recycling and disposal | Monitoring DFG | Development of prevention and mitigation measures | Raising awareness of the causes and impact of DFG | Project communication
In planning your DFG activities, you will need to ensure that the vessel is appropriately equipped. If hydraulic equipment is to be used to retrieve the DFG, vessels used should be equipped with winches of sufficient power, because of the considerable resistance encountered when pulling up DFG buried in sand. Vessels should also be equipped with modern navigational equipment.
Other technical parameters for vessels relate to length, tonnage and engine power. Generally, retrieval actions could be carried out with a medium-sized vessel (with a length between 12 and 24 metres) that can accommodate a crew of at least five to seven persons (including a captain, crew members and potentially a team of divers), with engine power between 100 and 180 Kw and a tonnage between 20 and 40 GT. Vessels that meet these specifications allow unconstrained 24/7 operation of the search and retrieval gear. They also provide for prompt stopping of the vessel to avoid breaking hooked nets, adequate power for easy handling the retrieval gear and longer stays at sea.
The speed at which the retrieval equipment is towed contributes to its effectiveness. Past experience has shown that a speed of 1 to 1.5 knots permits the best contact between the hooks and the bottom and thus increases the likelihood of retrieving DFG from the sea bottom. This optimal speed is one of the reasons why bigger vessels are not optimal for DFG retrieval, as they cannot maintain a steering capability at low speed, due to their higher sensitivity to wind direction and their higher tonnage.
When smaller gear or net fragments are targeted, smaller vessels could be used. For example, in the Baltic Sea, most retrieval operations have been carried out with 12 – 15 metre gill-net vessels. They have been able to handle, with their net-haulers, whole net-fleets up to 3-6 km length. In some cases the net-fleets were loaded with algae, animals and debris, to the extent that they were too heavy to lift. In such cases the nets were marked with a buoy and later collected with a larger vessel. Working in pairs may also be an option, with a lighter vessel with lower tonnage, for dragging the creeper, and a larger vessel for storing the DFG, which is often heavier and takes more space than normal operational netting as it is loaded with algae, animals and debris.
Storage of the nets on-board
A medium-sized trawler and a larger gill-netter will have the necessary storage space to store the retrieved DFG on deck. Storing the retrieved nets directly on board has an important benefit: when landing the nets in the port, they are once more hauled through the net-hauler and thereby further cleaned. This reduces the odour when stored in the port. Smaller nets (such as recreational fishing gear) or fragments of nets could be stored on board in flexible intermediate bulk containers (commonly referred to as ‘big bags’) or watertight plastic containers (ca. 600 l) with lids to avoid spillage of dirt.