May 9th, 2010 
molitva leyli Purse seine winch and davit technology application
The basic form of the tuna purse winch has not changed substantially in thirty years, consisting of a hydraulically driven towline drum, stern drum and bow drum (Figure 1). The sole purpose of the uppermost towline drum is to secure the vessel to the stern oertza, or stern end of the seine during the setting process after which it is hauled to the vessel during pursing.
Figure 1. Tuna purse winch, three drum purse seine winch-Westec TW 8063
The bow drum connects to the bow end of the purse cable during ring pursing. The stern drum holds all of the purse cable during the beginning of the set, paying out cable through the purse rings as the net is set in a circle. At the completion of the encirclement phase, the cable is connected to the bow drum and pursing begins on both bow and stern drums simultaneously.
Modern purse seine winches
Modern purse winch consist of the same three drums but are significantly larger in size to accommodate thicker diameter purse cables necessary for larger and heavier seines (Figure 2). Of greater importance is the increase in power of the newer winches which have been engineered to achieve fast pursing speeds with much deeper and longer (heavier pull) nets. The necessary power has been achieved by installing dedicated auxiliary diesel engines to power the purse winch.
Figure 2. Tuna purse winch circa 2003
A graphic illustration of the increase in purse winch sizes over this time period can be seen in a comparison to purse davits and sheaves. A typical purse davit to accommodate the pull and stresses of a 1970s era tuna purse seine may have measured about 2 m in height (Figure 3). In comparison, Figure 4 shows a huge purse davit and purse blocks on a 100 meter tuna purse seiner vessel currently in operation.
Figure 3. Purse winch, davit and blocks on a 1970s era tuna seiner.
Figure 4. A huge purse davit and blocks ona modern tuna purse seiner (c 2003)
There are several types and makes of power blocks that have been used in the WCPO purse seine fishery. Most of the fleets use some form of the boom suspended “Puretic” type hydraulic power block first introduced to the region by US flag vessels. The entire seine from chainline to corkline passes through the power block, descending to deck level for manual stacking by the crew. Correct positioning of the net is assisted by vertical and lateral movements of the main boom to which the block is attached.
Figure 5. Hauling net on a Taiwanese seiner.
The concept is simple, but requires a great deal of hydraulic power to haul the net high in the air prior to stacking. However, the process allows ample time to clean the net of debris and gilled fish and inspect the net for holes and damage. The main disadvantage of this type of net hauling gear is that it is restricted to calm areas of the world. Net hauling and stacking with this type of gear is extremely difficult or impossible in moderate to strong winds. Figure 5 shows a typical Puretic type power blocks in operation.
Power blocks have increased in size and rated net pulling power in step with the increased depth and bulk of new seine nets. As vessels increase their ability to load and freeze very targe sets, the fishermen have been able to fabricate nets capable of handling catches in excess of 400 mt per set. This means very deep, long nets with thicker diameter corklines, doubled or bunched corks in critical areas, heavier chainlines and very heavy or doubled net bunts (sack end). Figure 6 shows a modern Puretic style power block with greatly flared and expanded sides to accommodate the larger net volumes. Modern power blocks are also equipped with cleats and hydraulic net press to reduce net slippage, two-speed operation for high speed net stacking, and low speed high torque piston drive systems to pull extremely heavy loads prior to sacking up. All of these features combine to reduce the time it takes to complete a haul, sack up and begin brailing.
Figure 6. MARCO B56F Puretic power block.
There are several other types and styles of power block besides the Puretic style single boom mounted block. These systems are more popular in regions of the world subject to much rougher seas compared to the WCPO as the net is hauled from deck level. A good example is the Petrel system (Figure 7), that hauls net from deck level and stacks the seine inside an enclosed net bin with the assistance of an articulated crane mounted block. An unusual “duplex” system was noted on a New Zealand tuna and mackerel seiner (Figure 
.
Figure 7. Petrel net hauling system.
The Triplex system is commonly used in many temperate water fisheries and is recognized as a strong net hauling equipment capable of operation in very rough and windy conditions. The three vertical sheaves provide a very strong net pull with minimal slippage (Figure . A Japanese single purse seiner was experimentally equipped with a Triplex system for operation in the WCPO during the 1980s. (Gillett, 1986). Figure 9 shows the vessel hauling and stacking net using the Triplex system.
Figure 8. “Duplex” style double sheave power block
Figure 9. Triplex power block (Gillett)
Figure 10. Triplex system hauling net on Japanese tuna purse seiner Takuryo Maru (Gillett)
The Japanese use several classes of pelagic purse seiner, many of which normally operate within their coastal or east coast temperate water fisheries. However some of these vessels have or still do operate seasonally within the WCPO. Figure 11 is an example of a double block group seiner that formerly operated in Micronesian waters for the Caroline Fishing Company. Most of the net was hauled and stacked on the stern with some netting pulled on the bow block during the sacking up stage which was greatly assisted by a long rail roller. A large carrier vessel then tied up to the corkline with all fish brailed directly to the carrier. At the completion of the operation, all netting was released from the bow and hauled through the stern block and re-stacked for the next set.
Figure 11. Japanese style double block group seiner.
Figure 12 is a typical Japanese group seine vessel, similar to the vessel described in detail by Gillett (1986b) and Farman (1987). Note that the vessel is designed to set in a clockwise direction in contrast to most single tuna purse seiners. Being a group seiner, the vessel has no fish holds and works in conjunction with refrigerated carrier vessels that load and transport the catch. Note that this vessel is equipped with a deck mounted power block on the stern, a boom mounted block to haul the net up for stacking and a travelling block on the boom that aids in net stacking.
Figure12. Japanese group seiner with travelling boom block for net stacking
Figures 15 shows a more modern style Japanese group seiner as described by Itano (1991) during the final stages of sacking up alongside her refrigerated carrier. This vessel was also equipped with a retractable, swiveling deck mounted power block that was stored below deck during the setting process (Figures 14 – 15). The net bundle passed over the deck block, under an idling sheave to create pulling tension, up to a crane mounted power block that could be moved in any direction toassist net stacking (Figure 16).
Figure 13. Modern Japanese tuna group seiner
Figure 14. Retractable deck mounted power block.
Figure 15. Deck mounted power block in action.
Figure 16. Net hauling and stacking machinery on Japanese group seiner.
Source; ”Documentation and classification of fishing gear and technology on board tuna purse seine vessels”. David G.Itano
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