4.0 Main Factors in the Design of a Tuna Longliner
The offshore large pelagic fish resources survey, 1995-1997, conducted by the National Aquatic Resources Research and Development Agency ( NARA ) and financed by the ADB Sri Lanka Fisheries Sector Development Project, concluded that the offshore gillnet fishery, conducted by about 1,700 vessels catching an estimated 55,000 t, had already achieved a maximum economic profit and that a further increase in the gillnet fleet should be prevented. Expansion should be in tuna longlining which targets the larger yellowfin and bigeye tuna. The potential yield of all fish caught by tuna longline in the 200 n.mile economic zone was estimated at around 6,700 t which indicated a need for a cautious approach in fleet development.
The NARA Survey recommended a consultancy in prototype longline vessel design, to be locally built but without some of the deficiencies that were apparent in the boats being built at present.
This 10 day consultancy was financed by the UNDP Fisheries Management Project
( SRL/91/022 ). The findings of this mission are as follows:
1. The trend in offshore gillnet fishing is towards boats of 13-16 m (43-52 ft) fitted with engines of 75-120 hp, suitable for extended trips. There is a subsidy of
Rs 900,000 for new boats above 12.2 m (40 ft ). The boats have a suitable deck-
arrangement for gillnetting, with wheelhouse aft and newer boats are fitted with
locally produced hydraulic net haulers. Many of the boats have a barge-like shape
which leads to slow speed and high fuel consumption.
2. Sri Lanka has one of the most active FRP boatbuilding industries in the Region and several yards are able to compete on the export market. There is a need to upgrade the ability of the boatyard staff in developing new designs for fishing boats and in improving the working conditions for persons exposed to high level of styrene emission.
3. Rules and regulations for the construction of new fishing vessels have not been clearly stated.The technical staff of the Department of Fisheries and Aquatic Resources Development( DFARD ) need to receive training in the asessment of drawings and specifications submitted by the boatyards for the approval of the Department.
4. The catch is presently preserved on ice and this is the simplest method that will give the highest price on the export market.Cooling coils in the fish hold or on-board icemaking machines are not recommended.
5. Three different alternatives for a new tuna longliner have been evaluated. The size of
the boat is expressed in:
Cubic Number = CUNO = Length over all x Beam moulded x Depth moulded
Alt. 1: Boat of a CUNO =103 m3, length around 13.7 m ( 45 ft ) with a 83 hp engine. Fishing with 800 hooks using a locally made hydraulic hauler. Trip duration = 10 days with 7 fishing days. Investment = Rs 3.99 million. Yearly catch = 62 t.
Alt. 2: Boat of a CUNO = 155 m3, length around 15.7 m ( 51 ft ) with a 121 hp engine.Fishing with 1,200 hooks using an imported hydraulic longline reel. Trip duration = 10 days with 7 fishing days. Investment = Rs 6.53 million.
Yearly catch = 98 t
Alt. 3: Boat of a CUNO = 296 m3, length around 19.5 m ( 64 ft ) with a 234 hp engine. Fishing with 1,600 hooks using an imported longline reel. Trip duration = 14 days with 10 fishing days. Investment = 10.90 million. Yearly catch = 151 t.
6. The economic evaluation using the accounting rate of return, shows that Alt.1 and Alt. 2 are only slightly better than Alt. 3. The economic evaluation is made with the same assumed bait and fish price as in the NARA Survey, that is Rs 70 / kg for local bait and Rs 124 / kg for yellowfin and bigeye tuna and Rs 80 for other fish. Ref. 1 estimates the sustainable yield from tuna longlining of 6,700 t within the 200 n. mile economic zone of Sri Lanka. For this total catch, Alt. 1 will give a maximum of 107 boats employing 642 men, Alt. 2 will give 70 boats employing 420 men while Alt.3 will give a maximum of 44 boats employing 308 men. The economic calculation is sensitive to cost of bait and price obtained for the catch. Additional information is required on the cost and availability of bait and price of tuna on the export market before a decision on the boatsize is made. For a fully developed fishery catching yearly 6,700 t about 2,100 t of bait is required.
7. Assuming a satisfactory economic return, the following factors will generally favour smaller fishing vessels:
8. The deck layout should be with wheelhouse aft since this is most common in tuna longlining and is also the deck arrangement that Sri Lankan fishermen are accustomed to. The fish hold must have horizontal partitions to avoid crushing of fish in the lower layers.
9. The larger sizes of present gillnet boats can be converted to tuna longlining by fitting a reel for 800 - 1,200 hooks, but due to the deck space required they cannot do this in combination with gillnetting.
1. Further investigation regarding availability and cost of bait and expected price on the
export market of yellowfin and bigeye tuna is required before a decision on the boatsize is made.
2. Rules and regulations for the construction of FRP fishingvessels needs to be clearly defined based on accepted classification standards in other countries. Advice from a person experienced in the survey and classification of FRP vessels is required. He should also be responsible in training of the technical staff of the Department of Fisheries and Aquatic Resources (DFARD) to improve their ability in judging plans submitted by the boatyards for approval.
3. Assistance should be given to the boatyards to reduce the styrene concentration during FRP work in the interior of the boats. This has a proven adverse effect on the health of the workers. An FRP Specialist with wide experience should be recruited for four weeks. He should work in close contact with the boatyards in order to give practical advice that can be implemented. Possibly this mission can be combined with the assistance recommended under point 3.
4. A one month Fishing Boat Design Course should be arranged in Negombo for key persons involved with design work in the boatyards. Technical staff from DFARD should also participate. The participants should attend the course four days of the week and work two days in the boatyard to attend to duties there. During the course, the design of a new longliner for Sri Lanka should be developed interactively between the course leader and the participants. A Naval Architect with experience in fishing boat design should be recruited for a five week period to act as a course leader.
5. The possibility of making a joint venture with a foreign company for local manufacture of longline reels should be investigated since imported reels are costly and there is a good potential for savings in investment. Alternatively NORAD should be contacted to obtain assistance from a person with wide experience in design and construction of deck equipment in order to develop a hydraulic longline reel for local manufacture in Sri Lanka. This type of longline reel can also be fitted to existing larger size gillnetters for conversion to longlining.
The development of the fishery in Sri Lanka can be split into three periods:
Before 1958: Mainly unmotorized traditional vessels fishing close inshore.
1958 - 1985: Introduction of the 8.5 m (28 ft) inboard powered boats fishing with large mesh driftnets and later FRP 5.5 m (18 ft) outboard powered boats fishing with small mesh gillnets. Mainly overnight or one day fishing.
1985 - today: Introduction of 10.4 m ( 34 ft ) boats financed by Abu Dhabi loan scheme. Gradual increase in the number of days per trip and use of shark longline in addition to large mesh driftnets. Fishing trips extend up to one month and the requirements for more fish hold capacity leads local boatyards to build FRP boats up to 60 ft length.
Between 1995-1997 NARA conducted an Offshore Large Pelagic Fish Resources Survey financed by the Asian Development Bank. Three vessels of 11.9 m (39 ft), 14.6 m (48 ft) and 16.2 m (53ft), fished alternately with 2.5 km of large mesh driftnets and with a tuna longline of 21 km with 300 hooks. The report on the survey (Ref. 1) concludes that the offshore gillnetting which targets skipjack tuna, smaller yelowfin tuna and shark had allready achieved maximum economic profit and that future development should encourage tuna longlining catching bigeye tuna and the larger yellowfin tuna. The report also made the following recommendation:
"Provide consultancies for the development of prototype vessel designs and specifications suitable for use by local boat builders. This seeks to achieve improvement in the efficiency and seaworthiness of the offshore fleet. It will be essential that boatbuilders produce vessels designed for the specific purpose (e.g. longlining). This has been made difficult by the absence of locally based naval
architects. The offshore survey revealed great differences in fuel consumption between vessels (unrelated to the age and size of the engines) suggesting substantial mis-matching of hulls with engines. Breakdowns and loss of vessels at sea are common."
The offshore fleet consists of 1700 vessels ranging from 10 m to 18 m (34-60 ft). The trend has been towards vessels of 13-16 m (34-52 ft) ( Fig 1 ). The total yearly catch of these vessels is 55,000 t. Many of the new boats have an extreme barge-like shape partly dictated by the limitation on draft at the entrance to Negombo harbour and the wish of the owners to ensure a maximum volume of fish hold and fueltanks into a given length of hull (Fig. 2). A twin engine installation was favoured in the larger boats and this , together with the extreme hull shapes, led to a low service speed of the boats and high fuel consumption. The owner of the 16 m (53 ft) boat used in the NARA survey, reported a cruising speed of only 6.0 knots. In a future boat he wants to use a single engine.
Owners of smaller multi-day boats are extending the range of the boats by carrying extra drums of fuel and water tanks on deck. This practice increases the possibility of capsize in adverse weather conditions. (Fig. 3 and 4)
At present only two Sri Lanka registered boats are fishing with tuna longline, both owned and operated by the TROPIC FISHERY ( PVT ) LTD. which is part of
the TESS Group of Companies. The smaller boat is a 16.8 m (55 ft ) boat built by BLUE STAR MARINE (Fig. 5). This boat is fishing with a 1,000 hook longline. It has
a hydraulic linehauler ( Fig 6 ) and stores the mainline on three reels which are hand-driven (Fig 7). The larger boat is a 110 ft Japanese style tuna longliner fishing with a 1,700-2,000 hook longline. The boat is fitted with a linehauler and the mainline is stored on one reel driven by an electric motor.
A joint venture between LANKA FISHERIES and a Japanese company ordered a series of 11 m (36 ft) boats from BLUE STAR MARINE and fitted them with tuna longline haulers. The company seems to have failed in this operation since several boats lie inactive in Negombo.
DIAYKAWA FISHERIES is a joint venture using a number of Taiwanese longliners.
The largest boat used in the NARA survey (Ref. 1), the " Seychell Maru ", used a 600 hook tuna longline for three months after the end of the survey. The owner reported good catches but the longlining operation had to be discontinued due to lack of locally caught bait. This points to a major problem in development of a tuna longlining fishery: the cost and availability of good bait.
Construction of FRP fishing boats in Sri Lanka started with the construction of the 18 ft outboard powered boat and the 28 ft boat at the beginning of the sixties. The two major boatyards, NEIL MARINE in Negombo and BLUE STAR MARINE at Pannipitiya, between Negombo and Colombo, gradually expanded to build larger boats for export. The demand for larger fishing boats for multi-day fishing, which started in the mid eighties, led to a rapid development of the size of fishing boats built, first a 10.4 m (34 ft) boat and then gradually up to the largest fishingboat delivered so far being a 18.3 m ( 60 ft)boat. In addition to NEIL MARINE and BLUE STAR MARINE there are three more boatyards in Negombo and one on Beruwala building boats above 12 m (40 ft). Two of these boatyards do not use a permanent mould. One of the yards uses a hybrid wood/FRP construction method erecting first a wooden keel and frames, applying longitudinal battens and then fixing thin FRP plates on the outside to the battens and the frames (Fig. 8). The FRP materials are then applied on the inside and outside until sufficient thickness is reached. It is doubtful whether this method would be approved by any classification society such as Lloyds due to problems with secondary bonding.
Another boatyard uses a disposable mould method where a female mould is made with outside framing and the inside clad with plywood and plastic laminate. Double curved surfaces are sheathed with short sections of thin FRP laminate. The hull is then moulded in the conventional way. The mould has to be taken apart after completing the hull. NEIL MARINE has a 24.4 m (80 ft) passenger catamaran under construction in a newly established yard in Beruwala using the same one-off construction method. The same company is working on a 23 m (76 ft) mould where the forebody is taken from a traditional Maldive Dhony and the aftbody fitted with a transom stern. A Negombo fisherman has placed an order for this boat and intends to use it for tuna longlining.
Comparing boat sizes only on the basis of the length over all is misleading. A better measure for boat size is:
Cubic Number = CUNO = Length over all x Beam moulded x Depth moulded.
Below is a table showing the main particulars of the larger fishing boats that have been built or are under construction in Sri Lanka.
Table 1: Main dimensions of boats above 12 m ( 40 ft ).
| Vessel | Length over all m |
Beam moulded m |
Depth moulded m |
Cubic number m 3 |
| A | 12.3 | 4.3 | 1.8 | 94 |
| B | 14.2 | 5.0 | 2.5 | 177 |
| C | 14.8 | 4.5 | 2.1 | 139 |
| D | 16.8 | 4.1 | 2.5 | 172 |
| E | 18.3 | 5.6 | 2.9 | 297 |
Table 2: Cost of hull excluding engine and equipment
| Vessel | Cubic Number CUNO m 3 |
Cost of hull Rs million |
Cost of hull / CUNO Rs / m 3 |
| A | 94 | 1.52 | 16,000 |
| B | 177 | 1.80 | 10,000 |
| C | 139 | 1.80 | 13,000 |
| D | 172 | 4.80 | 29,000 |
| E | 290 | 3.70 | 13,000 |
The average cost per m3 CUNO is Rs 16,000 and this is used in the economic calculation.
Most of the boatyards design their own hulls and there are many examples in Negombo that the knowledge of basic design of economical fishing boats are missing. General errors are hull designs with a very blunt bow, which leads to excessive fuel consumption in a seaway (Fig. 2). The reason for this shape is due to the limited depth of 1.5-1.8 m at the entrance of Negombo harbour. Even with this limitation there is no need to use this bow shape. Another case is the use of a typical planing hull design suitable for a speed of 20 knots for a fishing boat having a speed of 8 knots (Fig. 5).
The managers of the boatyards are aware of the problems and expressed the wish for a training course that could upgrade the ability of the staff connected with design and construction. Rather than presenting the boatyards with a ready-made design for a new longliner, selected staff members from the boatyards would benefit from a training course where the design is evolved interactively together with a Naval Architect experienced in the design of fishing vessels. This course should last for 4 weeks and cover the basic steps in evolving a new design from interview with the boat owner to the final drawings. The training course could be held at the Fisheries Training Institute in Negombo since the majority of the boatyards are situated nearby. The Training Institute has students for the whole year except March. Alternatively another site in Negombo with space for 10-12 students can be selected, if possible avoiding the hottest time of the year. The training should be for 4 full days of the week since the staff will have to attend tasks at their boatyards for the remaining 2 days. Technical staff from the Fisheries Department should also attend this course.
For boats above 40 ft the following engine types were observed in Negombo:
Table 3. Engine types and cost including sterngear
| Engine make | Model | Continuous power hp/rpm |
Cost Rs thousand |
Cost / hp Rs / hp |
| YANMAR | 4CH3 | 78 / 2,250 | 1,050 | 13,460 |
| YANMAR | 6CH3 | 115 / 2,250 | 1,305 | 11,340 |
| ASHOK LEYLAND | 90 / 2,000 | 825 | 9,170 | |
| ASHOK LEYLAND | 110 / 2,000 | 900 | 8,180 | |
| VOLVO PENTA | TAMD 31 | 110 / 3,250 | 1,100 | 10,000 |
Recently Chinese made diesel engines have been introduced at considerably less cost than than the makes given in the table above.
In the economic evaluation a cost figure of Rs 11,000 / hp is used.
For safety reasons twin engines were quite common earlier. However the increased cost and complication of this type of installation has created a trend back to single engine installation. Generally the size of engine is correct for the newer boats but service speed is low due to poor hull shape. Some examples of over powering were seen, for example in a 16.8 m (55 ft) tuna longliner (Fig.5) of CUNO= 172 and estimated service displacement of 34 t, fitted with twin engines totalling 220 hp. An engine of 140 hp would have been an adequate and economic powering in this case provided a suitable hullshape.
There is at present a local engineering shop in Negombo producing a hydraulic net hauler which is copied from a Norwegian model. Future longliners will require, as a minimum, a hydraulic line hauler together with plastic bags for storing the mainline (Fig. 9), alternatively one or several hand driven drums for storing the monofilament mainline ( Fig. 6 ). Otherwise one should go directly to the type of hydraulic longline reel commonly used in other areas which both hauls and stores the line (Fig. 10). This type of equipment requires the minimum of deck space. Initially it would be wise to import this equipment from a reputable supplier, but eventually it should be the aim to manufacture the main components locally, except the hydraulic pump, motor and control valve. Possibly a joint venture with a foreign company can be established, alternatively one could try to obtain assistance from a Norwegian winch manufacturer through NORAD.
The FRP boatyards in Sri Lanka show too little concern for the safety of the workers. Styrene emission during the curing process of the polyester resin has been clearly demonstrated to be a health hazard leading to loss of memory and other mental disorders.
This is especially a problem when working in enclosed, poorly ventilated interior parts of the boat such as the fish hold. The boatyards in Sri Lanka need assistance from an FRP
Boatbuilding Specialist to see what measures would be most effective in counteracting this problem.
The boatyards have to submit drawings, details of FRP layup and stability calculations to the Fisheries Department for all boats to be built under the Government Subsidy Scheme. At present a subsidy of Rs 700,000 is given for boats of a length over all between 11 m
(36 ft) and 12.2 m (40 ft) and Rs 900,000 for boats above 12.2 m. It is stated that generally Lloyds scantling rules are followed, but clearly some of the "one off " construction methods seen in Negombo are not covered by Lloyds. It is not known on what basis one accepts deviation from Lloyds. There is a need for clearly defined rules and regulations for the construction of FRP fishing boats. "Nordic Boat Standard for Commercial Boats less than 15 m" could serve as a guide. This standard is used in Norway, Sweden, Denmark, Finland and Iceland and is especially suited to fishing boats and other work boats. Assistance in this field is required from a person with wide experience in FRP survey and classification work. The same person could possibly also assist the boatyards in improving the workers safety during the moulding process mentioned under 3.7. Possibly Bilateral Aid could be sought in order to finance this assistance. A mission of one month duration would be required to study local conditions and give on-the-job training.
New vessels are to undergo an inclining test supervised by a Naval Architect in order to assess the stability. It does not seem that this test and the stability calculations take into consideration the worst possible case when the gillnetter is returning to port with a heavy, watersoaked gillnet stacked on top of the deck and with most of the ice melted, little fish and almost empty fuel tanks and water tanks. For the smaller boats seen in Negombo this certainly represents a stability risk.
The number of sea days and fishing days per trip is governed by the distance to the fishing area and the number of days that the yellowfin and bigeye tuna can maintain export quality on ice. The three boats used in the NARA survey had on average a trip duration of 10 sea days with 7 fishing days to cover the survey area within the 200 n.mile economic zone (Fig. 11). When well iced it is considered that tuna will be of acceptable quality for about 18 days after being caught. In the economic evaluation of different vessel sizes it is assumed that the two smaller boats have 10 sea days and 7 fishing days per trip and the larger boat 14 sea days and 10 fishing days per trip. During the high season the trip duration will be shorter and during the lean season it will be longer. The average number of sea days per year were 237 in the NARA survey. The largest boat in the survey, the 16 m "Seychell Maru" with a CUNO = 222 had on average 277 sea days, while the smallest boat, the 12 m "Chathura Putha" with a CUNO = 96 had 245 sea days. The medium sized boat, the "King Fish 1" with a CUNO = 142, had only 191 sea days. It seems here that the "crew factor" is more significant than the boat size but it is reasonable to assume that a larger boat can fish in rougher condition and have more sea days than a smaller boat. In the economic evaluation below it is assumed that the number of sea days are related to the CUNO as follows:
Sea days per year = 200 + 0.22 x CUNO
The NARA survey vessels used on average 243 hooks per set. The largest survey vessel, the " Seychell Maru", continued fishing commercially for three months with a 600 hook longline. Commercially up to 2,000 hooks are used on larger tuna longliners. The number of hooks that can be set per fishing day, together with the catch rate and the number of seadays, have a significant effect on the boatsize and the economic return, as shown in the economic evaluation. The number of hooks also has a bearing on the workload of the crew. The hauling of a 800 hook longline of 38 km length might take up to 8 hours while a 1,600 hook longline of 77 km might take 16 hours. These are considerably longer working hours than when using gillnets, which have to be compensated by higher earnings of the crew.
The report on the NARA "Offshore large pelagic fish resources survey" gives the following catch rate for tuna longlining as kg per 1,000 hooks:
Low season in December: 404 kg
High season in August: 865 kg
Average for the whole year: 648 kg
Fig. 12 shows the monthly variation in catch rate. The survey vessels were equipped with a longline with 300 hooks, but on average used only 243 hooks/fishing day. To cover a larger area the spacing between the hooks/ branchlines was 70 m which gave a total length of longline of 21 km. The large spacing between the hooks compared with the 40-50 m used by commercial tuna longliners can possibly have increased the catch rate. It is also realistic to assume that the catch rate will fall with an increase in fishing pressure. An average catch rate of 500 kg/1,000 hooks is used in the economic evaluation later in the report.
The average catch composition was as follows:
Yellowfin: 15.7 %
Bigeye: 21.8 %
Marlin: 10.6 %
Sailfish: 2.2 %
Swordfish: 15.4 %
Shark: 32.9 %
Other: 1.4 %
In the economic evaluation of a 36 ft tuna longliner in Ref. 1, the following prices for the landed catch were used:
Table 4. Landed value of catch
| Fish species | % of Catch | Kg/1,000 hooks | Rs / kg | Rs/1,000 hooks |
| Yellowfin | 16 | 80 | 124 | 9,920 |
| Bigeye | 22 | 110 | 124 | 13,640 |
| Other | 62 | 310 | 80 | 24,800 |
| 100 | 500 | 97 | 48,360 |
The price is based on local prices obtained by the "Seychell Maru" doing commecial fishing with a 600 hook longline in November 1997 and is the same as used in the economic evaluation of a 11 m ( 36 ft ) longliner in Ref. 1. Yellowfin and bigeye tuna exported chilled by airfreight will fetch higher prices. Due to the financial crises in Asia, the prices are now depressed and in the Singapore market the price is at present reported to be US $ 3.50-5.00 / kg ( Rs 224-320 ) for yellowfin tuna and US $ 3.00/ kg ( Rs 192 )for bigeye tuna. Provided the quality of the fish landed is high, export to Asian markets could significantly increase the income. In the economic evaluation the local prices showed in table 4. and used by Ref. 1 is maintained.
The NARA survey used 79% squid and 21% saury (sanma) as bait. All the bait was bought from DIYAKAWA DEEP SEA CO. at an average price of Rs. 146/kg. The average bait consumption per hook was 0.26 kg per hook. This is a high figure since the squid is bought frozen in 13.5 kg boxes containing 80-90 pieces giving an average weight of 0.16 kg per piece. The average weight of the sauri is 0.10 kg per piece. Squid is considered a better bait than sauri but bait consumption per hook is also higher. In the Pacific Ocean, sauri is the most common bait. For the economic calculation it is better to err on the high side and it is assumed that squid is used and that the bait consumption is 0.16 kg per hook. The cost of imported squid is given as Rs 130-145/kg by one of the importers. Locally caught bait that can be used are squid, milkfish, halfbeak and Indian mackerel. The problem is to achieve a constant supply since these species are only available seasonally. The "Seychell Maru" had to cease commercial longlining because of lack of locally caught bait. In the economic survey the same bait cost of Rs 70 / kg has been maintained as in Ref. 1, assuming that local bait can be secured when more longliners create a demand. Imported bait can only be considered if the yellowfin and bigeye tuna are exported at a considerable higher price than can be obtained locally. With a potential yearly longline catch of 6,700 t from the 200 n.mile economic zone (Ref. 1) approximately 2,100 t bait will be required.
The NARA survey reported an average ice consumption of the three survey vessels of 3.2 kg ice / kg catch. However there were significant differences between the vessels from
2.6 kg ice / kg fish on the "Seychell Maru" to 4.0 kg ice / kg fish for the "King Fish". In Sri Lanka the ice consumption is measured in the number of blocks of ice. Each block is assumed to weigh 50 kg, but a closer examination reveals that the blocks only weigh about
41 kg. The actual ice consumption in kg is therefore about 82 % of what is given in the report, that is 2.1 kg ice/ kg fish. Assuming that a new longliner will have an insulation thickness of 150 mm and being equivalent to the best boat in the survey, the ice consumption is assumed to be 2.5 kg ice / kg fish.To cool down one kg of fish from + 30o C to 0o C takes 0.4 kg of ice. The remaining ice is used to cool down the fish hold and to counteract heat-leak through the walls of the fish hold and the fish hold hatch during the duration of the fishing trip. It is further assumed that on return to the port, the fish is well covered with ice to a ratio of 0.7 kg ice/kg fish. Good insulation is important to keep down the heat-leak. On new boats built for the multiday fishery in Sri Lanka it is now common to use polystyrene foam in two layers with joints staggered to a total thickness of 100-150 mm. The stowage rate of crushed block ice is normally 1.5 m3/1,000 kg but in the calculation for fish hold volume a figure of 1.8 m3/1,000kg is used taking into account that it is not possible to fill the sidebins in the fish hold completely. The required storage space for the ice and bait when leaving the port will determine the required volume of the fish hold. There is a possibility of reducing the ice consumption by installing a cooling system in the fish hold. The problem is to avoid partial freezing which would lead to inferiour fish quality. An onboard ice machine would be another possibility but the added complications and risk is judged as not warranted in this case.
It is assumed that a boat based in Negombo will on average have to travel 250 n.miles to fish in the 200 n.mile zone. (Fig. 11) . Assuming further that the boat will travel about 100 n.miles during the 7 fishing days at service speed. Total distance travelled at service speed is then about 600 n.miles on an average 10 day fishing trip. The engine will then work at 75% of nominal installed power. During setting and hauling it is assumed that 60% of full power is used for 18 hours per fishing day. Specific fuel consumption for a diesel engine is about 0.22 litre/hp hr. At normal cruising speed in average wave condition it is assumed that power requirement is 3.0 hp / tonne displacement of the boat. Installed power should be around 4.0 hp / tonne displacement.
The time required to cover the 600 n. mile will depend on the boat size since economical speed is: Vs = 2.08 x \/ Length of waterline in m. We will use a 14 m boat with a length in waterline of 12.6 m as a base case and then correct the travelling time for larger boats.The 14 m boat will have an economical service speed according to the above formula of : Vs = 7.4 knots and will require 81 hours to cover the 600 n.miles.
The Specific fuel consumption per hp installed engine power for this boat will be:
Travelling at service speed: 81 hours x 0.22 litre/hp hr x 0.75 x installed hp. = 13.4 litre / installed hp. Because of higher service speed, the longer boats will have lower "Specific fuel consumption, travelling" as shown in the table below. The fuelconsumption during travelling at service speed will be:
Specific fuel consumption, travelling x Installed hp of engine.
Per fishing day the "Specific fuel consumption, fishing" will be: 18 hours x 0.22 litre/hp hr x 0.60 x installed hp. = 2.4 litre / installed hp. It is assumed that this is the same for all boats. Fuel consumption during fishing will then be:
Specific fuel consumption, fishing x Number of fishing days x Installed hp of engine.
Total fuelconsumption per fishing trip will be the sum of the the fuel consumption during travelling and during fishing
Table 5. Specific fuel consumption.
| Specific fuel consumption | |||
| Boat Length over all m |
Service speed Knots |
Travelling litre / hp |
Fishing Litre / hp / day |
| 14 | 7.4 | 13.3 | 2.4 |
| 16 | 7.9 | 12.5 | 2.4 |
| 18 | 8.4 | 11.8 | 2.4 |
| 20 | 8.8 | 11.3 | 2.4 |
Fuel tank capacity should be 70% higher than the average consumption per trip to cover trips to fishing areas further away.
Fresh water for washing is assumed to be 12 litre per man per day. For a maximum three week trip this gives 250 litre / man. The drinking water should be stored in separate plastic cans that are easy to keep clean. Drinking water requirement is 2 litre/ man / day. For a three week trip this gives 42 litre / man.
Development over the last 10-15 years has shown that monofilament mainline and branchlines are superior to the old rope system. The mainline can be divided into bundles which normally have 5 branch lines or it can be continuous. The branchlines are clipped on to the mainline at intervals of around 40 m using special stainless steel clips.
For Sri Lanka there are basically three systems for storing the mainline that can be considered:
When the line comes off the hydraulic hauler it is coiled directly into plastic bags placed inside a tub. ( Fig. 9 ). Each bag or basket can take 10 bundles of line corresponding to 50 branchlines ( hooks ). Each bag has a diameter of 0.75 m. For a 600 hook longline of 29 km length, 12 bags are required and these take up 6 m2 of deck-space which make this system impractical to use on boats below 40 ft length. For longlines with more than 1,000 hooks and for small boats, a system of storing the line on a reel is preferable for ease of handling and reduced deckspace requirement.
When the line comes off the hydraulic hauler it is stored on several hand-driven drums. Fig. 7 shows a three drum system locally made in Sri Lanka and fitted to a 16.7 m (55 ft) boat storing a 1,000 hook mainline.
A hydraulic powered reel both hauls and stores the line. No separate line hauler is required. The line is led over one or several blocks and into the drum. This is the system almost universally adopted on modern tuna longliners fishing with 1,000 - 2,000 hooks.
The most known manufacturer of this equipment is LINDGREN-PITMAN in the USA (Fig. 10) but there are also several other brands. Unfortunately the equipment is expensive. A hydraulic line setter is an optional extra. The line setter permits more control over the curvature of the mainline between the buoys, thereby deciding the fishing depth of the middle hooks in relation to the outer hooks. It is assumed that only the largest boat will use a hydraulic line setter.
The economic evaluation in Ref. 1 was made for a 11.0 m (36 ft) tuna longliner with a 45 hp engine fishing with a 600 hook longline using the basket system for storing the main line. Based on experience with the fleet of 11 m boats built for tuna longline fishing in Sri Lanka. The consultant considers these boats to have insufficient deckspace for the longline operation and fish holds too cramped to effectively be able to ice the catch for top quality. However, a larger boat fishing with only 600 hooks will not be economically viable. The minimum number of hooks is considered to be around 800. The following three alternatives will be evaluated:
800 hook longline of 38 km (21 nautical miles) using the basket system or preferably the hand driven reel system for line storage. The hydraulic hauler and the hand driven reel can be made in Sri Lanka.
1,200 hook longline of 58km (31 nautical miles) using the hydraulic reel system, but without a line setter. To locate the line in case of a break, 3 radio buoys are used attached to the ends and the middle of the line. A radio direction finder is placed on the boat.
1,600 hook longline of 77 km (42 nautical miles) using the hydraulic reel system with a hydraulic line setter and 3 radio buoys.
The cost estimate of the equipment for the 1,200 and 1,600 hook system is based on import of the LINDGREN - PITMAN longline reel. It is possible to find brands at lower cost and the alternative of making this equipment in Sri Lanka should be evaluated.
Table 6. Fishing equipment. Cost ( Rs thousand ) 1 US $ = Rs 64
| Number of hooks | |||
| 800 | 1,200 | 1,600 | |
| Hydraulic hauler and manual storage,local | 400 | ||
| Hydraulic drum, imported | 960 | 1,100 | |
| Hydraulic line setter, imported | 320 | ||
| Radio direction finder, imported | 250 | 250 | |
| Total fishing equipment | 400 | 1,150 | 1,670 |
Table 7. Fishing gear cost ( Rs thousand )
| Number of hooks | |||
| 800 | 1,200 | 1,600 | |
| Longline, 3.6 mm monofilament | 400 | 600 | 800 |
| Branchline, 2.0 mm monofilament | 70 | 100 | 130 |
| Snaps, buoys, buoyrope, hooks etc. | 160 | 240 | 320 |
| Total fishing gear | 630 | 1,140 | 1,520 |
Existing gillnetters of the larger type can be converted to tuna longlining by fitting a longline reel of the type mentioned above (Fig. 10) without major alterations. However , the space required for the reel forward of the wheelhouse make it impossible to combine this with gillnetting.
The size of the boat is mainly governed by the size of the fish hold. The volume of the crushed block ice together with storage space for the bait will determine the fish hold volume. The relationship between the fish hold volume and the boat volume expressed by the CUNO is based on experience. The relation between the CUNO and the length over all of the boat is also based on experience and will give a boat of normal proportions avoiding the most extreme cases seen in Negombo. The installed engine power is 4hp / tonne displacement, with the displacement taken as the average condition between full load leaving the port and the arrival port condition. The average load is then = 0.75 x full load. The service speed in average wave condition is calculated on the basis of 3 hp / tonne displacement which avoids excessive fuel consumption. On the next page the boat size is calculated for three different alternatives of hook number and duration of the fishing trip:
Table 8. Boat data
| Item | Calculation | Unit | Alt. 1 | Alt. 2 | Alt. 3 | |||
| a | Sea days per trip | day | 10 | 10 | 14 | |||
| b | Fishing days per trip | day | 7 | 7 | 10 | |||
| c | Number of hooks | hk | 800 | 1,200 | 1,600 | |||
| d | Catch rate, kg/1000 hk | kg | 500 | 500 | 500 | |||
| e | Catch | b x c x d / 1000 | kg | 2,800 | 4,200 | 8,000 | ||
| f | Bait | e x 0.32 | kg | 900 | 1,340 | 2,560 | ||
| g | Ice | e x 2.5 | kg | 7,000 | 10,500 | 20,000 | ||
| h | Fish hold volume | ( f + g ) x 1.8/1000 | m 3 | 14,2 | 21,3 | 40,6 | ||
| i | Boat CUNO | h x 7.2 | m 3 | 103 | 155 | 296 | ||
| j | Boat length over all | 3\/ i / 0.04 | m | 13.7 | 15.7 | 19.5 | ||
| k | Displacement, light | I x 100 | kg | 10,300 | 15,500 | 29,600 | ||
| l | Full load | f + g + q + s | kg | 13,900 | 19,600 | 38,600 | ||
| m | Displacement, service | k + 0.75 x l | kg | 20,700 | 30,200 | 58,500 | ||
| n | Installed engine power | m / 1000 x 4 hp | hp | 83 | 121 | 234 | ||
| o | Specific fuel cons. | Table 5 | l /hp | 30.1 | 29.3 | 35.3 | ||
| p | Fuel / trip | n x o | litre | 2,500 | 3,545 | 8,260 | ||
| q | Fuel tank capacity | p x 1.7 | litre | 4,500 | 6,000 | 14,000 | ||
| r | Number of crew | men | 5 | 6 | 7 | |||
| s | Water tank capacity | r x 14 l x 21 days | litre | 1,500 | 1,800 | 2,100 | ||
| t | Service speed | 2.08 V j x 0.9 | knot | 7.3 | 7.8 | 8.8 | ||
| u | Sea days / year | From 4.1 | day | 223 | 234 | 265 | ||
| v | Trips / year | u / a | nr | 22.3 | 23.4 | 18.9 | ||
| w | Fishing days / year | b x v | day | 156 | 164 | 189 | ||
| y | Catch / year | e x v | Kg | 62,400 | 98,300 | 151,200 | ||
The most common arrangement for tuna longliners is with the wheelhouse aft. This has the advantage that the helmsman can clearly see the incoming line and the activity on deck. It also gives a position of the crew quarters with less movement and better ventilation than being placed in the bow, thereby giving a better possibility for rest, an important point in a fishery with long working hours. In Sri Lanka it also has the advantage that the fishermen are accustomed to this arrangement on the gillnet boats. An example of the General Arrangement of a tuna longliner fitted with a hydraulic longline reel is shown in fig.13. The engine should be placed partly in a streamlined bulb in order to shift the engine aft and avoid forward trim in a full load condition. Safety features given in Ref. 2 should be followed where practical.
The hull design should give low resistance without compromising on stability and deck space. A good example of such a hull shape is the "Low L / B Vessels " model tested by the University of Columbia, the so called " UBC Series " ( Ref. 3 ). These vessels have ample beam and are characterized with a relatively sharp bow to cut down on wave resistance. Fig. 14 shows a typical lines plan of the "UBC Series" with low block coefficient which will fit the Length / Displacement Ratio of the boats in Table 6. The models are based on maximum use of developable surfaces for use in aluminium or steel construction and should be modified for FRP construction although for simplifying the mould fabrication one should maintain the general characteristics of this hull. This is of especial importance if "one off" moulds are made as used by several yards in Negombo. The scantlings for new longliners should follow the Rules and Regulations of " Nordic Boat Standard for Commercial Boats" or another approved Regulation.
Below is an economic evaluation of the three vessel alternatives taken from table 8.
Table 9. Economic evaluation ( Rs thousand )
| Alt. 1 | Alt. 2 | Alt. 3 | |||
| 1. INVESTMENT | |||||
| 11 | Vessel | i x Rs 16,000 | 1,650 | 2,480 | 4,740 |
| 12 | Engine | n x Rs 11,000 | 910 | 1,360 | 2,570 |
| 13 | Fishing equipment | From 4.4 | 400 | 1,150 | 1,670 |
| 14 | Electronic | 400 | 400 | 400 | |
| 15 | Total vessel cost | 3,360 | 5,390 | 9,380 | |
| 16 | Fishing gear | From 4.4 | 630 | 1,140 | 1,520 |
| 1 | Total investment | 3,990 | 6,530 | 10,900 | |
| 2. REVENUE | y x Rs 97 | 6,052 | 9,535 | 14,666 | |
| 3. FIXED COST | |||||
| 31 | Depreciation | 15 over 12 years | 280 | 449 | 781 |
| 32 | Insurance, vessel | 15 x 1.8 % | 60 | 97 | 169 |
| 33 | Insurance, fishing gear | 16 x 5.0 % | 32 | 45 | 76 |
| 3 | Total fixed cost | 372 | 591 | 1,026 | |
| 4.TRIP OPERATING COST | |||||
| 41 | Fuel | p x v x Rs 13.30 | 741 | 1,103 | 2,076 |
| 42 | Bait | f x v x Rs 70 | 1,405 | 2,195 | 3,387 |
| 43 | Ice | g x v x Rs 2 | 312 | 491 | 756 |
| 44 | Food | u x r x Rs 150 | 200 | 210 | 278 |
| 45 | Other | y x Rs 2 | 124 | 196 | 302 |
| 4 | Total trip operating cost | 2,782 | 4,195 | 6,799 | |
| 5. CREW SHARE | ( 2 - 4 ) x 50 % | 1,635 | 2,670 | 3,934 | |
| 6. REPAIRS | |||||
| 61 | Hull and equipment | (11+13+14)x3% | 74 | 120 | 204 |
| 62 | Engine | 12 x 10 % | 91 | 136 | 257 |
| 63 | Fishing gear | 16 x 30 % | 189 | 342 | 456 |
| 6 | Total repairs | 354 | 598 | 917 | |
| 7. TOTAL VARIABLE COST | 4 + 5 + 6 | 4,771 | 7,463 | 11,650 | |
| 8. TOTAL YEARLY COST | 3 + 7 | 5,143 | 8,054 | 12,676 | |
| 9. PROFIT | 2 - 8 | 909 | 1,481 | 1,990 | |
| 10. ACCT. RATE OF RETURN | 9 / 1 | 22.7 % | 22.6 % | 18.2 % | |
The evaluation shows that Alt. 1 and Alt. 2 are only slightly better than Alt. 3. In all cases the rate of return is not particularly high. Only by export of high quality tuna would it be possible to increase the yearly revenue.
Other factors that needs to be considered are:
The economic return is highly sensitive to the cost of bait and the price that can be obtained for the fish and there is a need to make a closer examination of realistic prices on the local and overseas market before a decision is made concerning the best size of a tuna longliner for Sri Lanka.
The common crew share system used in Sri Lanka where 50% goes to the crew after subtracting the trip operating cost, gives considerable higher earning per crew member on the larger boats. The yearly income per crew member will be:
Alt. 1 - Rs 327,000
Alt. 2 - Rs 445,000
Alt. 3 - Rs 562,000
Ref. 1 indicates an upper limit of 6700 t as the potential yield for all species caught by tuna longline within the 200 n.mile economic zone of Sri Lanka. It would be of interest to calculate which of the above three alternatives would give the highest fishery profit to the country. The opportunity cost of a crew member is assumed to be Rs 72,000 as the estimated yearly earnings of an inshore fisherman (Ref. 1).
The opportunity cost of capital is assumed to be 14.5 %. The cost of operation is the total yearly cost (Point 8 inTable 9) minus the crew cost (Point 5).
Table 10 Fishery profit / vessel (Rs thousand)
| Alt. 1 | Alt. 2 | Alt. 3 | |||
| CUNO | 103 | 155 | 296 | ||
| Hooks | 800 | 1,200 | 1,600 | ||
| A | Opportunity cost, crew | r x Rs 72,000 | 360 | 432 | 506 |
| B | Opportunity cost, capital | 1 x 14.5 % | 578 | 920 | 1,580 |
| C | Fixed + Operating cost | 8 - 5 | 3,508 | 5,384 | 8,742 |
| D | Total yearly cost / vessel | A+B+C | 4,446 | 6,736 | 10,828 |
| E | Fishery profit / vessel | 2 - D | 1,606 | 2,799 | 3,838 |
Table 11. Fishery profit with maximum yield = 6,700 t (Rs million)
| Alt. 1 | Alt. 2 | Alt. 3 | |||
| CUNO | 103 | 155 | 296 | ||
| Hooks | 800 | 1,200 | 1,600 | ||
| F | Number of vessels | 6,700,000 / y | 107 | 70 | 44 |
| G | Total fishery profit | E x F | 172 | 196 | 169 |
| H | Total employment, men | r x F | 642 | 420 | 308 |
From this table can be seen that the maximum fishery profit is achieved with the medium sized boat although the employment is lower than with the smallest boat for a given maximum yield. As noted earlier the result is highly dependent on cost of bait and the price that can be obtained for the fish. Other factors such as employment and value added ashore in fish processing, boatbuilding and boat maintenance are considered to be approximately the same in the three cases.
It is interesting to note that with a high opportunity cost of the crew as found in an industrial country,the largest boat will give the highest fishery profit.
Ref. 1. Report on Offshore Large Pelagic Fish Resources Survey, 1995 - 1997
by Leslie Joseph, Pauline Dayaratne and Michael Sanders
NARA
Ref. 2. Safety at Sea, Safety Guide for Small Offshore Fishing Boats
by Oeyvind Gulbrandsen
Bay of Bengal Programme, BOBP/MAG/16.
Ref. 3. A Resistance Study on a Systematic Series of Low L/B Vessels.
by M.C. Sander and Dan McGreer.
Marine Technology, Vol. 30 No. 4, Oct. 1993.
H. P. C. Fernando Dpt. Director of Fisheries
D. S. Jayakodu Director General, NARA
Gajaba Perera Project Director Sri Lanka Fisheries Sector Development
Project (ADB)
Leslie Joseph Team Leader/Resources Survey Specialist
Michael Sanders Stock Assesment Specalist , UNDP Fisheries Management Project
Cyril Binduhewa Lecturer, Fishing Gear and Method, National Institute of Fisheries Training, Maligawatta
Upali Jayatissa Marine Engineer Assistant, D.F.L Office
W. Jude Fernando Fishing Boat Owner, Negombo
Roshan Fernando Director, TESS Group of Companies
Anura d. Buthipitiy General Manager, TESS Group of Companies
Ruwan Munasinghe Project Engineer, Neil Marine, Negombo
Percey Karunaweera General Manager-Production, Blue Star Marine
M.P.E.P. Fernando Proprietor, New V.J. Boatyard
E.M.A.B. Ekanayde Pricipal, Fisheries Training Centre, Negombo
Figure 1 Multi-day gillnetters in Negombo.
Figure 2 Bow on some fishing boats, gives excessive resistance in wave condition.
Figure 3 A 2000 litre fresh-water tank mounted above deck level on the stern reduces the stability.
Figure 4 Extra fuel drums carried on deck is a dangerous practice.
Figure 5 16.8 (55 ft) Longliner with "speedboat" hull and excessive power.
Figure 6 Hydraulic line hauler built for rope mainline.
Figure 7 A1000 hook longline stored on hand-driven reels on a 16.8 m. longliner.
Figure 8 Unconventional wood/FRP construction.
Figure 9 Storing of monofilament mainline in plastic bag.
Figure 10 A common type of hydraulic longline reel.
Figure 11 200 n. miles economic zone and grid for NARA survey.
Figure 12 Monthly catch rate kg/1000 hooks from tuna longline.
Figure 13 14.9 m. Tuna longliner
Figure 14 An efficient hull form
