Fishing continues to be the most energy-intensive food production method in the world today, and depends almost completely on internal combustion engines based on oil fuels. There are as yet no signs of any other energy source that could substitute the internal combustion engine in either the medium or short term. The industry continues to be exposed to global fuel prices and it cannot be assumed that these will remain stable indefinitely. Indeed, with the current rate of consumption of fossil fuels, some analysts predict dramatic energy cost increases in the next 15 to 50 years.
Small-scale fisheries account for nearly half of the world's fish production and, although they are generally more labour-intensive than larger industrial fisheries, they are increasingly affected by energy costs. In developing countries, in spite of the energy conservation initiatives of the 1980s (subsequent to the dramatic rise in the cost of fossil fuels), mechanization continues to increase. Fuel costs have ever more influence, not only on consumer prices but also on the fishers' and boatowners' net incomes. When levels of employment and cost-sharing systems are considered, it becomes even more important from a social perspective to improve and maintain energy efficiency within small-scale fisheries.
The significance of energy costs within a particular fishery is determined principally by the technology in use and the local economic conditions, including taxes, subsidies, labour and operational costs. Typical figures put energy costs in the region of a little under 10 percent of gross earnings for a trawl fishery down to as little as 5 percent of gross earnings for passive methods such as gillnetting.
It must be recognized from the outset that there are considerable differences in energy optimization needs between fisheries, reflecting local economic conditions, available technology and the cultural context.
AIM OF THIS GUIDE
This guide is not a result of new fieldwork; instead it draws on much of the research and experience of the past two decades, updated where possible to include new technical developments. It presents information on the key technical areas affecting energy efficiency, but only part of the material presented is applicable to any particular fishing situation.
The guide aims to assist owners and operators of fishing vessels of up to about 16 m in improving and maintaining the energy efficiency of their vessels. The basis is technical but, where possible, indications have been given as to possible fuel and financial savings to be gained through improved techniques, technologies and operating practices. Also covered are some aspects of hull design and engine installation for energy efficiency, which should be of interest to marine mechanical engineers and boatbuilders. Fisheries department officials and fieldworkers should also be able to use this guide to assist them in both advising private sector operators and prioritizing intervention activities.
The focus of the guide is exclusively on slower speed displacement vessels, which dominate small-scale fisheries throughout the world, and no attempt has been made to cover technical and operational issues related to higher-speed planing craft. However, in many cases, the basic principles outlined are applicable to both low- and high-speed vessels.
The contents comprises two main parts, Operational measures and Technical measures. The first deals with changes that can be made to improve energy efficiency without changing the vessel or equipment. The topics discussed are related to changes in operational techniques rather than changes in technology. The second is more relevant to vessel operators considering the construction of a new vessel or overhauling and re-equipping an existing vessel.
No attempt has been made to propose complete technical solutions - because of the scope and variation of fishing vessels within the size category, any attempt to do so would be meaningless. The main areas where energy efficiency gains can be made are highlighted and, where possible, the likely magnitude of such gains are indicated. The significance of these gains will be determined primarily by how much energy is used in the fishery as well as by the cost of that energy.
The guide should be considered as part of a decision-making process, and it is inevitable that owners and operators of fishing vessels will have to seek more specialized assistance before implementing many of the ideas presented here. A basic mechanical knowledge is assumed throughout and, while dealing with several quantitative issues, some mathematical ability is also required.
The fuel savings outlined in this publication must be taken as guidance figures only, and neither the author nor the Food and Agriculture Organization (FAO) accept responsibility for the accuracy of these claims or their applicability to particular fishing situations.
SOURCES OF ENERGY INEFFICIENCY
In addressing the problem of energy efficiency it is useful to understand just where the energy is expended in a fishing vessel and what aspects of this can be influenced by the operator, boatbuilder or mechanic.
In a small slow-speed vessel, the approximate distribution of energy created from the burning of fuel is shown in Figure 1. Only about one-third of the energy generated by the engine reaches the propeller and, in the case of a small trawler, only one-third of this is actually spent on useful work such as pulling the net.
In a vessel that does not pull a net or dredge, of the energy that reaches the propeller:
So where can gains be made, or at least losses minimized?
Figure 1: Energy losses in a small trawler
Engine. Most of the energy generated by the fuel burnt in the engine is lost as heat via the exhaust and cooling system, and unfortunately there is not a lot which the operator can do to usefully recuperate this energy. In certain cases, some of this can be regained through the use of a turbocharger (see the section Engines) but, in general, the thermal efficiency of small higher-speed diesel engines is low and little can be done to improve this. However, some engines are significantly more fuel-efficient than others (especially among different types of outboard motors). Engine choice is detailed in the section Choice of engine type.
Propeller. The energy lost in turning the propeller is controlled by two principle factors - the design of the propeller (how well suited it is to the engine, gearbox, hull and fishing application) and its condition. These factors can be influenced by the vessel operator and are dealt with in the section The propeller.
Mode of operation. The effect of wave resistance, although determined principally by the dimensions and form of the vessel (section Hull form), increases dramatically with speed. Significant fuel savings can be made by maintaining a reasonable speed for the hull, irrespective of vessel type. The factors determining the choice of an optimum operating speed is described in the section Engine operation and in Annex 3.
Fishing operations also influence energy consumption and efficiency through gear technology and operating patterns, particularly trip length. Neither of these are particularly easy to change in practice and are discussed in the section Fishing operations.
Hull maintenance. The significance of skin friction is controlled principally by the quality of the hull's finish - hull roughness as well as the amount of weed and marine growth that is allowed to accumulate on the hull. Both of these factors are under the direct influence of the operator's maintenance programme but, depending on the type of vessel and fishery, a significant expenditure on hull finish is not always worthwhile. This is discussed further in the section Hull condition.
When trying to prioritize what can be most easily done to improve fuel efficiency, it is worth considering the results of related research work carried out in New Zealand (Gilbert, 1983). The results indicate that the major causes of fuel inefficiency, in order of priority, are:
The operator is the most significant factor in the system - technical improvements for fuel efficiency are effectively meaningless without corresponding changes to operational practices. A technical development that allows a vessel to consume less energy at an operating speed can often also be used to increase operating speed, therefore cancelling any gain. In order to make an effective energy gain, this must be kept apart as the savings.
If the surplus energy created as a result of technical or operational changes is used to go faster (or to do more work), then there will be no savings - control over energy utilization invariably depends on the decisions and judgement of the ship's master on the day.