Crimond Enterprises Examines Fuel Efficient Gear
Crimond Enterprises presents this information so that Canadian fishermen can choose vessel and gear specifications that offer a more economic operation both in the short and medium term
To assist in your decision, Crimond can perform a rough statistical analysis based on your vessels existing trawl and give a general idea of the reduction in surface area which could be acquired using the new type Dyneema material.
In 2003 fuel costs accounted for around 15-20% of vessel earnings for many demersal trawlers. This figure has risen dramatically in 2008 due to increased oil prices. (some estimates are 40%) Skippers and vessel operators are therefore interested in any way of reducing fuel consumption or consuming fuel more efficiently.
When towing, there are small changes such as reducing speed which can lower fuel consumption but generally this will result in reduced catch and hence earnings.
To maintain catch levels but reduce fuel costs, the skipper of a trawler can only realistically do one of the following
- reduce the drag of the trawl gear
- use a more efficient propulsion system
Either of these two things gives the skipper the option of either towing at the same speed and saving fuel or, towing faster and consuming the same amount of fuel but potentially catching more fish.
There are a number of other changes that may have a marginal effect, but reducing gear drag is the one which will probably have the most significant effect in the short term.
In calm weather the vast majority of fuel is consumed to overcome the drag of the trawl gear and only a very small proportion to propel the vessel (perhaps 10-20%). This means that gear drag is the main element which needs to be reduced to save fuel.
Drag of gear can be reduced by making the trawl smaller, reducing the opening (wingend spread and headline height), reducing the twine surface area of netting, reducing the ground contact friction or using lower drag doors and components.
Twine surface area can be reduced either by using larger mesh sizes and/or reduced Polyethylene twine diameters. Larger mesh may result in a decrease of fishing efficiency depending on the target species behavour.
If the same design of trawl is used but with smaller diameter Polyethylene twines the drag will reduce compared with the original trawl with larger diameter Polyethylene twines. Openings may increase if the same doors and floats are used, lessening the benefit of the reduced drag potential.
On a cautionary note, there is a minus factor in this equation, reducing the Polyethylene twine diameters also reduces strength and abrasion characteristics. In effect the longevity and service performance of the finer twine may not be satisfactory.
If the skipper chose to keep the trawl opening of the new trawl the same as the old, he would have to use smaller doors and a reduced number of floats.
Or he may choose to go for fishing efficiency by construction a larger trawl with high tenacity Dyneema material, and keeping his existing doors, bridles, and sweeps.
More positive reductions in trawl drag can be achieved by applying panels of higher tenacity twine panels (Dyneema) in selected areas of the trawl known to affect drag most. These could be applied to the top wings, square and top bellies of the trawl away from areas of high damage and abrasion. Or in a best case scenario, the total frame of the trawl could be constructed of Dyneema giving the maximum savings.
Also see Increasing Fishing Energy Efficiency