Tom Wray's Gear Talk (As seen in Fishing News International)
INCREASING FISHING AND ENERGY EFFICIENCY
Written by David Tait, Sr., of Crimond Enterprises. In a joint project with the Canadian Fisheries and the Government of Canada.
The vessel used in the project was the MV “Leonard S”,
Recent increases in fuel prices and growing concerns over greenhouse gas emissions have highlighted the need to improve energy efficiency in the fishing industry. Trawling is one type of fishing technology, however, which provides significant opportunities for such improvements in energy efficiency.
Two methods of improving the fuel efficiency of fishing trawls are:
To increase the horizontal mouth opening of the trawls, resulting in a larger area of the sea or lake bottom being swept per hour of towing and thereby increasing catch rates. This will reduce the fuel consumed per kilogram of fish harvested, especially if such enhanced trawl geometry is achieved with minimal or no corresponding increases in hydrodynamic drag.
To reduce the towing drag or resistance of trawls by using smaller diameter twines in the trawl netting.
In response to the first of these approaches for improving trawl efficiency, the technical staff at Crimond Enterprises have developed new Duplex and Triplex trawl designs having two and three codends, respectively. The design objective was to provide trawls having the advantage of a wider horizontal opening (ie: foot-rope spread) than a standard single trawl, with a correspondingly smaller vertical opening (ie: headline height). As illustrated in Exhibit 1.
A comparison of the estimated frontal view geometry of a standard trawl with one codend and the new Triplex and Duplex trawl design is shown in Exhibit 2.
These Duplex and Triplex designs were expected to provide:
- Significantly less drag compared with a standard trawl having a comparable horizontal opening (ie: wing) spread.
- An increased foot-rope spread comparable to that achieved by twin trawls. This offers a ‘middle road’ alternative to owners that for financial or technical reasons are unwilling to convert to twin trawling.
- An improvement in fishing performance and energy efficiency, particularly when targeted fish species, which are located near the bottom, and where headline height (ie: the height of the net mouth opening) is not a priority.
Preliminary performance evaluations of these new designs were obtained by:
- The technical staff at Crimond Enterprises trawl simulation computer program, and by
- Extensive testing of models in the flume tank at the Marine Institute in St. Johns, Newfoundland.
The simulation program indicated that the Duplex and Triplex designs might offer up to 20% and 47% more swept area, respectively, as compared with equivalent single trawls. In addition, most of this increase in footrope spread would be concentrated in the middle of the trawl, rather than in the wings, thereby maximizing potential increases in fishing efficiency. Although these simulations suggested that the Duplex and Triplex designs would have about 24% and 32% less headline height than comparable standard trawls, respectively, this is not expected to significantly reduce catch rates when targeting species such as shrimp or flatfish which usually stay close to the sea bottom.
It should also be noted that these increases in swept area provided by the Duplex and Triplex trawls should also be achievable with minimal or no increase in towing drag forces. Such improved hydrodynamic performance is expected since 30 to 60% less netting is required in these new designs as compared to that needed to achieve a similar foot-rope increase in traditional trawls with one codend.
The design team at Crimond Enterprises have also used the other approach for improving trawl energy efficiency by testing and marketing trawls constructed partially or completed with modern high-strength netting materials such as Spectra and Tricolor Elite High Tenacity Braided Polyethylene. These new materials allow smaller diameter twine to be used in the netting, thereby reducing the towing drag or hydrodynamic resistance of the trawls. For example, Tricolor Elite is thinner and stronger per unit weight than the Regular Braided Polyethylene material, which has traditionally been used in trawls.
In order to test the effectiveness of the above-mentioned two approaches for increasing fishing and energy efficiency, a project was conducted using both new technologies simultaneously in the fresh water trawl fishery of the Canadian Great Lakes.
The specific objectives of this project were:
To compare the towing resistance, fuel consumption, trawl geometry, and fishing performance of two trawls in this fresh water fishery:
- A standard trawl with one codend and constructed with Regular Braided Polyethylene, and
- A new Triplex trawl design having three codends and constructed from Tricolor Elite High Tenacity Braided Polyethylene.
- To raise the profile of energy conservation in the fishing industry by making vessel owners and operators more aware of the potential fuel savings from the use of such higher efficiency trawls. This would be achieved through a variety of approaches including the distribution of reports and videos on this project.
The participants in this project included:
- The Department of Fisheries and Oceans, Responsible Fishing Operations (Mr. Andrew Duthie), which was responsible for the overall co-ordination of the project.
- David Tait, Sr. and William Tait were responsible for constructing the trawls, conducting the experiments, analyzing the results, as well as preparation of the project report and video.
- Captain Rick Misener of the MV “Leonard S”, who is also the president of Mitowmar Ltd., which owns this trawler.
- The Marine Institute in St. Johns, Newfoundland (Mr. John Foster), which was involved in the planning and experimental protocols for this project.
- The vessel used in the project was the MV “Leonard S”, which is a steel trawler operating from Port Dover, Ontario. This vessel is 22.9m in length, with a 420 hp main engine. Reduction gear 6:1, engine type Caterpillar 3408 TA, driving a 59” diameter 54” pitch propeller.
The two trawls used in the experiment were:
Standard trawl - 368 x 15cm constructed of Regular Polyethylene
(Circumference = 5,280cm, footrope = 5,170cm, headline = 4,384cm)
Triplex trawl 650 x 15cm constructed of Tricolor Elite Polyethylene.
(Circumference = 9,030cm, footrope = 5,290cm, headline = 3,662cm)
The same Bison #13 Trawl doors were used with both trawls.
The experiments were conducted during 9 days of commercial fishing activity in Lake Erie during late October 2000. Four test tows were first conducted with the Triplex trawl to optimize its geometry by adjusting ancillary equipment such as numbers of floats and sweep lengths. One test tow with the standard trawl confirmed its optimum operation. Following this, seven (7) valid experimental tows were completed with each type of trawl. Generally, an attempt was make to provide each trawl with equal fishing time.
During each tow, fuel consumption, gear geometry and gear tension were monitored with electronic sensors and all such data was stored electronically for later analysis. The tension meters were fitted behind the doors between the backstraps and the bridles. Environmental conditions during each tow were also recorded, as well as the weight and species composition of the catches. Swept area calculations were derived by multiplying the actual distance run during the tow and multiplying this by the average wing end spread.
The specific types of data collected during each tow is illustrated in
|Exhibit 3 Results Table
|Mean Headline Height
|Mean Wingend Spread
|Wind Speed and Direction
|Mean Door Spread
|Standard Deviation of Door Spread
|Light Conditions (surface)
|Swept Area of Trawl
|Start Tow Time
|Swept Volume of Trawl
|End Tow Time
|Swept Area of Gear
|Swept Volume of Gear
|Distance Towed from Start to End
|Speed over Ground
|Catch Weight and Composition
|Mean Log Speed
The performance of these two types of trawls averaged over the seven tows conducted with each type is shown graphically in Exhibit 5 and in a tabular format in Exhibit 6. Catches of commercial species with the Triplex trawl consisted of 65.6% small species (eg: smelt, alewife and shad), 15.6% whitefish, 16.6% burbot, and 2.1% non-commercial species (eg: sheepshead). Catch composition with the single trawl was very similar. Catch values were based on landed prices per kilogram of $0.51 for smelt, $2.75 for whitefish, and $0.44 for burbot.
Exhibit 4 Graphs of Results
Exhibit 5 Experimental Results
Type of Trawl
Standard Trawl with Polyethylene
Triplex with Tricolor Elite
Gear Tension (kg)
Door Spread (m)
Wing Spread (m)
Headline Height (m)
Swept Area (m3)
Fuel - Liters / Hour
Commercial Fish Catch /hour (kg)
Non-commercial Fish Catch / hr (kg)
Catch Value /hour
Commercial Catch (kg) / liter fuel
The results of these experiments can be summarized as follows:
The Triplex trawl had a 71% greater mouth circumference than the single trawl (ie: 9,030cm vs. 5,280cm) however it could be towed with:
An increase in gear tension of only 8%, and with
Only 1% more fuel consumption per hour.
This suggests that the hydrodynamic drag efficiency of the larger Triplex trawl, and its resulting energy efficiency, is significantly better than a standard trawl with a similar mouth opening. In other words, a trawler with a given engine horsepower could tow a much larger Triplex trawl compared to a traditional trawl with one codend.
As previously explained, computer simulations and flume tank tests suggest that the larger mouth opening of the Triplex trawl would result in a significantly larger swept area (ie: up to 47% more) compared to a standard trawl, and a correspondingly significant decrease in headline height (ie: up to 32% less).
During these experiments, the measured wing and door spreads with the Triplex trawl were 24.1% and 23.8% less than those of the standard trawl, respectively, and the headline height was only 9.5% less. It should be noted, however, that these wing and door spread measurements are not the same as the footrope spread, which is the true measure of the actual sea or lake bottom which is being swept. In fact, it was suspected that the Triplex trawl was being over-stretched, and that either:
This trawl might operate better with smaller doors, which would most likely reduce the overall gear drag, thereby reducing engine loads and fuel consumption, or A bigger Triplex trawl could be towed with the existing engine and doors, resulting in higher catch rates per liter of fuel used.
Although the Triplex trawl might not have been operating in an optimum way, it still provided a 14% higher catch rate of commercial fish species as compared to the standard trawl (ie: 2,535 kg vs. 2,224 kg/hr.). This resulted in a 6.6% increase in the catch value per hour of towing (ie: $965 vs. $905).
The improved fishing performance of the Triplex trawl is thought to be the result of its more effective mouth geometry. For example, the mouth opening of a standard trawl is similar to a triangle with rounded corners, with the maximum headline height at the center of the net. As a result, most of the fish are captured at the center of a standard trawl. In contrast, it is thought that the mouth geometry of the Triplex net is more like a rectangle with rounded corners, which provides a more uniform catching potential across the whole footrope.
This theory appeared to be verified in the experiments since about 50% of the catches in the Triplex trawl were in the center codend, whereas only 25% of the catch was in each of the side codends.
The additional catch revenue provided by the Triplex net amounted to $60 per hour of fishing. This was achieved with an increase in fuel consumption of only 0.37 liters per hour, which is negligible.
In summary, this experiment showed that even when its operation was not optimized, the Triplex trawl could reduce the fuel consumption per kilogram of harvested fish by about 13% in this Great Lakes trawl fishery. This demonstrates the significant energy savings potential of this new trawl design.
Further testing and refinements of this Triplex trawl are required to have it operate properly as designed. This will include adjustments to ancillary equipment such as the use of appropriate doors. It is reasonable to expect, however, that the fishing and energy savings performance of this new trawl design will eventually be substantially better than was achieved in these preliminary experiments.