■ Conditions which favour fishing with light
| Not favourabe | Average | Favourable | |
| Colour of the Sea | Brown-yellow | Yellow-Green | Green-Blue |
| Transparency (visibility m) | 0 to 5 | 5 to 10 | 10 to 30 |
| Moon phase | Full | - | New |
| Current | Strong to Medium | Medium to Weak | None |
■ Type of Lamp and utilization
|
Petrol (gasoline) |
Electric |
|
| Advantages | inexpensive easy to maintain and use |
effective above the surface or in the water |
| Disadvantages | fragile used only above the water |
expensive heavy bulky batteries or generators |
It is better to use several lights of moderate intensity, sufficiently spaced apart, rather than a single light of strong intensity
When a lamp is mounted above the surface, only half its light effectively penetrates the water, due to reflection from the surface.
■ Resistance of electric cables
Running lamps with low voltages (for example, 12-24 V) may involve significant power losses through con-ducting wires. Therefore, wires used with low voltages should be thicker than those needed for higher voltages.
Resistance to a continuous current (in ohms/km) in a copper conductor is a function of the cross section area of the cable (mm2).
From Ben-Yami, 1976. Fishing with light. FAO Fisning Manuals, Fishing News (Books) , Oxford.
Depth Range
Frequency Common frequencies are 30-400 KHz
| High Frequency Echo-sounders (100 to 400 kHz) |
Low Frequency Echo-sounders (50 kHz or less) |
|
|
Common use |
shallow water |
deep water |
Width of Beam |
narrow |
wide |
Precision |
very good |
less precise |
Size of transducer |
small |
large |
Usual Use |
fish detection |
navigation |
Electric supply required on the vessel (voltage, power)
If the echosounder's power supply is a bit weak, its performance will be poor
The type of display may be lamp display (flasher), paper (chart recorder), or colour screen.
| Paper display (dry, black and white) |
Television type display (colour) |
|
| Advantages | paper record may be kept | different colours may indicate very small differences in strengths of echoes |
| Disadvantages | differentiation of different echo strengths is limited (shades of black and grey) cost of Recording Paper | no memory or limited memory, but note that recording equipment is now available |
■ Other predetermined characteristics
Wavelength (m) = 1500/frequency (Hz)
The smaller the wavelength the greater the precision of detection.
Pulse length :
Short 0.1 to 1 millisecond
Long more than 2 milliseconds
The shorter the pulse length, the greater the precision but, in fact, this is predetermined according to the frequency and the depth or sounding.
Beam-width :
| Wide | : 20 to 30 degrees |
| Narrow |
: 4 to 10 degrees |
Output power ranges from 100 to 500 watts.
The greater the power, the better will be the strength and precision of detection.
| Navigation echosounder | Fish-finding echosounder | |
| Depth of Water Limited to 100 m |
Frequency 20-100 kHz Beamwidth 10-20 degrees Output Power less than 1 kW |
Frequency 100-400 kHz Beamwidth 4-15 degrees Output Power around 1 KW |
| Pulse length less than 1 millisecond Flasher display may be sufficient |
Pulse lengtn less than 1 millisecond Usually with TVG and whiteline |
|
| Deeper Water | Frequency
10-20 kHz Beamwidth 4-10 degrees Output Power 5 - 10 kW depending on depth Pulse length greater than 2 milliseconds |
Frequency 30-50 kHz Beamwidth 4-10 degrees Output Power 5-10 kW depending on depth Pulse length 1-2 milliseconds, with TVG and whiteline |
■ Power required
where
| P |
= actual power of winch or hauler (HP) |
| F |
= pulling force needed (kgf) |
| V |
= speed of hauling needed (m/s) |
When estimating the engine power required to produce the actual power at the winch, it is necessary to add 25% for power loss through mechanical transmission, or 100% for hydraulic transmission. For example, if actual winch power (P) of 10 HP is required and transmission is mechanical, then 12.5 HP engine power will be needed to produce this.
■ Turning speed required
where
| R |
= turning speed of winch or hauler (RPM) |
| V |
= speed of hauling required (m/min) |
| Ø |
= diameter of full drum (mm) |
■ At a constant hauling speed, pulling force available decreases as a drum fills
Pulling forces
The torque of the drum is constant (at 5, in the example in next column).
■ At a constant drum diameter, the pulling force available decreases as speed increases
Work done by drum = pull × speed = constant
Example :
pull at mid-drum at 1 m/s : 1.6 t
pull at mid-drum at 1.6 m/s : 1.0 t
(1.6 t × 1 m/s = 1.0 t × 1.6 m/s)
■ Tension on the material being hauled
Where
| T |
= tension on the material (kgf) |
| P |
= power of the winch or hauler (HP) |
| v |
= speed of hauling (m/s) |
Note : Main characteristics of a winch or drum are the dimensions, the capacity and the pulling force (in tonnes force or in daN; see pages 150, 152)
The pulling force of the purse line winch required for a seine of given weight can be estimated by the following formula :
F = 4/3 (Wn/2 + Wr + Ws)
where :
| F |
= pulling force of the winch (tf tons force) |
| Wn |
= weight in air of the retting (t, tons) |
| Wr |
= weight in air of the footrope and purse rings (t) |
| Ws |
= weight in air at the ballast or the footrope (t) |
Characteristics of some purse line winches in use (after Brissonneau and Lotz)
| Vessel Length (m) |
No. Drums |
Drum Capacity | Pull (t) (bare drum) |
Speed (m/s) (bare drum) |
P(HP)* | |
| cable Ø (mm) |
length (m) |
|||||
| 20 |
2 |
15.4 |
1300 |
8 |
0.5 |
44 |
| 20-25 |
2 |
15.4 |
1800 |
11 |
0.42 |
70 |
| 25-30 |
2 |
17.6 |
1800 |
17 |
0.37 |
100 |
| 30-40 | 3 |
17.6 |
1800 |
21 |
0.30 |
100 |
|
17.6 |
800 |
21 |
0.30 |
|||
|
17.6 |
600 |
21 |
0.30 |
|||
| 45-60 | 3 | 20 |
2220 |
27 |
0.35 |
150 |
|
20 |
975 |
27 |
0.35 |
|||
|
20 |
975 |
24.5 |
0.35 |
|||
| 60-75 | 3 |
22 |
2420 |
27 |
0.35 |
300 |
|
22 |
1120 |
27 |
0.35 |
|||
|
22 |
1120 |
24.8 |
0.35 |
|||
■ Seine drums
some examples
| width of drum inside flanges (m) |
3.00 |
3.90 |
| flange diameter (m) |
2.45 |
2 44 |
| drum diameter (m) |
0.6 |
0.45 |
| Seine dimensions: hung length × stretched height (m) |
360 × 30 |
450 × 64 |
| stretched meshsize (mm) (centre section) |
32 |
|
| twine size (centre section, Rtex) |
376 |
* Power (HP) = 1.36 × Power (kW)
| Power* of trawler(HP)
|
Power of winch(HP) | Capacity of drums |
|
Pull at mid-drum (kg) drums combined | |
| Length(m) | Ø of wire(mm) | ||||
| 50-75 | 200 | 6.3 | 500-750 | ||
| 100 | 25 | 700 | 10.5 | 1.00 | 900 |
| 200 | 40 | 1000 | 12.0 | 1.20 | 1600 |
| 300 | 60 | 1250 | 13.5 | 1.35 | 2500 |
| 400 | 80 | 1350 | 15.0 | 1.40 | 3500 |
| 500 | 120 | 2100 | 16.5 | 1.50 | 4500 |
| 700-800 | 165 | 2000 | 19.5 | 1.50 | 6500 |
* Brake horsepower (BHP) or Apparent Nominal Power (ANP), see page 95
Power in (HP) = 1.36 × Power in (kW)
At constant drum RPM, pull × diameter = constant; thus,
■ Performance
— Power :
— Maximum Pull : At the most, equal to 1/3 the breaking strength of the warp. In order to haul the trawl the winch has to develop more power than tha' which is exerted in towing the trawl.
The pull of the winch at mid-drum should be at least 80% of the maximum bollard pull of the vessel. It is best to use the formula :
Pull of the winch (at mid-drum)
= 1.3 × pull of the trawler
■ Dimensions
— Diameter of the bare drum : about 14 to 20 times the diameter of the warp.
— Depth of drum at least (A-B)/2: at least equal to the diameter of the bare drum
■ Capacity of a winch drum
— With automatic spooling (level - wind) and drum dimensions given above, If L = length (m) of warp, and Ø = diameter (mm) of warp :
— Manual spooling reduces this capacity by about 10%.
Note : Tolerances must be taken into account when accessories (i.e. chains, shackles, swivels) are hauled on with the warps.
■ Capacity of a drum
Usable volume of drum
Note : The volume of a trowl (V) can be estimated from its weight W:
midwater trawl V (cubic m) = 3.5 × W (tonnes)
bottom trawl V (cubic m) = 40 × W (tonnes)
Note : when sweeps and/or the bridles of combination rope are to be reeled onto the drum with the net, their volume must be taken into account. The same is true for the floats, ballast, sinker chain and bobbins.
■ Main dimensions
For a given application (requiring a certain pull, speed and capacity) there may be several alternatives to choose from.
The bare drum diameter B generally does not vary much for a given pull.
| Pull (tonnes) |
B average |
| < 3 |
240 |
| 5-8 |
300 |
| 8-13 |
450 |
| 20-30 |
600 |
Thus, A and C will be chosen depending on the type of net, use of the drum (storage and/or hauling) the volume of the net, and deck space available.
■ Pulling force
In order to maintain the speed of hauling, the pull of the net drum at bare drum should be at least equal to the pull of the winch at full drum.
■ Hauling speed is generally greater than or equal to 30 m/min.
A few guidelines:
Note that for a given capacity, the pulling force and speed may vary a great deal, according to the strain on the winch.
| Vessel horsepower | Capacity (cubic m) | Weight of net (kg) | Pull (t) (bare drum) |
Speed (m/min) | Weight of Drum (t) |
| 100 | 0.5 |
120 |
|||
| 200 | 1 |
250 |
|||
| 300 | 1.5 |
400 |
1-1.2 | ||
| 400 | 2 |
550 |
2-4 | 10 | 1.5 |
| 500 | 2.5 |
700 |
|||
| 600 | 3 |
800 |
6-10 | 13.5 | 1.7-1.8 |
| 700 | 3.5 |
1000 |
|||
| 800 | 4 |
1100 |
7-12 | 17 | 2-2.5 |
* Broke horsepower (BHP), or Apparent Nominal
Power (ANP) sec page 95
Power in (HP) = 1.36 × Power in (kW)
■ Choice of model
The netting should fill only the groove (throat) of the power block. The model is chosen according to the circumference of the seine gathered together, estimated by two different methods :
■ Pull available
The power block should be capable of pulling 20% to 50% of the total weight of the net (in air), at speeds of between 30 m/min for a small seiner to 80 m/min for a larger seiner.
Values of pulling force available at mid-diameter for power blocks of different capacities in common use.
| Capacity (circumference of net, mm) | Pull tonnes |
|
500-800 |
0.5-1.5 |
|
800-1100 |
1.0-2 0 |
|
1100-1800 |
3.0-5.0 |
|
1800-2500 |
6.0-8.0 |
■ Performance of power blocks in common use according to the size of the vessel
|
Seiner length (m) |
Pull (tonnes) |
Speed (m/min) |
Power (HP*) |
|
9-12 |
0.5-1.0 |
30-40 |
8-16 |
|
12-24 |
1.0-1.5 |
30-40 |
13-20 |
|
18-30 |
2 |
40-50 |
30-45 |
|
24-39 |
4 |
40-50 |
60-85 |
|
24-34 |
5 |
40-70 |
80-150 |
|
30-75 |
6-7 |
40-90 |
90-220 |
* Power in (HP) = 1 36 × power in (KW)
Other than power blocks (page 130)
■ Hauler (gurdy) for trolling lines
■ Haulers for vertical lines, jigging machine
■ Haulers for longlines
■ Hydraulic pot hauler
■ Pot hauler powered by outboard motor
| Note : within the power limits of the engine (constant torque) : | |||||
| At the hauler : |
as speed V increases, |
|
pulling force F decreases (the inverse is also true) |
|
F × V = constant = power of hauler |
| as drum diameter decreases |
|
pulling force F increases (the inverse is also true) |
|
F × Ø = constant | |
■ Longline haulers
For longlines up to about 30 km long, with relatively short branchlines (5 m or less), the following pertain to a few types in common use.
|
Vessel Length |
Ø Line (mm) |
Pull (kg) |
Speed of Hauling (m/min) |
|
<10 |
<6 |
200-300 |
20-40 |
|
10-15 |
6-12 |
300-400 |
60 |
|
15-20 |
8-16 |
500-700 |
70 |
For drifting midwater longlines (i.e. Japanese-type longlines for tuna), length is of the order of 100 km, with snoods spaced 50 m or more apart.
|
Vessel Tonnage |
Speed of hauling (m/min) |
|
10 |
70-80 |
| 20 |
70-90 |
| 40 |
150-210 |
| 100 > |
180-260 |
■ Net haulers : the following pertain to a few types in common use.
|
Vessel Length |
Depth of water |
Pull |
Speed of hauling (m/min) |
|
5-10 |
< 100 |
150-300 |
20-35 |
|
10-5 |
< 200 |
200-500 |
25-45 |
|
15-20 |
300 > |
500-900 |
50-70 |
■ Pot/trap haulers
Performance is very variable depending on the model, and comparable to that of line haulers and net haulers, except for the existence of models with pulling force greater than 1000 kg (1000, 1350, 1500 kg) and higher hauling speeds.
