Get ready: crew, boat and weather
Every fishing trip starts on land. The skipper checks the weather and sea forecast. The crew checks:
- Life jackets for everyone, and a lifebuoy with a rope.
- Fuel, engine, bilge pump, lights and radio.
- Nets, ropes and winch. Look for cuts and wear.
- Ice and insulated boxes for the catch.
- First-aid box, drinking water and a flare.
Each person has a job: skipper (steers and decides), engine hand, net hands and a lookout. Tell someone on shore your plan and your return time.
Steering and finding the fish
A compass shows direction. GPS shows your position as numbers (latitude and longitude). A chart shows depths and dangers. Time to travel = distance ÷ speed. At sea, speed is in knots (nautical miles per hour) and distance in nautical miles.
An echo sounder (fish finder) sends a short pulse of sound down. Sound travels about 1500 m/s in sea water. The pulse bounces back from fish and from the seabed. The device measures the time and works out the depth:
depth = 1500 × time ÷ 2
We divide by 2 because the sound goes down and comes back. A group of fish shows as a bright patch on the screen, the shoal.
Shooting, towing and hauling the net
Shooting means putting the net into the water. Towing means pulling it slowly through the shoal. Hauling means pulling it back on board with the winch.
- Set the net at the depth of the shoal. A net above or below it catches nothing.
- Keep clear of ropes under strain. Never stand in the loops of a rope.
- Haul slowly. Keep everyone away from the open side.
- Use the legal mesh size so young fish can escape.
Looking after the catch and keeping records
Fish begin to spoil as soon as they are on deck. Sort the catch quickly, wash it with clean sea water, and layer it with ice in boxes. Keep it in the shade.
Write a log: date, position, depth of the net, tow time, weight of each kind of fish, and the weather. Logs help the crew find good grounds and help scientists see if the stock is healthy.
Try it
Take a long string and a stone. Tie a knot every 10 cm for a "depth rope". Lower the stone into a bucket or pond and read the depth. Then use the 3D sliders to put the net at the shoal depth.
Key formulas and definitions
- Echo sounder depth = 1500 × time ÷ 2 (m, with time in s)
- Time = distance ÷ speed (nautical miles ÷ knots = hours)
- 1 knot = 1 nautical mile per hour ≈ 1.85 km/h
- Net must be within the shoal depth range to catch fish
- Fish on ice: about equal weight of ice and fish
Worked examples
1. An echo returns from the seabed after 0.08 s. How deep is the sea?
Depth = 1500 × 0.08 ÷ 2 = 60 m.
2. The fishing ground is 12 nautical miles away. The boat goes 6 knots. How long does it take?
Time = 12 ÷ 6 = 2 hours.
3. The sounder shows a shoal at 40 m. In the 3D model a net reaches 8 m above and below its depth. Does a net at 50 m catch fish?
The net covers 42 m to 58 m. The shoal is at 40 m, outside this range, so it catches nothing. A net at 45 m covers 37 to 53 m and does catch.
Common mistakes
- Forgetting to divide by 2 in the echo depth. The sound travels down and back.
- Setting the net where it is easy, not where the fish are. Match the shoal depth.
- Standing inside rope loops or near the net winch while hauling.
- Leaving the catch in a heap on deck. It spoils fast; ice it at once.