A cast net is a circular weighted net that you throw by hand over a school of fish or bait. It works in two phases: spreading open into a flat disc as it flies through the air, then closing into a bag as you pull it back. The combination of rotational force, lead weights, and a drawstring system makes this possible.
How the Net Opens Mid-Air
When you throw a cast net, you’re spinning a weighted circle of mesh off your body. The lead weights sewn along the bottom edge (called the lead line) fly outward due to centrifugal force, pulling the mesh into a wide, flat pancake shape. The heavier the weights, the more forcefully the net opens and the wider it spreads.
The throw itself matters more than raw strength. You load the net onto your throwing arm and shoulder, then use a rotational release that lets the weights carry the net outward. Experienced throwers make it look effortless because, once the release is right, the physics do most of the work. A well-thrown net hits the water as a nearly perfect circle, trapping everything underneath it.
How the Net Closes and Traps Fish
The real engineering is in what happens after the net lands. Running from the lead line up through the body of the net are lines called brails (or retrieval lines). These lines all connect to a single hand line, which is the rope you hold onto during the throw. When you pull the hand line, those brails cinch the lead line together like a drawstring on a bag, gathering the weighted bottom edge into a tight pouch. Any fish or bait caught under the net gets trapped inside this pouch as the bottom closes beneath them.
Timing the pull matters. You want the net to sink past the fish before you start retrieving. Pull too early and the bottom hasn’t closed beneath the school. Pull too late in deeper water and the fish scatter out through the sides. In shallow water (under about 8 feet), this timing is forgiving. In deeper water, it becomes the difference between a full net and an empty one.
Weight, Sink Speed, and Mesh Size
Three variables determine how a cast net performs: how much lead is on the bottom edge, how large the mesh openings are, and how thick the mesh material is. These factors interact, and choosing the wrong combination for your target species means the net either sinks too slowly, lets bait slip through, or gills fish you’re trying to catch alive.
Cast nets are rated by lead weight per radius foot. The standard options are 3/4 pound, 1 pound, and 1.5 pounds per foot of radius. A heavier net sinks faster and holds its shape better in current, but it’s also harder to throw. A 10-foot net with 1.5 pounds per foot carries 15 pounds of lead on the bottom edge alone.
Mesh size controls what stays in the net and how fast it sinks. Larger mesh lets water pass through more easily, so the net drops faster. Smaller mesh catches smaller bait but creates more water resistance on the way down. As a general guide:
- 3/8-inch mesh: The all-purpose size. Good for shrimp, shiners, shad, sardines, finger mullet, and medium to large white baits (roughly 3 inches and up).
- 1/2-inch mesh: Better for larger bait like herring, medium mullet, pinfish, and croakers (5 inches and up).
- 3/4-inch mesh: Built for big targets like adult mullet, menhaden, tilapia, and catfish (8 inches and up). Sinks the fastest of the three.
The thickness of the mesh strands also plays a role. Thicker twine is more durable but creates more water resistance, slowing the sink. Thinner strands cut through the water faster but wear out sooner around rocks and oyster beds.
Monofilament vs. Multifilament Nylon
Cast nets come in two main materials. Monofilament is a single clear strand, similar to fishing line. Multifilament nylon is woven from many smaller fibers into a thicker, more opaque thread.
Monofilament is nearly invisible underwater, which means fish are less likely to see it and dodge. It’s also much easier to maintain. Sticks and debris fall right out if you shake the net. The tradeoff is that monofilament isn’t quite as strong as multifilament nylon, so it tears more easily around sharp structure.
Multifilament nylon is tougher and lasts longer under heavy use, but it catches debris. Sticks and cockleburs get tangled in the woven fibers and have to be picked out by hand. In murky water where visibility doesn’t matter, nylon’s durability can be worth the extra cleaning. In clear water, monofilament typically performs better because fish can’t avoid what they can’t see.
Why Depth and Current Matter
Cast nets work best in relatively shallow water. The practical ceiling is about 25 to 30 feet, and even that requires a heavy net, large mesh, and bait concentrated near the surface. In deeper water, the net begins closing on its own as it sinks, so by the time it reaches the depth where the fish are, the pouch has already tightened and fish swim right past the shrinking opening.
One workaround experienced anglers use in deeper water is attaching a ribbon or strip of fabric to the outside of the net. This creates drag that slows the closing action, giving the net time to sink deeper before the brails cinch shut. Anglers who chum bait to the surface can sometimes net fish in 40 feet or more this way, but it only works when the bait is right at the top of the water column.
Current creates a different problem. Moving water pushes the net sideways as it sinks, distorting the circular shape and giving fish an escape route along the edges. Heavier lead lines help the net punch through current and reach the bottom before drifting too far. Cheap, lightweight nets with minimal lead struggle in anything beyond slack tide.
How Net Size Affects the Throw
Cast nets are measured by radius, so a “6-foot net” creates a 12-foot-wide circle when fully open. Beginners typically start with a 4- to 6-foot net because it’s light enough to throw cleanly while learning the motion. Experienced throwers work with 8- to 12-foot nets that cover a much larger area but can weigh 20 pounds or more when loaded with lead.
A bigger net doesn’t just cover more water. It also sinks more evenly because the weight is distributed over a larger circumference, creating a more uniform “wall” that fish can’t easily escape. But throwing a large net poorly is worse than throwing a small net well. A net that lands folded over or bunched on one side leaves a gap, and bait finds gaps immediately. The goal is always a flat, round opening on the water’s surface, regardless of net size.