I started using a castable fishfinder a few seasons ago to solve a simple problem: how to find the lanes bass use at night without spending hours blind-casting rocky margins. Night fishing from shore is a different animal — fish are less predictable, tides and light matter more, and you can’t always see the subtle features that hold fish. A castable sonar changed that for me. Below I walk through how I use one, the three sonar settings I switch between, and the practical steps I take to map reliable bass lanes along Welsh coasts.

Why a castable fishfinder is worth taking to the beach

Onshore night fishing, I want information fast. A castable fishfinder (I mainly use a Deeper PRO+ and have tried a Garmin Striker Cast) gives me a real-time picture of what's under the water beyond the visible break. It’s compact, simple to deploy, and — crucially — lets me mark waypoints so I can come back later with confidence. For bass at night, I’m not looking just for individual fish; I’m looking for corridors where they repeatedly move between feeding and shelter — the lanes.

Gear and setup I use

My standard kit for this kind of survey night includes:

  • Castable fishfinder (Deeper PRO+ or similar) paired with my phone.
  • A headlamp with red-light mode — I avoid white light that can spook fish and ruin night vision.
  • 50–80g lure or weight to replicate casting distance while surveying (depends on reach).
  • A small float or tether line for retrieval if the device gets snagged.
  • Power bank for long sessions, and a waterproof phone case.

    • I pair the fishfinder over Wi‑Fi rather than Bluetooth when possible — the connection is more stable at distance. Before I head out, I check the device battery and update the app so I don’t lose mapping features mid-session.

    The three sonar settings I use and why

    Over the years I’ve settled on three go-to sonar modes that together form a simple but powerful survey routine. I switch between them depending on what I need to see: bottom structure, baitfish activity, or individual targets (bass) moving through a lane.

    Setting Purpose How I use it
    Low Frequency / Wide Beam Map broad contours and locate major features (ridges, gutters, sandbanks). I start here on an outgoing or incoming tide to get the lay of the seabed beyond visible surf.
    High Frequency / Narrow Beam Resolve details — deeper gullies, concrete blocks, drop-offs, kelp edges where bass ambush. Once I know where the main shape is, I use this to zero in on potential lanes and features bass might use.
    Fish Mode / Sensitivity Boost Detect bait schools and moving targets; watch for movement that suggests passing bass. I run this in short bursts to pick up mid-water activity and to confirm lanes are active.

    Step-by-step: How I map a night-time bass lane

    I usually arrive before dusk and work through a checklist in the following order.

  • Visual reconnaissance: I scan the shore line for likely features — points, gullies, rock edges and where the surf changes. Marks that look promising at dawn can be hidden at night, so I lean on the fishfinder for confirmation.
  • Start with the low-frequency wide beam: I cast beyond the breakers and let the device drift while keeping an eye on the app map. This gives me a wide swathe of seabed profile and highlights major gullies or sandbanks that can channel bass movement.
  • Mark waypoints: Whenever I see an interesting contour or a transition (e.g., sand to rock), I drop a waypoint in the app. These are the anchors of my night map.
  • Refine with high-frequency narrow beam: I revisit waypoints with tighter beams to resolve ridges, boulders or kelp lines. Bass often hug the edge of cleaner flow next to rough structure. Narrow-beam helps me find those edges, even when surf masks them.
  • Switch to fish mode: I run fish mode intermittently, especially during tidal change. I’m looking for arcs or cloud signatures that indicate baitfish or larger targets moving. A line of moving arches that pass consistently along a feature is almost always a lane.
  • Note timing and direction: When I see movement, I note the tidal state and direction the targets are moving. Bass lanes are often tidal — fish will move along lanes with the tide to intercept displaced prey. I keep these observations in the app’s notes or on paper to cross-reference later.
  • Repeat passes: I don’t expect the perfect picture on the first pass. I’ll make several casts over the same area at different ranges and on both incoming and outgoing tide phases. Consistency across passes is what tells me a lane is real, not a temporary bait patch.

    • Interpreting sonar returns at night

    Interpreting sonar is partly technical and partly pattern recognition. A few things I look for:

  • Soft, diffuse returns just above the bottom are often bait schools. They form the buffet that brings bass to a lane.
  • Arched returns rising and falling in the sonar view are typically individual fish. A stream of arches moving parallel to a feature indicates fish moving consistently — a lane.
  • Hard returns from the bottom show rocks or wreckage. The edge between hard and soft returns is often a productive place to fish.
  • Shadow lines behind hard structure indicate flow disruption — places where current funnels prey and predators.

    • At night, I pay attention to motion more than static targets. Bass often cruise along edges, and a single pass can miss them. Seeing repeated movement in the same spot at similar tide states is the best confirmation.

    Mapping and saving spots for future nights

    I use the mapping features to build a small library of lanes. For each waypoint I save:

  • GPS coordinate and a short label (e.g., "NW Gully - edge").
  • Tide state when I saw activity (e.g., incoming 2.5m).
  • Sonar setting that showed the lane best.
  • Gear that worked or was planned (lure size, weight).

    • Over time these notes let me predict when a lane is likely to be active. On a busy weekend I can return to a lane I mapped months ago and expect a similar pattern if tides and moon phase match closely.

    Practical tips and common pitfalls

  • Keep casts short and controlled. Letting the device drift behind waves can reduce signal clarity.
  • Watch for false positives — schools of sandeels or sprats will show up but may not attract bass depending on season.
  • Don’t rely solely on technology. Use wading, sighting and local knowledge together with the fishfinder.
  • Be mindful of battery life; map offline copies if your app allows it. I always carry a power bank for multi-hour surveys.
  • Use a tether if you’re fishing between rocks. I’ve lost a unit to a snag once and learned the hard way.

    • Mapping bass lanes with a castable fishfinder has made my night sessions more efficient and more successful. It’s not a magic bullet — bass still read the tide better than any gadget — but it gives me a reproducible way to find the corridors they use. When I combine those mapped lanes with the right lures, timing and a little patience, the night fishing takes on a new rhythm: fewer blind casts, more confident, targeted presentations under the stars.