Fishfinders

CHIRP sonar, side imaging and live sonar on the screen:

the cheapest kind draws the bottom as a line and fish as arches, and on a Garmin Striker or Lowrance Hook it uses CHIRP, a sweep of frequencies that separates a fish from the rock beside it. Down imaging adds a picture-like view straight below the hull, good for telling rock from sand on a shoal. Side imaging throws that picture out to either side, which pays off in shallow water at slow speed and much less over deep water or on the plane. Live forward-facing sonar, sold as Garmin LiveScope, Lowrance ActiveTarget or Humminbird MEGA Live, shows fish moving ahead of the boat in real time. Castable sonars such as the Deeper pair with a phone and are thrown from the rocks or a kayak. Full chartplotters sit under GPS and radar, and radios and autopilots under marine electronics.

The transducer, the hull and the brand on the plug:

choose the transducer for the boat before you choose the screen. A transom mount is the usual fit on a panga or skiff. A through-hull reads best at speed and in deep water but means a hole below the waterline, so it tends to stay with the boat. An in-hull transducer shoots through the bottom without a hole, and only through solid fibreglass: not aluminium, wood or a cored hull. Kayak anglers use scupper or arm mounts and a small sealed battery. Transducers do not cross between brands, and an imaging screen sold without its imaging transducer does only half its job. To hold the bottom over the deeper Pacific rock, look for a lower-frequency, higher-power transducer; the high frequencies that make imaging so sharp lose the bottom long before that.

Small sonar heads against a live sonar rig:

a small sonar with GPS and its transducer starts around $250 new in Panama, while a live forward-facing system with a screen able to run it costs upwards of $2,500. Second-hand, the small units fetch little, since a new one is cheap and the transducer often stayed bolted to the seller’s old boat. Live sonar holds its value far better, but only as a complete set of screen, black box, transducer and mount, because the transducer is the costly part and buying it on its own eats most of the saving.

Simulator mode, cut cables and a lifting screen:

a fishfinder switched on at a kitchen table with no transducer detected drops into simulator mode and draws a convincing fake bottom, fish and all, so a screen full of arches proves nothing. Ask to see it on the water reading real depth, or at least on its own transducer with no simulator banner. Follow the transducer cable end to end: cuts, splices and crush marks from a hatch or a trailer are common, and so are bent or green pins in the plug. A transom bracket that has hit a ramp or a log shows cracks or sits crooked. On the head unit, look at the edges of the screen for bubbles or a rainbow sheen where the layers are lifting, and press every button.

The sonar, its transducer and the marks you wipe before selling:

start with the waypoints. Most sellers wipe the marks on their best rocks, and no buyer should count on inheriting them. Then give the make and model, which transducer comes with it and how it was mounted, and say whether the cable is its original length or was cut to route it. Photograph the screen on the water showing a real depth, the plug pins, the transducer face and the bracket and list the power cable, mount and sun cover. A panga owner coming in from Cambutal will want to watch it find the bottom from a dock or a boat, not on a table, so arrange to meet near the water.