GPS & Radar

Radar domes, open arrays and handheld GPS:

a radar dome hides a small rotating antenna inside a sealed shell and bolts onto a hardtop or a short mast, which suits centre consoles with no room aloft for anything wider. An open array is the long bar spinning over a bigger sportfisher, and its longer antenna gives a narrower beam, so two boats running close together show as two targets instead of one blob. Either kind needs a display it can talk to, and the screens sit under marine electronics. On the GPS side, a floating handheld such as a Garmin GPSMAP keeps a panga’s position and waypoints with no wiring at all, while an external antenna mounted in the open gives a plotter tucked under a hardtop a clear view of the sky. Sonar units with GPS built in are with the fishfinders.

Magnetron or solid-state radar for finding birds off Dominical:

billfish crews on the southern Pacific find sailfish by finding frigate birds working bait, and radar picks up a flock of diving birds well beyond binocular range. Magnetron radars, the older and cheaper technology, fire short high-power pulses and have a long record at it; Raymarine and Garmin magnetron domes carry a dedicated bird mode. Solid-state radars such as the Garmin Fantom or Simrad HALO send longer low-power pulses, transmit the moment they are switched on instead of warming up, and go easier on the batteries during a long day offshore. They find birds too, and many add Doppler colouring that shows whether a target is closing or pulling away, which earns its keep when an afternoon squall fills the screen with rain and a boat is hiding inside it. Either type goes above head height with the beam clear of the hardtop edge, so a dome on a low T-top often needs a taller mount; the backing plates and stainless fasteners for that are under marine hardware.

Magnetron hours, cloudy domes and GPS units showing the wrong date:

a magnetron loses output with use, and a tired one paints weak, patchy returns long before it dies. Most makes log transmit hours in the diagnostics menu, so read them. Solid-state radar has no magnetron to wear out, which is part of why it holds its value. Watch it transmit, on the boat or on the ground with the dome raised above everyone’s heads: it should paint the shoreline or nearby buildings cleanly at short range. A chalky or crazed dome with staining round the base seal suggests water has got inside, and on an open array, grinding or a hesitating sweep points to the motor or drive gear. Older handhelds and plotter antennas can show the wrong date since the satellites’ week counter rolled over. The position stays right, but track logs and sunrise times run off a bad clock and not every model got a firmware fix, so switch it on and check the date, then open the battery door for green contacts or a split seal.

Taking a radar off the hardtop to sell it:

film it running before you unbolt it, a short clip of the screen painting the coast or the harbour, because once it is down the buyer has only your word. Give the exact model, whether it is magnetron or solid-state, the transmit hours and which displays it worked with. Include the radar cable in one piece, with the mount and bolts if they go too; a cable snipped at the arch to free the dome is a part the buyer then has to hunt for. For a handheld, photograph it holding a position fix with the date on screen, and say which charts are loaded. Most radars come up for sale when a boat moves to a bigger array, and whoever drives to Jacó to collect one wants to have watched that clip and read those hours before setting off.