The kingfisher didn't see much service anywhere or anytime other than early war pacific, mostly used a spotter plane. I think it could serve the same purpose as the Catalina would... mostly for spotting Enemy CV's and displaying them.
I've suggested something similar in the past, however as far as how long the boat is visible, I wouldn't have it be tied to the proximity of the PBY, but make it a "last spotted" thing. Say, PBY approaches the boat and the clipboard map updates. So long as the PBY is in continuous contact with the CV, its position is continually refreshed. If the PBY is shot down or leaves X distance, the boat's icon remains on the map as a "Last Known Position" for a period of time (whether it's 15-30mins, or whatever) before being removed.
General characteristics
Crew: Two, pilot and observer
Length: 33 ft 10 in (10.31 m)
Wingspan: 35 ft 11 in (10.95 m)
Height: 15 ft 1.5 in (4.61 m)
Wing area: 262 ft² (24 m²)
Empty weight: 4,123 lb (1,870 kg)
Max. takeoff weight: 6,000 lb (2,721 kg)
Powerplant: 1 × Pratt & Whitney R-985-AN-2 radial engine, 450 hp (336 kW)
Performance
Maximum speed: 164 mph (264 km/h)
Range: 805 mi (1,296 km)
Service ceiling: 13,000 ft (3,960 m)
Armament
Guns: 2 × .30 in (7.62 mm) M1919 Browning machine guns
Bombs: 650 lb (295 kg) of bombs