"6224 where no one can probably find us"
Love it. Compared to, say, 6870 kHz USB or 6095 kHz USB or any of the other out-of-band frequencies they use. There's your proof that their radios are programmed to display frequency directly. Per the USCG website, 6224 kHz is one of the 6 MHz marine HF SSB ship to ship simplex frequencies - "shared and are not available for the exclusive use of any station", along with 6209 kHz, 6212 kHz, 6227 kHz, 6230 kHz, 6510 kHz, 6513 kHz and 6516 kHz.