"Larry W4CSC" wrote

If you're screaming your head off, waist-deep in seawater, on your Icom HF
radio and THEY are waiting for a DSC call without the speaker making all
those nice, old HF noises.........you ain't gonna git saved.

Larry, the navcenter website is a bit confusing, I agree.
Here are the guarded (voice) marine channels:

ITU
SHIP SHORE Sched (UTC)
NMN NMN/NMF NMG
424 4134 4426 2300-1100 2230-1030 24 HRS
601 6200 6501 24 HRS 24 HRS 24 HRS
816 8240 8764 24 HRS 24 HRS 24 HRS
1205 12242 13089 1100-2300 1030-2230 24 HRS
1625 16432 17314 ( -- on request only --)

And unofficially only,
2182 is guarded 24 hrs by CG Groups, limited range
2182 is guarded 24 hrs by WLO Moble Radio, long range

The United States does not maintain Sea Area A-2 yet, and will not until
RESCUE-21 is completed. But 2182 continues to be monitored even as DSC was
supposed to replace it. Our coverage of 2187.5 DSC is also somewhat limited
due to multi-purpose antennas not being specifically tailored to that
frequency (yet).

CAMSLANT may hear a general call on those guarded channels (above) and not
be able to respond to it if there is a broadcast marine information
bulletin, weather fax/sitor, etc going out at that time. ALWAYS in the case
of a distress call though, any broadcast would be terminated immediately and
the call answered.

"HF DIGITAL SELECTIVE CALLING
Portsmouth/NMN, Boston/NMF, Miami/NMA, New Orleans/NMG, Pt. Reyes/NMC,
Honolulu HI/NMO, Kodiak AK/NOJ

2187.5 kHz
4207.5
6312
8414.5
12577
16804.5

Note: For radiotelex and digital selective calling,
frequencies listed are assigned. Carrier frequency is
located 1700Hz below the assigned frequency."

No voice is ever guarded there. This is the case worldwide as well. However,
since I asked us to monitor for interference caused by our own transmitters
(HFDX, broadcast wx fax, etc) there are now speakers connected to these
receivers, but there is never voice traffic expected or listened for on DSC.
DSC procedures describe an appropriate voice channel to switch to after a
DSC distress call is sent. The DSC distress channels are overloaded with
safety testing most hours of the day and night since IMO originally required
daily testing. Now the requirement is weekly, but that word is slow in
getting out to the commercial fleets. It hasn't slowed down much!

Hope this helps,

Jack