Alex
Looking through your log and your handwriting it looks pretty clear to me that it is a 6 and not a B - All your 6s are identical and you printed all the callsigns - so its a 6.
Even if it was some error and it was FFBN - this would mean it was a French ship and FFBN was/ is allocated for French warships and othat call is no longer in use - which is OK - it could have been in use in the 1990s when you logged it.
FF6N ? I’ve not heard of such a format (ltr, ltr, fig. ltr) for use by either merchant or naval vessels.
I actually think it is/was a Prank SOS for a number of reasons, particularily relating to the 1990s.
- Your log shows the SOS sent on 7mhz. SOSs were sent on 500khz. I’ve not heard of any exceptions, but……..

2. The format and procedure for sending an SOS is very, very different from what you have recorded. a. An SOS is always prefixed by 3 X SOS, The ship’s name is always included, and the position is notated slightly different if I remember. Details of the distress are normally kept brief and normally contain detail that is much more relevant than the crew’s /passengers mood!! - It would/could have stated how many were onboard - not the state of their mood!!! Even in serious life threatening situations they end in …… // Master AR SOS K.
However, lets assume its genuine.
a) Why would a warship send an SOS? I can’t think of a reason. You’d normally be in pretty quick comms with your own people ships- shore stns etc.
b) 1990 CW was a rather outdated way of sending an SOS - I think the last sos was sent around 1982 as it had been largely replaced by GMDSS (Sat comms using (Golobal Maritime Distress Safety System.) Basically press a button on the bridge and it’ll send all the information you want to a rescue centre/ co-ordinator.
c) Lets say the callsign was different and wrongly transcribed and it was a Yacht. A yacht would carry 2182khz (the international safety and distress frequency for voice (Mayday) equipment, MF SSB radio, or ch16 (vhf) Even large Yachts do not normally carry CW equipment..
d). If it was a cargo vessel, then by law it would carry a qualified radio officer who by definition would know exactly how to send an SOS and would send it on 500khz, the International Safety, Distress and calling frequency 500khz and not on a ham frequency. It is almost always the Captains responsibility to decide if an SOS is needed and it would not be for a fire which was put out a short time after sending the SOS, nor would he/she ever bother mention their name. All captains sign themselves off with “Master”. Why on earth send it on an amateur frequency?
e) etc., 
Dave