What a day, I am only just catching up.
I think it has already been clarified, but Frank is on M1 aka 37. The safety boat was I guess from Hayling Island Sailing Club, we used to supply all their radios and they used to use Horizons where the channel is indeed shown as n1. They have since changed suppliers and I do not know what they are using, but I have put a call in to their marine dept to clarify.
As has already been suggested, do not be afraid to call the CG on 16 - they will decide what action if any to take.
Chichester entrance can be very scary, I know exactly what you mean about that and I think you did really well to cope with that.
Another lesson that might come out of this is - be familiar with your radio, use it at every opportunity and also get a list of all the useful channels in the whole area: sailing clubs, marina, port ops etc etc. Also listen in on routine radio traffic so that you get a feel for what is going on.
I should also say that when there is a RIB.net meet going on it might be an idea to agree a working channel, had KY been able to call the rest of the group up and describe there engine probs I suspect someone would have gone out to accompany them?
All that aside, a bad day on the water is better than a good day indoors.
Live and learn, in that order.
Edit: Re radio chanels, it might be worth making up and laminating a local version of a table like this: