I don't know about yotties "shooting" you, both Chichester & Langstone harbour launches are equipped with radar guns and they will if you exceed 8knts & 10 knts respectivley.
I have launched from Chichester Marina (£16.50) but it is a drag going down the harbour to the sea. At Northney Marina (£16.00) if the tides right you can go under Hayling Bridge into Langstone Harbour and pop along at 10 knts to the entrance.
I think that some of the members launch from Itchenor but have not done so myself.
Hope this helps
Peter (nick, nick) T
Age and treachery will always overcome youth and skill! Bullshit and brilliance only come with age and experience.