Another sim I can recommend is Motorboat Simulator by Stentec -
http://www.stentec.com/motorboatsimulator_i/
There's a variety of different types of boats on there to choose from including a twin jet rib - you can give it different wind/swell conditions too.
If you do get it, download all the extra packs for it, which give you places like marinas and extra islands to go around - parking (sorry, berthing) the biggest boat in the smallest space in a good breeze is great fun
However, you can't beat real experience though - ditto what everyone else has said about a L1 & 2 course......
-Alex