Do you have any photos of boats with flowers Keith?
If you have seen something you'd like to recreate, that would be a good starting point for us to suggest flowers.
I would imaging the popular bedding plants would be "in" as they are best for long flowering periods over summer, and could be grown easily in pots and containers.
e.g. Petunias, Lobelia, Verbena, Surfinias, Impatiens, Tagetes and my personal favourites, Argyranthemums and Osteospermum.
Perhaps even Antirrhinum (snapdragons)