My Yacht Club, Alamitos Bay Yacht Club in Long Beach, has been using RegattaNetwork for a couple of years and it has been working well. There was a hesitancy implementing it for fear of sailors not wanting to use it and not coming. That never happened. On the plus side there is always an attending page for potential competitors to look at enticing more to show up if they see the group is going to be there.

You could make:
pre pre registration which includes t-shirts
pre registration no t-shirt but no late fees
late registration add on late fees (or no food included)

Later,
Dan