Yes, there is a ferry, but my daughter did some research on it and says they have a very poor reputation for not being on time, cancelling trips with no notice., etc.

Perhaps they build an overnight in for Martinique, and go the next day to Grand Case?

Thanks all for your suggestions.

btw, my suggestion was to get married on the beach in SXM. Our rented villa is in Anse Marcel. What would be wrong with a private wedding on the end of the Anse Marcel beach??? Anyway, not my wedding, and that's not what they wanted. C'est la vie!

Cheers!