You need to get from the port to downtown to do almost anything in St. Maarten. There are a few shops near the port but that's it. However, if you are able to get in and out of a vehicle on your own, I would think the van cabs could lift your chair in and out of the van. How heavy is the chair? I use a scooter (4 wheeled) and have had it lifted into vans. Is there any way you might be able to rent a fold up wheel chair for the trip? You might even talk to the cruise line prior to going to see if you can use a chair on shore (most cruise lines don't do this any more but it can't hurt to ask).