If you are going to be working on fabric for your boat (sails, bimini covers, cushions, etc.), you may want to check out Sailrite. They sell fabrics, commercial sewing machines and all manner of supplies.
Sailrite is truly a canvas worker’s hardware store. The company’s full product line of nearly 6,000 items is viewable online. As a full stocking retailer of marine fabrics, fasteners, thread, webbing, sail hardware, industrial and semi-industrial portable sewing machines, clear vinyl, awning hardware and do-it-yourself sail/canvas projects you will be able to find everything you need!