Yes, you could use an outdoor carpet in place of a marine carpet. While this option may be sufficient, particularly if you are on a budget or if you need bulk amounts of floor covering, do keep in mind that outdoor carpeting may not be as resistant to moisture, stains, fading, and other issues that can commonly occur with boat flooring. Marine carpeting is specifically designed to combat those issues, so to ensure high-quality, long-lasting floor covering for your boat, marine carpeting is the best bet.