Below is some educational information about boat tarps:
The Pontoon Boat Tarp is a trailerable cover. It's a heavy-duty tarp that keeps your boat in top condition. Its contoured design provides an excellent fit on most pontoon boats. The resistance to mold and mildew of this cover helps maintain its overall cleanliness and freshness.
Small: fits 17' - 20'L pontoon boats with beam widths to 102"
Medium: fits 21' - 24'L pontoon boats with beam widths to 102"