The NRS Split Kayak Flotation - Stern fits in the back of your boat to stop your boat from filling with water in the event of a swim. The less water in your boat the easier it will be to get to shore. Don't lose your boat! These bags come with a lifetime warranty. The Stern Bag size fits in most Creek/River Running boats. To determine the correct size of float bag for your boat, measure the inside compartment and order a bag that is slightly larger in dimensions to fill the space in your boat completely.