In my kayak there is styrofoam in the bow and the stern. If I need more flotation is it a good idea just to replace the styrofoam with larger pieces? I know I would loose cargo space but hey I would rather float.
A major point to consider: How high does it float now, does it really need more flotation? And, if the hatches don’t leak, does it need flotation at all?
boats I have seen using styrofoam in the bow and sterns for floatation have only enough to keep the boat barely afloat so you they get sunk and get lost. Styrofoam also degrades much faster over time than other types of foam, like ethafoam and minicell (closed cell) foam.
It’s a good idea to put in as much floatation as possible, without impeding your cargo carrying needs on most trips. More floatation means more displacement of water, making self rescue possible. The floatation has to be sufficient to allow you to climb back into the swamped boat and still have the gunwales above the water line. If not the boat can’t be self rescued. More displacement of water also means quicker pump out time and easier time of swimming the boat to shore if that be the case.
Correctly sized float bags are a good way to go because these can be deflated slightly if need more cargo room. Make sure that you find places to tied the float bags in, or they pop out on a capsize. Float bags are not cheap, but probably cheaper than getting the quantity of ethafoam or minicell foam for the same displacement. If you’re handy, you can actually buy heat sealable nylon from Seattle Fabric, .5" silicone tube from hard ware store and valves from NRS to make you own float bags. The material can also be used to make drybags of varying sizes for your needs. It’s very easy to make float bags and dry bags and the cost is half or a third of buying the bags from a retailer.