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Since most kayaking is done for recreation ...
Some kayaks have bulkheads and hatches - they create water resistant chambers and add a lot of floatation. If one is worried about floatation despite having bulkheads and hatches, float bags or dry bags might alleviate those fears.
Other kayaks might not have much in terms of built in floatation - typical bulkhead/hatch-less design is an example of that. Float bags are then used to make sure that boat stays above the water.
Absence or presence of bulkheads and hatches does not differentiate between recreational and non-recreational kayaks. WW playboats, racing K1 don't have anything in terms of floatation, but no one will attempt to bundle them with rec boats
And, other folks become ingenious by using other methods of giving extra floatation - inflatable travel/relationship companions, expanding marine foam, pool noodles, beach balls, whatever floats your boat.
Lifting a boat out of the water - to drain it -
will involve muscles and technique to be efficient.
Each gallon of water weighs 8 lbs .
Now consider that weight sloshing around, inside the kayak.
Securing those float bags so they don't slip out is important.
Just because they fit when its upright doesn't mean,
they'll stay in position when the boat is flipped over.
What is keeping them in place, a tether, a clip, etc. ?