How Does Buoyancy Work? Adding an Inflatable to a Boat

Question
If you put a inflatable sleeping pad inside a rubber fishing boat and sit on it. Does the buoyancy of the boat increase or is it useless if you want to increase the overall buoyancy?

Answer
Your buoyancy comes from the water your boat displaces. About 68 lb. per sq. ft.  Because the inflatable is inside the boat you don't gain buoyancy.  If you strap it to the died like the river rafters do, then you displace more water and gain buoyancy.  The inflatable does do a nice job of keeping water form filling up the hull dropping displacement.  Thanks for the question, most people only want to know how to start their motor.