want to build self propelled recreational water craft from imagination?
Make a bigger version of one of those candle-powered steam boats! You will need a large saucepan, some thin springy sheet steel, 28mm. copper pipes and plumbing fittings. You need to have two pipes coming from the bottom of the pan, along the length of the boat and emerging out of the stern, where they will dip in the water for several cm. And you will have to attach a springy diaphragm to the top of the pan somehow -- it needs to be able to bulge or sag, as much as possible, and it must not leak around the edges. This forms a very simple steam engine. Prime the engine by injecting some water up the pipes into the pan. Remember one millilitre of water will produce nearly two litres of steam. When the pan is heated from beneath, the water inside boils and the steam forces the diaphragm to bulge up. When the diaphragm cannot move any further, steam is forced down the pipes and out the back of the boat. By Newton's Third Law, the boat is pushed forwards. As soon as the steam reaches the cold water, it cools and condenses. This creates a partial vacuum in the pipes and draws in water. Meanwhile, the diaphragm has contracted; ensuring that this suction does not have quite enough force to drag the boat back.
I think you need something more than imagination. An engine, some wood at least
