Steam engine boat

For my science fair i chose to do a steam engine boat: How does the steam engine change from a bigger steam engine to a smaller steam engine out of the duration and speed. I will try run a boat with a candle and with a piece of coal. I expect the boat to be faster with the coal. I think this experiment can change the world because The world is getting really populated and not clean like in the olden days so what i want to do is that i want to make the world a cleaner and environment so i'm going to make a envirometal boat so people can transport to another place without polluting the world.Hypothesis:

The higher the temperature the more steam is produced, the higher becomes the pressure and the faster the boat is driving.

Independent variable Heat coming from a candle and heat coming from coal

Background question: How to make a steam boat.Which length should be good for a little steam engine to fit in.

Should i put foil on top of the boat or another type of material.Which is hotter a candle or a piece of coal on fire.

Dependent Variable Quantitative Visible steam that’s produced by heating with a candle or by heating with coal. Qualitative The speed of the boat when heated with a candle or heated with coal.ConstantsAmount of water, Size of can, Size of pipes through which the steam goes out, Weight of the boat.Experimental Groups and Control Group Control group: I do a trial with 3 times a candle and 3 times with coal. Exp Group #1. Put boat in the water once with a candle and once with a piece of coal.Exp Group #2Put boat in the water once with a candle and once with a piece of coal. Exp. Group #3:Put boat in the water once with a candle and once with a piece of coal.