ok so I did some reasearch on steam engines and then I had a big birght I idea use a hydrogen falme to boil the water instead of coal you would get H2O (water) as a byproduct perfectly clean water I have a blue print and everything but not a picture of my blue print I will have to take a picture my disighn is based on the uniflow steam engine it would work perfectly on a solor powered boat! you use electrolisis to get hydrogen when you are low on hydrogen oxygen from the air and water from the sea! of course you would need a compressor to but you get what I mean!