LOL. Sugar won't ruin the engine, you can bet your fuel filter is toast, you will want to pull the gas tank to flush it out, if the in tank pump has a screen on it replace it, and obviously drain/replace the fuel.
The old legend that sugar would dissolve in the gasoline can caramelize in the engine is nothing more than a legend. This is a problem I would bring to the attention the insurance company, provided you have insurance on the boat. The better question is what did you do to get sugar in your gas tank?
