On VH/VH building boats is suicidal. You can't fight the battles, so you just bleed tons of money this way. The AI is programmed to build masses of boats, so why fight it on its terms using autoresolve? Autoresolve is nutty and unfathomable. MTW's naval warfare made more sense...and that is really scarey.

I keep a few boats around just for moving armies or blockading ports for a turn if needed. I might even use them to remove a particular factions boats from the area. I use the approach of only building them when I have a strategic task. Other than that I don't build them.