My current game is pretty stable. I get crashes occassionally when frames spike to an unacceptable level or randomly in a dungeon but they never happen again on a reload, they are one off things. Normally I can play for hours with no problem.

I am having a consistent crash in the bloated float quest though. Once I have rescued them all and the owner tells me to go and get some sleep until they reach the Imperial City I go downstairs and get some sleep and when the sleep timer gets to 0 I get a crash to desktop. This happens every time. If I go down to my room and wait the appropriate time the timer ticks to 0 and doesn't crash but the boat has not moved no matter how long I wait. I think I have to sleep for the quest to advance but the crash prevents me from doing it.

Any idea what could be causing this crash?

There is a conflict with another quest on a boat in the waterfront..... Thieves guild? Got any other quests down there?

No I am not part of the thieves guild and my character never will. I haven't joined any guilds yet and no quests that involve the waterfront.

Have a look http://www.uesp.net/wiki/Oblivion:An_Unexpected_Voyage, and see if anything in the bugs section applies to you.

Any mods that affect the waterfront area??

If you have the quest The Elven Maiden running at the same time you try to do An Unexpected Voyage, the game will crash every time when you are supposed to be returned to the Waterfront.

If this is indeed the crash you are running into, the only fix possible is to reload a save from before you started An Unexpected Voyage and don't attempt it until you have finished The Elven Maiden.