Well. There are so many problems with the story, if it is based on any real event, and not but a myth, it must have been a very localized flood.
Dissecting the story as if it were fact and one runs into a flood (Ha Ha!) of issues. First off, for it to float and NOT be directed, as Joe suggested, is a ship doomed to founder. The only way to survive savage seas is to have propulsion to turn into the waves. Otherwise you capsize very quickly.
The only way you 'might' survive without a powered vessel is if you had a 'sea anchor', which is essentially like an underwater kite on a very long rope. A sea anchor at least will attempt to keep the ship facing into the wind. Sea anchors are the option of last resort when you have no propulsion.
Secondly, well here is a typical pic of a Noah's Ark scene. Storm clouds and lovely whitecaps which would be typical of a stormy ocean inside a bay or other mostly enclosed section of ocean.
Unfortunately, that is not the Ark story. It is on a planet of ocean. Atlantic and Pacific storms can be powerful indeed, but they are constrained because the force of wind and waves is broken up by continents.
There is only one place in the world where the ocean runs unencumbered by land completely around the Earth. An area of ocean just north of Antarctica, aptly named the Screaming 60s.
I could not quickly find a good pic, so here is a description "The prevailing high-speed, westerly winds which can generate large waves in excess of 15 m (50 ft) and peak wind speeds over 145 km/h (90 mph)."
That is not a from time to time situation. It is constant. With more powerful waves easily reaching twice that height coming at you from all directions of the compass. Not even modern vessels travel these waters if they do not have to. Even a modern steel vessel would very likely not survive if they were to lose engine power.
Now take that example and make it world wide. No land anywhere to block wind and waves. And you are looking at hurricane force winds and mountain sized waves. Again I doubt any modern vessel could stay afloat in such a hypothetical situation. Much less one built of wood or reed.
Of course one can gut all the real world issues with the standard religious copout that God caused it to happen so none of the real world issues are relevant.