Roughly how many VLCCs are at sea right now?

Build it from seaborne crude volumes. Around 40 million barrels a day moves by sea. A VLCC carries roughly 2 million barrels, so that is about 20 loadings a day.

A round voyage on a long haul route is perhaps 60 to 80 days including waiting and discharge. Twenty loadings a day across a seventy day cycle gives something on the order of 1,400 vessels engaged, against a global fleet of around 900 VLCCs.

That mismatch is the interesting part, and saying so is the point: it means the average voyage is shorter than assumed, or that a meaningful share of the trade moves on smaller vessels. Noticing your own answer is inconsistent scores better than a clean wrong number.