Hello Bellringer,
an 8" log will never "dry" in one piece. It will certainly lose moisture, but it will be uneven loss and remain essentially green wood whilst still in the log.
If you cut it along the length on the central line, it will eventually dry, with the rule of thumb for air drying timber being 1 year for every inch of thickness (with the proviso of a maximun thickness of 4" or there abouts).
Leave it long so that any end checking can be cut off later when dry.
The alternative is to rough turn your vessels and then put to one side for about four to six months to season. Then you can finish turn them.
hope this helps
Andy