It's been suggested that I should move this request to this forum from Scuttlebutt:-

I was asked this morning about sailing on the Bristol Channel. An acquaintance has been asked to deliver a Westerly Griffon from Swansea to Portishead one day in June, probably around the 26th; he is a YM, but his sailing experience is mainly in the Solent.

He asked me because he’d heard that I have sailed on the Bristol Channel, but my experience is only on a Laser at Portishead Sailing Club, so I couldn’t really help.

I told my acquaintance that the YM Scuttlebutt forum is a great source of wisdom and experience, but it takes a while to be registered, so I said I would post this on his behalf.

Any advice on the best time to leave, how long the passage might take, any hazards to avoid, would be greatly appreciated.