Good evening Peter,
this post interested me as I've always liked "mucking about in boats", plus a RFDGS friend of mine drowned in a Severn boating accident some years after we left school, they were competent sailors but the Severn is a particularly difficult river.

Anyhow some net searching has found this 2009 thread which I suspect you are already aware of and indeed may have been part of at the time ?
It seems the ship was the sailing smack "Gem" out of Newport carrying iron ore, floundered in a gale and sank at the mouth of the River Usk, only one survivor of the four man crew.

I hope this helps, J.

http://www.rootschat.com/forum/index.php/topic,416045.0.html