Yesterday I built a ring-flash - that is powered by a pair of Inon Z240s. Its not really a ring flash - more a ring-shaped soft box - but the lighting effect is the same.
I decided on this approach - as it makes it lightweight - so it can be taken on a trip with no weight penalty - and could be taken off during a dive if necessary. Plus there is no need to water proof it.
Anyway - much to my surprise - it works really well. On land, that is. Gives lovely light for flower photos and only costs about 1-1.5 stops of light compared to straight strobes.

Alex
p.s. I thought I'd post this in the Team Wetpixel area - as this is work in progress. I have no idea how it will perform in the ocean. It could be a total failure. But I am off to Cayman on Friday - so updates soon!