To get this back on thread a little bit, My son used to drive an Ali boat with a Steyer and a jet drive (about 6.5 metres ) when he was working for an oil exploration company in Poole harbour a few years back.
And they were excellent boats so I think a rib with a Steyer and a jet drive would be a very useful craft. The other thing to remember is that Diesel is V cheap so any loss of eficioecy doesn't really reflect in the running costs.
We have a Jet drive boat but havent used it enough yet to offer an informed opinion but my gut feel is that if the engine had a prop attached the boat would be faster, but not as much fun
I need a little bit of Rhythym and a little bit of Blues