Alan, Hi.
I've just read quite a few pages on this topic..They all agree it must be A4 because of the molybdenum (2-3%) that's added.
Here's one you might like to peruse:
http://www.canalworld.net/forums/index.php?showtopic=51126
Spot on, John.
(And Strow's post while I'm typing this!)
But don't think it's an easy (or cheap) option, Steve and Deb, to replace a petrol engine with a diesel one!
Whilst we (non-Scottish) may consider this a great opportunity to 'send-up' the Scots, might I just point out that they consider this completely serious.
(Yes, I know. I'm half -Scottish, but I've lived in England nearly all my life).
Diesel is far more common, apart from Brooms I don't think there's anywhere else you can buy it 'Darn Sarf'!
Others will disagree but bye and bye diesel is a safer bet for pleasure boats on the Broads. YES, a safely constructed and well maintained petrol engine is safe, but petrol, or its fumes, are inherently more combustible!
Steve and Deb, Hi
For river use (where there are speed limits) a displacement boat will usually be best as they are more stable at slow speeds.
A displacement boat will almost certainly be easier to helm at these low speeds.
I'll leave it to the "techies" if you want more detailed info!