For 7 Mtr, I would consider something bigger than the 1.7. The thing about the 1.7 is that it is light. But newer ones come out all the time!
As for diesel increasing to road prices. Well, that's what they say but even if it does, you will (or should) still go further than you would with petrol because it is a more efficient fuel. (That's why diesel cars go so far on a gallon!)
But.... On the Continent, as far as I am aware, they have two diesel pumps. One white, one red. You have to be a commercial operator to buy the red. I haven't seen much movement in this country for marinas to put in extra pumps yet. So, what's the betting they will just put a tax onto red diesel in 2006, (or whenever it is - can't remember). That would be far simpler..... and if that happens hopefully it will start off small and may be many years before its gets to road prices.
In other words, who knows what will happen in 2006 (ish)? I can't imagine them just stuffing the full duty on red.... The fisherman will go mad..... and there seems to be no movement for a two tear one.... So maybe we should wait and see and in the meantime fill up a boat for £45!
Oh, and if you catch fire.... what would you sooner be sitting on? 150 Litres of petrol or diesel???!!!