Originally Posted by Polwart
...allow (or insist) on people carrying reserves (not sure how much you will just trust people not to switch to these or top up...
Why just ribs though? If I had a "fast fisher" or something then I might feel I was missing out?
You are right, there is no reason to exclude any boats. At the very least it will increase the chance of learning something new about fuel efficiency in the real world.
As for fuel, the thinking at the moment is to encourage boats to carry a good reserve in their usual tanks (weight issues are up to the skipper).
The "challenge tank" should be an ordinary portable petrol tank ideally with a reserve baffle/ridge in the bottom, this will be charged with 16.0L and sealed in some way to prevent topping up.
It is then up to the skipper to know how much of the 16 liters his boat will need at what speeds, to plan for that and allow for safe margins within the conditions on the day.
As you say the ratio of 1nm for 1L is a popular rule of thumb, so conking out should be avoidable for all but the most throttle happy drivers. Anyone who would not
undertake a passage of 100 miles with fuel of less than 160L should think very carefully about the suitability of their boat for such a challenge.
A quick boat is going to get around in about 20 mins, so the engine of this theoretical boat would need to consume nearly 50 lph in order for the challenge tank to be sucked dry; ie a 115HP two stroke.
My own boat does 1:1 at 20 knots, so I would anticipate having 6L left and to take half an hour to get round. I would describe this as fairly common economy and not exactly prize winning