I was hoping someone would pick up on that \\\'Dinghy Cruising\\\' article and do the sums for a Swallow Boat or two. Thanks, Graham. The writer is suggesting that the Sail Area/Displacement ratio is a valuable indicator of what he calls \\\'the cruising performance of small sailing dinghies\\\' (without defining what he thinks \\\'cruising performance\\\' actually is).

The intriguing thing is that the sums seem to work, rather elegantly actually, for the boats you have compared. Just out of interest I did them for my Storm Petrel and my in-build Trouper 12, and the results are, frankly, gobbledygook. For starters, the results suggest that the SP is more stable (if that\\\'s what the Sail Area/Displacement ratio is \\\'measuring\\\', or at least indicating in some way) than the T12, which is nonsense. The SP is notoriously (don\\\'t tell Mr Newland Senior I used that word) tippy, whereas the T12 - 2 ft shorter, 7 ins beamier,  with a wide transom and completely different underwater shape - is reportedly as stable as anything. Also the \\\'Motion Comfort\\\' (sounds transatlantic?) figures are so low as to imply that both boats try hard to throw their occupants overboard. I can\\\'t speak for the T12 yet; but given her tenderness, the SP is much more comfortable in a seaway than one might expect.

What\\\'s the difference? I wonder whether those sums work better the greater the displacement of the dinghy under consideration, and vice versa, although the article\\\'s figures for a Mirror dinghy look OK. Certainly, boats don\\\'t come much lighter displacement than the two I looked at. I notice that the BR\\\'s displacement, even without water ballast, compares more with a keel boat than a \\\'small dinghy\\\', and I note that the calculator used in all these discussions (Graham has given the link) is headed \\\'KEEL boat metric calculator\\\' (capitals mine).

My conclusion was that this was a fun exercise of sorts, and seems to work better for larger boats, but that it doesn\\\'t seem to indicate anything useful for \\\'small\\\' dinghies. Perhaps someone clever can chew this over and give us a much more useful opinion than mine? Is there a graph buried in there somewhere with a funny shape indicating at what sort of length, displacement and sail area these figures start to mean something?

As an aside, I was intrigued how relatively little faster the hull speed is for a \\\'large\\\' boat compared with, say, a Mirror dinghy (= 4.3 Knots). I know this is a standard calculation. You get about 1.5 knots extra if you go for double the LWL of a Mirror. Purely in terms of speed through the water, the ability to plane is obviously the thing. I have hopes for my T12 with the rig I\\\'ve designed for her!