PY / Top Speed formula?

Originally posted by SoggyBadger I seem remember someone from Kielder posting about the speeds achieved over their measured points. Even the 49er was "only" 14.something knots and the Ospreys were similar. Back in pre-history I believe that Uffa Fox's Jollyboat was timed at 13.something knots on the sea and 17.something on the flat water of Edgbaston Reservoir.

What was the last known PY of a Jollyboat?
I think 17+ out of one of those is fairly impressive, particularly if it's timed over a fixed distance.
Hugely difficult to get the measured distance in the same direction as the fastest point of sail, as well as picking the best time to start a run.

It's the difference between your speedo touching the ton and averaging a ton on a section of B road.

I think we need a better way of measuring speed if we want to compare peak speeds, doppler radar perhaps?

I think a jolly boat was the same as a 505
Nice boats from the pictures

I understand there are ways and means of avoiding the spurious peak speed problem with GPS, the board guys have put a lot of effort into working out how to make things reasonably credible.

The nice thing about a top speed challenge is that it is something very different from the usual measure of vmg round a course. However if its based on historical handicaps then I'd put my money on a 97 rules single string Cherub to do the trick if one manages to get the right run in. In fact I even know which would be the very best boat to have - Will, keep FS on the trailer ready to head for Datchet on seriously windy days. But its very dependant on getting the perfect gust in the perfect boat with the skill to exploit it.

Edited by JimC - 13 Mar 13 at 9:53pm

To go back to the OP, then Jim is right you just multiply the speed by the PY to equalise. But of course, PY isn't related to top speeds. Potential top speed is really just a function of heeling lever, righting moment and weight. And efficiency, but that's not easy/possible to measure.

I'm using a GPS at the moment to get accurate measures of speed and location, but it cost £50k+. A speed puck is good enough in most cases.

That's the efficiency bit. But, within limits, big speeds happen in big winds, so you need plenty of righting moment and/or low heeling lever. Weight is simply an approximation for drag at high speed. It doesn't matter how good the hull shape is if you can't harness the power.

Edited by Peaky - 13 Mar 13 at 11:04pm