**Anonymous wrote:**
In prep are pdfs showing polars for 1) all boats, all even wind speeds, 2) all boats , all odd wind speeds, 3) scaled stw's (Alan's factors) all boats, max upwind vmg's, max downwind vmg's and beam reach (90 deg) stw's.

The rescaling, i.e. multiply STW's by Alan's factors, I think attempts to isolate the effects of the rig type by correcting for the boat's characteristics ...length, displacement, sail area, etc.

rself

Here are the results of comparing boat speeds, **after scaling** by Alan's factors (see his spreadsheet below). My approach is to compare the frequency distributions of boat speed in three categorys: max upwind vmg's, beam reach and downwind. The histograms are unambiguous if sufficient sample size is available. These data were collected at 1 second intervals. Around 1000 points or seconds or 17 minutes of data appears to be a minimum to get a close approximation to a bell-shaped curve. To gain sample size I've had to combine boat speed results from more than one true wind angle and more than one true wind speed.

Upwind vmg: combined 40 & 50 deg twa and 6-12 knt tws.

Beam reach: combined 80, 90, 100 deg twa's and 6-12 knt tws's.

Downwind: combined 170 & 180 deg twa and 6-12 knt tws.

The more points the nicer the shape and less ambiguous the comparison across boat designs/rig types/before and after conversions to junk rig (in the future). I'd advocate more data (keep or increase the current data rate) not less.

In Alan's scaling factors Poppy is deemed fastest (longest waterline, fairly high SA/D) and calculates a factor of 0.94. When applyed (multiply every boat speed by 0.94) reduces Poppy's boat speeds by 6%. Miranda, deem slowest of the four, had a factor of 1.29...all boat speeds were increased 29%. Weaverbird's factor was 1.05 and Calisto's 1.14.

The Poppy and Weaverbird histograms tend to overlap on all courses. Conclusion, the scaling correction explains boat speed differences in the original data.

Miranda is the slowest boat on heeling courses (upwind and beam reach) even after the 29% factor boost. Downwind, although the data count is sparse at only 40 points, it tentatively looks like Miranda would keep up with the other boats. My best guess at an explanation is that Miranda had the lowest ballast-to-displacement (B/D) ratio and (B/D) is not one of Alan's criteria. A higher ratio would mean less heel, carry more sail, reef later probably resulting in higher speeds on heeling courses.

Calisto (bermuda rig) was the fastest boat upwind but on the other courses there was overlap with Poppy and Weaverbird. Combining Poppy and Weaverbird mean upwind vmg's by eye I get around 2.6 knts. Calisto's vmg is about 1 knot or 38% faster. Alan's 1.14 factor is reasonable meaning that a 14% boost to boat speed for this comparison does not explain the difference. The Varne 27 design is moderate in most respects: SA/D, B/D, LWL. The design does have the highest D/L which would tend to make it slower not faster. Given everything that is known the 38% higher upwind speed is **anomalous**.

I look forward to analyzing next summer's data. For me the hard part of writing the code is done. Today it'd take me hours not days to process 40,000 lines of data ( 4 boats 10,000 lines each) from raw csv's to polars to summary histograms.

rself