Finally ... we have the polar diagram results for all the boats tested to date. I apologise for taking so long to produce these, but since 2019 Anthony Cook has been working to "automate" the analysis of the results, and the creation of the polar diagrams, which I used to produce by hand.

Attached is the 7 boat multi boat comparison sheet, with polar diagrams at 2 knot windspeed steps from 6 knots up to 16 knots, displayed for port and starboard tacks as though the wind is blowing down from the top of the chart. Some boats did not have any data for some wind angles at some speeds and tacks, so there are some "missing" bits of the curves. The speeds have been adjusted for sailing length to 25ft.

The curves have been smoothed by finding the "high points" in the filtered data and interpolating between them linearly. You can see how this is done in the individual sheets for Gung Ho and Weaverbird WS.

I have also calculated the VMG for each boat, wind speed, and wind angle between 20 and 85 degrees (true), and extracted the maximum values for port and starboard tacks, and plotted them against wind speed so you can see exactly how the windward performance compares at different wind speeds. I have excluded VMG values below 2 knots because where they occur, they are caused by a lack of data in the upwind sector.

By taking the average VMG between 8 knots and 16 knots, and across port and starboard, we can get to a single figure for windward performance, which could be called "Average Max VMG" This is obviously a great simplification, but is interesting and has some validity as a quick comparison.

Anonymous wrote:

Correct me if I'm wrong, but I don't think Robert is applying any downwash correction to the data. I think he is just using the raw recorded data.

The correction for Amiina's length and sail area and displacement does suggest that the formula we are using does not work across the range of boats tested, so I have decided to just use the square root of sailing length = (2 x waterline length + overall length)/3 for future comparisons, and ignore sail area displacement ratio effects, which I now think are second order effects.

Hi Alan--

Correct I use the raw data after transformation from apparent to true.

I do search for and remove data lines/sentences that are duplicates, i.e. exact same date-time stamp (and column values) and lines that are missing column values. This cull only removes a fraction-of-1-percent of the original data.

Re: sailing length. Do I understand that the factor you'll apply is this line in your spreadsheet?

                                     weaverB, calisto,miranda,poppy,amiina

"Factor to Sqrt LWL of 5     1.13    1.04    1.11    0.96    1.17"

Rather than this line:

 robert self

Well, before the output from the instrumentation is throughly trashed I'll publish my summary graphs and opinions.

The new boats added this year were Weaverbird fitted with a new wing sail JR (same sail area as the 2018 single-ply JR) and Amiina with a split JR.

Weaverbird comparisons;

Upwind the wing JR and single-ply, hinged, cambered JR are nearly equal.

On a beam reach I'd say a slight advantage goes to the single-ply although there is substantial overlap.

Down wind the advantage goes to the wing JR.

In the down wind plot note the small print in the individual panel titles. My attempt to uncover bias in the frequency distributions due to inadequate sample sizes for high or low wind speeds. The ideal is an equal number of measurements in all combinations of TWA and TWS. But there is no way to fully control the wind speed and course sailed on the day data is collected. The idea is to make the viewer aware. Up to them to disregard, in part or in whole, the graph. For example Amiina is missing data from 6-9 knt wind speeds. Only showing data for 10,11,12 knt wind speed. Higher windspeed, boat sail faster. So there is an inherit upward bias to the Amiina graph, out of the control of the data takers, when the viewer compares Amiina boat speeds to boats which are not misssing wind speeds in this category. Perhaps, if the 6-9 knt data had been collected the Amiina frequency distribution would extend down into the 2 knt boat speed region.

Amiina comments;

I found Amiina a surprising overall performer. Alan's scalar says it all (see spec spreasheet below). The higher the scalar the slower the expected boat speed. The scalar is an imperfect handicapper or rating designed to normalize boats of unequal length, weight, sail area, etc.

That said, Amiina has the shortest waterline hence lowest maximum speed. Moderate D/L of 252 hence is not a light-displacement planer like a X-99. Low-ish ballast ratio of 32% not indicative of standing up to the wind when beating like a folkboat with 50% ratio. Lowest SA/D of 14. Under-powered relative to the other sailboats. By these numbers Amiina's "as measured" boat speeds should be measureably less than the other designs. But they are not. Amiina performs on level upwind and abeam. Down wind speeds are potentially biased high.

Applying the scaling factors (red histograms), intended to achieve an apples-to-apples comparison, Amiina is a visible outperformer. Unless there has been some radical changes to Amiina compared to the Splinter 21 specs on the sailboatdata page. Perhaps something is going on here(?) i.e. the split JR.

view and download link:

https://drive.google.com/drive/folders/1b3zneYJrA8ATxeI8bsgFa3Q2025VAFEy

robert self

Anonymous wrote:

Robert,
that polar diagram of Weaverbird makes sense. It shows that best VMG is reached at 40-50° from the wind, and is dropping at 30° from the wind. I even understand the green VMG-dots, although I don’t see a need for them as they are just the horizontal component of the STW curve (vertical component on the Contessa’s diagram).

However, several of Amiina’s polar diagrams indicate that she is at her best when pointing only 30° from the wind.
Amiina has shown before that she sails smartly to windward, but there is nothing supernatural about her close-windedness  -  which the polar diagram below appears to indicate.
This is why I suspected that there was something wrong with the algorithm.

Arne

Arne--OK.

I did not realize this orientation would be so confusing. Between now and next year when (hopefully) data from new boats becomes available I'll look for a matlab prog which defaults to the usual sailing orientation--0 degrees up and clockwise rotation.

Anonymous wrote:

I agree, Arne, there’s something wrong somewhere. My observations as a seat of the pants sailor are that Weaverbird points a little closer, and has more power through the seas, with the wing sail than with JR; and that Weaverbird points a little higher than Amiina but is no faster. I’m not seeing that reflected in the diagrams. 

Alan, I found that there was a lot of upwash with the wind sensor on the bow, so that doesn’t help.   

I guess it would need to be on a super long bowsprit!

Unfortunately mounting the wind sensor at the top of the mast makes shifting it from boat to boat very difficult, and junk masts wobble about a lot which could also affect the results.

So making a 10 degree correction for downwash is probably the best option at the moment, especially for the data we already have.

Other crazy ideas could include mounting the sensor on a drone!