Minimum Wind Polars

[Suijin]

I'm still puzzled by the OP's objective. There is no "minimum" other than zero.

As Thinwater explained, polars reflect what the boat should be able to do in ideal circumstances. They are a benchmark you use to analyze various changes, either to the boat itself or how it is sailed. As a result, it's the outside points on the plot that are meaningful if you are performance oriented, but they are only meaningful if you know how you achieved them.

Similarly the lower performance data points are somewhat meaningless unless you also have contextual data that explain why they are lower. Like "Wow, putting another 300 lbs. of chain in the bow really had an impact." or "Wow, not cleaning the bottom for three weeks results in a 1.5 knot loss of boat speed when close hauled in 15 knots of wind in flat water."

[slug]

Very difficult for an amateur to achieve polar speed targets

Your instrument system and your whole boat must be set up correctly

Once this is all calibrated and correct you then have to deal with details like wind sheer , mast twist , updraft , .sea state ...

On race boats it’s s full time job performed by s specialist

[Montanan]

Originally Posted by mglonnro

Greetings!

-- PREAMBLE RANT --

Let me start by saying that I love data and I think the whole sailing market would benefit from getting more of it Well hey, I believe we may have something we share as to valuing, I love beer and think the whole sailing market would benefit from drinking more of it. - especially data that paints realistic pictures of sailing performance, and all of its different aspects.

Anecdotes are cool as well, but sometimes hopelessly unreliable. Sailing magazine reviews bring some sailing facts into the equation, but usually they are valid only for a very limited set of wind conditions - whatever the weather happened to be when they did the test sail.

So, it would be great to see more real life data about everything, partly produced by manufacturers, but mostly by people actually sailing the boats.

-- PREAMBLE RANT ENDS HERE --

In addition to the displacement, sail area, etc figures, the most usually available sailing performance data comes in the form of manufacturer produced (and/or ORC/VPP calculated) polar diagrams.

These polar diagrams show resultant max speeds for different wind conditions. I thought it would be nice to see the inverse, ie what different wind conditions are required to achieve a target speed?

The question I was initially trying to answer was not "how fast will this thing go with wind speed X from angle Y?" but "how much wind did we need to go at least speed S". Hmmm, okay, I'm pondering as to why one would manipulate the data set so as to be determined based on a factor that one has zero control over. The wind speed is what it is. What is the relevance of knowing how much wind we need to go at least some speed S? A skipper can't change the velocity of the wind. When our boat is going really fast, too fast, I for one am usually wishing that the wind would calm perceiving the wind to be too much. That is to say, I take a cruiser's mindset to sailing, having long left the racing circuit.

Here's an example picture showing our last season data and what the wind conditions were when we were going at least three knots (but less than four):

So, wind polars! Or by juxtaposition, say, polar wind - The polar wind or plasma fountain is a permanent outflow of plasma from the polar regions of Earth's magnetosphere, caused by the interaction between the solar wind and the Earth's atmosphere. Sailing the polar wind, now that is real sailing!!

I think they show useful information. Do you agree?

(The full blog post I wrote can be found clicking the link in the signature!)

Note my pondering comments above.

[thinwater]

Perhaps my first post was too harsh. Please allow me to rephrase.


* Polars are for racers or people interested in detailed performance information. They must be created in controlled conditions and they must be repeatable. They are used while racing as targets and when tuning or modify in the boat as benchmarks.
* A cruiser is more interested in average passage speeds. For example, my F-24 trimaran is faster on every point of sail than my PDQ 32. But unless I'm racing or day sailing, the PDQ might actually be faster on a passage, because it requires less concentration and is less tiring to sail. In lighter winds the F-24 will win. In moderate winds, The PDQ will be easy to sail, where as the F-24 will require concentration. In heavy winds the PDQ will probably win. What matters, is having some idea what the passage time will actually be, not what the boat can do.


The problem is that the latter is subjective. Sailing with a competitive buddy in a breeze, the F-24 is fast even over a distance. Sailing solo for 40 miles or with my wife, I will push the PDQ harder, leaving it on auto-pilot, and probably sail faster. And there is also my mood. Do I feel like putting the hammer down?


But the OP had an interesting question. I have no answer. It would be nice if boats came with real polars, just like cars come with mileage figures, but just imagine the temptation to cheat!

[Sailor279]

Originally Posted by slug

Very difficult for an amateur to achieve polar speed targets

Your instrument system and your whole boat must be set up correctly

Once this is all calibrated and correct you then have to deal with details like wind sheer , mast twist , updraft , .sea state ...

On race boats it’s s full time job performed by s specialist

I'll second the comment made by @slug about being very difficult to achieve. The wind instruments and speedo need to be tuned correctly, the boat optimized for weight (as noted in various other posts), hull clean, rig tuned, sails in decent to optimal condition, crew trimming/adjusting constantly and a capable driver at the helm.

You should be able to get a set of baseline polars from your boat builder. But remember, it's a theoretical model derived from a computer design. On the boats I race, we have a set of "Performance" polars and a set of "Navigation" polars, which are primarily used for ocean racing where sea state impacts. Nav polars are about 80-85% of the Performance polars. We track "polar percentage" (eg. how close to 100% of polar targets that we achieve) and we strive for 90-95% of this number in optimal conditions. We are well-performing amateurs but on a pro crew (think Comanche, etc.) a pro tactician/navigator will have taken the original polars and further refined them based on observation. They are much more meaningful in that scenario.

Final point -- don't even bother to sail to polars in very light air (on a raceboat, "light air" is <5kts wind speed), the shear, sea state/current and other factors make it meaningless other than to tell you to reach off and find a possibly faster point of sail.

[contrail]

I am guessing that the OP is simply trying to put some science into the type of estimate we all make;"Let's see, it's blowing at about ten knots and we will be on a beam reach, more or less, so just divide the distance to our desired destination by X knots, to get a ballpark on what might be expected. Since he is looking for a minimum, he would probably say, "Let's see, we need to do about X knots to reach our anchorage by late afternoon, so we will need about y knots of wind, or else we will start the motor." Maybe nothing more precise than that.

[mglonnro]

Oh wow! A lot of interesting comments!

Instead of addressing each comment individually, I'll make an attempt to clarify what I want achieve (and WHY? ).

First, a small note on terminology. I've used the term 'polar diagram' in a broader sense, meaning just a circular chart where you plot dots. The standard sailing polar chart is one common version of this circular chart, but obviously it's possible to plot whatever you like in a similar fashion.

Secondly, and this is the main point: since for various reasons it might be hard to understand real life performance of a sailboat based on manufacturer polars (as they are published at he moment), I wanted to:

1) Plot "real life" dots on a circular diagram to show what we (in our specific boat, loaded with our specific stuff and people, with our sailing abilities) actually did during all of our sailing. So not the only the fastest at any given wind conditions, but a visual overview of "everything".

Here's our "standard" actual data polar diagram of everything (circles = boatspeed):


The comparison in the diagram above is to the official Hanse 388 polars (with just main and jib!). The red solid line is our maximum, the dashed black line is the official data.



Here's the sama data for us, but the official comparison is now to a Hanse 388 with main and SPINNAKER. We have only a code zero so the gap gets bigger further down.

2) Answer the question: "What WAS, generally, the least amount of wind we needed to start moving ... at least a bit". So, if point 1 was about the max speed we could achieve, point 2 is about minimum wind to achieve a target speed. In this chart i tried to make the individual dots transparent enough so that it might be possible to distinguish clusters and shapes in the plot.


The "flipped around" polar, with circles = wind speed. The red line is showing averages:



3) So, finally, I think contrail's comment hit close to my own thoughts. The goal was/is not to get exact figures but rather to plot a lot of data to try to get a general feeling about a big and complicated issue. (And if there were more than one Hanse 388 doing the same thing, it would be interesting to compare! EDIT: Well, any other boat actually!)

I am guessing that the OP is simply trying to put some science into the type of estimate we all make;"Let's see, it's blowing at about ten knots and we will be on a beam reach, more or less, so just divide the distance to our desired destination by X knots, to get a ballpark on what might be expected. Since he is looking for a minimum, he would probably say, "Let's see, we need to do about X knots to reach our anchorage by late afternoon, so we will need about y knots of wind, or else we will start the motor." Maybe nothing more precise than that.