Route Planning with GRIB - Work in Progress

[sinbad7]

Piotr..

So you are saying that on a course of 209 and a wind of W6 it is normal to expect a speed of 8.19 kn, an increase of 2.19 kn on your regular 6 kn speed?

Yet,with a course of 294 and a following wind of SE2 you can only expect a reduced speed of 4.39 kn.?

Just goes to show how little I know about sailing..

Tore

[PjotrC]

Tore,

Your case 1. is 20kts or more of wind 61 deg from stbd. The polar used says 8.05 kts for 60degs. It fits. Note that the boat modelled here sails well 40degs to the wind...

Case 2. is 6 kts of following wind. ORC polar says 3.8-4.39 kts. It fits...

Probably the ORC sample concerns modern racing performance in sheltered waters (it stops at 20 kts). It is not unrealistic. The mechanism seems to work well. If you disagree with these values:

- change them to suit your opinions
- add more rows to handle lower wind speeds 2, 4 kts etc...
- add more rows to handle higher speeds 25, 30 kts etc..

All works well in these cases, I believe.

However, for cruising passage planning I would use another polar...

Please appreciate the difference in your judgement between program behaviour and polar data. Polars are like charts - they are external to OCPN, can be more or less accurate. I do not intend to produce polars other than for the boat I sail and know well, and I think I am going to use only polars that I understand well, knowing their limitations and peculiarities.

Please keep testing, it is of great use.

P.

[sinbad7]

Piotr..

Thanks for your elucidating explanation of the polar mysteries....

Can you suggest another 'cruising polar'? Is there available a list of polars for typical sailboat makes,i.e. Bavaria 38,Beneteau 28 etc. etc. catamaran, etc.?

Thanks for your efforts.

Tore

[PjotrC]

Tore, type in 3 lines of numbers for the boat you know and remember best and you will have a nice polar to test the software...

Looking for polar data, and judging its quality is a different branch of science altogether... :-)

[sinbad7]

Get Your Performance On Target
Racer's talk targets, but few understand how best to use them.
Stan Honey brings us up to speed.

© Joseph Comeau

Step aboard any well-sailed raceboat today and you're guaranteed to find somewhere in the cockpit a laminated sheet of paper showing a spreadsheet full of letters and numbers. For everyone directly involved with the performance of the boat as it makes it way around a racecourse, this "Target Table," a detailed matrix of optimum boat speeds and wind angles, is the all-essential cheat sheet. Every boat with instruments should have one because the information on these target sheets will guide you to your next mark, or destination, at the optimum speed. And that is what performance sailing is all about.

So how do we come up with these "targets" that get us around a racecourse as quickly as possible? Well, it all starts with polars. Let's begin there, and later get to how to use your target tables.

Polars are boatspeed predictions across a range of wind angles and wind speeds. In its simplest form, a polar is a curved plot showing boatspeed versus course angle to the wind (true wind angle), for a fixed wind speed. This curved plot is called a polar because it is typically plotted using polar coordinates. Polar coordinates are simple: you have the origin (or center point of the plot), an angle radiating away from the plot axis, and a distance from the origin. Angle and distance, combined, determine a unique point on the plot.

The polar plot(for a Cal 40) displays the optimum sailing angles (marked with an X) for a given true wind speed and direction.

In the first diagram, straight lines radiate from the origin at 10-degree angles from the vertical axis, up to 180 degrees. Our polar plot assumes the true-wind is coming straight down from the top (see wind arrow on diagram) so all these 10-degree radiants are simply measuring the true wind angle. There are also half circles at fixed distances from the origin; these curves represent increasing intervals of boatspeed (in this case 0 to 10 knots). Our diagram actually shows a family of polars for a Cal 40. The yellow curves are our polars when sailing with a headsail; the orange polars are used when sailing with a spinnaker. The respective curves for sailing in 10 knots of wind are bolded.

What does this polar plot tell us? And how do we apply it to our race? With this visual it becomes very easy, and intuitive, to determine the best sailing angles, which will get us to the next mark in the least amount of time. Let's say you're racing to an upwind mark. Sailing upwind at any wind angle less than 90 degrees will get you there, but only one angle will be the fastest. If you pinch (sail too close to the wind), you'll be pointing the boat closer to the mark, but your boatspeed will suffer as a result-the downward curve of the polar confirms this. It will take longer to get there. If you foot off too much, you'll certainly gain boatspeed, but at the cost of not pointing close to where you want to go.

So the polar diagram shows us that too high is too slow and too low is too fast. How do we use the polars find that perfect angle? In the diagram above, we take a closer look at the upwind portion the polar chart. The solutions for optimal upwind sailing are marked with Xs. The polar chart makes it quite clear that this optimal point is where a horizontal line is tangent to the polar curve. This point is the point on the curve "furthest upwind," and it is this speed upwind that we are trying to maximize. This upwind component is referred to as velocity made good (VMG), and sailing at that optimal angle gives the best VMG. [For all you vector heads, this is the vertical component of the velocity vector, drawn as an arrow from the origin to a point on the polar curve, as we've done in the diagram.

When sailing to a leeward mark you do the same thing, using the bottom portion of the polar curve. The interesting thing about offwind polars is they are generally much flatter in the region of maximum VMG; if you deviate slightly from your optimum angle, you actually lose very little of your VMG. In other words, there is very little penalty for sailing slightly high or low. This flatness in the curve, however, can also make it difficult to judge your optimum offwind angles. Judging these angles is especially difficult with lighter boats carrying lots of sail area, for which angles can change dramatically with windspeed. Heading up a few degrees from optimum increases apparent wind speed, increases the sail plan's driving force, and increases boatspeed, which further increases the apparent wind, and the boat accelerates to a new equilibrium. High-powered, lightweight boats may easily speed up sufficiently to have a larger downwind VMG. This is why an accurate set of polars is so valuable in maximizing your offwind performance.

How to build and use your target tables
The most valuable use of a polar plot is also the simplest, and is one available to nearly any boat, even boats that have simple instrument systems. This is the use of the polar files to generate a table of target angles and speeds to sail when you're trying to maximize your VMG, upwind or downwind. Extrapolating the data from the polar chart, I plug it into a basic table, print the table on paper, laminate it, put self-stick Velcro on the back, and post it where the helmsperson, main trimmer, and headsail trimmers can all see it.

Using the target table upwind
Before you read the table, get your true wind speed by either reading TWS from your instruments-if your instruments calculate it-or estimate the windspeed from the sea state. Most sailors can guess TWS within a knot. Once you know TWS, look up the "opt BS UW," and then keep that number in mind as you race upwind. Do not use target speeds as gospel, however. Instead, use them as a reference and keep a constant dialogue going amongst your speed team (helm and trimmers). On a well-sailed boat you will hear such chatter as:

Helm: "On port tack, here, we're slapping into a bit of a chop so the targets are too tough. Let's live with two-tenths low."

Helm: "We've got a well-mixed wind here and flat water, and I'm hitting targets too easily, let's use 0.1 fast as our number."

Trimmer: "We've got lots of right twisted wind aloft. Let's use targets that are one-tenth slow and watch out for an increase in wind and a veer if the twisted wind drops down to the water."

Even the grand-prix boats use their theoretical targets only as a reference, and on any given day use target numbers that are adjusted above or below the reference table. But once the crew picks the target for the current conditions, they pay tons of attention to it. You'll hear lots of chatter like:

Trimmer (coming out of a tack): "We need a half a knot more here . . . need two-tenths more, OK we're up to speed."It's best to not change the target table without a discussion with the trimmers and afterguard. Even if one column is off, and you're always one-tenth low, even in perfect conditions, the crew gets familiar with the table so you should not change it without general agreement and awareness. On the Volvo Ocean Race, we set our target tables two weeks after first sailing ABN AMRO One and never changed them. They were not perfect, but everybody knew how to sail relative to them.

Using your downwind targets
Start by reading the TWS from your instruments, or estimate it. Using the TWS, look up the optimum apparent wind angle (AWA). The same caveats apply as with upwind targets: you will sometimes use a number that is higher or lower of the target from the table, based on how the boat feels, the sea state, and whether there's lots of wind sheer or whether the wind is well mixed, vertically.

Whether it's better to use target true wind angle or target apparent wind angles when sailing downwind is a religious argument for which there is no right answer. As you can tell, I list both true wind angles and apparent wind angles on the target table and typically set up the instrument systems to display both so the helmsperson can use his or her preference.

Here's the basic argument: On a fast boat, as the boat surfs and the boatspeed changes, the measured AWA will change dramatically. You don't want the helmsperson chasing these AWA changes, so some feel that people steer better to a TWA target on fast boats. However, if you use TWA as a target, you also need to watch your target boatspeed (BS) to prevent an inattentive helmsperson from sailing along at the target TWA, but too slowly and with the AWA far too deep. This can be a stable state and the boat can stay at target TWA, but continuously sailing far too slowly, and never accelerating to the downwind target speed. So, when steering to target TWA, the helmsperson needs to watch the target BS and be sure to sail hot of target TWA until the boatspeed reaches the target BS, and then bear off to target TWA.

The benefit of steering a target AWA is that some things work naturally. For example, if the boat is sailing too slowly you will naturally come up to get the AWA to the target angle, and then as the boat speeds up and the AWA comes forward, you will naturally bear off to keep the AWA at the targets. But, again, as the boat accelerates and decelerates on waves, the helmsperson needs to be sure to not chase the AWA.

Different helmsmen use different approaches depending on their experience and on the conditions. Helmsmen with strong dinghy sailing backgrounds generally prefer AWA targets and are skilled enough sailors to naturally not chase the AWA as the boat surfs. When conditions are very windy (and likely dicey) downwind, many experienced sailors also like sailing to AWA because AWA (or measured wind angle MWA) is a raw value on instrument systems that responds quickly and is not subject to the vagaries of getting weed in the paddlewheel or the paddlewheel coming out of the water on surfs.

[PjotrC]

Interesting case developing for Canaries-Gibraltar route...

The green route is automatic from Bluewater Racing.

The red route is made by hand by following the polar display in Append Waypoint mode.

The polar is orc_sample_int.

[sinbad7]

Polars & Performance
Below is a collection of polar diagram from various sources.
Mostly in numerical format to easily plug into routing software. They’re published here just to play around with. For serious/real use you should get a real one for your specific boat. Also some links to tuning guides and other perfomance related info. Share and enjoy!

1D35 (North, UK, Quantum)
606 (Gransegel, Hamel, North)
806 (trimguide)

A-35
A-40RC
Albin Express (Sten Bergqvist, Edman, North, Ottosson, UK Syversen)
Albin Nova (Blur)
Arcona 430

Beneteau 25 (North)

Capri 22 (Ullman)
Cal 40
Catalina 22
Catalina 36
Class 40

Dehler 38/Pacer 376
Dehler 44
Drake (Høj Jensen, North Tuning Guide)

Etchells (Doyle, North, Quantum)

Farr 36 (Farr Performance Prediction)
Farr 40 (Doyle, Farr PP, North, Quantum)
Farr 52
Farr 395 (Doyle, North)
Farr 1020
Fenix (trimguide)
Finn Flyer 36 Club
First 31.7
First 34.7 (Farr PP)
First 36.7 (Doyle, Farr PP, North, Quantum/pdf, UK/pdf)
First 40
First 40.7 polar1 polar2 (Farr PP)
First 44.7 polar1 polar2
First Class 8 (North)

H-båt (Edman, Henrik Lundberg. Høj Jensen, North)

IF (Edman, North)
IMS 43
IMS 53
IMX-40 (X-yachts)
IMX-45 jib only
IRC 32

J/22 (Haarstick, North, Quantum)
J/24 (Doyle, Haarstick, Jardine, North, Quantum, Shore, UK, Ullman)
J/27 (Ullman)
J30 (UK)
J/35 (Quantum)
J/46
J/80 (North, Shore, Quantum, UK, Ullman)
J/92 ()
J/105 (Doyle, North, Quantum, Ullman)
J/109 vpp-od/vpp-genua (Doyle, North, North England, Quantum)
J/120 (North, Quantum)
J/122 (polar + pleliminary IRC cert)
J/130
J/133 (vpp)
J/160

Landmark 43

Melges 24 (North, Quantum, Ullman)
Melges 32 (North, Quantum)
Mumm 30/Farr 30 polar1 polar2 (Doyle, Farr PP, North, Quantum + Cookbook
Mumm 36

Nelson-Marek 43

Olson 25 (Scot Tempesta)

Prima 38 (Quantum Tuning Guide)

Santana 20 (Ullman)
SeaCart
Sigma 33
Soling (Doyle, North, UK)
Sun Fast 3200
Sydney 36CR
Sydney 38 (North)
Swan 42 “ClubSwan” (North, Quantum)
Swan 45 (B&G, Hall. North, Quantum)
Swan 62RS
Swan 70

Tartan 10 (Doyle, North, Sobstad)

Ultimate 20 (Ullman)

VO 70

X-35 polar1, polar2 (B&G, North)
X-99 (North, X-yachts)
X-332 (trimguide)
X-332 Sport

Yngling (Doyle, Høj Jensen, North, Ullman)

Various polars from Sailinline.org

Albin Express
Arcona 400
Arcona 460
Bavaria 38 Match
First 44.7
Comfortina 38
Dehler 33
Dehler 36
Dehler 44
Diva 35
Dufour 34
Dynamic 3000
Farr40
Facil 30
Finngulf 33
Grand Soleil 341
Grand Soleil 37
Grand Soleil 40
Hanse 400
IMX 38
Linjett 33
Linjett 40
Mumm30
Mumm 36
Omega 34
Wasa 410
X-332
X-41 (assy for pole)
Scanmar 33
Swan 37

Get the polar diagrams here: Boats & Polars | BLUR

Tore

[jonasaberg]

Originally Posted by sinbad7

Wasa 410...

Amusing, the polar for our boat. Not our kind of boat, but actually our boat...Maggie!!

;-)

[jonasaberg]

Originally Posted by sinbad7

Polars & Performance
Below is a collection of polar diagram from various sources.

Good find Tore!
Thanks.

I downloaded and zipped them, seem to be 105 different files with polars, so most likely 105 boattypes. Did not check for duplicated...
.
Maybe we could put them on the website later or somewhere? Would be good to have them collected for use with the Route Planner.

Any idea were to put them? Anyone want them?


/Jonas

[sinbad7]

What a coincident Jonas!

All the polars seems to be in different format and need to be changed to .pol
Do you have the Wasa41.pol file? Could you share it with us?

Good idea to set up a polar directory in OCPN where sailors could also enter their own boat's specific polar.

Tore

[sinbad7]

I have set up a location to up/download polar files.

I would appreciate your assistance to both upoad the polar set of YOUR OWN boat as well as some assistance converting the listed polar files to the .pol format readable by OCPN.

Here is the URL: 4shared folder - POLAR FILES

Tore

[jonasaberg]

Yes, I will in a few days fix a polar for our boat suitable for Pjotr's plugin. Will probably be next week..

If you want I can just email you the zip, its a few megs, not too big.

/Jonas

[jonasaberg]

It was very easy, the Pjotr's format is virtually the same as in the boattype.txt files. I opened it in excel, cut&pasted the data (leaving out the column headings, and the first column for windspeed in knots and, voala!

If you have the time, please try it.

[sinbad7]

Jonas..

Thanks for the Wasa410.pol file,worked fine in OCPN and I have uploaded it to:
4shared folder - POLAR FILES

Tore

[PjotrC]

Originally Posted by jonasaberg

I opened it in excel, cut&pasted the data (leaving out the column headings, and the first column for windspeed in knots and, voala!

The lines containing no numeric data will be skipped, so the texts with column headings can be kept in the file. Better test it to make sure, but that's what I intended...