Creating polars for an older cruising boat

[Bill Youmans]

Just keep it in perspective this polar fuss. Might be a fun exercise but even with weather "advice" in the real world does it make a palpable difference. Joshua Slocum, Francis Chichester, Bernard Moitessier, Nathaniel Bowditch, James Cook, Robin Knox-Johnston, Chay Blyth, Ernest Shackleton all did not have "polars" for their boots as they just knew how they handled on all points of sail and wind.

[Dave_S]

Originally Posted by GILow

OK, this thread is nice, but just to be clear, I’m looking for people’s self-created polars if I can.

The theoretical stuff online is ok, but as noted, don’t always reflect real-world boat speeds.

When I say “polars”, I’m not talking about the pretty pictures, I’m talking about the data set that creates them. And, as explained, I cannot create that data set here in my current home waters due to the significant wave action.

For now I am able to make a reasonable assessment from the Taman 42 polars on the sea pilot site by extrapolating the differences on my sub 15 knot wind speed knowledge of this boat up into the higher wind speeds. I got some credible numbers using this approach. Probably good enough for passage planning software.

For the record, I’m using fastseas which will create the pretty pictures for you if that’s what you are after.

I think what your doing is the best you will get unless the factory produced one. No one has the same setup as you or conditions as you and no one thinks they have it just right or good enough to share. Start with something close and tweek it.

There is a web site that has polars for lots of boats, you might be lucky and your boat might be on it but you will still have to tweek it.

[Dave_S]

Originally Posted by Bill Youmans

Just keep it in perspective this polar fuss. Might be a fun exercise but even with weather "advice" in the real world does it make a palpable difference. Joshua Slocum, Francis Chichester, Bernard Moitessier, Nathaniel Bowditch, James Cook, Robin Knox-Johnston, Chay Blyth, Ernest Shackleton all did not have "polars" for their boots as they just knew how they handled on all points of sail and wind.

I bet they did

[GILow]

Originally Posted by Bill Youmans

Just keep it in perspective this polar fuss. Might be a fun exercise but even with weather "advice" in the real world does it make a palpable difference. Joshua Slocum, Francis Chichester, Bernard Moitessier, Nathaniel Bowditch, James Cook, Robin Knox-Johnston, Chay Blyth, Ernest Shackleton all did not have "polars" for their boots as they just knew how they handled on all points of sail and wind.

Those guys didn't have the sort of weather routing computational power we have at our fingertips.

This stuff seems pretty valuable to me. I've got a 600 mile passage planned and running the numbers today gave me passage times from 5 to 9 days depending on when I departed.

But the critical.part was that all of the quicker routes deviated significantly from the rhumb line and involved a gybe with a significant course deviation around three days into the trip.

Personally, I think this is a lot more than just a fun exercise.

[ArmyDaveNY]

Originally Posted by GILow

I've got a 600 mile passage planned and running the numbers today gave me passage times from 5 to 9 days depending on when I departed.

But the critical.part was that all of the quicker routes deviated significantly from the rhumb line and involved a gybe with a significant course deviation around three days into the trip..

How much quicker were the routes that deviated significantly from the rhumb line? Also, how much longer were the faster routes?

[Oceanride007]

Can anyone tell me how to open *.pol file. Have PC.


Interesting,tried to create my own a while ago, was able to get all necessary NMEA data using Vesper to transmit it to PC, then Navmon PC to log it. What snookered me was Magnetic Deviation in steel hull, and fast tidal streams.

[Spot]

Originally Posted by Oceanride007

Can anyone tell me how to open *.pol file. Have PC.


Interesting,tried to create my own a while ago, was able to get all necessary NMEA data using Vesper to transmit it to PC, then Navmon PC to log it. What snookered me was Magnetic Deviation in steel hull, and fast tidal streams.

The Tayana42.pol file was just a tab delimited text file
So right-click > open with > Notepad

[GILow]

Originally Posted by ArmyDaveNY

How much quicker were the routes that deviated significantly from the rhumb line? Also, how much longer were the faster routes?

Quicker...? Four days quicker. As per the post, the range was from 5 to 9 days. Significant variation.

In fairness, I think if I did it by hand I could get it done in 6 pretty reliably.

Actually, one prediction was four days. (3 days and 22 hours to be precise.)

I looked pretty hard at the path it was projecting, and ran windy in conjunction to see what it was thinking, and yeah, it was a reasonable projection. But it was too prone to major problems if I got a turn wrong or failed to meet an expected speed. Basically it ran a constantly changing course on the edge of a big rotating low pressure that kept me deep reaching for a day and half at the top of my accepted wind speed range. (30 knots) Great if I had a crew of three or four skilled sailors, but not sustainable as a solo sailor.

Distance travelled on the faster but longer routes added about 40 to 50 miles vs the rhumb line approach. Again, seemed reasonable.

[ilenart]

Originally Posted by peterbeale

Can someone explain Polars?

https://en.wikipedia.org/wiki/Polar_diagram_(sailing)

[ilenart]

Hi GILow,

what weather routing software are you using? Have recently been testing out Predictwind for a trip accross the Bight (Albany to Tasmania) which has been an interesting exercise. Note that for this progam you did not need a complete polar, just three speed / wind combinations, plus when you start motoring.

Ilenart

[GILow]

Originally Posted by ilenart

Hi GILow,

what weather routing software are you using? Have recently been testing out Predictwind for a trip accross the Bight (Albany to Tasmania) which has been an interesting exercise. Note that for this progam you did not need a complete polar, just three speed / wind combinations, plus when you start motoring.

Ilenart

Hi mate,

I’ve been playing with fastseas. But perhaps I should also try predictwind too? It would be interesting to compare the two on a prediction for the same route.

The fastseas site has a similarly simple polar definition but it will import more detailed polars if you have them.

Edit: I see that predictwind does not appear to have a free trial of the weather routing component. Fast seas does have a free trial so I would love to hear how you feel the two compare.

[Emouchet]

Why not go sailing and connect OpenCPN to your instruments: wind (speed and direction from the bow) and speedometer to get speed over water.

Then, OpenCPN includeS a plugin that will record the data as you are sailing and it will generates the polar for you. This will get you real data, including sea state.

It will take a few days to build as it will only generates point in the polar chart for the measured conditions. But then you can extrapolate from there.

A great tool indeed.

[GILow]

Originally Posted by Emouchet

Why not go sailing and connect OpenCPN to your instruments: wind (speed and direction from the bow) and speedometer to get speed over water.



Then, OpenCPN includeS a plugin that will record the data as you are sailing and it will generates the polar for you. This will get you real data, including sea state.



It will take a few days to build as it will only generates point in the polar chart for the measured conditions. But then you can extrapolate from there.



A great tool indeed.

Yes, I would, but if you read my post you’ll see that I cannot get accurate data due to where I am sailing.

[ilenart]

Originally Posted by GILow

Hi mate,

I’ve been playing with fastseas. But perhaps I should also try predictwind too? It would be interesting to compare the two on a prediction for the same route.

The fastseas site has a similarly simple polar definition but it will import more detailed polars if you have them.

Edit: I see that predictwind does not appear to have a free trial of the weather routing component. Fast seas does have a free trial so I would love to hear how you feel the two compare.

Hi GILow,

had a quick look at Highseas. They sound pretty similar. Looks like FastSeas uses one model, GFS, which I assume has a 50km resolution? Predictwind uses GFS plus three other models. The two Predictwind models are PWG which uses the NCEP global initial conditions and PWE uses the European Center for Medium Range Weather Forecasts global initial conditions. Both have Resolutions of 1km/8km & 50km global available. It also uses ECMWF forecast from the European Center for Medium Range Weather Forecasts model. They have just announced two additional models (SPIRE & UKMO) which I have not looked at yet.

Both have routing and departure planning. Looks like the Predictwind forecast remote ability sounds a bit more sophisticated as it ties in with Iridium Go and can download GRIB files, which can be displayed on their Offshore program. I assume Fastseas remote response is an email route which you load into another program.

With Predictwind I found the summary page provided with routing and departure planning very handy, particularly the percentage upwind with each forecast. This provided an easy and quick way to compare different routes and departures. Does Fastseas have a summary page?

Predictwind also has a large number of Polars built in, which you can use. However when I tried the one for my boat (Hallberg-Rassy 40) I found it to optimistic and not matching my experience with ocean sailing. My guess is that it was calculated in flat water with brand new sails. My sails are from 2003 and I generally sail in the ocean with lots of waves. Therefore I have ignored the polars and input my own details (ie average speed in 15 knots whilst closehauled, reaching and running).

Found this article, which talks about Predictwind and Fastseas. Hope this helps.

https://www.cruisingworld.com/weathe...e-for-sailors/

Ilenart

[GILow]

Ilenart, sorry for the delayed reply, I missed your response.

I did not know about the granularity of the weather models. You've given me some homework, thank you.

Fastseas does have those summary pages buried in there. They are terrific.

There's such a price difference between the two. I wish Predictwind had a free trial or something so I could make a meaningful comparison of the two.

I'll see what my reading on forecast model granularity suggests. If it comes down to really only being an issue for racing boats wanting a cutting edge, then Fastseas will be good enough for me. But if there are significant safety implications I'd be prepared to pay more.