Anyone Have A Polar File for the M boat?

[Be Free]

Boat,
Your "M" is going to respond differently due to the differences in hull shape and centerboard design. This is a good starting point for you but don't take it as "gospel". I've been working on this one off and on for almost ten years and it still needs work. Of course, it doesn't help that I keep changing the boat.

Bill

[BOAT]

Not to worry skipper, I have new sails on order with a different cut than the current ones and I am changing the sail plan so I was going to put these into excel and run through them one at a time underway and make adjustments.

Right now it's way too cold to go out and vet the polars so what I will do for now is create a spreadsheet where anyone can insert numbers and get a polar plot for your boat but more on this later.

Thanks greatly for helping me get started.

[Be Free]

Another thing for the "M" owners to consider is that if you use your traveler properly you should be able to get better upwind performance that we can get on the "X". Maybe bump the first few entries up a bit for starters.

Some general advise to anyone who wants to produce polars: Don't get too carried away with numbers after the decimal point. I see a lot of polars (like the one Boat posted earlier) where the True Wind Angle is down to the tenth (or more) degree and speed is calculated to five or more decimal points.

None of us have equipment that can accurately measure wind, course, or speed with that amount of accuracy and even if we did the wind is not going to be that steady and I know I can't hold a course better than a couple of degrees either way in any kind of waves.

Finally, even if we could measure and steer that accurately, 1/100th of a knot difference in speed is going to translate to less than 500 yards PER DAY sailing around the clock. Don't get lost in the woods down there on the right side of the decimal point.

[Be Free]

Not to worry skipper, I have new sails on order with a different cut than the current ones and I am changing the sail plan so I was going to put these into excel and run through them one at a time underway and make adjustments.

Right now it's way too cold to go out and vet the polars so what I will do for now is create a spreadsheet where anyone can insert numbers and get a polar plot for your boat but more on this later.

Thanks greatly for helping me get started.

Before anyone spends a lot of time inputting the data I posted here just PM me and I'll send you the spreadsheet I copied these numbers from.

Anyone who is using OpenCPN can also put them into the Weather Routing plugin. It will produce polar plots and allow you to edit the text file if you want to tweak it.

[Ammiraglio]

There was an interesting thread on this topic a few months ago: viewtopic.php?t=29096&hilit=polar, started by @DaveC426913 who tried to build the polar for his 26X.

Good polars are not easy to build and use, but it depends on one's expectation, i.e., whether one wants to have a general idea of a sailboat performance, or to try to squeeze the last 0.1 kt of speed.

Just a few points to consider:

• A polar is only valid for a given set of sails.

• A polar is strictly valid for steady conditions, e.g., steady wind and flat water.

• Any point on a polar is really for a specific sail trim, so it should really be a "blob". For any value of wind speed and angle, boat speed will be determined by sail shape, and there is a zillion ways to affect shape.

• It's not easy to measure wind speed and direction accurately, and this applies both when drawing the polar, and when using it under sail (and this, assuming a reasonably constant wind speed vector)

• Calculating sailboat performance accurately (e.g., from VPP) is very complicated, especially for non-professionals. VPPs contain a lot of modeling approximations.

Still, it would be interesting to have "a" polar, even if "the" polar for a Mac (or any other boat) does not really exist. Extracting at least a portion of the polar for one's Mac could be a fun group project for the list this summer.

[BOAT]

Hmmm . . Things have changed over the years.
I have been using navigation software for quite some time. There are some really expensive iridium sat programs to help find the best course through the wind as you plan a long leg from say, Long Beach to Hawaii. These systems give you the wind direction and speed across your entire leg and calculate base on real time what you wind position will be at any given point along your route. Because we now have computers the size of cell phones it's possible for navigation software to plot where you approximately will be at any time along your route based on the tack you should use for the wind at that exact time of the day without the need of expensive iridium receivers. Since my travels are all within 100 miles of the coast I can use the internet to get similar results.
We all set a course but we also know that the wind will change what we do. By knowing what the wind will do ahead of time you can predict what will happen - let me give an example:

Here is the standard route to Avalon from Oceanside - been doing this route for years - it's like a milk run for me. This is the standard route I always start with - this route is in my plotter at all times:



Alas, but what happens when I set off at zero 800? I find the best wind and it sets me out to sea away from the island:



What is nice about the software is that it knows what the wind will do for the entire day and it shows me ahead of time that I will be making a broad tack out to sea because a wind change at around 1803hours (near 6PM) will give me a straight shot downwind to Avalon and as we all know - our MAC boats love to sail downwind - the polars for 'boat' are loaded into the software so it knows that and plotted the tack at 18:03 accordingly as you can see in the top of the screen shot above.

Then here at 2200 hours in the dark you can see the gentle winds giving 'boat' a nice comfortable downwind push into the sleepy harbor town of Avalon:



Now, understand - this is just an example - in reality I may not make such a wide tack or I might go north towards Dana Point and then decide at dusk depending on conditions if I will continue crossing to the island in the dark or dive into Dana Point Harbor for the night and then resume in the morning. The nice thing about the wind GRIB and the polars working together with real time weather data makes the changes on my plotter instantly as my course changes and also as conditions change.

Polars are not just for racing - they are great tools for navigation and plotting.

I hope I have not been to long or bored you guys - I'm trying to get you to understand why I want better polars for 'boat'. (For the past two years I have been using polars for a Catalina 22 and a Jensen 24 depending on my point of sail).

[Be Free]

There was an interesting thread on this topic a few months ago: viewtopic.php?t=29096&hilit=polar, started by @DaveC426913 who tried to build the polar for his 26X.

Good polars are not easy to build and use, but it depends on one's expectation, i.e., whether one wants to have a general idea of a sailboat performance, or to try to squeeze the last 0.1 kt of speed.

Just a few points to consider:

• A polar is only valid for a given set of sails.

• A polar is strictly valid for steady conditions, e.g., steady wind and flat water.

• Any point on a polar is really for a specific sail trim, so it should really be a "blob". For any value of wind speed and angle, boat speed will be determined by sail shape, and there is a zillion ways to affect shape.

• It's not easy to measure wind speed and direction accurately, and this applies both when drawing the polar, and when using it under sail (and this, assuming a reasonably constant wind speed vector)

• Calculating sailboat performance accurately (e.g., from VPP) is very complicated, especially for non-professionals. VPPs contain a lot of modeling approximations.

Still, it would be interesting to have "a" polar, even if "the" polar for a Mac (or any other boat) does not really exist. Extracting at least a portion of the polar for one's Mac could be a fun group project for the list this summer.

100% correct!

I'd like to add that it is a fools errand to attempt to use polars for a Mac for anything other than general route planning or to set expectations. The powersailers are not racing boats and never will be racing boats. No amount of sail trim will change that. The main takeaway from the polar I posted (backed up by empirical data) should be that they don't point well but they can are very happy with the wind anywhere behind them, particularly if you raise your centerboard appropriately.

Before I bought my "X" I sailed a very fast beach cat that had been heavily modified for racing. It was literally capable of sailing circles around a monohull almost twice it's size. I know it could because I used to do it for fun. It had the same sail area as a Mac with 15% the weight and wetted area. I was used to sailing it in ways that I found I could not even approximate with the "X". That's why I began to develop polars for it. I wanted to know if I was really that bad at sailing a monohull or was it the boat. Turns out it was a bit of both. Once I could see what I should expect from the boat I was able to modify my own skills to get more out of it.

Think of your polar as the EPA mileage estimate for your new car. What it says is technically possible, but it is practically unachievable under real-world conditions. You can get some pretty consistent winds offshore but not on most lakes or rivers and when was the last time you saw flat water with a stead 15 knot wind? To paraphrase captain Barbossa, "And thirdly, the [polars are] more what you'd call "guidelines" than actual rules."

[BOAT]

Just a few points to consider:

• A polar is only valid for a given set of sails.

• A polar is strictly valid for steady conditions, e.g., steady wind and flat water.

• Any point on a polar is really for a specific sail trim, so it should really be a "blob". For any value of wind speed and angle, boat speed will be determined by sail shape, and there is a zillion ways to affect shape.

• It's not easy to measure wind speed and direction accurately, and this applies both when drawing the polar, and when using it under sail (and this, assuming a reasonably constant wind speed vector)

• Calculating sailboat performance accurately (e.g., from VPP) is very complicated, especially for non-professionals. VPPs contain a lot of modeling approximations.

All the things here are correct - in fact the first item listed IS THE MOST IMPORTANT. That I found out the hard way when I set up just a couple of polars for 'boat' for wind speeds 2,4,6,8,10,12,14 because anything over that turns into a huge cluster f-k out in the real world because the sea state goes nuts over 15 knots out here. In those times I am fighting the sea even more than the wind and waves have a big effect on my course. I don't need polars over 14 knots. Similar issue with wind angles - on the M boat there is not a real big difference between a broad reach or a beam reach so I only use a few wind angles. The thing is that I am changing the sail plan from genoa to jib and going to a different cut on the main so I was hoping to get polars for the entire compass instead of just every 20 degrees like I do now. I just figured if someone had a full set of polars I could start from there.

The polar I use has realy lousy numbers for pointing as you can see in the plot the nav software made for the first leg in the picture. You can see that the polars prevented the program from plotting a starting course that was very close to the wind:



In reality, 'boat' can point better than this but still as you can see according to the forecasted wind conditions for the date and time of my departure my ultimate destination is directly into the wind near zero degrees! This is why I find great value in polars in the software - I can in some cases see that I would make my destination SOONER if I left an hour later! That's what predicting the wind at a particular location and time can do for you.

Aside from that I agree that polars are not much use for most of us unless we are sailing legs over 30 miles.

[Be Free]

Yes, I find route planning to be the most valuable use for polars. The tool I use can calculate as many what-ifs as you want from point A to point B. I've done the same as you and found that an hour one way or the other can make a big difference. Sometimes leaving earlier, sometimes later. You never know until you run it. I usually set it to run it for multiple start times and multiple start days to try to find the best window.

I've also found that when you are within a day or so of your departure using the higher resolution GRIB files is very handy. Around here none of them are very accurate inland or even close to shore but once you get out a couple of miles they are pretty accurate. I seldom stay out for more than a week so I run the return trip as well before I leave so I have an idea of what to expect on the way back.

Another thing to consider if you incorporate any of my data is that the weight of the boat is going to make a difference. If you are stripped down for racing or even day sailing you will do better in low winds but will get stopped more easily if you are pounding into the waves and will tend to heel to an inefficient angle in less wind. My numbers are based on my "cruising weight" a little bit north of 4000 pounds.

[BOAT]

Yes Bill, you are as usual very correct and very helpful. It's important that I remember the advice from folks like Ammiraglio and you so I don't go overboard trying to tune up my computer software too much. Ever since I got an autopilot (so many years ago now) it seems that I get obsessed with trying to create precise and perfect headings - it's all this technology dang it! I get so wrapped up in it but really it's not that important.

I forget that 30 years ago we were always by the seat of our pants praying to the sea gods about wind and weather.

We humans, always trying to outdo mother nature.