Sailboat polar diagrams usually tell us what the boatspeed will be, based on wind speed and angle. I thought it would be nice to flip it the other way: if we want to achieve at least, let’s say, three knots of boatspeed, what kind of wind will we need to achieve that?
I’m much more into sailing than motoring. A few days ago I got curious about how much wind did we really need last summer to get the boat to move at least a bit.
(“At least a bit” is when the ETA still shows something barely acceptable, like “late evening”, instead of “oh, it just jumped to the day after tomorrow!”)
And, in the same line of questioning, how much wind did we need to get match decent motoring speeds, about five knots and more?
Having good light air performance (being able to move with very little wind) is great. I don’t really think our Hanse 388 is designed to be a fast light air sailboat, but still, it’s really interesting to look at the data.
1-2 knots boatspeed
So, this is the first wind polar picture.
The green and blue dots show what the wind speed and direction have been, whenever the boat has traveled with at least 1 knot (and less than 2 knots) of boatspeed.
(Note: 1 knot of boatspeed isn’t moving very much at all. Standard walking speed is about 2-3 knots. If you’re staring at a bubble in the water, it will take that bubble more than 20 seconds for the whole boat, bow to stern, to pass that single bubble!)
Looking at the picture, you can see that there are a lot of dots scattered around in the upper right quadrant (wind between 0-90 degrees angle), but also a couple of distinct groupings or clusters.
The scattered dots, with wind up to 12 knots, are from the acceleration phase, I assume. With 12 knots of wind, final boatspeed will be much more than 1 knot, but when accelerating from zero, it will between 1-2 knots for a short period of time.
The groupings are more indicative of what kind of average wind will get the boat moving. There’s one grouping in the upper right quadrant that starts from 4 knots of wind, and another small one in the lower left quadrant that starts from about 3.5 knots.
Conclusion: During our last season, we needed about 4 knots of wind to start moving at all. That’s 2.0 m/s and Beaufort force 2, “light breeze”!
In this picture, we’re going at least 2 knots, but less than 3.
(One funny detail is that we sailed much more with the wind coming from starboard. That is why the left side has so few dots!)
Looking at the groupings again:
- The upper right quadrant (0-90 degrees) shows that 2+ knots of boatspeed needed at least 5 knots of wind.
- In the lower quadrants (135-180 degrees) there’s this interesting upside-down V shape. I don’t really know what’s that all about. It seems to indicate that going dead downwind (180 degrees), 2 knots of boatspeed needs just 2 knots of wind. And then when changing course slightly, more wind is needed.
Conclusion: Getting the boat up to walking speed upwind and reaching needed 5 knots of wind. That’s 2.6 m/s and still force 2, “light breeze”. (A bit less of wind was needed when going downwind.)
For me personally, 3-4 knots of boatspeed is enough to leave the engine off. And it can be even less if we’re not in a hurry (and we seldom are!). Still, above 3 and I’m usually not even thinking about it.
- Getting 3+ knots upwind needed at least 6 knots of wind.
- Getting the same speed with around 80-100 degrees wind angle needed (seemingly) only 4-5 knots of wind.
- Broad reaching, again about 6 knots.
- Dead downwind between 4-6 knots.
Conclusion: Depending on the wind angle, getting to 3 knots of boatspeed required 6 knots (3 m/s, force 2 “light breeze”) upwind and broad reaching. Again, a bit less when beam reaching and running.
- 40-50 close hauled upwind, between 10-12 knots of wind.
- beam reaching, about 6 knots of wind.
- broad reaching, 7-8 knots of wind.
- running, 4-8 knots of wind
Conclusion: For 4+ knots of boatspeed, going upwind needed at least 10 knots (5.1 m/s, force 3 “gentle breeze”) of wind. Reaching between 6-8 knots and running a (strange) 4-8 knots.
Above 5 knots is where the magic starts to happen as this is when sailing speed equals motoring speed!
- Upwind about 11 knots of wind speed.
- Beam reaching about 8 knots of wind speed, with a few patches showing even less, between 7-8 knots. I assume these are with the crossover sail hoisted.
- Broad reaching also over from 8 knots up.
Conclusion: To get to motoring speeds close hauled upwind, we needed 11 knots (5.7 m/s, force 4 “moderate breeze”) of wind. For other sailing angles, about 8 knots (4.1 m/s, force 3 “gentle breeze”) was enough.
- For close hauled upwind, we did better on the port tack, achieving 6+ knots with more than 12 knots of wind. The dots are scattered quite thinly, though, so it seems we didn’t get over 6 knots very often. (Will have to do better next season!)
- Going down to the reaching angles, it seems we often got 6 knots with at least 10 knots of wind. Except for one area around 90-100 degrees, where we got the right speed already at 8 knots of wind. This exception has to be with the crossover hoisted.
Conclusion: Getting 6+ knots upwind wasn’t that easy for us, but achievable with 12 knots (6.2 m/s, force 4 “moderate breeze”) of wind. For the other angles, 10 knots (5.1 m/s, force 3 “gentle breeze”) was enough. On a beam reach with the crossover hoisted, about 8 knots (4.1 m/s, force 3 “gentle breeze”).
The plot is getting sparse, which means that it wasn’t that common for us to sail over 7 knots.
- No tight upwind sailing anymore. With our configuration, we never went over 7 knots close hauled.
- On a beam reach, higher than 90 degrees, more than 12 knots of wind gave 7 knots of boatspeed.
- Further down from the wind, first 10+ knots, then 11+ knots was enough.
Conclusion: At good angles, 7 knots is possible with 10 knots (5.1 m/s, force 3 “gentle breeze”) of wind. At slightly worse angles, it’s possible with 12 (6.2 m/s, force 4 “moderate breeze”).
More than 8 knots
The final picture there! Each point (same as in the other pictures) represents a six-second average speed. Maybe next summer we’ll get more of those 🙂
How Did We Do?
Did we do well or not so well? I don’t really know.
During a lot of our sailing, we had a substantial amount of barnacles on the bottom. And sail trim was probably often off by a bit since more focus went to keeping the family happy than to making the boat go quickly. (And that was certainly the proper way to prioritize!)
It’s cool to see the data, though. And to give some thoughts to our next season, and if there’s something we could do to get slightly better numbers.
Finally, it would be wonderful to hear your comments!
What kind of light air performance do you get with your own boat? Any other thoughts? Please send us a comment below! 🙏
What kind of electronic are you using to constantly collect those data while traveling ?
I wish I have something like that.
It’s a Raspberry PI plugged into the NMEA network and using a combination of open source and my own custom software. It first stores, then tries to upload to the cloud everything that it sees on the network and senses using its own sensors.
I would be cool to make a more “productified” version of this that could be shared with others 🙂