Introducing the Calibrator from SailingPerformance
by Sailing Performance 21 May 04:00 PDT
Sailing with Sailing Performance © Eloi Stichelbout/Dong Feng Race team
Have you ever sailed on a boat where the wind numbers coming from the onboard electronics were constantly wrong, where every time you tacked, the wind seemed to back by 15 degrees?
Pretty hard to pick a lay line in those conditions. On the other hand, what a sensation when you hit the perfect tack just before the top mark, and see your closest rival who was, until then, leading you by a couple of boat lengths, now trailing behind because he overstood!
Instrument calibration is a tricky subject. To start with, picking the right electronics, sensors and processors is not easy. Prices and quality seem to vary considerably and are not necessarily correlated. And then, even given the best tools in hand, getting the wind calculations correct is a real challenge, requiring patience, dedication and discipline.
In today's AI-ruled world, you would think this would be a fully solved problem. But it isn't. AIs cannot replace the eyes of a good navigator, evaluate the sea-state, guess how much wind-shear there is at the top of the mast. One day maybe...
In the meantime, a new tool has just come out. A software application called the Calibrator, published by SailingPerformance S.L, a company based in Valencia, Spain, who has been developing performance analysis tools for sailors since its inception after the 2007 America's Cup.
Although not fully automated, the Calibrator will be a massive help for all levels of sailing and racing. Let's have a look at this tool.
When running the software for the first time, you will need to give it some information about your boat, and about what parameters your electronics lets you play with.
Start by letting the software know what type of boat you are sailing on. Then tell it how many speedos you have onboard, and how you can calibrate it. The most basic electronics will let you specify a conversion from hertz to knots for your paddlewheel. Others will also take in account the non-linearity of the speedo and let you specify a full linearization table
With top level electronics, you may be on a fast boat which has multiple speedos, and where you can adjust speedo values in function of heel.
Then it's on to your mast-head unit. Here again, the software will adapt, from the most basic where you can only adjust the alignment offset, to the most advanced, where you may have different wind upwash tables for different sail combinations.
Once the configuration process is completed, you can run a calibration session. To start with, you will need to have a log of your sailing data. Most charting software such as Expedition© and Adrena© have that feature. It usually comes in the form of a.csv or.txt file. Once you feed this file into the Calibrator, it will read it and start the analysis. You will first go through a pre-processing stage where the Calibrator will assist you in finding moments during your sailing session where the boat was sailing in a steady straight line. You will also have the opportunity to double check the tacks and gybes that the software will have pre-selected as being the best executed manoeuvres of the day.
The next steps are the same as a navigator would do on a boat while trying to calibrate the electronics. It all starts with the speedo. Because the boat speed is used in the calculation of true wind, a mis-calibrated speedo will systematically result in a dissymmetric wind.
To calibrate the speedo, the Calibrator displays a graph where each point represents one of the pre-processed straight-line phase, commonly the average of 30 seconds of sailing. We then look at the delta between the the speedo numbers and the gps's speed over ground. But that is not precise enough because the gps measures more than the boat speed. It also includes the tidal current. If your data log contains current information, or if you specify an approximate set and drift in the software, it will let you compare the delta between the speedo and the speed over ground, now corrected for current. You can now try to play with the hertz to knots factor, and your speedo correction tables until the delta gets as close to 0 as possible. See image below for a graph of the data while sailing, and after having post-calibrated it.
Once you are satisfied that you have optimized your speedo calibration, the Calibrator will take you through the process of checking your compass. Is it properly aligned in the boat? Are there metal objects that may affect its deviation? You will have the chance to test a deviation table in order to get better compass readings. You will also have the possibility, if your electronics has that feature, to refine how it computes leeway. On a common mono-hull, most electronics use an empirical formula for computing leeway, which accounts for boat speed and heel.
The next step consists in checking the offset of your masthead unit. On a day with steady wind and normal sea-state, you would expect the boat to sail at similar wind angles on each tack. The Calibrator will display the difference in wind angle from tack to tack for the manoeuvres that were carefully selected. You will then be able to simulate a new MHU_offset and immediately observe whether the tack to tack symmetry improves.
During the final step, the Calibrator will walk you through fine tuning your true wind angles by playing with upwash tables. If your compass says that you tacked through 90 degrees but your (now symmetric) true wind angles read 50 degrees on each side, they are reading two wide by 5 degrees, and if you follow your instruments, you will probably systematically be overshooting lay lines. Once again, the app will let you work on upwash tables to refine your TWAs upwind and downwind. It will also let you correct TWS readings when sailing downwind. Having a spinnaker up will often increase the actual wind reaching the wind sensor because of air flow upwash. This needs to be corrected for.
Since the Calibrator actually recomputes the wind at every time step, you can confidently go back to your boat with the next day and type in those new calibrations in your electronics. The app will even generate a summary of all the proposed updates for you to save and take with you. And since you now have post-calibrated data for you day of sailing, it will even let you output a 'clean' log of your day, which you can use to analyse your performance for the day.
Hopefully this is just the beginning of a new way of addressing calibration issues for your instruments. The next step will include even more machine learning algorithms and AI to save time and effort on this complex subject. And if we let ourselves dream a little, one day we could even imagine a fully automatic self-calibrating system !
See demo videos and tutorials of the app at:
Ask for a trial license of the calibrator at info@sailingperformance.com
More information at sailingperformance.com