SailTimer: Optimal Tacks and TTD®
Sailboats often tack to their destination, which affects the distance and travel time. The SailTimer™ tacking calculations were developed a decade ago because GPS chartplotters didn't know how far your tacking route would be. But if they didn't know that distance, how could they calculate the ETA correctly? The SailTimer tacking results solved this problem, and set a new standard.
The SailTimer app provides an instant display of your optimal tacking route, distance and Tacking Time to Destination (TTD ®). It can also learn polar plots for your individual sailboat's performance in all wind speeds and directions, to provide more precise tacking results.
This changes everything. It is often hard to know whether to head off the wind to get more speed (but at a longer distance), or beat closer to the wind to reduce the distance (but at lower speed). Traditionally that is known as The Helmsman's Dilemma. Now, you can use the patented SailTimer tacking results to display your optimal tacks as a chart overlay, and see the precise distance, time and heading on each tack. No more guessing or superstition to determine the optimal tack, or arriving hours later than you expected.
This may be a low-cost app, but it has sophisticated tacking results. It is kind of ironic that you can generate better tacking results on your phone than on an expensive GPS chartplotter; a sign of the times. Many GPS chartplotters don't have any sailing functions at all. But if the ETA is not accounting for your tacking distances, it is wrong. For decades, the standard response from all of the major manufacturers was to use VMG rather than tacking distances (even though distances are obviously easy to get in a GPS). But although the concept of VMG is logical, the actual calculations on a GPS are fraught with errors and usually poorly explained in GPS owners manuals (see VMG link on menu above for further details).
Some GPS chartplotters and mobile apps are now trying to catch up, and have started displaying laylines based on your tacking angle. That is an antiquated method from before GPS and personal computers even existed. The first problem with this is that your tacking angle varies with wind speed. In stronger winds, you can point much higher to the wind. They may therefore allow you to import polar plots of boat speed (if you can obtain your polars anywhere other than in the SailTimer app) to create different tacking angles for different wind speeds. But generic, one-size-fits-all polar plots for all boats of the same model do not give you accurate results. They treat a clean, empty racing boat with new sails the same as a cruising boat with bagged out sails, moss growing on its waterline, and lots of anchors and canned goods on board. The polars would be very different for those two boats even though they are the same model. SailTimer Inc. pioneered polar plot learning, but that is not available in any GPS chartplotter.
However, the most important problem with GPS chartplotters/apps using a tacking angle to display laylines is this: the optimal laylines depend on both your speed and tacking distance, but the tacking angle only accounts for speed. You need speed as well as distance to solve the Helmsman's Dilemma, and find the optimal tacks. If a GPS chartplotter or app displays a layline based on a tacking angle and then later measures the distance of the laylines produced, that will not give you the optimal tacking angles that will get you there fastest. And as many sailors know, being off by just 4 or 5 degrees could make a difference of many minutes for when you cross the finish line.
The situation comes up in this recent review of a 35-foot production boat in Yachting World magazine (Jan. 2016): "Upwind we made 7-7.5 knots in 11-12 knots of true breeze, reasonable figures that come with a pointing penalty though. In comparison with the Hanse 315 nearby, for example, we were pointing 10° lower, despite having a 3m deep lift keel". The optimal tacks for those two modern production boats are quite different. Upwind, the RM1070 boat reviewed may need to point 10 degrees lower than the Hanse and get more speed (and longer distance) for its best arrival time.
Fortunately, the inexpensive SailTimer app simplifies all of this. It can use default polar plots or can learn custom polar plots for your individual sailboat. It lets you plan your tacking route and TTD® (Tacking Time to Destination) even while still at the dock (which is another thing that is not possible using a GPS chartplotter with VMG; VMG can only be measured while underway).
If you are wondering how long it would take to drive a car 100 miles at 50 miles per hour, you would divide the distance by the speed. 100 / 50 = 2 hours. Simple. There would be no reason to try to figure out the ETA (or optimal route) without the distance. Obviously that is not going to be accurate. But for sailing, that is the way it has always been done on GPS chartplotters. In contrast, the SailTimer calculations are unique in using tacking distances to define your optimal tacks and Tacking Time to Destination. This is a fundamental new paradigm for sailboat navigation and racing.
The SailTimer app can display the optimal tacking distances, headings and times in all wind speeds and directions, for both the port and starboard tacks and each individually. It gives you a quick and easy display of your optimal tacks and Tacking Time to Destination (TTD ®).
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