SailTimer (tm)

GPS chartplotters like this one assume that your sailboat goes in a straight line to your destination. Have you ever noticed that when you tack, the ETA suddenly goes blank? That is the way it was designed to work! SailTimer puts these problems to rest, with the first chartplotting software that accounts for sailboat tacking.

Technical Discussions

One of the main benefits of using SailTimer as a tool for generating optimal tacking routes is that it helps you to plot routes that may be counter-intuitive. Ordinarily, to get somewhere fast we want to take the shortest route. But when sailing, sometimes it is better take a longer tacking route with more speed.

These speed-distance tradeoffs lead to a number of technical issues. If you have comments or more to suggest, please let us know.

Bypassing Land. To ensure that tacking routes are plotted on water rather than across land, here are a few suggestions for bypassing land:

(1) Shorten Legs: For simplicity, SailTimer gives you two long tacks to your destination. Sometimes you may find it preferable to use multiple shorter legs on the same headings.

(2) Do the Other Tack First: You may be able to reverse the port and starboard tacks. Do the other one first, to avoid an obstruction.

(3) Specify a Closer Target: Instead of telling SailTimer your final destination, specify a closer waypoint that avoids an obstruction.

Velocity Made Good (VMG). This is the measure of how fast you are moving towards your target. It is a clever approach, when you are on a winding path. It is the standard approach for calculating Estimated Time of Arrival (ETA) for marine GPS. However, this causes problems for sailboats. VMG decreases the farther you get off the rhumb line, because your destination becomes more and more off your beam (as if you are increasingly heading away from your destination). This means that even if you are on the correct tack, VMG gives the illusion that you are slowing down. Any device that relies on VMG to predict the arrival time for tacking sailboats is therefore giving incorrect readings. This is why ETA goes blank on all standard GPS units and GPS chartplotters when you start tacking. Since ETA is based on VMG, which erroneously slows down the longer you stay on a tack, ETA becomes unreliable. This is a major issue. For correct readings, you need to use SailTimer or The Sailing GPS (patent pending).

Pinching to the Wind. We have received some comments from sailors with boats that will not sail much closer than 45 degrees to the wind. SailTimer is consistent with this, rapidly dropping sailing performance as you try to point higher. But don't forget that even if you only get about one-third of your maximum lift heading 30 degrees to the wind, in a strong gust you may still be able to reach hull speed with enough wind.

Downwind Tacking. Most boats heading straight downwind are being pushed and are not developing lift to power their movement. This screen shot shows that SailTimer sometimes projects the optimal route to be based on tacking downwind, rather than being pushed in a straight line by the wind.

Use SailTimer for Precise Speed-Distance Tradeoffs. SailTimer shows it is often better to head off the wind and travel a greater distance, which is sometimes counter-intuitive. However, simply keeping the telltales horizontal to get maximum speed is also not always the optimal strategy. In this screen shot, SailTimer shows a situation in which the reduced distance trades off against the slightly lower speed, and the boat going slower arrives first.