SailTimer Inc.

Standard GPS chartplotters do not account for tacking distances when calculating ETA. But if they don't know how far you are going to travel, how can they calculate your ETA correctly? Some brands actually blank out the ETA when you stay on a tack for too long. The patented SailTimer software solves this problem. It is able to display your exact tacking distances, optimal tacks, and Tacking Time to Destination.

Technical Discussions

Velocity Made Good. 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 problem for sailors. For correct tacking results, you need to use the SailTimer software/app or The Sailing GPS. There is further detail on our web site for The Sailing GPS about problems with different measures of VMG to a mark and VMG to windward.

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.

*Racers may also prefer to do multiple short tacks on the headings given than two long tacks.

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