[IndepthNavigation]

One of the longstanding seafaring dilemmas is how close to the wind to sail, when tacking upwind. Whether in a nutshell pram or a big cruising catamaran, there is always the question of whether it would be faster to (a) minimize the distance by sailing close to the wind, or (b) head off the wind for more speed but a greater distance to cover.

Maybe you have tried to answer this question by using the ETA on your GPS chartplotter. But when you have been on a tack for awhile, the ETA on many brands will suddenly go blank right when you need it most.

And did you know that Velocity Made Good (VMG) decreases all by itself, the further you get off the rhumb line (the straight line to the destination)? If your speed is constant, even if you are on a correct tacking angle, VMG erroneously shows slower and slower speeds the longer your tack continues.

SailTimer solves these problems. It quickly tells you (1) how long is it going to take to tack to my destination, and (2) what are the optimal sailing angles to get there?

Even on an $800 GPS chartplotter, your normal sailing on tacks is viewed as "cross-track error". But now, if you have an iPhone or iPod Touch running SailTimer, you can plot a waypoint on an aerial photo and calculate the time to get there with tacking correctly accounted for. As you can see from the graphics below, you can also calculate the distances on each tack, and much more. SailTimer Lite is a FREE download from iTunes, and the full version is US $13.99.

The link to SailTimer in the App Store is at: IndepthNavigation.com





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[IndepthNavigation]

Version 2 of SailTimer adds overlays to Google Maps with a red line showing each tack. It is now submitted to the App Store, and should show up on iPhones and iPods as an update soon. Click here to see a short video demonstration on YouTube.

[image]http://thesailinggps.com/SoutheastLayLines.jpg[/image]

[AugustH]

I'm curious, do you have polars for all the boats out there, so you know what point of sail is fastest for a given boat? Some boats point high and still go fast, while other boats have to point lower to maintain a decent speed, and some can't point very well at all (cats come to mind here, that extra hull can help sometimes, hurt other times. But wow do they go fast!). If you don't take this into account, your app could lead to losing races if the driver tries to struggle upwind.

And do you also compute gybing angles?

[IndepthNavigation]

Thanks for your question. Actually, there is varying support for different amounts of polar plot data on the different platforms that SailTimer runs on.

For example, you can define polar plots with MacENC for your own boat's unique performance. At present there is a generic model of polar plots, hullspeed and wind speed in the current version of the SailTimer app for iPhone and iPod.

If I understand your question about gybing angles correctly, the polar plots with all of these approaches do inherently take into account both tacking and gybing angles.

It would be impractical to try to keep a database of polar plot data for every different model of boat. But we have an even better approach with the new dedicated handheld called The Sailing GPS (patent pending)... Even two different boats that are the same model could perform very differently, if one is covered in barnacles, weighed down with cruising gear, and has bagged-out sails. So The Sailing GPS actually learns the unique polar plots for your individual boat. That is the ultimate way to get the most precise projections possible for speeds and arrival times.

Further information: www.TheSailingGPS.com

[GPSNavX]

It might be useful if the generic polars used are published here as a response post.

One thing to keep in mind is if one were to sail the recommended course by Sailtimer they would be "banging the corners". That is the corners of the layline. The risk with this is if a wind shift (even subtle) occurs one could find themselves over standing the destination (i.e. sailed further then needed). So a standard approach is to sail up or down the middle of a course so one can take advantages of wind shifts.

MacENC will use the instruments wind angle and speed and constantly refresh the layline plot (SailTimer route).

http://www.gpsnavx.com/images/windshifts.jpg

[IndepthNavigation]

Yes, it is possible to use the optimal tacking angles for lots of small tacks instead of two long tacks. You have to do more coming-about that way, which may be a bit more effort and time. But you can use the optimal tacking angles this way if you want to stay close to the rhumb line in case of wind shifts.

You can enter different wind speeds and your boat length in the SailTimer app. It will calculate your hullspeed for you, and also has a large knotmeter display. Nevertheless, as the previous comment notes, you will get more features if you can use SailTimer with the full chartplotting capabilities in MacENC. For PC users, SailCruiser from NavSim.com is a navigation program that allows you to plot multiple waypoints and use SailTimer to see optimal tacking routes between all of them at once. Setting more waypoints is another way to stay close to the rhumb line if you want to.

The Sailing GPS also has additional capabilities beyond the SailTimer iPhone app: it is waterproof, it learns the unique performance of your boat on different points of sail, it is easy to mount at the helm, and can be seen in direct sunlight. But it is certainly an interesting age we live in, where it is even possible to get the basic SailTimer navigation functions with the low cost, easy download and convenience of your iPod Touch or iPhone.

[IndepthNavigation]

SailTimer App on Sale + GPS Attachment for iPods

For anyone interested in trying out SailTimer on an iPhone, iPod or iPad, it is currently marked down from its regular price to $3.99

You can get the iTunes link at www.IndepthNavigation.com where you will also see a link to the Apple Online Store for that cool new GPS attachment for iPod Touch. (We like the one from Dual, which can be detached from its mount, although Apple also has others from Magellan and TomTom.) There are also soft waterproof bags that allow you to control the touchscreen right through the soft plastic.

[image]http://www.TheSailingGPS.com/iPod_GPS.jpg[/image] [image]http://www.TheSailingGPS.com/Drypak.jpg[/image]

[IndepthNavigation]

The SailTimer app in iTunes now also includes a new Compass Heading screen.

Located with the large speed (in knots) display, it shows your current heading, and a visual slider that shows if you are inadvertently angling away from the optimal tacking route.

You can get the iTunes download link for the app ($14) here:
http://www.IndepthNavigation.com