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Future MacENC release. Stay tuned.
Scott Dillon
Sydney Australia
North Shore 38
CYCA
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will the sailtracker routine be more precise for setting wind direct then the cardinal point N NNE NE etc. of wind direction or will one be able to put in degrees of wind direction (and then couple that with an apparent wind indicator)?
Otherwise, if one simply follow a VMG function from a GPS at the beginning at beginning of leg its ..... much simpler to operate/follow
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SailTimer will compute the optimal heading and tacking/gybing location based on true wind direction (0 - 360 degrees), true wind speed, desired destination and your boats performance characteristics. Wind data can be manually entered or come from instruments. More details soon.
Scott Dillon
Sydney Australia
North Shore 38
CYCA
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I'm impressed by this routing method.
But will future versions take of tide currents too (if these data is freely available)?
Thx.
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I agree... Tidal routing would be superb. I believe that tidal stream data is included on the maptech charts, certainly for the UK but obviously this wouldn?t work for MacENC...
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While in theory, tidal routing would be nice the reality is that any implementation would ultimately by flawed. Tidal Current data are predictions and as such, any attempt at routing based on this data would be at some point, inaccurate. Now, having said that, any Nav SW that is capable of steering a track to a waypoint is inherently compensating for tidal vectors, in real time. The problem with using a polars based Nav system is that polars are performance targets based on wind only. In some situations, tidal offset (which will vary) will overcome any gains. Indeed, in some cases, depending of course on the tidal vector, sailing a simple Waypoint track and trimming for best SOG/VMG will be faster than using polars.
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I think some are not understanding what SailTimer is.
SailTimer is not a routing algorithm. SailTimer is a tool that will recommend a course (heading) and a target (speed) to an active waypoint. This course is based on wind speed, wind direction and the performance polars. SailTimer does not compensate for external factors such as obstructions or current.
In order for SailTimer to be accurate, the wind speed and the wind direction and the polars provided must be accurate. Polars provided by boat builders and designers make some assumptions: clean fair bottom, new and properly trimmed sails, properly tuned rig, and a displacement that is the same as the designed displacement.
Scott Dillon
Sydney Australia
North Shore 38
CYCA
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Since obtaining Polars can be difficult and / or an expensive, it is possible to calculate an estimation of them from data recorded by the “track” feature of MacENC provided the data is recorded when the boat is being well sailed (e.g. racing) and there is sufficient data (e.g. data over a number of races) to arrive at reasonable boat speed averages for a given set of TWS and TWA.
Ray
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Version 2 of SailTimer will have the ability to create polars from the track log. That being said one could easily export the track log(s) to an MS Excel spread sheet, sort it by True Wind Angle and True Wind Speed then create linear averages for each wind range. If you have MacENC using Apparent Wind then you would first convert to True wind.
Formulas can be found here..
http://www.sailingusa.info/true_wind_calculator.htm
Scott Dillon
Sydney Australia
North Shore 38
CYCA
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SailTimer is already incorporated into MacENC. It provides the optimal tacking/gybing angles (laylines plotted right on the chart for an active waypoint and angles from the position icon drawn). No plans to add calculations/adjustments for currents because the data for currents is not accurate enough for any given geo-referenced location at any given time. While its useful for planning, the data is not accurate enough for real-time generation of tacking angles. We also realize that typically wind speed and angle do not remain consistent for an entire leg and as such drawing anything more than laylines for the current tacking angles would not be accurate. So while such plots are entertaining they rarely reflect the realties of the actual locations of where tack or gybe would occur.
Scott Dillon
Sydney Australia
North Shore 38
CYCA
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I have just started experimenting with SailTimer and have a question about how it works. I notice that as the wind direction changes, the intermediate waypoint changes as well, as it should. But the starting point does NOT change. Is this correct? Wouldn't it be better to calculate the new route at each iteration assuming that the starting point is at the current location of the ship? It seems irrelevant where one started from several hours ago, but rather where one is right now. Is that right, or am I not understanding things correctly?
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The starting waypoint of the route does not change because it can actually be a waypoint in a route. You will see this if you activate a route, then activate SailTimer and you will see the SailTimer route merge into the activated route.
You will notice the starting point of the active waypoint (layline) does change (the red dot).
Keep in mind the newly created SailTimer route is the layline to the destination waypoint (that is you do not want to sail past the line or you will have overstood - sailed too far)
Scott Dillon
Sydney Australia
North Shore 38
CYCA
