I would like to suggest a new plugin - if I were a programmer, I would do it myself, but unfortunately I am not, so I am hoping someone will be inspired enough to do this.
What I would like is a plugin that builds up a polar diagram for my boat for all wind
speeds and all my different sail plans. Since I have NMEA input from my wind speed, wind direction, boat speed and GPS, this should not be too difficult to do. Here are some of the features I would like to see:
There are several pieces of useful information that one could get from the plugin, once data has been built up. For example:
1) The wind is X kts and I need to sail dead downwind - am I faster if:
a) I sail a dead run with just the spinnaker
and no white sails
b) Tack downwind with main and spinnaker
at 130 deg apparent?
2) Wind is X kts and I want to sail a course of Y deg. What is my optimal sail plan?
3) The wind is X kts. I need to sail dead upwind and am in a hurry to get to the anchorage before dark. Should I:
a) take down the sails
and just motor
b) leave up the main, but not the jib
, and motor
sail at 30 deg apparent
c) leave up full sail and motor sail at 40 deg apparent
d) turn off the engine
and just sail
(to answer this and other upwind VMG questions we would want to calculate leeway by using the GPS data in addition to the boat speed data.)
Ultimately one could also build a passage
planning plugin that would take a route
plotted on openCPN, combine it with GRIB file information plus the polar chart info and produce a suggested optimal passage route
with apparent wind / magnetic course routing and optimal sail plan - and projected ETA.
As an added feature, my data could be uploaded to a central server and averaged with data from other boats identical to mine to provide an average for the boat model. Then when people ask 'how fast does a 'brand x' go?' the answers will be right there.
Enter type of boat (over time we could build up a drop down list)
Select available sails. Here people would select the sails available to them in their sail locker - eg Genoa
2, Storm Jib
spinnaker, Symmetrical spinnaker, Main (forward), Main (aft), Mizzen, Engine
, Engine (port), Engine (starboard). These could be presented as checkboxes with the option to add additional sails (eg topsail if they happen to be in a square rigger) or change the description of the sail.
When enabled, the plugin would show its status on the screen
, including the current
sail-plan, with a 'Stop' and 'Start' button which would stop or start the recording of information. The start button would also ask for a confirmation of current
There would also be a 'Change Sails' button. When pressed, that would automatically stop the recording while you enter the new sail plan, and then start recording again when the 'done' button is pressed. I would suggest that the sail plan be displayed a a set of checkboxes so you just check the box for Jib
and Main and press 'done'. Probably it should also have a dialogue to enter the time for the end of the old sail plan and the start of the new sail plan. That way you could enter the data after you reefed, and have it remove the last 15 minutes of recording while you were messing about doing the reef.
The options in the 'change sails' dialogue would include actually changing sails - eg putting up the spinnaker - as well as changing the reefs
on a specified sail. The engine would also have the options for 'cruising', 'semi-fast', and 'fast' - or this could be specified as rpm
While the plugin is recording data, it combines the current speed with the current true wind speed and direction. It records this as a linear record
. It then averages this data point with previous data points for the same wind speed, direction and sail plan, and saves that in a separate database.
Thus, over time, one builds up an average boat speed for any given set of conditions of wind plus sail plan (including the engine as a sail).
I would suggest that the program also checks the current data with the data from, say, 15 seconds ago. If there is a significant change of direction (eg > 20 deg) then the data from 15 seconds ago until the data stabilizes on a new direction would be excluded from the calculations. This would eliminate errors caused by, for example, tacking, gybing or broaching. Perhaps the same should be done if the wind speed changes dramatically, so as to allow the boat time to accelerate or decelerate to the new wind speed.
It should also stop recording if the boat speed (and maybe wind speed) drops below a certain limit - eg 1kt - so as to not distort the averages when you aren't actually sailing but forgot to turn off the recording. For example you are anchoring
or heaving too.
In a later iteration, I would suggest we include GPS data so that we can calculate leeway. Of course we would have to figure out how to exclude current and tide from affecting this. Or maybe the 'include GPS' data would be an additional option to be used only when we know we are in current-free waters.
Suppose one sets the plugin to record
, and then you change sails or switch on the engine but forget to tell the plugin?
There would need to be an option to exclude the data between two time points. Ideally it would be nice to display the speed on a graph as that would help one to spot when you made the change, but at the minimum you just need to enter in a beginning and end time and the plugin would exclude that data from the calculations and recalculate the averages.
That way if you suddenly realise you have been motoring for two hours at 6kts but the plugin thinks you are sailing with full sail in 2kts of wind you would be able to remove that erroneous data.
Initially just a digital interface would be sufficient. Ultimately it would be nice to actually display graphical polar charts, but that is probably less useful than having a dialogue.
Mostly one would want to ask for:
a) optimal sail plan for a given wind and bearing
b) expected speed and ETA for a given destination
, wind, and sail plan
c) expected VMG for given destination
, wind and sail plan
later one could add:
d) display / export as jpg or pdf / print the polar charts
e) upload to central server to combine with others
f) comparative VMG - better to run or tack downwind? Better to pinch, or sail free and fast?
So, any takers? What do you think?