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Old 01-05-2015, 20:17   #1
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Weather Router Question

How can I tell the router to switch to motoring at 5 kts when the wind (or boat speed) drops below a specified value?

I've used qvtlm and it is fairly obvious in that app but can't seem to find it here.

Getting ready to depart NZ for Fiji in a few days and looking forward to a stop at Minerva Reef. Hoping to use this plugin to help select the departure day, but having the ability to switch to motoring mode in light winds is a must.

Kudos to Sean on this (and all) plugins. I'm running the Linux version on Ubuntu 14.04 and everything else seems to work very well.

(Sorry if this has been answered elsewhere, I read all the manuals I could find (Weather Routing Plugin | Official OpenCPN Homepage, file:///usr/share/opencpn/plugins/weather_routing_pi/data/WeatherRoutingInformation.html, and Weather Routing Plugin). I'm on an extremely slow, limited bandwidth connection and have given up searching the 50+ pages of comments in the Weather Router thread after 6 hours.)

Thanks,
Tim
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Old 02-05-2015, 01:05   #2
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Re: Weather Router Question

modify the polar used to make the boat move 5 knots when the wind is zero.
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Old 02-05-2015, 01:52   #3
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Re: Weather Router Question

Ok, I added a new sail plan with a custom csv polar (with motoring speeds) and added a rule for wind less than 4kts. Gave myself a slight bonus going downwind and subtracted some heading into it (Lagoon 400 windage...). This way I can just change the wind speed rule and motoring speed will update accordingly.

Was hoping for something that would show in the summary as "Motoring Time or %", like the "Upwind %" so that I could include that factor in selecting a departure date.

Great tool, by the way. Buy you a beer in Indonesia next summer?

Cheers
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Old 02-05-2015, 05:08   #4
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Re: Weather Router Question

I'm leaving indonesia soon... Since I'm engine free, I'm not really motivated to implement anything related to motoring, but I am accepting patches.

I was going to support solar-electric drives as the sun shades the panels differently on different headings at different times of day, and depending on the position of the sails and how much they shade the panels (if motor sailing) but my electric motor failed...

Really I'm more interested in dealing with different seastates as a typical polar diagram may work in flat water, or a particular sea state, but not with changing swell combinations. It's no problem to support this from user data, but there isn't much data available. One solution is to have a basic wave polar which is applied on top of the flat-water sailing polar which isn't perfect but improves things a lot. I never did find good data for this. I wanted to compute typical values as well which is very difficult.
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Old 02-05-2015, 11:52   #5
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Re: Weather Router Question

Sean I think your idea is good. Perhaps the sea state polar is adjusted manually as empirical/ use requires? Having it easy to adjust and compare to the boats regular polar might help.

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Old 02-05-2015, 11:54   #6
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Re: Weather Router Question

For example we have to head off 5 degrees when going upwind in 2' chop!

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Old 02-05-2015, 17:13   #7
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Re: Weather Router Question

I'm playing with creating different "sail plan" configurations with rules for each, but I can't get the "New Plan" name to save after I rename it. So if I have more than 2 sail plans, the routing fails because (I think) the rules end up referencing the wrong plan.

Is there a trick to getting the new name to save?
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Old 02-05-2015, 17:42   #8
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Re: Weather Router Question

Love the wave idea... Problem I see is 1) wave effect on boat speed is a two variable (quadratic maybe?) function, which would need a 3D polar (speed vs wave height vs wave period) (3m seas at 20sec have much less impact than 3m at 7 sec) and, more importantly, 2) wave data in weather models rarely reflects the actual conditions I've seen (between California and NZ, at least).

It would be interesting to be able to try different equations that had wave height, period, and direction as inputs and simply kicked out a scaling factor for boat speed... Maybe I'll throw some numbers into excel and see how it looks...
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Old 02-05-2015, 18:35   #9
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Re: Weather Router Question

Quote:
Originally Posted by Rock37Man View Post
I'm playing with creating different "sail plan" configurations with rules for each, but I can't get the "New Plan" name to save after I rename it. So if I have more than 2 sail plans, the routing fails because (I think) the rules end up referencing the wrong plan.

Is there a trick to getting the new name to save?
Hmm.. yes you could have a separate plan for your motor then you would see on the plot when the plan switches. I don't understand why it isn't saving but I will try this out

Quote:
Originally Posted by Rock37Man View Post
Love the wave idea... Problem I see is 1) wave effect on boat speed is a two variable (quadratic maybe?) function, which would need a 3D polar (speed vs wave height vs wave period) (3m seas at 20sec have much less impact than 3m at 7 sec) and, more importantly, 2) wave data in weather models rarely reflects the actual conditions I've seen (between California and NZ, at least).
It's more complex than this, because another dimension is needed for wind direction as the boat handles much differently at different points of sail in this seastate. There is also secondary swell which makes a huge difference. Actually when I left new plymouth NZ there was 15 knots of wind and at one point 3 distinct swells from different directions, and it was completely impossible to sail, the boat just did circles until the wind picked up to 20 knots.

Another experience I had was in the komodo straits with 3 knots of current, but so much churning that the boat was doing a 360 every 10-15 seconds with completely loss of control even though there was 5 knots of wind which is normally enough to sail.

It would be interesting to be able to try different equations that had wave height, period, and direction as inputs and simply kicked out a scaling factor for boat speed... Maybe I'll throw some numbers into excel and see how it looks...[/QUOTE]
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Old 05-05-2015, 22:29   #10
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Re: Weather Router Question

Sean, any luck with the sail plan naming issue?

Also, even when keeping the default names, I cannot get the router to switch between plans (I made one of the plans make the boat go 20kts just so it was obvious when the wind drops below 12 kts (which it does several times in the grib) and it does not switch.

Thanks!
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Old 07-05-2015, 09:34   #11
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Re: Weather Router Question

I was just on a 3 day passage... I will look into the sail plans, they are not very well tested.
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