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Old 26-11-2016, 12:02   #1
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How the plan speed is calculated ?

Hi,

Can someone explain me how the "plan speed" presented in the "route manager properties" is calculated ?

What are the parameters for its calculation (boat type, length...) ?

Is this information stored somewhere?; I do not see anything refering to this in the "own ship" windows

Thanks

Serge
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Old 26-11-2016, 12:18   #2
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Re: How the plan speed is calculated ?

You might like to give us some more details on the system you're referring to. We're not psychic.

I assume you mean hull speed. Which is the theoretical max speed for a displacement hull that is not planing.

Simple calculation 1.34 x square root of the LWL. Waterline length. Plenty of proofs on the interwebs.

For our Liberty 458 with a 40.5' LWL the hull speed is 8.5 kts.

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Old 26-11-2016, 12:21   #3
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Re: How the plan speed is calculated ?

Serge, see - Is there a way to make it clearer?

Route & Mark Manager | Official OpenCPN Homepage

Quote:
Plan Speed
Quote:
The overall planned speed for the route. The speed for each leg can be set by going to the waypoint Properties->Description tab for the waypoint that starts the leg, and write in the speed. For example " VMG=9.7". [Unfortunately this approach presently excludes writing descriptions for the waypoint. One or the other, be warned!] The Plan Speed value is persistent and will be used for further routes, unless changed. The default value is 6.0 knots.
Leftbrain, I believe it is just a value, not calculated at present. Sean's plugin weather_routing used to calculate hull speed accordingly, and make an estimated polar from boat parameters, displacement, sail area etc. That has been simplified to just use polar files, but Sean would still have the code available.

The waypoint & route properties should be expanded at some point to accommodate an average speed for each leg, IMHO without affecting the ability to have a description. However I have not used this feature much, but others do use it extensively.
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Old 26-11-2016, 12:32   #4
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Re: How the plan speed is calculated ?

Quote:
Originally Posted by rgleason View Post
Serge, see - Is there a way to make it clearer?

Route & Mark Manager | Official OpenCPN Homepage

Thanks for the quick reply Rick, I was not aware of that information.

From my point of view the Plan Speed should be part of Ownship specifications as specified in FS 1102 (next version ?)

Thanks again.

Serge
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Old 26-11-2016, 12:37   #5
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Re: How the plan speed is calculated ?

Yes, Serge, I agree it would be ideal to have much more complete Ownship specs which can be shared in common with all plugins.

However, I would like to see the Plan Speed for each leg, be a completely separate value that can be edited or filled in and completed by a plugin, such as weather_routing. This would require some effort in programming, but it is certainly possible. I am sure I have not completely thought this through and there are other considerations, so it would be good if others were to add their thoughts.
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Old 26-11-2016, 16:24   #6
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Re: How the plan speed is calculated ?

Quote:
Originally Posted by leftbrainstuff View Post
You might like to give us some more details on the system you're referring to. We're not psychic.

I assume you mean hull speed. Which is the theoretical max speed for a displacement hull that is not planing.

Simple calculation 1.34 x square root of the LWL. Waterline length. Plenty of proofs on the interwebs.

For our Liberty 458 with a 40.5' LWL the hull speed is 8.5 kts.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
This question is in:
"Cruisers & Sailing Forums > Seamanship, Navigation & Boat Handling > OpenCPN".

He's talking about the 'Plan Speed" used to predict leg times in OpenCPN route planning.
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