Expedition Navigation Software 
1 of 1- JohnA
- Expert
Offline - Registered: 2/06/2017
- Posts: 28
Change of Leeway as function of BSP and HEEL formula?
It appears that the formula in Expedition to (optionally) calculate Leeway from Heel and Bsp has changed from
(1) Leeway=-K*heel/(BSP^2)
to
(2) Leeway=K*heel/(BSP^2) .
The change must have taken place from version 9 to 10 or there around.
In the help file chapter: "Inside the Instrument System" it says that Heel shall be negative when sailing on port. I.e according to formula (1).
In chapter "Calculation" the opposite is stated. I.e according to formula (2).
What is the wanted behaviour? In any case, a possiblility to change sign of Heel in the SW would be helplful. My clinometer is rather hardwired ... .
As for the Leeway calculation one could obviously "switch sign" by using a negative K. I am afraid though that
a Heel with the "wrong sign" might also affect the "Correct for Heel in TW calc" calculations - or?
- ZeeZee
- Expert
Offline
- Registered: 3/30/2016
- Posts: 321
Re: Change of Leeway as function of BSP and HEEL formula?
Another (related question):
Exp has the option to set a calculation option "correct for heel in tw calc". What does this exactly do / how does it differ from the calculation that the "use pitch & roll rates in tw calc" option perform?
Last edited by ZeeZee (2/23/2017 11:05 pm)
- Nick
- Moderator
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- Registered: 9/16/2015
- Posts: 2,964
Re: Change of Leeway as function of BSP and HEEL formula?
I think it did get tidied up a few years ago for consistency. From my notes
define heel and leeway positive on port
Heel/roll is normally signed in aviation and marine so it is positive for a roll to starboard - on port.
Leeway is normally signed so clock-wise leeway is positive, thus leeway is > 0 on port.
lwy = k * heel / (bsp * bsp)
- Nick
- Moderator
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- Registered: 9/16/2015
- Posts: 2,964
Re: Change of Leeway as function of BSP and HEEL formula?
That TW option is there to be disabled for Nexus who already allow for the effect.