Expedition Expedition Navigation Software

You are not logged in. Would you like to login or register?

8/25/2018 9:31 am  #1

Damp time to layline?

What's the proper way to damp time to laylines (or time to mark)?

There's "layline time on x ratio", but I can't see it making difference. 



8/25/2018 11:38 am  #2

Re: Damp time to layline?

It uses the damped twd, tws etc so doesn't have its own damping option


8/26/2018 10:47 am  #3

Re: Damp time to layline?

Nick wrote:

It uses the damped twd, tws etc so doesn't have its own damping option


I'm not sure I want to damp out the laylines themselves (as they are very useful when you get up close) but time/ratio seems more like tools to figure out positioning on the course.

I'll experiment some more.

     Thread Starter

8/26/2018 12:14 pm  #4

Re: Damp time to layline?

Putting in the proper damping for the various channels is important to obtain useful data.
How much damping will depend on your instruments (how much is the data the send to Exp already damped) and what type of course you sail (e.g. for log distance legs you can use much higher damping.

Start e.g. with a TWD/TWS damping of 60-90 seconds,   TWA and BSP of 10-15.  This likely gives a useful time and distance to layline which is somewhat constant and not fluctuating all the time.

What values are other on this forum using?


2/02/2020 6:31 pm  #5

Re: Damp time to layline?

When using laylines to a mark to judge the time to tack or gybe i am having problems
If I tack/gybe as it says then I never lay the mark, that is expedition places the layline too early.
Can I adjust the settings somewhere to make it more realistic to the actual conditions i face.



2/02/2020 10:13 pm  #6

Re: Damp time to layline?

It is based on the target twa values in your polar - if you want to change the laylines, that is where to do it.


2/02/2020 11:42 pm  #7

Re: Damp time to layline?

I see 3 possible reasons why you are not able to lay the mark:

  • Your polar is not correct (a too narrow tacking angle)
  • You don’t point high enough to reach your polar upwind angle
  • Your instruments are not properly calibrated

I would start ensuring your instruments are properly calibrated.  If they are not, TWD and TWA will be incorrect and as a result Expedition cannot calculate proper laylines. Getting TWA and TWD correct needs calibrating all of your instrument settings: HDG, BSP, Want angle, Leeway, Upwash etc.
Supposing your instruments are calibrated and your polar is correct, you will likely still not be able to lay the mark when tacking at Expeditions laylines. The reason being that you will (on average) never sail 100% of your polar.  Not only boat speed might on average be a bit lower than the polar upwind BSP,  but also your average TWA is likely not as narrow as the polar says.  A way to compensate this is to use a separate navigation polar (in additional to the performance polar) in Expedition. In this nav polar you can indicate that e.g. the boatspeed is 95% of the polar numbers and you can tune this nav polar to contain slidely wider tacking angles.  As Expedition bases its laylines on the nav polar, this allows you to tune everything perfectly.  But again, start by calibrating your instruments.

Last edited by ZeeZee (2/02/2020 11:43 pm)


2/03/2020 1:37 am  #8

Re: Damp time to layline?

I understand how the lay/polars work and normally make allowances for the conditions.  Is it possible for expedition to take into account the actual TWA/TWS rather than the polars.  The current polars I have are good for flat water, but when offshore with a lumpy sea, we start sailing fatter up wind as this gives us the best VMG in a sea way. 

Also I have seen variations between our polars and actuals at times due to variation in wind speeds between that at sea level and the top of the mast.  This difference can vary in 10 knots of true wind at the top of the mast from almost nothing to only a couple of knots at sea level.  These difference in average wind speed across the sails has a big effect on actual speed. E.g. TWS says 10knots but effect polars sailed are closer to 6knots.

What is the best options for working arround these issues?


2/03/2020 1:49 am  #9

Re: Damp time to layline?

Ummmm, big philosphical topics, but the obvious answer from the last is the Scale 10m Wind setting, and the Help File has a calculation about that.  But you have been around lots, I don't think it is that simple.
As Zee identified, the problem typically lies somewhere elsewhere, either your polars are out for that TWS/TWA combination, or your speedo is telling you porkies, and so your processor is explaining the BSP/SOG difference as set/drift.  As ever, do a compass spin and a speedo recailbration.  "If I had $1 for every time I'd been told, etc etc".


2/03/2020 2:58 am  #10

Re: Damp time to layline?

Calibration is good, but as always could be better as is constantly being refined.

The problem is assuming that the calibration is perfect and the polars are right 75% of the time, what do you do when the best VMG's are achieve by not sailing to the polars.


Board footera


Powered by Boardhost. Create a Free Forum

Zapfware North University. Racing Tactical Software - Expedition.
Online courses