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Old 07-04-2014, 03:37   #1
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Rule of thumb for current flows

Hello,

I'm wondering if there is any rule of thumb to use when compensating for current flows. For example; the course of my destination is 210°, but I know that there are current flowing at 3-5 knots going at a E-direction, what should my actual course be in order to compensate for the current?

Thanks in advance,

Kaspar
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Old 07-04-2014, 04:29   #2
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Re: Rule of thumb for current flows

Search for a 'Course to Steer' thread. This was discussed extensively there.

Theory (likely oversimplified) in a nutshell:
- _estimate_ your trip duration,
- find a total vector of currents influence over the estimated duration,
- do vector math with your bearing to target.
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Old 07-04-2014, 05:16   #3
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Re: Rule of thumb for current flows

Or you could read Dean Wells's article at http://westviewsailing.co.uk/wp-content/plugins/download-monitor/download.php?id=27
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Old 07-04-2014, 08:19   #4
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Re: Rule of thumb for current flows

The rule of thumb is that currents always flow against you unless you are going into the waves - then they flow with you and make the waves steeper. They are tricky buggers.

Since the currents are always either directly on your bow or on your stern, no vector math is required at all.

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Old 07-04-2014, 08:21   #5
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Re: Rule of thumb for current flows

My notes on determining course to steer

http://www3.telus.net/jackdale/navle...g%20Course.pdf
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Old 07-04-2014, 09:40   #6
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Re: Rule of thumb for current flows

This isn't mine but its not a bad one

For every 10% of tide to speed
Adjust your course by ± 6° if the tide is on your beam
Use ± 4° if the tide is on your bow or quarter

E.G. If you have 2 knots of tide and your speed is 10 knots; the tide is 20% of your speed.
Adjust your course by ± 12° if the tide is on your beam
± 8° if the tide is on your bow or quarter

be aware of the deficiencies of all "rules of thumb"


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Old 07-04-2014, 09:48   #7
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Re: Rule of thumb for current flows

A rule of thumb for staying on course.

Look ahead to your destination for two land-based objects that are in line. Keep them in line. That will keep you on course.

This only works in good visibility in sight of land.
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Old 07-04-2014, 10:08   #8
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Re: Rule of thumb for current flows

Wow, thank you all very much for your input and advice!
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Old 07-04-2014, 10:11   #9
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Re: Rule of thumb for current flows

The pre-electronic piloting solutions are great of course, but this is very easy if you have GPS. Just keep your COG the same as your predicted course on the chart.
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Old 07-04-2014, 10:35   #10
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Re: Rule of thumb for current flows

As a rule of thumb, to me, means a non maths calculation.

The current not being tide.
Using a plotter.

Check the COG and see if I can find the highest current flow on average then hit the auto pilot up a few degrees from that.

Same as with wind its better to be 'up' a few degrees because its easier to go down than up.

Also if I am going too fast for my arrival time I will keep my boat speed up untill I am close to the objective. Cos the wind likes to drop when you didnt think it would.

These are just some of my rules of thumb. They dont denigrate those posters who have exact mathematical formulas.

Its just the way I actually sail and navigate.
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Old 07-04-2014, 10:51   #11
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Re: Rule of thumb for current flows

Quote:
Originally Posted by Vivid View Post
The pre-electronic piloting solutions are great of course, but this is very easy if you have GPS. Just keep your COG the same as your predicted course on the chart.
Even easier if you choose the correct autopilot. Ours has a "no-drift" mode that continually corrects for current and leeway.

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Old 07-04-2014, 11:00   #12
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Re: Rule of thumb for current flows

Kane Mk VI Dead Reckoning Computer. Front is basically a circular slide rule and does time, speed and distance calcs, fuel etc. It's for aircraft, but the back is an analog plotting graph/wheel that will do the heading to steer compensating for cross wind/current vector problem for you if you have the right scale card.

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Old 11-04-2014, 01:13   #13
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Re: Rule of thumb for current flows

You can easily calculate your corrected corse using a ruler and apiece of graph paper
Your true course is the sum of the vector representing your speed and heading and the vector for the current not including the effect of wind on your true course
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Old 11-04-2014, 04:23   #14
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Re: Rule of thumb for current flows

Please see here:

http://www.plaisance-pratique.com/gerer-les-courants-un-logiciel

then download the software by clicking on

Installation du logiciel « Courants »This software is very intuitive, even in french language:

Move the red dot (flux) to simulate current flow
Move the blue arrow (vent) following wind direction
Move the blue dot (Cap) according to your apparent course and speed
Green dot is the result (COG & SOG)

Enjoy
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Old 11-04-2014, 07:20   #15
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Re: Rule of thumb for current flows

Quote:
Originally Posted by pupuce View Post
Please see here:

http://www.plaisance-pratique.com/gerer-les-courants-un-logiciel

then download the software by clicking on

Installation du logiciel « Courants »
I have not been successful installing Courants on Windows 7 x64.

Error log file starts:

%% NE PAS MODIFIER NI SUPPRIMER CE FICHIER! %%
%% Ce fichier contient des informations relatives à l'installation d'une application. %%
%% Il est utilisé pour supprimer automatiquement de votre ordinateur tous les composants de l'application, si vous le souhaitez. %%


NOTE: Début de la section du programme d'amorçage

CONFIG: Title: "Courants"

ACTION: RegKey: "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Cur rentVersion", "SharedDLLs"

ACTION: SystemFile: "C:\Windows\System32\VB6STKIT.DLL"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\VB6FR.DLL"
(Fichier introuvable ou périmé -- nouveau fichier copié)

ACTION: SystemFile: "C:\Windows\System32\COMCAT.DLL"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\stdole2.tlb"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\asycfilt.dll"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\olepro32.dll"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\oleaut32.dll"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: SystemFile: "C:\Windows\System32\msvbvm60.dll"
(Le fichier présent sur le disque était déjà à jour.)

ACTION: DllSelfRegister: "C:\WINDOWS\SYSTEM32\COMCAT.DLL"

ACTION: TLBRegister: "C:\WINDOWS\SYSTEM32\stdole2.tlb"

ACTION: DllSelfRegister: "C:\WINDOWS\SYSTEM32\olepro32.dll"

ACTION: DllSelfRegister: "C:\WINDOWS\SYSTEM32\oleaut32.dll"

ACTION: DllSelfRegister: "C:\WINDOWS\SYSTEM32\msvbvm60.dll"

NOTE: Fin de la section du programme d'amorçage

NOTE: Exécution dynamique du programme d'installation principal 'Setup1.exe'....

ACTION: CreateDir: "C:\Program Files (x86)\Courants_HetO"

*** Erreur: Type mismatch
*** Erreur: Une erreur d'installation inattendue s'est produite!
*** Erreur: (L'utilisateur a répondu 'Annuler'.)

What did I do wrong?

Al
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