Course to steer

[david_e]

just can't fully understand this and get my head around why on the ym course they say just work this out roughly, seems to go against all the principles of navigation. if you know where you are, and where you are going, the tidal set & drift, the amount of leeway, why only approximate?

 

[Badger]

They want to see that you can work it out QUICKLY without having to go down below and draw a load of spidery lines on the chart. Quick tip, six is a magic number in navigation.If the yacht is doing 6 knots and the cross tide is 1 knot then point up 10 degrees, 2 knots 20 degrees, 3 knots 30 degrees etc etc. Works every time.

 

[tony_brighton]

As I recall one of the other reasons was that practice demonstrates helmspeople rarely steer an accurate course anyway.

 

[bedouin]

I can't comment on the RYAs reasons, but I tend to agree with them for a number of reasons.

Firstly, working out the course to steer will involve a number of approximations as to tide set and rate, speed made good, leeway and so on that means that at best it can only be a rough idea.

Then, even if you do work out an accurate course to steer, it is not feasible to steer the course accurately. In practice you probably don't have an accurate value for the compass error on that course - then it is difficult to steer a course accurately to within a couple of degrees, and in any realistic conditions the boat's heading will vary a bit as wind and waves affect it - making it difficult to guarantee you are maintaining an accurate mean course (most helmsmen have a systematic error to one side or other of the course).

 

[Magic_Sailor]

As mentioned below, the reality of sailing means you can't "instantaneously" keep a boat going in a given "exact" direction say 271M - you just get knocked of course - never mind all the errors in measurement etc. So, if your lucky, you can only tell the helm to steer 270M or 275M for instance - DON'T on your exam tell the helm to steer 271M - it shows lack of experience.

The important thing though is that you have to know how to do it accurately AND understand the constraints of equipment and human error in order to then provide a good, fast estimate.

Once you've decided on a course - if you can - choose some fixed object to steer to. Even better get a transit.

Magic

 

[Magic_Sailor]

\"helmspeople\" - very pc! nm

,

 

[halcyon]

Is this a case of working out accurately the course you are roughly going to follow, not roughly working out the course you are roughly going to follow.

It makes sense to me, I think?

Brian

 

[aztec]

"six is a magic number in navigation.If the yacht is doing 6 knots and the cross tide is 1 knot then point up 10 degrees, 2 knots 20 degrees, 3 knots 30 degrees etc etc. Works every time."

motor boaty person here.... explain please.

do i see if 12k with 1k cross tide= steer extra 5deg. into tide? (if so ...i see)




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[david_e]

Thanks all. It is now clear, suppose the confusion is because nearly everything they have you doing is to an accurate fiugure the all of a sudden - 'work it out approximately'

So if we put an accurate figure such as 271, will they mark it wrong?

 

[Badger]

Sounds logical to me.

 

[snowleopard]

if you can pop out of the hatch after 15 secs at the chart table with an accurate course, very good. if you emerge after 15 minutes of increasingly desperate pleas from the helm, nothing can save you!

don't forget that tidal vectors taken from charts aren't necessarily correct. for one thing, the diamonds represent a point, actual values even quite close may be very different. once went round ushant against what the chart claimed was 2 knots: log showed 8 though the water, gps showed 2 over the ground!!

 

[aztec]

cheers, thanks for that.


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[Cornishman]

As you refer to a 'ym course' I must assume you mean the shore based theory course, there being no ym practical course (unless you mean the Co Sk practical). If you can work a C to S in a nice warm classroom to within say 1 degree you have a fair chance of doing it well on a yacht which is pitching and tossing and you have a bucket between your knees.
You won't be expected to tell somebody to steer a course of 271 on a YM practical exam, especially if you have one of those cheaper steering compasses with 5 degree intervals

 

[rhinorhino]

I doubt that you every really "know" the tidal drift, leeway etc tey are just guesses.
It is often better to have a quick answer than get into difficulties waiting for the answer accurate to .1 degree.

 

[Guest]

See that buoy .....

try to keep on the port side without hitting it ..... lass !

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Guest]

Age old story .... like >

Old boy on Rail station asks the porter ..... why do you publish a timetable and all the bloody trains are late ...... ?

Answer - No timetable - how would you know they are late !!!

Everythings ok in theory - gives something to disprove in practice !!

Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[Roberto]

Maths background is lim(x->0) of (tan(x)/x)=1, x being an angle measured in radians. For small angles, you can consider the tangent roughly equal the angle (in radians). The actual difference is navigationnally negligible up to 20/30 degrees.

Being a radian nearly equal to 60 degrees, and the tangent equal to the ratio: perpendicular component of current/speed, the amount of degrees to be added/subtracted is 60 times current speed divided by boat speed.
In your case 60 times 1k divided by 12k equals 5 degrees, you got it right!

 

[aztec]

ok, you've met me aint cha?

you either didn't appreciate how thick i was, or are taking the piss!

thanks if the advice was genuine.... but how the hell would i know?

funny.... it was, i giggled for minutes!

thanks again.... steve.(not too bright)

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[Badger]

It's OK Aztec he's half french and half Italien.. nuf said

 

[Gunfleet]

The Raymarine thingy can steer to a couple of degrees. On a long keeled boat I can manage 5. I think an inexperienced helm steering within 10 degrees steadily is doing quite well!