Christmas Brain Teaser

[wooslehunter]

Now that lots of us have to make do with thinking about sailing, here's something to think about.

A skipper plans a course as follows: his boat speed is 5 kts. Charted course to the desination is 000T. The start time is exacty at high water and the tide ebbs to the west and then floods to the east - 270T and 090T exactly. The maximum ebb and flood tide is 2kts and the speed changes sinusoidally with a period of exactly 12hrs. The distance from start to finish is 60nM exactly.

There is no reason whythe skipper should stick to the exact track so, for the fastest passage, should the skipper:

A - add up the tidal flow for the whole passage and correct the course for that.
B - steer a different course each hour, corrected for the differing tide each hour.
C - it doesn't matter, A and B result in the same passage time.

Anyone else got any others like this?

Happy fiddlng,

Dave


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[slipknot]

Who is steering?

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[peterb]

Traditional answer: A

Modern answer: Put the destination in as a waypoint, engage autopilot, sit back with G&T and wait.

 

[paulineb]

42

<hr width=100% size=1>Pxx

<A target="_blank" HREF=http://www.paulinebeddoes.co.uk/php-cgi/gallery2>Perils of Pauline in Pics</A>

 

[Guest]

This is unfortunately ....

similar to the :

Ship steams for 12 hours east, 12 hours south, 12 hours west, 12 hours north at same speed all the time ...... where does she end up if there are no currents / tides / leeway etc ?

Logic says at original start point ...... but in fact is not true .... now I will leave it for the 'experts' to answer mine as well ...... ??


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I came - cos they said was FREE Guinness !
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[peterb]

Re: This is unfortunately ....

Not when she's sailing on a sphere.

You can see the effect if you imagine her making 10 knots and starting a few yards from the North pole. For 12 hours, sailing east, she makes small circles round the pole. Then she heads south, ending up about 120 miles from the pole. Turning west now and making another 120 miles, she will only have changed her longitude by about 57 degrees. Turning north and making 120 miles she will be back at her original latitude, but it's very unlikely that she will be at the same longitude.

Alright, you can't actually sail like that (at least, not until global warming has melted the ice) but the same effect will apply at almost any starting point unless the southerly and northerly legs are across the equator.

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[Guest]

Blimey .....

Sorry .... but what a long-winded answer to get to the answer that you will be displaced from origin.

It's all down to the non-linearity of Latitude and also the earth being oblate-spheroid ......

<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I came - cos they said was FREE Guinness !
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[qsiv]

Thank God that someone understands the truly seminal works of English literature..

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[chas]

Where is the wind? NM

'

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[stevebirch2002]

Re: Blimey .....

Hi Nigel

I agree totally... If only I knew what an OBLOID SPHEROID was..... (Sounds a bit like a rugby ball to me which brings me back to the great World Cup - Away the lads.......).

<hr width=100% size=1>Albin Vega "Southern Comfort" V1703

 

[stevebirch2002]

Dont care as long as the white wine, moules and frittes are ready when you get to Cherbourg... I have been asking this question to my clever friends (Professor of Maths etc) and still no proved answer....

<hr width=100% size=1>Albin Vega "Southern Comfort" V1703