Question on tides & course to steer

[KellysEye]

There were about a dozen boats waiting weeks in Grenada for the very strong wind to die down for an overnight passage to Trinidad. An American yacht had the solution to being pushed down by the current. Every four hours he would stop, drop the sails and motor back to the GPS track, then put the sails back up and turn on course. It took a while to work it out what he was doing and when we did we couldn't believe what we were seeing.

 

[andygc]

Traverse tables ... Unlikely you could even buy them today, maybe in some second hand shop.

How about here?

 

[newsailorboy]

The American Way

There were about a dozen boats waiting weeks in Grenada for the very strong wind to die down for an overnight passage to Trinidad. An American yacht had the solution to being pushed down by the current. Every four hours he would stop, drop the sails and motor back to the GPS track, then put the sails back up and turn on course. It took a while to work it out what he was doing and when we did we couldn't believe what we were seeing.

Are the American Way

 

[jwilson]

Cumbersome printed tables that essentially allow you to convert changes in longitude into nautical miles (and vice versa) so that you can use lots of arithmetic to achieve what you did in your class just by drawing lines on the chart.

The do not, in fact, date back to the days before the invention of the pencil, but they do go back to the days of black and white charts, printed from plates that were hand-engraved onto copper sheets, that were so valuable that no-one would dream of drawing on them.
Their continued existence is a mystery that can probably only be explained by those who devise the exam syllabusses for Merchant Navy cadets.

Traverse tables were part of the syllabus when I did Yachtmaster, along with a several hour long nav exam at the same place in Cardiff and with the same examiners that did merchant navy exams. I remember one of the questions included "You are steaming at 11 knots....". There was also a Morse test.

 

[stephenh]

Robin said :
"Going back to your main question, one of the Channel Tide Atlases (Reeves Foulkes I think) did give an explanation and calculation of both methods times in the preface. I no longer have a copy so can't look it up. "

From my old and battered copy :

From Portland to Cherbourg at 5kts -

1) Keeping to the track, with hourly course changes - passage time 14 hrs

2) Agglomerating the tidal offsets and 'going with the flow' - 12hrs 40mins

Time for more than one coffee or one pint !

 

[Ricd]

+1

I always plot the hourly tidal vectors on a bit of scrap paper then transfer only the 12 hour resultant vector to the chart...that way less graphite to rub out HB, 2B or other...Plus, can use a larger scale on the scrap paper making measurements much easier.

 

[Conachair]

How about here?

It's a fair cop Though seems to be a reprint from 1876 so maybe not quite so new anymore.

Available free for anyone looking for some light bedtime reading
http://www.archive.org/stream/anewandcomplete00boilgoog#page/n78/mode/2up

Did anyone really ever use these for coastal nav??

 

[nigel1]

It's a fair cop Though seems to be a reprint from 1876 so maybe not quite so new anymore.

Available free for anyone looking for some light bedtime reading
http://www.archive.org/stream/anewandcomplete00boilgoog#page/n78/mode/2up

Did anyone really ever use these for coastal nav??

Nope, only for my exams, but also when calculating ITP for sights, but thats not coastal is it.
Nories Tables should include Traverse Tables