Nelson & His World

Am I correct that all bearings entered in a master's log book were magnetic bearings, not corrected for magnetic deviation? Does this also apply to entries for course steered and for wind directions?

As magnetic variation was much greater then (20 degrees plus) than it is now, this is rather critical to a theme I am pursuing at the moment!

Tony,

I believe you are correct. Bearings, courses steered and wind directions would all have been noted in the log as magnetic bearings, and not corrected for deviation. Wind direction, of course, was noted as 'from' rather than 'to'.

It would appear that some nations, like the Dutch, did correct for deviation at the time of making the bearing, but this does not seem to have been the norm in the RN. My guess is that it kept things simple, sometimes events happened too fast to allow of corrections, and perhaps the person making the observation may not either have been that quick, or was not that gifted, in the brain department! However, those corrections as were necessary were made later by the officer of the watch or master, such as for example, when calculating for leeway or the average course 'made-good' during the period of a watch. I'm not sure about the practice in the HEIC or the merchant fleet.

Of course all of these entries in the log would have been noted with reference to the thirty-two points of the compass and using the old method of referring to cardinal, intercardinal and 'by' points, since the 360° notation of the compass card, although known, wasn't then in general use. A favourite exercise of masters or instructors was to get a mid. or whoever to 'box the compass', that is to recite all the thirty two points from memory and starting anywhere on the compass card.

Will you, at some stage, be enlightening us as to your theme?

probably even more complicated given the amount of ferrous metals within a short distance of the compass. I'd think deviation from true North would be the least of your problems.

When the Apollo led a convoy on an invasion of Portugal, the hard way, blame was placed on her newly installed cast iron water tank. http://ageofsail.wordpress.com/2009/03/ ... ms-apollo/

Bill,

There is that too... from the quarter deck guns, for example, though they might just be out of range. Even more disasterous would have been the knife in the helmsman's belt should he have happened to be wearing one!

I know when I used to sail that it was advised you check, just before your 'trick', to make sure you had removed knife, keys etc. from your person.

don't know about that.

Going back to my experience as an infantry officer, you had to be 50 ft (16 m) from your vehicle to take a reliable reading with your lensatic compass. If you were laying a mortar section with an M-2 aiming circle you removed your helmet/weapon, and observed the separation from your gun carriers. There is nowhere you can go on a ship and get the standoff from ferrous metals that you need to obtain an accurate reading from a magnetic compass.

I'd be much more concerned about the several tons of cast iron in the form of quarterdeck guns, or by sailing in close proximity to another ship, than I would by the knife but the point remains the same. When using a compass in the environment of a wooden sailing ship, you have worries about its accuracy that exceed that posed by the declination constant for your latitude.

Thanks both, for your input. My theme, Kester, is some of the conflicting observations from ships at Trafalgar. From your input, Bill, I am probably looking at this the wrong way round - perhaps it's surprising how many of them agreed!

Another question on reading ship's logs - if anyone can help - Am I correct that double dots, or double strokes, in columns of numbers (speed in knots and fathoms) are not ditto marks, but represent zero? I appreciate that it would be extremely sloppy to use ditto marks in this way, but then some of the logs were pretty sloppy! I also appreciate that ditto was usually represented by 'do'.

Tony,

That sounds interesting and I wish you well with that. I'm sure we'll hear more! The various logs certainly did vary by quite a lot.

As to your question, I don't think I can help you there, but you may very well be right.