View Full Version : DEAD RECKONING

04-20-2013, 00:24
In marine navigation a "dead" reckoning plot generally does not take into account the effect of currents or wind. Aboard ship a dead reckoning plot is considered important in evaluating position information and planning the movement of the vessel.[3]
Dead reckoning begins with a known position, or fix, which is then advanced, mathematically or directly on the chart, by means of recorded heading, speed, and time. Speed can be determined by many methods. Before modern instrumentation, it was determined aboard ship using a chip log. More modern methods include pit log referencing engine speed (e.g. in rpm) against a table of total displacement (for ships) or referencing one's indicated airspeed fed by the pressure from a pitot tube. This measurement is converted to an equivalent airspeed based upon known atmospheric conditions and measured errors in the indicated airspeed system. A naval vessel uses a device called a pit sword (rodmeter), which uses two sensors on a metal rod to measure the electromagnetic variance caused by the ship moving through water. This change is then converted to ship's speed. Distance is determined by multiplying the speed and the time. This initial position can then be adjusted resulting in an estimated position by taking into account the current (known as set and drift in marine navigation). If there is no positional information available, a new dead reckoning plot may start from an estimated position. In this case subsequent dead reckoning positions will have taken into account estimated set and drift.
Dead reckoning positions are calculated at predetermined intervals, and are maintained between fixes. The duration of the interval varies. Factors including one's speed made good and the nature of heading and other course changes, and the navigator's judgment determine when dead reckoning positions are calculated.
Before the 19th-century development of the marine chronometer and the lunar distance method, dead reckoning was the primary method of determining longitude available to mariners such as Christopher Columbus and John Cabot on their trans-Atlantic voyages. Tools such as the Traverse board were developed to enable even illiterate crew members to collect the data needed for dead reckoning. Polynesian navigation, however, uses different way-finding techniques.

04-20-2013, 06:52
So... I am wondering how hard it would be to add "set and drift" to the movement aspect of the game? It could certainly add an interesting level of complexity and movement calculation, that I don't think would be too difficult to factor in. Maybe a seperate type of "drift" indicator on the game mat and once movement has been completed a "set and drift" adjustment is made in the proper direction? This could be a simple as moving the ship the width of the distance ruler?

Thanks for posting this Paul.

04-20-2013, 07:17
Sure thing. I thought this would open up some interesting discussions. :talk:

04-20-2013, 07:57
I don't think drift is relevant - on the areas/distances of a typical engagement it would affect all ships in the same way and that would be very small...
On daily navigation, in open sea, you add the drift arrow once a shift, if the current is known to be very significant.
Usually you ignore it and let the evening star fix correct your position.

04-20-2013, 08:12
In this age of GPS I thought it interesting to talk about a term and time from when men Knew where they were headed without computers and satellites. As for game mechanics it would affect ships similarly as you say irrelevant. Besides I wanted to use that cool graphic somewhere. :wink:

04-20-2013, 08:51
I think you are still legally bound to have a proper chart with navigation markings on it...
And its defiantly common practice on Naval ships.

04-20-2013, 08:53
I think you are still legally bound to have a proper chart with navigation markings on it...
And its defiantly common practice on Naval ships.

Of course...pun intended.

04-20-2013, 19:04
"'Dead reckoning' -- so named because if you do the latter poorly, you will end up the former."

04-20-2013, 22:31
Currents might affect game play, if a ship was near land or a reef.

04-20-2013, 23:25
Maybe something like this?

04-20-2013, 23:53
Currents might affect game play, if a ship was near land or a reef.
Another example:
A fire ship, used in the days of wooden rowed or sailing ships, was a ship filled with combustibles, deliberately set on fire and steered (or, where possible, allowed to drift) into an enemy fleet, in order to destroy ships, or to create panic and make the enemy break formation.

David Manley
04-21-2013, 00:25
There's always scope for house rules like this. Another aspect I thought about was limiting the ability to manoeuvre depending on loss of masts, damage to steering, etc. (for example, a SOL not under command tends to bear up, and ships with substantial amounts of damaged masts, sails and rigging fallen alongside acts as a sea anchor and drags the ship in the direction that the wreckage has fallen, hence the need to chop it away quickly - there's also an enhanced fore fist, especially if the wreckage has fallen over the engaged side. All areas where extra detail could be added if you wished.

04-21-2013, 00:39
Excellent points David. I like the information pertaining to wreckage and the directions it will tend to travel.

04-21-2013, 01:35
Nice examples of drift - all affected by wind.
I had my head strongly fixed on currents....:embarass:

Billy Ruffian
04-21-2013, 04:31
Some good points made by David, without making things too complicated, in our house rules the ability to manoeuvre became less as the mast damage increased until the ship just drifted with the wind direction if it became dismasted so many inches per turn, i suppose a jury rig could be erected in so many moves to restore some movement. It would be interesting to see any ideas regarding ships becoming entangled as they closed together for boarding and their ability to extricate themselves too.