Weston Middle School

Massachusetts Grade 8

Technology/Engineering MCAS Review

Dead Reckoning

Navigating a square in Robolab Pilot 3 using time and direction(heading) is analogous to the method of dead reckoning used by sailors and pilots to chart a course in the absence of accurate location information.

In dead reckoning, the pilot starts with a known starting point (fix) (determined using a map and/or star fix). Course is then estimated, by plotting a vector, based on heading and velocity.

Errors are introduced by various factors including currents, wind, inaccurate velocity measurements.

For more information on dead reckoning:

• US Coast Guard, Coastal Piloting for Boat Crew and AuxNav

• Wikipedia- Dead Reckoning

• Bowditch Online-Dead Reckoning

Image: http://education.qld.gov.au/curriculum/area/maths/compass/images/cn8.gif

John Harrison's H4 Marine Chronometer

In Robolab Pilot, navigating using time to estimate distance is not very accurate.

The same problem faced the British Royal Navy in the 1700's, in part because of a lack of accurate shipboard clocks. These were needed both to determine longitude for the initial fix ( by comparing local noon to the noon in Greenwich, England ), and to measure velocity.

The timekeeping problem was solved by legendary clockmaker John Harrison.

For more information on Harrison and his amazing clocks:

• Greenwich Observatory, John Harrison and the Longitude problem

• NOVA, "Lost at Sea: The Search for Longitude"

• Dava Sobel, Longitude