Protractors - Navigation
As noted in the Introduction, the earliest use of protractors was probably in navigation. Protractors assisted with laying out angles to indicate the actual or desired direction of a ship. Makers might have also marked protractors with additional scales to be employed in computing a ship’s speed or direction, such as rhumbs or seconds. When coastal surveying projects were conducted in the 19th century, navigators used substantial protracting instruments called station pointers both to ascertain their position along a coastline and to record the topographical measurements of that coastline. In the 20th century, protractors were also utilized in aviation navigation.
"Protractors - Navigation" showing 1 items.
- This white plastic circular protractor is mounted on a clear plastic square plotting board with green grid lines. The board bears a white arc for correcting against compass errors of VARIATION, divided to single degrees and marked by tens from 30 to 0 to 30. The letters E and W are printed above the 25° points. The protractor is divided by single degrees and marked by tens from 0° to 350°. A compass rose, with an arrow at North and the letters E, S, and W inside triangles, appears inside the degree circle.
- An extending arm is affixed to the center of the protractor. The end of the arm on the protractor is marked with +2 (in black), +4 (in green), and +1 (in black). The arm also bears an arc for correcting against compass errors of DEVIATION, divided by single degrees and marked by tens from 20 to 0 to 20. The letters E and W are printed above the 15° points.
- The part of the arm that extends for 9-3/4" beyond the protractor is divided by tenths and labeled for NAUT[ICAL] MILES. Markings by ones from 1 to 5 are for a scale of 1:40,000 n.m.; markings by ones (in green) from 1 to 10 are for a scale of 1:80,000 n.m.; and markings by ones from 1 to 2 are for a scale of 1:20,000 n.m. The arm is marked with instructions for use: Set 0 on compass circle to variation on square base. Align arm with course. Align cross lines on base with any meridian or parallel on chart so arrow on base points north. Read compass course on compass circle opposite deviation on arm. Deviation may be marked inside compass circle.
- A sheet of instructions is also provided with the instrument and its clear plastic sheath. The arm is marked with the object's name—DE LUXE COURSE PROTRACTOR (/) PAT. PENDING—the Danforth/White company logo—the letters DW with the slogan, THE MARK OF SAFETY AFLOAT—and the maker's mark: DANFORTH/WHITE (/) PORTLAND, MAINE (/) ©1959, by R. S. Danforth. Felsenthal Instruments Co. manufactured this protractor for Danforth/White, which made well-regarded nautical compasses in the 1960s. Since the 1980s, the company has sold weather stations and instruments under the name Maximum Inc. For Felsenthal, this protractor was product number FDD-7.
- See also 1977.1141.01, 1977.1141.02, 1977.1141.03, 1977.1141.05, 1977.1141.08, 1977.1141.09, 1977.1141.10, 1977.1141.11, 1977.1141.12, 1977.1141.18, 1977.1141.19, 1977.1141.20, 1977.1141.21, 1977.1141.22, 1977.1141.23, 1977.1141.24, and 1977.1141.30.
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- National Museum of American History, Kenneth E. Behring Center