Interactive Spreadsheets for Celestial Navigation
T-Plotter
T-Plotter™ is a plotting aid consisting of two mutually perpendicular arms: the plotting arm and the azimuth arm. The main purpose of this device is to simplify the plotting of celestial lines of position (LOP) by eliminating the need for the drawing of the azimuth line from the assumed position (AP) to the intercept. Also, with the help of the T-Plotter, distances can be both marked and measured without dividers.
NOTE: The sales of the spreadsheets and T-Plotters are currently on hold. Please check back soon.
Currently there are two versions of the T-Plotter: Basic and Blank.
NOTE: The sales of the spreadsheets and T-Plotters are currently on hold. Please check back soon.
Currently there are two versions of the T-Plotter: Basic and Blank.
T-Plotter Basic
The "Basic" model is intended to be used primarily with Universal Plotting Sheets (VP-OS) on which the distance of 1 inch represents 20 nautical miles on the Earth's surface.
T-Plotter Basic is particularly useful if the AP of the St. Hilaire method coincides with the center of the compass rose on the plotting sheet. This choice for AP is always available if an electronic sight reduction method, such as the spreadsheet intercept.xls, is used. Then, if the intercept is AWAY, the T-Plotter can be positioned on the plotting sheet by simultaneously using the intercept distance and the azimuth. If the intercept is TOWARD, the T-Plotter position can be obtained using the same intercept distance but AWAY from the reciprocal azimuth.
Alternatively, the grid marked along the plotting edge can be used to find the locations at which the LOP intersects the AP's parallel and meridian (as computed by the intercept.xls spreadsheet) which allows the plotting of the LOP simply by connecting those two points without referring to any angular information.
The following image shows the spreadsheet intercept.xls containing data illustrated in the above T-Plotter image. For more information about this spreadsheet, click here.
Azimuth transfers from the compass rose to a non-centrally located AP can be accomplished with the help of a straightedge by first sliding the correctly oriented T-Plotter along the plotting arm direction until the azimuth line covers the AP, followed by sliding along the azimuth arm direction into the prescribed intercept distance.
Click here to view a T-Plotter Basic demonstration video.
T-Plotter Basic can also be used on charts of any scale, with the extra step of having to identify the requisite number of T-Plotter tics to represent the required distance according to the latitude scale of the given chart.
There are dry-erase markers (not included here) with which one can mark on the T-Plotter as well as erase. This is useful if the intercept distance comes out longer than what the azimuth arm allows. In such a case that distance has to be partitioned into pieces, each one shorter than the azimuth arm. The LOP is then arrived at in stages, in which each piece of the intercept distance is covered by the requisite additional sliding and marking along the azimuth arm direction.
T-Plotter Basic specifications:
Material: acrylic
Thickness: 1/8"
Width (plotting arm): 11"
Height (azimuth arm): 8 1/2"
Arms' widths: both 1 1/2"
Made in USA
T-Plotter Blank
We also have a simpler version called T-Plotter Blank equipped with only the central azimuth line but no additional grid or lettering.
We also have a simpler version called T-Plotter Blank equipped with only the central azimuth line but no additional grid or lettering.
Intercept distances can be marked on the T-Plotter by dry-erase markers (not included), as shown in the demo video here.
T-Plotter Blank specifications:
Material: acrylic
Thickness: 1/8"
Width (plotting arm): 11"
Height (azimuth arm): 8 1/2"
Arms' widths: both 1 1/2"
Made in USA
