US2269841A - Course protractor - Google Patents

Description

Jan. 13, 1942. R. s. BLAIR 1 COURSE PROTRACTOR Filed Oct. 29, 1937 IIII"IIIIIIIIIIIIIIIIIITII' sunskilled users.

Patented Jan. 13, 1942 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to course protractors for plotting courses on navigation charts and the like.

One of the objects of this invention is to provide a simple, inexpensive, and practical course protractor well adapted to meet varying conditions of use. Another object is to provide a course protractor of the above character which will be eflicient and reliable in operation. Another object is to provide a course protractor of the above character which will be neat and attractive in appearance and yet be of such sturdy construction as to withstand hard usage. Another ob-ject is to provide a course protractor of the above character whose use will be simple and which may be quickly and easily operated by Another object is to provide a course protractor of the above character which may be constructed from inexpensive and light materials. Another object is to provide a course protractor of the above character which will be inexpensive to manufacture and easily assembled. Another object is to provide a course protractor of the above character which is accurate in operation. Another object is to provide a course protractor of the above character which may be operated with a minimum of adjustments. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the various possible embodiments of my invention:

Figure 1 is a top plan view of the instrument in operating position upon a chart;

Figure 2 is a side view of the device shown in Figure 1;

Figure 3 is a vertical sectional view taken along the line 3--3 of Figure 2;

Figure 4 is an enlarged perspective view of a part of the device shown in Figure 1;

Figure 5 is a detailed assembly view of the part shown in Figure 4; and

Figure 6 is a top plan view of a part of the device shown in Figure 1.

.Similar reference characters refer to similar parts throughout the several views of the draw- 111 As conducive to a clearer understanding of certain features of this invention, it might here be pointed out that previous devices designed to plot courses on navigation charts have been accompanied by excessive cost and inefi'icient operation. Some of these devices require numerous manual settings of the instrument before the course may be ascertained. This is burdensome to the operator and furthermore at any time a slight movement of these instruments during the various settings will lead to an inaccurate result. Furthermore, the use of some of these instruments is restricted to the use of a chart table or a flat surface which is not usually available in a small boat. Without such a flat surface these instruments are extremely difiicult to operate if an accurate course is to be followed. Among the several objects of this invention is to provide a device for overcoming the above-mentioned difficulties as well as many others.

Referring now to the drawing in detail, the instrument generally indicated at Ill (Figure l) is shown in position upon a section II of a navigation chart. A pivotally mounted arm I2 slides along a body member I3. Arm I2 is first aligned with a course l4 plotted on the chart and is then slid along member l3 until its edge crosses the center of compass rose I5. When the instrument is properly aligned, as will be more fully described hereinafter, the user may find the direction of the course I4 by noting the direction arm I2 crosses compass rose I5. The arm I2 is preferably formed of resilient material with a tendency to assume the position indicated in dotted lines at I2a in Figure 3 of the drawing, or, in other words, to spring upwardly away from the chart or supporting surface. It can, of course, be readily flattened into the position shown in full lines so as to register with the course or with compass points.

Member I3 is preferably flexible and resilient and both it and its enlarged end portion I6 are made of metal or from some other light flexible material such as transparent Celluloid. Secured to the under surface of end portion I6 and extending up the center of the under surface of member I3 is a pad I'I (Figures 1, 2, and 3) made of rubber or similar material. The exposed surface of the pad I1 is preferably roughened (Figure 3) so that when the instrument is placed upon a chart it secures a firm grip thereon and resists lateral movement.

Mounted upon member I3 is a sliding member generally indicated at I8. This sliding member (Figure 4) has two channels I9 and 20 formed upon its outer edges. On one side of member I8 a tongue 2| is cut out of channel I9 (Figure 4). This tongue preferably extends out from member I8 in the same plane as its top surface 22 and has a portion drawn upwardly to form tube 23 (Figure 3). Tube 23 is so positioned on tongue 2I that when sliding member 26 is mounted on member I3 the center point of the tube lies directly above the edge 24 of member I3 (Figure 1).

The distance between the inner surface of channels I9 and 20 is greater than the width of member I3. A spring 25 (Figure 5) is inserted in channel and preferably has its ends 26 and 2! turned outwardly to prevent longitudinal movement of the spring when it is in position in channel 20 (Figure 5). When sliding member I8 is in position upon member I3, spring exerts a pressure against edge 28 of the body member and holds the inner surface of channel I 9 against edge 24 of the body member I3 so that member I8 is always held in alignment with body member I3 as it slides thereon.

Arm I2 (Figure 6) has a tongue 29 formed thereon. Through this tongue and part of the body of arm I2 is a hole 30. Hole 30 is so positioned that its center point would be bisected by a line drawn through the outer edge 3I of arm I2. Tube 23 (Figure 3) extends through hole 30, permitting arm I2 to pivot with relation to sliding member I3 on tube 23 as a pivot point. A spring washer 33 lies between the turned lip 32 of tube 23 and arm I2. This washer presses downwardly upon the arm and holds it by friction in any desired angular relation with respect to member I8.

Thus arm I2 may be slid along member I3 and the center point of tube 23 coincides with the edge 24 of member I3 (Figure 1). The sliding member I8 is held in alignment with member I3 by spring 25 and arm I2 has been secured to the sliding member in such manner that it maintains any position desired by the user with respect to members I3 and I8.

Referring to Figure 1, in operation, member I3 is so placed that its edge 24 crosses the course I4 plotted on the chart and is also aligned with the center 34 of compass rose I5. Then arm I2 is moved along member I3 and turned until its edge 3I is in alignment with course It. Then holding the instrument I0 by its enlarged end portion I6, member I8 is slid along member I3 until the user views the center point 34 of compass rose !5 in the center of tube 23. During this movement arm I2 is held in a definite position with respect to member I8 by spring washer 33. Lateral movement of body member I3 is prevented at this time by rubber pad I? (Figure 3) which extends below the lowermost part of member I8 and is held in contact with the chart by the downward pressure exerted by the user while moving arm I2 and member I8. During this movement the ends of the arm I2 will, if formed of the curved resilient material as hereinbefore noted, spring upwardly from the surface of the chart and hence avoid contact with folds or irregularities in the surface which might alter the angle at which it is set. It is to be understood, however, that if preferred the arm may be used in the fiat form shown in full lines in F;gure 3 of the drawing. When the user views the center point of the compass rose through tube 23, edge 3| of the arm I2 crosses the compass in a line exactly the same as the course plotted upon the chart and the user reads the direction of that course.

It will now become clear that I have provided a thoroughly practical and durable course protractor which is so designed that the user can find the direction of any course with a minimum of eiTort. Furthermore, the device is accurate and requires a minimum of manual setting. I have also provided a device which may be easily and efficiently operated by an unskilled user in small boats which do not have plane surfaces such as chart tables upon which to plot courses.

It will thus be seen that I have provided a thoroughly practical course protractor in which the several objects hereinabove mentioned as well as many others are accomplished. As many possible embodiments may be made of the above invention and a many changes might be made in the embobiment above set forth, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a course protractor, in combination, an elongated body member, means slidably connected to said body member, a resilient member having upwardly curved ends pivotally connected to said first mentioned means, and means formed on said second member adapted to register with a straight line, said last mentioned means being so positioned on said second member that it may be aligned with any line on a chart or across a compass rose.

2. In a course protractor, in combination, a body member, means secured to the under surface of said body member to prevent lateral movement thereof when said course protractor is in contact with a surface, a member slidably mounted on said body member, said member having portions extending around the edges of said body member and abutting against the under surface thereof, said means spacing said bodw member from said surface whereby said member may be slid along said body member without touching said surface, a cross member pivotally mounted on said sliding member, said cross member having a straight edge adapted to be aligned with a course or across a compass rose on a chart, and means adapted to yieldingly retain said cross member in diiferent positions upon said sliding member.

3. In a course protractor, in combination, a body member, an enlarged portion formed on one end of said body member, means secured to the under surface of said enlarged portion and said body member to prevent lateral movement thereof when said course protractor is in contact with a surface, said body member being formed of a resilient metal, a member slidably mounted on said body member, said means spacing said body member from a surface and preventing contact between said sliding member and a surface when said course protractor is placed on a surface, and a cross member pivotally mounted on said sliding member, said cross member having a straight edge whereby said cross member may be aligned with a course or across a compass rose.

4. In a course protractor, in combination, a body member, a straight edge formed on said body member, a member adapted to slide along said body member, two projections formed on said sliding member abutting against said straight edge, resilient means on said sliding member contacting the opposite edge of said body member at a single point, said resilient means holding said projections in contact with said straight edge, whereby said sliding member is held in alignment with said straight edge, a cross member pivotally mounted on said slidin member and resilient means adapted to yieldingly hold said cross member in any desired position on said sliding member.

ROBERT S. BLAIR.

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