Notes on the Dimensions of Semaphore Signal Posts.

Based on drawing S210 (28-2-1901).

Semaphore posts must have been a costly item, and thus for any location the shortest post consistent with appropriate visibility would have been used.

Posts were square in section and tapered to 7″x7″ at the top to fit the finial. In reality the post top was rebated so that the finial fitted as a cap. In these notes measurements are quoted to the base of the finial. All measurements from signal arms are from the centreline of the arm.

Single arm signals:

For all posts the arm was 1’3″ below the top of the post. The corners of the post were chamfered from 5’ above ground level to 2’9″ from the top of the post. Other post dimensions are given in table 1.

Table 1 Dimensions of single arm posts

Post

Height of arm centreline above ground

Dimension of post 1’ below ground level

Post A No 1

18’

10″x10″

Post A No 2

23’

10″x10″

Post A No 3

28’

10″x10″

Post A No 4

32’

10″x10″

Post A No 5

36’

12″x12″

Post A No 6

40’

12″x12″

Two arm signals: 

For all posts the top arm was 1’3″ below the top of the post. The lower arm was 6’ below the upper. The corners of the post were chamfered from 5’ above ground level to 1’6″ below the lower arm and from 1’6″ above the lower arm to 1’6″ below the upper arm. Other post dimensions are given in table 2.

Table 2 Dimensions of two arm posts

Post

Height of top arm centreline above ground

Dimension of post 1’ below ground level

Post B No 1

23’

10″x10″

Post B No 2

28’

10″x10″

Post B No 3

32’

10″x10″

Post B No 4

36’

12″x12″

Post B No 5

40’

12″x12″