1623 Hoekboog (reconstruction)

The 1623 Hoekboog reconstruction.
Figure 1: The 1623 Hoekboog reconstruction.
After finishing the 1618 Demi-cross reconstruction I continued with yet another navigational instrument that no longer exists: the hoekboog or "double triangle". It is not known who invented the hoekboog, but alike the demi-cross it has been mainly depicted by Blaeu in the early years of its existence (see figure 2).1

The instrument is of the same size and has similar features as the Davis Quadrant, but has chords instead of arches. The chords are divided in 60 (upper triangle, see figure 4) and 30 degrees (lower triangle, see figure 8), a ratio also found on period Davis Quadrants.

Although the instrument has been described for at least 91 years by a variety of authors, only two fragments of them survived. Based on these fragments and the descriptions and images found in those period works I made this reconstruction.

The 1623 Hoekboog depicted by Blaeu (collection Het Scheepvaartmuseum, Amsterdam).
Figure 2: The 1623 Hoekboog depicted by Blaeu (collection Het Scheepvaartmuseum, Amsterdam).
After four years of research, I finally was confident enough to create two different versions of the instrument, which took me about 70 hours each. Now the instruments should be a 95% accurate reconstruction of the originals, showing two stages in its development. The difference between them is the width of the main beam (see figure 6). Initially the instrument was made with a half an inch wide main beam, but during the 17th century this was increased by about 50%.

Materials used on this reproduction are ebony for the frame and scales and pear wood for the vanes. In addition to that the horizon vane is painted white on one side (see figure 5 and figure 6).

An article on the instrument has been published in the March 2011 edition of the Bulletin of the Scientific Instrument Society.1

Notes

[1]: For a full description of the instrument see: N. de Hilster, 'The Hoekboog: a Reconstruction', in: Bulletin of the Scientific Instrument Society No. 108, (2011), pp.20-33.

If you have any questions and/or remarks please let me know.

The sight vane of the hoekboog at 14░-50'.
Figure 3: The sight vane of the hoekboog at 14░-50'.
 
The shadow vane of the hoekboog at 30░. The 60░ chord is divided in 10░ sections.
Figure 4: The shadow vane of the hoekboog at 30░. The 60░ chord is divided in 10░ sections.

The horizon vane of the hoekboog.
Figure 5: The horizon vane of the hoekboog.
 
The two reconstructions show different frame widths.
Figure 6: The two reconstructions show different frame widths.

The frame is asymmetrical to allow the vanes to 'grab' it.
Figure 7: The frame is asymmetrical to allow the vanes to 'grab' it.
 
The 30░ chord is divided in 15' sections (the vane is here at 15░-05').
Figure 8: The 30░ chord is divided in 15' sections (the vane is here at 15░-05').

The signature on the hoekboog reconstruction.
Figure 9: The signature on the hoekboog reconstruction.
 
All vanes carry the same signature: the serial between two sea horses.
Figure 10: All vanes carry the same signature: the serial between two sea horses.

Celestial Navigation Coastal Navigation Distance measurement
1580s Mariner's astrolabe 1590 Hood's cross-staff 1618 Demi-cross 1623 hoekboog 1660 spiegelboog 1661 Kronan cross-staff 1720 Hasebroek cross-staff 1734 Davis quadrant Early 19th c. ebony octant Late 19th c brass octant 1941 U.S. Navy quintant Hirado navigation set