1661 Kronan cross-staff (reproduction)

The 1661 Kronan cross-staff reproduction.
Figure 1: The 1661 Kronan cross-staff reproduction.
In 1998 a very special cross-staff was found on board of the Royal Ship Kronan, a Swedish ship that sunk in 1676 of the coast of ÷land in the Baltic sea after fierce battle with the Danish-Dutch fleet. The instrument was stowed away in a chest (see figure 3).

It was the first ever found with the so called spoon shaped vanes. Until then all known cross-staffs, like the cross-staff reproduction I made before, were equipped with straight vanes. The spoon shaped vanes were only known from paintings, cartouches and prints.

In order to be able to make a copy of this instrument I needed to measure it. As the staff has been under water for well over 300 years the wood has become quite fragile, so taking measures of it required a special technique. For this I used photogrammetry, which allowed me to measure the whole instrument with a minimum of physical contact.

In the spring of 2005 I went to the Kalmar Lšns Mmuseum for the measurements. From these measurements I first created a 3D model and from this model I made the CAD drawings necessary to build the copy.

The 1661 Kronan cross-staff reproductionfrom a different angle.
Figure 2: The 1661 Kronan cross-staff reproductionfrom a different angle.
Thanks to cooperation of the NISA (Dutch Institute for Underwater and Ships Archaeology) and the ROB (Dutch National Service for Archaeological Heritage) the wood of the staff was identified as pine (Pinus Spec.). The vanes could not be examined as no loose samples were available, but by the structure of the wood it is believed that these were made of beech (Fagus sylvatica).

Materials used on this reproduction are pine for the staff and beech for the vanes. A second reproduction was made for the Kalmar Lšns Museum where it is suspended above the fragile remains of the original instrument (see figure 4).

Along the same lines as the Kronan cross-staff a third reproduction was made as part of a 17th century navigation set for the rebuilt Dutch factory (trading post) in Hirado. This time the staff was made of ebony and the vanes of pear wood. Whereas the Kronan staff was divided down to a 30 arc minute level, the staff of the Hirado set is divided down to a 10 arc minute level.

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

This is how the Kronan cross-staff was found.
Figure 3: This is how the Kronan cross-staff was found.
 
The reproduction suspended above the original in the Kalmar Lšns Museum.
Figure 4: The reproduction suspended above the original in the Kalmar Lšns Museum.

The horizon vane of the Kronan cross-staff reproduction.
Figure 5: The horizon vane of the Kronan cross-staff reproduction.
 
The vanes can be equipped with this aperture to improve the backward measurements.
Figure 6: The vanes can be equipped with this aperture to improve the backward measurements.

All vanes carry the same signature: the serial between two sea horses.
Figure 7: All vanes carry the same signature: the serial between two sea horses.
 
The Kronan cross-staff is divided down to a 30 arc minute level.
Figure 8: The Kronan cross-staff is divided down to a 30 arc minute level.

The reproduced signature on the staff.
Figure 9: The reproduced signature on the staff.
 
The modern signature on one of the other sides of the staff.
Figure 10: The modern signature on one of the other sides of the staff.

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