| Instrument | : | Master Hood's cross-staff |
| Manufacturer | : | N. de Hilster (Original Master Thomas Hood). |
| Country of origin | : | The Netherlands (Original United Kingdom) |
| Manufacturing year | : | 2007 (Original: 1590) |
After finishing the demi-cross reconstruction I continued with the next one on my list: Master Hood's cross-staff. It was invented by Master Hood in 1590, who wrote that the instrument had two purposes: "… to take the height of the Sunne and Starres…" and to "…take the length, height, depth or breadth of anything measurable…". So this instrument was designed for both navigation and land surveying. Similar instruments for land surveying did exist before 1590, but these were either for land surveying only or combined with astronomical functions for use on land. Master Hood's cross-staff had to serve the navigator at sea as well and that in a unique way.
The instrument has similar features as the cross-staff, but due to its shape it was thought to be more accurate in both applications mentioned above. In the first place the scale divisions were much farther apart than on the cross-staff and in the geometrical application it was more accurate as the staffs could be aligned with the object to be measured. Thanks to this Master Hood's cross-staff would directly give the dimensions from the proportions, while the cross-staff would only give us an angle.
Not only was it a land surveying instrument made ready for use at sea, but it also incorporated a new feature: measuring the sun's altitude using its shadow. Although the use was still in a forward manner this instrument influenced a number of people to development a wide range of shadow casting navigational instruments like the demi-cross, a development that would finally result into the Davis Quadrant.
Although the instrument has been described by two authors (Thomas Hood and Thomas Blundeville) for at least 32 years, none of them survived. As none are left I made this reconstruction using the information both authors left in their books.
After a year of research, building the instrument took me about 50 hours. Now the instrument should be a 95% accurate reconstruction of the original.
On November 5th, 2007 a field test was carried out in order to judge the usability and accuracy of the instrument. We tried both shadow measuring methods as described in the period literature. During half an hour we managed to get 5 fixes, 3 of them in excess of 8 degrees off. The other two were fixed using the help of a second observer who held the instrument horizontally. The first observer then only had to deal with aligning the two staffs with the sun and reading the instrument. Despite all that the measurements were off by 20.3 and 33.6 arc minutes, something that could easily be achieved with an astrolabe with less effort. All these observations were done on land, being at sea on a rolling vessel must have made things only worse.
Materials used on this reproduction are ebony for the staffs and brass for the vanes and screws.
I'm very grateful to Peter Ifland for introducing me to the instrument several years ago (through the work by Thomas Blundeville) and Robert Hicks for introducing me to the book by Thomas Hood. In addition to that Diederick Wildeman and Anton Oortwijn (both Scheepvaartmuseum Amsterdam) and Sjoerd de Meer (Maritiem Museum Rotterdam) supplied me with lots of information on this instrument and other contemporary instruments by allowing me to study period literature.
If you like to know more, don't hesitate to contact me.