Navigatie-instrumenten van de zeebodem, 16e tot 19e eeuw

Navigational instruments from the bottom of the sea, 16th to 19th century In the last twenty years diving activities of private persons have increased considerably. This has lead to an increasing number of historical objects retrieved from ship-wrecks. Some wrecks have yielded navigational instruments. This article investigates the contribution diving has made to the knowledge of navigational equipment and what is still to be expected. The article concentrates on Dutch material dating from between the end of the 16th century, marking the beginning of Dutch maritime expansion, and the beginning of the 19th century. Among the objects from wrecks which gave considerable information are sounding leads. Especially interesting, both in number and variety, are the leads from the Dutch VOC ship Hollandia (sunk 1743). Compasses are among the instruments rarely found in wrecks. Probably this is mainly due to the materials of which they were made. Examples found are usually incomplete or disintegrated, due to seawater. Knowledge acquired from archives and printed sources indicates that several types of compasses, of which so far as known no copy survived on land, may still be found in wrecks. Many wrecks, both Dutch and foreign, have yielded dividers. By comparing those finds with our knowledge of what the Dutch East Indies Company ships were equipped with, we now have a fairly accurate insight in the types of dividers which were used on the ships of the Company. Much has been learned about instruments for the measurement of the altitude of heavenly bodies. The number of known mariner's astrolabes has, mainly through wreck excavation, increased from 21 in 1966 to 62 in the Spring of 1987. Among the recently found copies are several Dutch ones. They have taught us about the Dutch contribution to the development ofthese instruments. More finds could increase the still scanty information on Dutch makers. To a lesser extent, the same can be said about cross-staffs. Hardly more of these (73 known to the author in mid-1987) than of mariner's astrolabes, have survived the ages. Many are kept in museums and are consequently in a reasonable condition. Nevertheless, staffs from wrecks have supplied additional information. E.g. from the wreck of the Dutch St. Michael (sunk 1747) in which a Dutch made cross-staff was found. It is the only staff presently known to be divided to a maximum accuracy of 2'. The staff found in the wreck of the Spanish Nuestra Senora Atocha (sunk 1622) promises to be the missing link between existing cross-staffs from 1597 and 1677. Hardly spectacul