celestial navigation compus (marine, industry , maritime, shipping navigation compus)- navigation compus (marine, industry , maritime, shipping navigation compus)by observation of the sun, moon and stars, and sometimes planets pilotage - using visible natural and man made features such as sea marks and beacons dead reckoning - using course and speed to determine position Off-course navigation compus (marine, industry , maritime, shipping navigation compus)- allows for variables in heading by deliberately aiming to the one side of the destination. electronic navigation compus (marine, industry , maritime, shipping navigation compus)- using electronic equipment such as radio navigation compus (marine, industry , maritime, shipping navigation compus)and satellite navigation compus (marine, industry , maritime, shipping navigation compus)ystem to follow a course to a waypoint Also Electronic Chart Display and Information System position fixing - determining current position by visual and electronic means collision avoidance using radar

In the province of Drente about years ago a dugout canoe was found which could be dated by radio­carbon at , years old. The canoe, made of fir, was therefore placed in the Mesolithic Age, a period from which until then only paddles were known from Maglemose culture, for instance from Denmark. The canoe from Pesse has been softened by burning in order to get the right shape. It is a small object, about three meters long. It is the oldest complete canoe so far found in Europe.

Last year a shipwreck was found near to Tiel in the Centre of the Netherlands, which was supposed to be of Roman date. By radiocarbon dating this was shown to be true. It had the typical construction wiiron nails known from the Roman ship remains excavated by Peter Marsden on the Thames some years ago.

Once the voyage has begun the progress of the vessel along it planned route must be monitored. This requires that the ship's position be determined. Traditional maritime navigation compus (marine, industry , maritime, shipping navigation compus)wia compass uses redundant sources of position information to determine the ship's position. A navigator uses the ship's last known position and dead reckoning, based on the ship's logged compass course and speed, to calculate the current position. If the set and drift, due to tide and wind, can be determined, an estimated position can also be calculated.

Celestial navigation compus
Main article: Celestial navigation compus
Celestial navigation compus (marine, industry , maritime, shipping navigation compus)ystems are based on observation of the positions of the Sun, Moon and stars relative to the observer and a known location. Anciently the home port was used as the known location, currently the Greenwich Meridian or Prime Meridian is used as the known location for celestial charts.

Timekeeping requirement
Accurately knowing the time of an observation is important. Time is measured wia chronometer, a quartz watch or a shortwave radio broadcast from an atomic clock. Without accurate time it is still possible to determine one's latitude by observing the highest point the sun makes in the sky each day - known as local noon.

A quartz wristwatch normally keeps time within a half-second per day. If it is worn constantly, keeping it near body heat, its rate of drift can be measured withe radio, and by compensating for this drift, a navigator can keep time to better than a second per mon.

The angle is measured wia special optical instrument called a "sextant" (and prior to that withe more limited octant). Sextants use two mirrors to cancel the relative motion of the sextant. During a sight, the user's view of the star and horizon remains steady as the boat rocks. An arm moves a split image of the star relative to the split image of the horizon. When the image of the star touches the horizon, the angle can be read from the sextant's scale. Some sextants create an artificial horizon by reflecting a bubble. Inexpensive plastic sextants are available, though they have less accuracy than the more expensive metal models.

GPS uses 3D trilateration based on measuring the time-of-flight of radio waves using the well-known speed of light to measure distance from at least three satellites. This can be accomplished using low-cost quartz clocks because the satellites send time correction signals to the GPS receivers.

However, most wrecks have been found in the Zuiderzee area during land reclamation after the dam closed the Zuiderzee and dikes made it possible to reclaim the Wieringermeerpolder (, acres), the Noordoostpolder (, acres), Oostelijk Flevoland (, acres) and since Zuidelijk Flevoland (, acres). In this ancient Zuiderzee area the dike for the last polder, the Markerwaard (, acres), is under construction. By these reclamation works, where dikes, canals and ditches are dug and later drainage and irrigation work is done, many archaeological objects are found, among them many wrecks. To date more than wrecks have been registered, of which are in Wieringermeerpolder, in the Noordoostpolder and more than in the polder which is under cultivation now. In the part that will remain a fresh water lake, souof the enclosing dam, some more wrecks have been found by fishermen. Until now these wrecks have not been studied under water because of the very muddy bottom which obscures visibility beyond a few centimeters. The water is rich in plankton and clay and the wrecks are completely covered by sand and mud, so that it is very difficult to study this material without draining.

to do the excavations on dry land in a systematic way. It has been possible to work out a system whereby the sinking of the ships into the subsoil can be studied. As soon as the ship comes to the seabottom it disturbs the normal conditions of the layers through which it sinks and meanwhile the sediments which are washed out by this sinking ship are deposited again in and around the wreck and new sediments cover the wreck site. It is possible to recognise the first undisturbed layer and to date this one from after the wreck. It is true that it is not possible to date the ships from their construction, which varies considerably. Therefore the dating of the period at which the ship sank is decided by examining the material in the ship: coins, clay pipes, pottery, etc. In this way we can date the wreck accurately to within or even years.

So the first thing to do is to excavate the ship, leaving undisturbed cross sections the lengand breadof the wreck so that the disturbance in the layers can be studied and drawn. Because the ship is buried a detector is sometimes used to locate the wreck. This detector does not work on metals but on changes in the subsoil so that disturbances can be detected. In this way it is possible to know in advance the situa­tion of the ship so that the excavation can be planned. The dating of the layers is useful for the study of the soil because the sedimentation history is rather complicated. More than twenty layers of different periods can be distinguished after the Ice-Age about , years ago brought the boulder-clay from

Scandinavia to southern regions. Parts of the layers can be dated by remnants of old habitations (also wiradiocarbon and pollen analysis), other parts of the newer layers are to be dated by the shipwrecks or by closed finds of materials from ships.

A second facet of the ship excavations is the study of cultural history using all the material which is found on board the wrecks. For this purpose the system of excavating is important as well, because it has to be determined whether all the material found in the wreck really belonged to the ship. It is possible that materials lost from ships that sailed over the wreck were washed into the wreck during the period when it was not completely covered wisediment. There is the possibility that the currents brought other material on board during the short period while the wreck was sinking into the sediment. But material on the bottom of the ship can be distinguished from what is in one of the disturbed layers. So there can't be made a mistake in dating. The newest material gives the dates of the wreckage and of the layers of the soil. If nothing is found on board the ship the disturbance line can be used for dating, because all the layers have been dated already.

There are also considerable differences between the two Skuldelev trading ships. The smaller of these is of oak, about . m long and . m broad, wian open hold amidships, where the mast has been firmly stepped in the keelson without the big mast-fish which is found in Norwegian Viking ships. The ship has had a half-deck fore and aft. Here, there were some narrow thwarts as in the warship, for oarsmen rowing wioars that passed through oarholes in the gunwale strake. The number of oars in this, a cargo ship, was far less though. There are oarholes on the port side at the forward end, and two starboard; while at the after end there appears to be only one oarhole at each side. But of these oarholes, only bear distinct traces of wear. Therefore the normal crew has not normally exceeded to men. This ship is presumably the Viking period's coaster type: a small cargo boat used in the Baltic and the NorSea. It is light, so that it could be hauled over land for short distances, and it could also sail far up rivers. The Skuldelev find's big cargo boat is the first ship to be reassembled at Roskilde. It measures circa . m in lengand . m in bread. It is built of pine planking, while the keel and the lowest portions of the internal timbers are of oak, and the upper portions of lime and pine. This ship is very different to the other ships in one respect. Whereas the elements of these are fashioned on slender lines for utmost resilience to make them easy for hauling ashore, the large cargo ship is heavily built wisturdy frames - designed first and foremost to withstand the battering of rough seas.