航海学3期末考试简答题答案

1,Gnomonic chart can be used to design a passage plan of ocean route. Please describe the steps which should be followed when use a gnomonic chart to design a passage plan of ocean route.

①Easy method but is not very exact

②Any great circle appears as a straight line.

③Consulting NP 131, choose corresponding Gnomonic charts.

④Draw a straight line connecting the point of departure and the destination on the chart.

⑤Inspect it to see that it passes clear of all dangers to navigation.

⑥If this requirement is met, the courses are then transferred to a Mercator chart by selecting a number of points along the great circle, determining their latitude and longitude and plotting these points on the Mercator chart.

⑦These points are then connected by straight lines to represent the rhumb line courses to be steered.

2，Gnomonic chart can be used to design a passage plan of ocean route. Please describe the steps which should be followed when use a gnomonic chart to design a passage plan of ocean composite route.

①Refer to relative navigation publications, determine the reasonable limiting latitude φL.

②From the departure A and destination B make the straight lines AM and BN tangent to the limiting latitude, and they are two great circle routes, the line between the two points of tangency M, N is limiting parallel track.

③Determine every rhumb line’s course and distance in the two great circle tracks.

④The course of parallel route course is 090°or 270 °, the distance could be measured in navigational chart.

⑤Make a table using the every rhumb line course and distance for next voyage.

3，The factors to be considered for ocean route choice.

①Meteorological conditions②State of the sea③Obstructions④Fixing and navigable water area conditions⑤Own ship conditions⑥Navigation regulations

4，The notes should be covered during ocean navigation.

①Do not ignore Dead reckoning②Use any resource to fix position③Note the safety problem when approaching shore④Receive and analyze forecast and weather facsimile⑤Receive navigational warning on time ⑥Adjust ship’s mean time (SMT) in time⑦Apply the position plotting charts⑧Select a suitable speed

5，There are four routes are usually chosen while in ocean navigation, please describe them.

①Great circle route②Rhumb line route③Parallel route④Composite route

6，List these factors to determine the safe distance off dangers during coastal navigating.

①The distance and time to a danger calculated from the final precise ship position

②Mapping accuracy near the dangers (high or low)

③Whether there are obvious objects or marks for fixing position or avoiding dangers

④Visibility conditions when transiting the dangers ( day or night)

⑤Winds and currents ( onshore or offshore )

7，The minimum safe depth of water required for passing through shoals may be related to some factors, please describe them.

①draft of departure②reduced draft because of consumption of oil and water (cm) ③changes of mean draft due to the specific gravity of seawater ④Increased draft due to transverse inclination or heel