How do you determine ship position?
If there is an object, which will reflect the wave back to the radar, the computer set up of the radar will determine the distance between the ship and the object along with its location. Hence, it can be said that the radar basically reads two things – The position of the object and the direction of the same.
If there is an object, which will reflect the wave back to the radar, the computer set up of the radar will determine the distance between the ship and the object along with its location. Hence, it can be said that the radar basically reads two things – The position of the object and the direction of the same.
One of the simplest methods for determining a ship's direction was to watch the movement of the sun across the sky. Sailors used the position of the sun as it moved from east to west to guide their route. At noon, they could determine north and south by the shadows the sun cast.
The ship's course line or “track” is a straight line drawn on a chart in the direction of it's course. It has arrow heads pointing in the direction of the course and the course is written in along the track.
The most commonly used method to determine position is then the classic terrestrial method based on bearings to landmarks (identified characteristic points) with known coordinates. Bearings are determined based on the recorded image of landmarks. Registration can be done using either vision or radar systems.
We identify a fixed object and draw a line parallel to our course. We then monitor the echo of this object on the radar. If the echo stays on the line drawn parallel to the course, we are on our course. If the echo deviates from the line, we are off track and we must alter the course to bring the vessel on track.
The earliest navigation methods involved observing landmarks or watching the direction of the sun and stars. Few ancient sailors ventured out into the open sea. Instead, they sailed within sight of land in order to navigate. When that was impossible, ancient sailors watched constellations to mark their position.
In later uses, the astrolabe was used beyond astronomy as a tool for sailors, and thus dubbed the mariner's astrolabe. Sailors could use this tool by lining it up with the sun or a specific star in relation to the horizon to understand latitude vertically. This helped them determine their location while at sea.
The navigator uses the celestial bodies to determine his location. With Coastal navigation, the navigator uses the shape of landmarks along the coast, and the direction of the coastline. With Inertial navigation, you use motion sensors to calculate your new position relative to the starting position.
- The front of a boat is called the bow, while the rear of a boat is called the stern.
- When looking towards the bow, the left-hand side of the boat is the port side.
- And starboard is the corresponding word for the right side of a boat.
What are the 3 basic ship motions and its directions?
Ship motions in waves
Three are translatory motions of the whole ship in one direction: (1) surge is the oscillation of the ship fore and aft; (2) sway is the motion from side to side; and (3) heave is the up-and-down motion.
Parallel indexing is a technique used as a measure to monitor the progress of a vessel on the track and to minimise the cross track distance and to keep vessel at a safe distance from the shoreline or rock.
Dead reckoning is a technique to determine a ship's approximate position by applying to the last established charted position a vector or series of vectors representing true courses and speed through the water.
A global positioning system (GPS) receiver is a display system used to display the location of a ship using a global positioning satellite in earth orbit. By recording the ship's position, you can calculate the speed, course and time required to cover the distance between the "two marked positions".
a) Parallel indexing and use of clearing bearings; b) Use of radar to check the accuracy of the charted position by comparing the location of the radar target against the charted symbol; c) Visual cross bearings; Obtaining a three-bearing fix.
The most accurate fixes occur when the position lines are at right angles to each other. Fixes are a necessary part of navigation by dead reckoning because dead reckoning relies on estimates of speed, course.
Main goal of ECDIS introduction on board the vessels was to lessen the workload and improve navigation safety. GNSS derived position must be checked - no question about it, but cross- checking it every 3 minutes is like moving back to paper charts age.
In the early days of sailing the Vikings would release a bird to fly above the ship. If the bird flew up above the ship and circled randomly then there wasn't any land near. If the bird flew with a purpose away from the ship then the ship would follow in hopes of the bird finding land.
Pirates would work out their longitude by seeing which direction was north and then guessing how far they had travelled east or west. Pirates made compasses at sea by stroking a needle against a naturally magnetic rock called a lodestone. Having a compass helped, but the most useful of all was a sea chart.
Common answers include – watch, clock (which were not reliable at sea due to the rocking and rolling of a ship), stars and sundials (which aren't consistent due to ship's movement and changing weather).
How does a sextant tell you where you are?
sextant, instrument for determining the angle between the horizon and a celestial body such as the Sun, the Moon, or a star, used in celestial navigation to determine latitude and longitude. The device consists of an arc of a circle, marked off in degrees, and a movable radial arm pivoted at the centre of the circle.
The magnetic compass, originally invented in China, allowed sailors to steer a ship in the right direction.
The sextant is an instrument that uses reflecting mirrors to determine the distance between a celestial object (sun, moon, planet, star) and the horizon, in order to calculate the latitudinal position of the vessel.
The astrolabe was used to determine latitude by measuring the angle between the horizon and Polaris, also called the North Star, the Pole Star, or Stella Maris (Star of the Sea).
We get the position line by calculating the azimuth of the celestial body. The position line is 90 degrees from the azimuth. We also need the position from which to draw this position line. This is calculated by using the Zenith distance of the body, which we can get from the altitude of the body.
Ordinary seaman
The lowest ranking personnel in the deck department. An ordinary seaman (OS) generally helps out with work that able seamen do.
Most sailors were right handed, so the steering oar was placed over or through the right side of the stern . Sailors began calling the right side the steering side, which soon became "starboard" by combining two Old English words: stéor (meaning "steer") and bord (meaning "the side of a boat").
The command "hard a-starboard" meant the wheel had to be turned to the left and not, as the instruction would suggest, to the right. Steamships, on the other hand, steered like cars. You moved the wheel to the right and the ship took the same direction. Not all steamships followed these rules, however.
At first glance, the ocean may appear flat, but it is anything but. A closer view offers a better look at the wind, currents, and wave action that influence how a ship moves in six degrees of motion: heave, sway, surge, roll, pitch, and yaw.
When a boat leans to one side, it is called listing. Listing occurs when the weight of the boat is unevenly distributed, causing it to tilt in one direction. This can be caused by a variety of factors, including an uneven load, improper ballast, or a damaged hull.
What is it called when a ship tilts?
When a ship tilts, it is called "heeling" or "rolling."
If another vessel is approaching you from the port — or left — side of your boat, you have the right of way and should maintain your speed and direction. 2. If a vessel is aiming to cross your path and they're on your starboard — or right — side, they have the right of way.
Ships can dock on either port or starboard side, depending on the layout of the port itself, the direction you are sailing in, and individual government regulations about how cruise ships can be arranged on a pier. It's also often at the discretion of the captain to choose how to position the ship in port.
You should pass at a safe distance to the port (left) or starboard (right) side of the other boat. If a safe route exists, you should always attempt to pass the boat on the starboard side.
Almost all radars use a directive antenna—i.e., one that directs its energy in a narrow beam. (The beamwidth of an antenna of fixed size is inversely proportional to the radar frequency.) The direction of a target can be found from the direction in which the antenna is pointing when the received echo is at a maximum.
Dead Reckoning or DR as it is usually referred, is the process by which one's current position is calculated based on/using a previously obtained position. A previously determined position can also be termed as a fix; the estimated speed and the course are applied to that fix to obtain a DR.
It's widely known that RADAR systems are not able to detect stationary objects, only moving ones. Actually, they are are to detect them but just not where they come from, so a barrier in the middle of the road and a traffic sign on the side of the street, they would look like the same to the RADAR system.
The basic principle behind radar is simple - extremely short bursts of radio energy (traveling at the speed of light) are transmitted, reflected off a target and then returned as an echo. Radar makes use of a phenomenon we have all observed, that of the ECHO PRINCIPLE.
Accuracy and Acceleration Limits
Under ideal conditions most police radars are accurate to about ±1 mph. Microwave moving mode radar also measures patrol vehicle speed to an accuracy of about ±1 mph. Moving mode target vehicle accuracy is ±2 mph.
The magnetic compass is used by sailors to find direction.
What is the dead reckoning position?
Dead reckoning (deduced reckoning) is the process of calculating current position by using previously determined reference position and advancing that position based upon known or estimated speeds over elapsed time and course.
ORIENTATION MODE
There are three orientation modes the navigator may choose from when setting up the radar: North-up, head-up and courseup.
Since radar can more accurately determine ranges than bearings, the most accurate radar fixes result from measuring and plotting ranges to two or more objects.
