Archive | Marine

The difference between a map and a chart

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Chart

A nautical chart has a very detailed and accurate map of the coast line, also taken into account with these maps are variations in tidal levels and water forms, this can be critical to anyone who is trying to navigate.

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Also a chart is a working document, it is used to plot out the courses for ships. These charts show a unique set of characteristics which helps navigation, some of them characteristics are a draft, bottom clearance, wrecks and obstructions which can lead to an accident if not correctly navigated away from. The map also has landmarks on it, this can be good if you get lost they can  then be used  as a reference and can  also be used if a change of course is needed.

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Another thing it shows you is the surface area beneath the sea, this cannot be seen by the human eye, and prevents many accidents.

Map

A map is only used basically for land, a map cannot be used to plot a course for a ship as the only image of the sea is at sea level. A map gives a pre plotted course, for example, a road, something which is normally followed. Also a map doesn’t count for what type of vehicle you are in, if you look for the quickest route but you are in a lorry and you have to  navigate tight bending roads then that would be a problem.

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Maps offer no reference to what the ground below is like, if a road had road works on it, you wouldn’t know because a map is a static document. It leaves it up to you to go to that road then make a visual assessment, normally by that time it is too late and you are forced to go navigate around it  or turn back. New maps do have some of this information but very rarely as the state of a road can change rapidly.

What marine GPS is right for you?

Marine GPS’s is one of the best investments you can get when you have a boat, it is a map which can constantly be updated by software downloads. This is extremely important because the sea can change just like that, for example, a storm might disrupt the sea surface below. Your map might say that it is 25ft deep but the storm  has now changed it to 15ft, this can be dangerous to a boat, so the GPS calculates the new measurement of the seas surface.

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When buying a marine GPS, the first thing you should make sure it is waterproof, this is a very important factor when purchasing one. Since the waves can be very unpredictable at some stages, it isn’t worth taking the risk on breaking the GPS the first time you buy it. Also another important thing you should consider when buying a GPS is the screen, firstly the size, make sure the size of the screen is suitable for your needs. If it is touch screen, make sure it is big enough for your fingers to clearly press against it. Also make sure it works under bright light and at night, sun light can make some GPS tough to read but there are screens out there which don’t get effected by this.

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What will you use your GPS for? this is a question which should be asked straight away, if you only need it for mapping out the ocean, then a normal GPS will be fine. If you need it for fishing and finding where the feedings grounds are, then a normal GPS might not be right for you. You might find a GPS you really like, but then find it doesn’t have what you need software wise, but don’t stop there. You might find that there is software  available which will make your choice the correct one. So before buying a GPS, do some research and make sure it handles the thing you need.

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If your stuck for information and you can’t find a map, I recommend this site: http://www.nauticalcharts.noaa.gov

What is a Nautical Chart?

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A Nautical Chart is a graphical representation of the marine environment, this provides the reader with the basic elements of the coast, like a blueprint of the sea. A chart is used as a road map for the sea really, which makes this type of map essential for navigating a boat. Another good thing about a nautical chart is that it allows you to be very economical and can potentially save you a lot of money. It allows you to pre plot your course, which allows it to be the safest and the cheapest, this is because it has all the information on the map needed to do so, the map shows, sea levels, wrecks etc… Which allow you to plot a safe course.

A very important part of a marine map is the marine depths it shows, this is extremely important to a navigator in a big ship. If they get it wrong on the navigation and go over a to shallower piece of land, the ship could hit the bottom and capsize. On a nautical chart the depths are marked with numbers, normally they have a key down the side explaining the levels. Colours can also be used to show how deep a depth is, they will be accompanied with a number but generally a colour scale or some sort of lines to.

How to use a nautical chart

A nautical map should always have a scale, especially if it is going to uses a navigation map. The scale is usually found in a free space on the map, normally around the edge some where. It is quit simple to measure how far you will be traveling, you can take a ruler or another measuring device and put it on the starting point and ending point. Then measure how long the distance is, then compare it to the scale. `

Compass

The map will have a compass heading on it, this will give the directions for; north, south, east and west. All you have to do to find out what direction you are going in is, find the end point of you journey. Then imagine putting your compass on your starting point of the map and looking at your end point, the direction the end point is from your starting point will give you the compass direction, e.g. if its directly right, thats east.

Nautical Depths

All nautical charts will have depths on them, this is quite possibly one of the most important parts of the maps, these depths give the boat driver a scale of how deep the water is in the areas he wants to travel in. It will give you a number in a area which will tell you how deep the water is. A lot of charts mark these differently, there will always be numbers but some times there will be a colour key with that or lines will mark out when it gets deeper or shallower.

The Map Key

Allot of nautical charts will come with a key, these keys are very important and can prove to be very useful and life saving. Combining this with the depths it is the best way to plot your route, for example if you are coming towards a buoy and on left is shallow water and on the right is deep water, you are going to go right because it is more safer. Also it displays ship wrecks or any crashed vessels, these are a must to avoid unless the water is that deep the vessel can go over the top of it safely.

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