With all the different types of transportation, shipping still remains one of the top methods. Shipping can be arranged either through a regular liner or through tramp services, which do not have a fixed schedule. Able to suit different needs and functions, these two services have long been the lifeblood of the vast transportation market. Liners carry goods in large quantities from merchants and consignors. Tramp ships, on the other hand, often carry cargo on a more random, per-load basis.
As time progresses, so does the size, science and structure of ships. Today, they are relied upon for an assortment of tasks that still cannot be done as successfully through other means. The primary advantage of ships is their ability to carry tons of merchandise and equipment. They transport many of the world's finite resources, including oil and coal.
The secondary advantage of liners and tramps is their low cost. Transporting goods across the sea is much cheaper than carrying them through the air, mostly due to the massive quantities that can be delivered at once with a tramp or liner. Shipping via air cargo would require several planes --- costing much more in fuel --- to equal the load of a ship.
Unfortunately, liners and tramps have disadvantages too. Although ships are better than planes for cargo loading, they are much slower than aeroplanes. Liners and tramps can travel for days and even weeks to deliver cargo. In many industries where time is of the essence, this can be a central issue. Although rare, problems with sinking or crashes can occur. Tankers that carry oil can cause a significant environmental impact if a catastrophic event takes place.