46 Captain Hammond


THE PEMBROKESHIRE HERALD FRIDAY JANUARY 30 2015


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IN MY column, I attempt to put


across to the small boat owner or even maybe the interested sea surfer how Mercantile shipping goes about its’ business.


I had a recent ship visit to a vessel


recently on a particular type of trade. That trade involved a North Sea Oil shuttle service to European ports. My intention here is to emphasise how they navigate around our coastal waters and pass on to my readers how they, the ship’s staff try to avoid the small boat sailors!


The ship I was on had, owing to construction of a bow loader for taking on crude oil, limited visibility forward from the ships bridge. There were a number of sectors of limited visibility around the vessel again, owing to ship’s construction, therefore on discussing keeping a safe navigational watch with the ship’s navigating officers, their view was that radar targets within the 6 mile range on their screens demanded their attention. Keeping a lookout for these targets until subsequently deemed no risk of collision exists is a full time concern. Lookout here means primarily visual sighting. In my view, most Watch Officers want to avoid close quarters situations with other vessels, as especially small craft encountered could be lost in a blind or limited visibility sector alluded to above. So, how does the Seaman, (you


and me, not anybody else!) avoid marine accidents? I have been called a pessimist in my time, but rather be a pessimist on navigational watch until proved otherwise. Expect an approaching vessel not to have spotted you and consider avoiding action


Can I see you?


following recognized steering and sailing rules. Tankers can range in size of capacity from several hundred tons, which includes vessels for servicing small harbours and coastal settlements, to several hundred thousand tons, for long-range haulage. Besides ocean- or


seagoing tankers there are also


specialized inland-waterway tankers which operate on rivers and canals with an average cargo capacity up to some thousand tons.


The Thomas W. Lawson (1902),


converted in 1906 into the world's first sailing tanker. Tankers are a relatively new


concept, dating from the later years of the 19th century. Before this, technology had simply not supported the idea of carrying bulk liquids. The market was also not geared towards transporting or selling cargo in bulk, therefore most ships carried a wide range of different products in different holds and traded outside fixed routes. Liquids were usually loaded in casks— hence the term "tonnage", which refers to the volume of the holds in terms of how many tuns or casks of wine could be carried. Even potable water, vital for the survival of the crew, was stowed in casks. Carrying bulk liquids in earlier ships posed several problems: The holds: on timber ships the


holds were not sufficiently water, oil or air-tight to prevent a liquid cargo from spoiling or leaking. The development of iron and steel hulls solved this problem.


Loading and discharging:


Bulk liquids must be pumped - the development of efficient pumps and piping systems was vital to the development of the tanker. Steam engines were developed as prime- movers for early pumping systems. Dedicated


cargo handling facilities


were now required ashore too - as was a market for receiving a product in that quantity. Casks could be unloaded using ordinary cranes, and


the awkward nature of the casks meant that the volume of liquid was always relatively small - therefore keeping the market more stable. Free Surface Effect: a large body of liquid carried aboard a ship will impact on the ship's stability, particularly when the liquid is flowing around the hold or tank in response to the ship's movements. The effect was negligible in casks, but could cause capsizing if the tank extended the width of the ship; a problem solved by extensive subdivision of the tanks. Tankers were first used by the


oil industry to transfer refined fuel in bulk from refineries to customers. This would then be stored in large tanks ashore, and subdivided for delivery to individual locations. The use of tankers caught on because other liquids were also cheaper to transport in bulk, store in dedicated terminals, then subdivide. Even the Guinness brewery used tankers to transport the stout across the Irish Sea. Different products require different handling and transport, with specialised variants such as "chemical tankers", "oil tankers", and "LNG carriers" developed


to handle dangerous


chemicals, oil and oil-derived products, and liquefied natural gas respectively. These broad variants may be further differentiated with respect to ability to carry only a single product or simultaneously transport mixed cargoes such as several different chemicals or refined petroleum products. Among


oil tankers, supertankers are designed for transporting oil around the Horn of Africa from the Middle East. The supertanker, Seawise Giant, scrapped in 2010, was 458 meters (1,503 ft) in length and 69 meters (226 ft) wide. Supertankers are one of the three preferred methods for transporting large quantities of oil, along with pipeline transport and rail.


Many modern tankers are designed


for a specific cargo and a specific route. Draft is typically limited by the depth of water in loading and unloading harbours; and may be limited by the depth of straits along the preferred shipping route. Cargoes with high vapour pressure at ambient temperatures may require pressurized tanks or vapour recovery systems. Tank heaters may be required to maintain heavy crude oil, residual fuel, asphalt, wax, or molasses in a fluid state for offloading. Tankers used for liquid fuels are classified according to their capacity. Even if this article highlights that visibility from some ship’s bridges is strictly limited and I have passed this point on, then I am satisfied my ship visits are worthwhile.


It is well to remember to put ourselves as the bridge watchkeepers aboard larger ships. Common sense or Seamanship dictates that ships like those above around our coast have a compelling duty to keep a good lookout by all available measures. Good sailing!


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