I was interested to read the correspondence on the above subject and think that some clarification is required. Both registration and tonnage are often misunderstood even, I am sorry to say, by some marine surveyors. Registration is a legal requirement for merchant ships over 15 tons gross. It does not apply to warships or vessels of ‘primitive build’. It is written, like tonnage, into International, European and British law and cannot be changed at the whim of an owner or marine surveyor. Tonnage has nothing whatever to do with the vessel’s mass, weight or displacement but both gross and nett figures are a measure of the vessel’s internal volume. Nor has it anything to do, these days, with how much cargo (grain, bananas, wine tuns) that a vessel can carry but everything to do with harbour and light dues and taxation. The use of the word tonnage is merely an historical hangover and has been dropped for some time.
There are three classifications of registration in British law known from the divisions of the relevant Act of Parliament (the 1894 Merchant Shipping Act and subsequent revisions) as Parts I, II, and III. Part I applies, in general to big ships but may be used for ships under 24 metres load line length, Part II applies to fishing vessels and Part III to small craft under the 24 m load line length divisor. The vessel has to be measured for tonnage by an MCA authorised marine surveyor and the vessel’s registered Official Number and Registered Tonnage has to be ‘carved into the main beam’. The latter point is often circumvented by the material from which the vessel is built and the required data may be bead welded or chiselled onto a steel hull or stamped onto a brass or wooden plate firmly affixed to the hull in other vessels. The vessel, these days, is then issued with an encapsulated A4 sheet with her registered dimensions and other details and which has to be renewed every five years. The famous Blue Book was dropped under European harmonisation some ten or so years ago. The registration is with the Registrar of British Ships and Seamen in Cardiff NOT, as I have been told by one proud owner, at Lloyds. The vessel’s name on the Register of British Ships is unique and there are strict guidelines. The vessel has to be registered in a recognised British port. A Part I registered vessel is required between the hours of sunrise and sunset to fly the red ensign (the Red Duster) and is, legally, part of H.M. the Queen’s Realms and Dominions overseas. She and her crew are entitled to the protection of the Royal Navy and to full Consular access. This has an interesting legal consequence. A foreign policeman legally, within his own country, carrying a firearm, if he walks onboard, however innocently, a British Registered ship is, under International law, carrying out an armed invasion of British territory and is likely to invoke a real furore with Ambassadorial noted flying hither and thither and, no doubt, some huffing and puffing by politicians.
Small ships, i.e. those under 24 m load line length may opt to be registered under Part III or the Small Ships Register (SSR). They do not have to prove ownership or be measured for tonnage only hull length and may have whatever name the owner chooses. They are given a unique SSR number which has to be displayed in accordance with regulations. They are entitled to Royal Navy protection and Consular access and must fly the Red Duster. For vessels plying the short sea routes to the near continent SSR is sufficient but for deep sea international voyages, Part I registration is essential.
Surprisingly, despite suggestions to the contrary, Part I registration is NOT proof of ownership nor does the Registrar keep a full record of all mortgages or other maritime liens against the ship as there is no law that requires the Registrar to be notified of such mortgages or liens. Although British law does require that all changes of ownership be notified to the Registrar at Cardiff this is often more honoured in the breech than in the observance particularly if the vessel changes hands without the intermediary services of a broker. The only legally recognised proof or ownership is a bill of sale. There is another side issue here of which the marine surveyor should be aware. A British registered ship has to have her name painted or otherwise inscribed on each bow and her name and port of registry on her stern. This, also, is often ignored by small craft owners totally unaware that, such a vessel by not complying with her national law, is legally unseaworthy however well found she may be. Bankers and mortgagors usually require Part I registration because they may use it to register a mortgage or lien within their own organisations and because, wherever the vessel goes in the world, she is traceable as part of Her Majesty’s realms and dominions.
The first tax on the hire of ships in England was levied by King Edward I in 1303 based on tons burthen. Later, King Edward III levied a tax of three shillings on each tun of imported wine, equal to about £58.35 today (using the last year of Edward III’s reign, 1377, as the base year). In order to estimate the capacity of a ship in terms of tun for tax purposes, they were measured by a simple formula based on their principal dimensions Taxation purposes is still the principal reason for tonnage measurement today. In passing it is worth noting that a wine tun of 252 gallons occupied 100 cubic feet and, when full, weighed one ton of 2,240 pounds and that is the origin of the Imperial long ton. As a side comment, had the wool trade preceded the wine trade we might now be measuring ships for taxation not in tunnage or tonnage but in sheepage or woolage. Edward I’s formula was: Tunnage = LBD/100 tons.
An Act of King Henry VI dated 1422 decreed that keels that carry coals at Newcastle should be measured and marked. No reference was made in the document concerned as to how the measurement was made. From about 1650, shipbuilders on the London River used a deadweight calculation method assuming that a ship’s deadweight or burden would be 3/5 of its displacement and its draught half its beam. This was called the Builder’s Old Measurement Rule. Since displacement is calculated by multiplying length x beam x draught x block coefficient (assumed to be 0.62) all divided by 35 ft³ per ton of seawater, the resulting formula for deadweight would be: Deadweight = [(Length – Beam x 3/5) x Beam2/2]/94 tons BOM.
Three fifths of the vessel’s breadth was subtracted from the length as this was assumed to give her Length on the Keel; the length in the formula being measured from the stem to the sternpost and the beam being the maximum breadth over the outside of the planking excluding any wales. As stated above it is a measure of cubic capacity although given in tons burden. The word burden comes from the Old English byrthen meaning a load carried. Then in 1694 a new British law required that tonnage – the old spelling of tunnage had been discontinued – again for tax purposes be calculated according to a similar formula: Tonnage = (Length x Breadth x Depth)/94 tons which was a rehash of Edward I’s rule and remained in effect in until the Builders Old Measurement rule was resurrected and again put into general use in 1720 to be replaced, in turn, by the Parliamentary Rule in 1773 under King George III. The Parliamentary Measurement formula remained in effect until the advent of steam propulsion. Steamships required a different method of estimating tonnage because the ratio of length to beam was larger and a significant volume of internal space was used for boilers and machinery Then, in 1849, under King William IV, the Moorsom System was created. Instead of calculating deadweight, the Moorsom system calculated the cargo carrying capacity and, thus, tax paying ability in cubic feet. Captain George Moorsom’s system involved measuring the internal dimensions of the vessel in a number of places then integrating these measurements. Certain spaces such as fuel and double bottom tanks were excluded. The capacity was then divided by 100 cubic feet of capacity per gross ton, resulting in the gross tonnage. Other spaces, such as crew’s quarters and navigation rooms and including an engine room allowance were deducted to give the net tonnage. The two figures were regarded as an approximation of the size of the vessel needing port facilities and her ability to earn money and therefore pay taxes, port and light dues etc respectively. The system, which was open to some manipulation, was incorporated into the 1894 Merchant Shipping Act and so became British Law. The same system with a few local modifications was adopted by many other countries and, outside Britain, became known as the Brutto method.
Both the Suez Canal and Panama Canal Authorities used the basic Moorsom system but had differing excluded and deducted volumes. Back in the 1940’s a new type of break bulk general cargo carrier was developed to make use of the manipulation of the then applicable tonnage regulations and this was known as the open/closed shelter decker. When the cargo to be carried was voluminous but light the vessel was used as an open shelter deck ship but when the cargo was heavy and dense some small modifications were made to the bulkheads and the after tonnage hatch and the vessel became a closed shelter deck ship. In the former, the shelter deck was an excluded space so that the vessel had different tonnages depending upon whether she was open or closed. When I was an apprentice many such ships were seen and, if they traded worldwide through the Suez and Panama canals, they would have had no less than TWELVE different tonnages, all different, all correct and all legal! With the coming of the container ship, the open/closed shelter deck break bulk freighter disappeared leaving a hiatus. The problem was solved by the International Maritime Organisation (IMO) which finally approved in 1969 the present system details of which can be found in The Merchant Shipping (Tonnage) Regulations 1997 Statutory Instrument as published by Her Majesty’s Stationery Office. Marine surveyors should have a copy in their offices. This gives the gross and nett (the word tonnage which was considered to be misleading was dropped) in the form of a simple formula based on the whole interior volume of the hull with no exemptions or deductions. This method of calculation has been incorporated into International, European and British law. It divides ships into two general types based on the load line length.
Part II tonnage (not to be confused with Part II registration) is for ships over 24 metres load line length and Part III tonnage (again, not to be confused with Part III registration) is for ships under 24 metres load line length. Those over the 24 metre divider have to use the full method but those under the 24 metre divider use a simpler formula based on the principal dimensions. Both require the services of an authorised (by the MCA) marine surveyor.
When yacht racing was introduced in the second half of the nineteenth century a simplified version of the Builders Old Measurement known as the Thames Tonnage measurement was used as a measure of rating. Thames Tonnage which is based, like its forerunner, on the vessel’s principal dimensions and has no other legal usages and no influence either at present or historically on the tonnage measurement and calculations developed by Captain Moorsom or IMO. It is, however, a useful method of calculating marine surveyor’s fees. It is calculated by: TM = (L – B)B2/188 tons.
So there you have it – registration and tonnage explained!
Article by Eur. Ing. Jeffrey N. Casciani-Wood