HMS Rattler
by John Ellis
The development of the steam engine for locomotion was a challenge taken up by engineers in the late 18th century. Richard Trevithick demonstrated his steam carriage at Cambourne in Cornwall in 1801 and three years later his locomotive, on an existing tramway in Wales, hauled ten tons of iron ore and 70 men at eight kph.
Many other engineers entered into steam locomotion, but it was the Rocket built by George Stephenson that conclusively won the Rainhill trials in 1829, heralding the age of the railway. During these trials the Rocket averaged 22 kph and reached 46 kph.
William Symington
William Symington built the first successful steam-propelled vessel that he demonstrated in 1802 in Scotland. Two years later, Robert Fulton, an American, demonstrated his steamer in France. From those early trials, my Lords Commissioners of the Admiralty also saw the potential for steam propulsion. Initially the concept was to develop tugs to get ships of the line in and out of harbour and the Admiralty put their toe into the pool of this new technology in 1815 with the order for a sloop named Congo. Something went amiss in the project office because the engine proved too heavy for the vessel and the engine was eventually commissioned for use ashore. The Navy’s first steam propelled vessel, then, was the Comet, built in 1819. Comet was a tug with a length of 35 metres a beam of 6.4 metres and a draught of 2.7 metres. Each of her twin engines was rated at 40 NHP(1). The Monkey and the Active, with two engines of similar output, followed in 1820 and 1822.
HMS Lightning, 1823
The first steam-powered vessel in the Navy List was HMS Lightning. She was built in 1823 but did not appear in the Navy List for another five years.
The first armed vessel propelled by steam was HMS Dee, completed in 1832. Dee was 51 metres long with a beam of 9.3 metres with two engines developing 200 NHP. One officer of the period who championed the use of steam was RADM J. Ross, who made his name as a polar explorer and also wrote a steam navigation treatise in 1828, setting out tactics for sea warfare using auxiliary steam propulsion.
The admirals began to stroke their beards following the success of steam packets, introduced from 1830 for external mail services operated by the Navy. Now, side-mounted paddlewheels propelled all these early steam vessels and for warships there were two main limitations. The wheel box on a ship’s side reduced space for mounting guns and the boxes and paddles were extremely vulnerable to enemy gunfire. Nevertheless many years of experimentation and debate passed before the Admiralty eventually cast aside the paddlewheel.
Evolutionary designs for the propeller.
Some early screws were just that, with the appearance of a short auger. Others were more recognisable as a screw propeller. In 1837 Ericsson used his screw steamer, Francis B. Ogden, to tow an Admiralty barge up and down the Thames.
Isambard Kingdom Brunel and Great Britain
The big leap forward for the screw propeller came in 1839. Ten months after Brunel laid down the Great Britain, the Archimedes visited Bristol where Great Britain was being built with paddlewheels. Archimedes was propelled by Francis Smith’s screw propeller and her performance was convincing. Even though Smith’s patent was similar to an Archimedean screw, Brunel converted the propulsion system of Great Britain to utilise a six-bladed screw propeller. This decision was vindicated in 1843 when Great Britain clearly demonstrated the advantages of screw propulsion during her crossing of the Atlantic.
The Admiralty, possibly motivated by Brunel’s courage, moved in 1842. The sloop Ardent was then under construction in Sheerness and the Admiralty directed the propulsion system be converted to screw propulsion. She was commissioned as HMS Rattler in 1843 and displaced 1078 tons. Rattler tested six different propeller designs, with six modifications being made to three propellers. The propellers ranged from 2.5 – 3.0 metres in diameter with a mean pitch around 3.4 metres. From these trials a propeller was selected. It was 3.01 metres in diameter with a pitch of 3.4 metres.
The famous trials with HMS Alecto were conducted in March – April 1845 over the 78 nautical miles between the Nore and Yarmouth Roads. Alecto was a paddlewheeler sloop of the same engine power as Rattler although she was 3.8 metres shorter. Rattler completed the course in 8 hours and 34 minutes. Alecto took a further 20 minutes.
(Ed note: There are persistent minor variations in the data reported arising from these trials, e.g. 78 versus 80 miles, 23½ versus 20 minutes, etc. See “Screw versus paddle” note, below.)
The plate on the display (above ) of HMS Rattler‘s screw propeller, displayed at the RN Museum, Portsmouth, says:
Screw versus paddle. Here displayed is the screw or propeller of the former sloop HMS Rattler, a vessel of around 800 tons (2) and 200 HP. This sloop in 1845 decided the future of propulsion of British warships in a series of experiments against another sloop, HMS Alecto, of similar displacement and horsepower but propelled by paddlewheels. On an 80-mile course in calm weather the Rattler defeated the Alecto by 23½ minutes. Later over a 60-mile course against a head sea, the Rattler again defeated the Alecto, this time by 40 minutes.
Finally, in the most conclusive experiment of all when the two vessels being fastened stern to stern and both steaming at their best, the Rattler towed the Alecto away at a rate of 2½ knots. In consequence from 1845 onwards new warships were driven by propellers.
Over a 52 nautical mile course in heavy seas and strong headwinds, Rattler averaged 7½ knots whilst Alecto averaged seven knots. The tests culminated with the two sloops secured stern to stern. Alecto worked up to full power with Rattler‘s engines stopped. Once Rattler started her engines ahead, she gradually overcame Alecto and eventually towed her astern at 2½ knots.
HMS Niger trials
Although the Admiralty declared the superiority of screw propellers in 1845, further tests were conducted in 1846 between the paddle-driven HMS Basilisk and the screw-propelled HMS Niger. The outcome was the same.
Despite the tests, some ships were equipped with paddlewheels for some time; the last major ship built for the Navy with paddlewheels was the Royal Yacht, Victoria and Albert II, launched in 1855. By the end of that decade the Navy List included 463 steam-powered ships of which 351 were propelled by screw.
Much of this information has been drawn from The Naval Steam Reciprocating Engine, by Norman Rivett, and he includes a copy of Admiralty Circular No 347/58:
Precautions to be taken against accidents when men are in them. Accidents of a serious and even fatal character having sometimes occurred on board Her Majesty’s Steam Ships and Vessels, by the Paddle Wheels being turned when men are in them. My Lords Commissioners of the Admiralty are pleased to issue directions, with the view of effectually guarding against such accidents in future, that men are on no account to be permitted to go into, or remain in, the Paddle Wheels, except when they are effectually secured by a bar being passed through them, by a secure lashing, or by some other simple mode, the efficiency of which can be judged of by any Seaman.
Main engine
HMS Rattler was fitted with two Maudslay and Field Siamese engines, that is, four cylinders of 1019 mm diameter and a stroke of 1234 mm. The nominal horsepower was 200 and the engine developed 437 IHP (3) at 26 rpm on a single shaft. This output was geared up to 104 rpm with a belt drive that was replaced with a spur gear drive. The boiler pressure is not known, however many boilers operated at five psi with some as high as 14 psi. HMS Alecto was fitted with a Seaward and Capel Gorgon engine of 200 NHP. The output of the engine was connected directly to the paddlewheels.
Footnotes:
1. NHP (nominal horsepower) was an 1840s standard adopted by the Royal Agricultural Society, comparing the power of a steam engine with that of a horse. There has been, and still is, a great deal of confusion about NHP and its relationship to actual horsepower. NHP is related to the size of the cylinder bore and the speed of the piston. Horsepower (HP) is a measure of the power produced. One HP is equivalent to 550 foot-pounds per second or 745.7 watts. It is not possible to convert NHP to HP or vice versa.
One measure of NHP is found by dividing the square of the cylinder diameter in inches by ten. So for a nine-inch bore engine: NHP = 9 x 9 / 10 = 8.
Another NHP formula is to multiply the square of the diameter of the cylinder in inches by the cube root of the stroke in feet, and divide the product by 47.
2. This 800 tons figure is a builder’s measure, based on hull volume, independent of weight. It is a lesser figure than displacement tonnage. In the Middle Ages, most cargo, dry or liquid, was carried in casks, the largest being the tun. A ship’s carrying capacity, or burthen, was given by the number of tuns she could carry and was known as her tunnage. Until iron allowed major changes to hull shapes and design, the tunnage (tonnage) was calculated for taxation purposes by multiplying length by breadth by depth below the main deck in feet, then dividing by 100.
The wooden ships tonnage formula varied from the above in the 18th century, but with iron and steel ships the tonnage was once more established by calculating the volume of the hull in cubic feet. One gross register ton equalled 100 cubic feet. Nett register tonnage, based on the volume of a ship’s cargo carrying capacity, is the figure used for determining fees for harbour dues, insurance, salvage and towing. To ensure confusion, bulk carriers nowadays use deadweight tonnage, or the tons weight of cargo, that takes them down to their Plimsoll mark.
3. IHP (indicated horsepower) is a theoretical power assuming complete efficiency. Actual power output may be only 70 to 90 per cent of this figure.
References:
Rivett, Norman. The Naval Steam Reciprocating Engine. Naval Historical Society: Garden Island, ISBN 0 9587456 0 9.
Ross, J. A treatise on navigation by steam. Longman, Rees, Orme, Brown and Green: London. 1828.