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Measured Miles

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Measured miles were critical in the days when the Firth of Clyde was a major shipbuilding area, All newly built or re-engined ships had to undergo sea trials before being handed over to the owners, and it was on the basis of these trials that the owners decided whether or not the ships were up to specification and agree to accept them. One of the most important tests was the maximum speed test, carried out over a set distance, usually a measured mile.

The decline in their usefulness coincided with that of the Clyde shipbuilding industry, although satellite technology, and the various electronic navigation methods (many born of World War II aviation needs) which preceded it, helped in their demise.

This test is now relatively simple, as the course can be set on the autopilot, and the maximum speed determined using GPS. Before the invention of this technology, things were more difficult and involved an officially recognised measured mile, and ships were required to cover a set course between the marker at full power. A lookout with binoculars would start a stopwatch when the first two markers lined up as the ship passed, and stopped it when the second pair of markers was passed, allowing the speed to be calculated. For greater accuracy these tests were only carried out in light wind conditions, and repeated in the opposite direction to minimise any directional effects. Testing would be carried out during the hour of slack water at high and low tides, to avoid any tidal influences on the results.

For an article including a number of vessel results, see the Clyde River Steamer Club article reference below, which revealed a number of measure miles (and half miles) not found in earlier searches.

Gare Loch Measured Mile

The first measured mile to be established on the Clyde dates from 1841 and was the Gare Loch Measured Mile. This lay on the west shore of the loch and was marked by the Mill Burn near Mamore towards the northern end, and the Meikle Burn near Barremman towards the south. It was created to test Thomas Assheton Smith’s Fire King wood paddle steamer of 1838.

Robert Napier (a Scottish marine engineer famous for his contributions to Clyde shipbuilding) had the mile re-built by the Institution of Shipbuilders & Engineers in Scotland in 1861, for trials of the transatlantic paddle steamer Scotia, which went on to win the Blue Riband in 1863, a prize given to the passenger liner which crossed the Atlantic westbound in regular service with the record highest speed.

In 1886 Dumbarton shipbuilder William Denny first used the Gare Loch Measured Mile for the paddle steamer Aurora.

The Gare Loch Measured Mile would later be used as two half miles, with the eastern half mile split into quarter miles.

In 1952 the mile was re-established by the British Ship Research Association, with help from Denny, for trials of the jet-propelled Lucy Ashton in 1952, when the posts were re-positioned to improve the accuracy of the mile.

In January 1977 McGruer & Co, a yacht builder based in Clynder, took over maintenance and insurance of the mile posts.

By the 1980s the Gare Loch Mile no longer in use.

Skelmorlie Measured Mile

Skelmorlie north high, NS191675, 2007
N High marker Skelmorlie
© Thomas Nugent

The Skelmorlie Measured was initially rather more than a mile, in fact it was over 13 miles long.

Before a new owner would agree to take possession of a vessel constructed in one of the Clyde shipyards, it was necessary for the builder to conduct sea trials, and prove the vessel performed to the specifications laid down in the purchase order. These trials were conducted with the vessel steaming at full power over a 13.666 nautical mile (15.736 statute mile) course between the Cloch and Cumbrae Head lighthouses, in a procedure known as Running the Lights. Tables from the period show that at 14 knots the run would take 58 minutes 34 seconds; at 20 knots, 41 minutes. Having completed one run, the vessel would then turn around as quickly as possible and repeat the run. The reversal was intended to negate the effects of any wind and tidal input to the vessel's performance. In reality, the time taken to complete the initial run, stop, and then turn the vessel for the second run meant that wind, tide, and weather could all have changed from those present during the first run, thereby tending to negate the averaging effect of the two runs.

To solve this problem, the test distance was reduced, with the steamer pier at Skelmorlie marking one extent, and the Skelmorlie Hydropathic Hotel, south of Skelmorlie Castle, the other. Measuring 6,080 imperial feet, this nautical mile came to be regarded as the most important Measured Mile in Britain.

Nautical mile

The nautical mile was later redefined within the international system of units (SI), and lost s little of its original, and being defined as 1,852 metres (approximately 6,076.1 ft or 1.1508 statute miles). Historically, it had been defined as one minute of latitude, or one sixtieth of a degree of latitude. Today, as an SI derived unit it is rounded to an even number of metres and remains in use for both marine and air navigation, and for the definition of territorial waters.

The measured mile at Skelmorlie was notified on 4 July 1866, in a Notice to Mariners, No 36, and installed by Robert Napier. The unlit beacons marking the mile were described as a single pole, 45-feet high, with arms 10-feet long forming a broad ( V and ‘inverted’ V ) angle 15-feet from the base, the whole being painted white. Once the 'V' and the inverted 'V' were aligned they became an 'X', at which point the tester's stopwatches would be started or stopped dependent on whether the start or finish of the run was being recorded. From the precise time recorded for the run, and the known distance between the beacons, the results were read off from standardised time and distance tables published in almanacs.

Prior to running the measured mile, vessels would be brought into a steady state of motion, maintaining steering and power constant to avoid any influence and distortion of the final speed calculations. Prior to passing the markers, vessels would always run a straight and steady course for up to four miles, allowing course and speed to be stabilised.

At the end of each run the vessel would turn and repeat the run in the opposite direction, using the same engine power and revolutions. This procedure was intended to cancel out any effects arising from wind, weather, and tide, once an average speed was calculated over the two runs. It was customary for at least two return trips to be made over the course, with results being deemed acceptable if they were in agreement. Variations are reported to have been in the order of 0.5%.

The Skelmorlie markers are no longer depicted on OS maps, suggesting that they have fallen into disuse.

The Skelmorlie Measured Mile served for some 120 years and was the mile used to measure the speed of Clyde steamers and ferries, as well as cross-channel ships and occasionally larger vessels.

The Skelmorlie Measured Mile was revived and used by Ferguson Marine Engineering in July 2016, for the speed trials of Catriona, then the newest ferry to be added to the CalMac fleet.

Arran Measured Mile

The Arran Measured Mile belongs to the Admiralty and was established in 1916.

It comprises two consecutive miles, marked by three sets of pylons or beacons on the north east of the island, between South Sannox and Corloch. The beacons are illuminated, and maintained by a marine service company operating out of Rhu Marina.

Originally established as a single mile south of Sannox Rock, it was later extended to two miles by additional posts to the north. In 1934 it was again extended to the north, and the southern posts were removed to accommodate the 68,000-ton Cunard liner Queen Mary (which reached 31 knots in April 1936).

The northern mile measures 1.8544 kilometres, while the the southern measures 1.8514 kilometres. The Arran Measured Mile has more manoeuvring space at each end of the run when compared to Skelmorlie, generally making it easier for vessels to carry out their test runs before the weather and other conditions can change significantly. Procedures at Arran also remove the stop and turn manoeuvre, allowing vessels to maintain speed and perform a turn in order to reverse direction for the second run.

In 1937, a question was recorded in Hansard, regarding the measured mile off Arran and its operation:

Royal Navy (Measured mile, Isle of Arran).

Sir C. MacAndrew

asked the First Lord of the Admiralty whether he has yet received a report from his expert who visited the Sannox measured mile on the island of Arran at the beginning of June; and, if so, what steps are going to be taken to alter the positions of the beacons?

Mr. Cooper

A report has been received on the observations made at Sannox Pier during recent runs by His Majesty's ships on an experimental track placed as far North of the existing track as was considered practicable. This report show that the use of the experimental course would only very slightly improve the conditions at Sannox Pier; and after the most careful consideration, it has been decided that the considerable expenditure which would be involved in moving the trial course to the experimental position cannot therefore be justified.

Arrangements will, however, be made to avoid, as far as possible, runs on the measured mile between 2–3 hours before high water and high water. With this precaution, in addition to the existing instructions that wherever possible the Northern half only of the two miles course is to be used, and that notice of trials is to be given to the Arran Barytes Company, I am satisfied that all practicable steps will have been taken to reduce local inconvenience to a minimum.

- HC Deb 06 July 1937 vol 326 cc188-9W 189W.[1]

According to the Clyde River Steamer Club[2]:

At the end of the Second World War a detachment of Polish soldiers was given the task of clearing the site and they cut down the posts — a fact discovered only when Britain’s last battleship, the 51,100-ton HMS Vanguard, began her trials. The posts were hastily re-erected and trials were re-run in July 1946, when Vanguard achieved 32 knots.

QE2 visit 2007

When the QE2 returned to the Clyde in September 2007, marking the 40th anniversary of her launch from the Clyde, one of the procedures she observed was a full-power run over the Arran Mile, recreating part of her original sea trials in 1968.

Loch Long Measured Mile

The Loch Long Measured Mile was established in 1940 by the Admiralty near Coulport, following the erection of the Cloch Boom. This enabled Clyde shipyards to continue carrying out speed trials for their ships during the war, and was especially useful for Robertson of Sandbank when they produced their motor torpedo boats (MTB).

The Loch Long mile was re-established by Yarrow Shipbuilders in 1959 as two half miles for the speed trials of their pusher tug Gongola with her train of eight barges. The Loch Long mile is no longer in existence.

Ardmaleish Half Measured Mile

The Ardmaleish Half Measured Mile, on the Bute shore of the East Kyle, was also erected by the Admiralty in 1940 to suit MTBs being constructed there. This mile has been removed.

Parklea Measured Mile

The Parklea Measured Mile, east of Port Glasgow, was erected by the Denny Hovercraft Company in 1963 for testing of their D1 hovercraft.

Although no longer in use, the three pair of posts - western, central, and eastern - marking its extent have been found and photographed.

The posts rise to approximately 6 m (18 ft), with the seaward post approximately 90 m (300 ft) north of the landward post.

No longer highly visible, the posts are reported to have been painted bright yellow in the 1960s.

In each case, the landward post carries an inverted triangular marker, while the seaward post carries an upright triangle. Mounting points for three guy wire are located below, with corresponding ground anchors nearby. Unlike the earlier markers, where alignment of the upper and lower marker to form an 'X' marked the instant at which the vessel under test crossed the start or finish (or intermediate) line of the Marked Mile, it loons as if these markers are intended to have the inverted triangle at the bottom, as the pole does not extend about it. This would seem to make it easier to watch the upper triangle approach vertical alignment with it, with no section of pole blocking a clear view behind, and start/stop timing.

Western pair

Western Outer, 2017
Western Outer 2017
© Thomas Nugent
Western Inner, 2008
Western Inner 2008
© Thomas Nugent

Western Inner Fallen Corroded, 2017
Western Inner Fallen 2017
© Thomas Nugent

Intact when photographed in 2008, a return visit by the photographer in 2017 found the inner post to have fallen as a result of corrosion at its base - the other five remained intact and standing.

Western Inner Fallen Guy, 2017
Western Inner Fallen Guy 2017
© Thomas Nugent
Western Inner Fallen Top, 2017
Western Inner Fallen Top 2017
© Thomas Nugent

While the inner post has succumbed to corrosion and may be lost, its position on the ground provided an opportunity for a more detailed look at the marker triangle and guy wire mountings

Centre pair

Middle Outer, 2017
Middle Outer 2017
© Thomas Nugent
Middle Inner Land, 2008
Middle Inner Land 2008
© Thomas Nugent

The only inland post of the set, the landward post of this pair lies above the high tide line, almost hidden within brambles to the right of a footpath.

Eastern pair

Eastern Outer, 2017
Eastern Outer 2017
© Thomas Nugent
Eastern Inner, 2017
Eastern Inner 2017
© Thomas Nugent

St Abb's Measured Mile

East-north marker, St Abb's,
East-north marker, St Abb's
© Chris Eilbeck

A set of four Admiralty Distance Poles is is identified on OS mapping, and also marked as a measured mile. The poles lie on the southern coast of the Firth of Forth, on rough ground and cliffs to the west of St Abb's.

The sea area off St Abb's Head is understood to have been used for testing of vessels from the shipyard to the west.


Skelmorlie north markers

Skelmorlie north high, NS191675, 2007
N High marker
© Thomas Nugent
Skelmorlie north low, NS191675, 2007
N Low marker
© Thomas Nugent

Skelmorlie south markers

Skelmorlie south high, NS192656, 2007
S High marker
© Thomas Nugent
Skelmorlie south low, NS192656, 2007
S Low marker
© Thomas Nugent


1 HC Deb 06 July 1937 vol 326 cc188-9W 189W

2 The Clyde’s Measured Miles - CRSC : Clyde River Steamer Club Retrieved February 01, 2017.

External links

Aerial views


Gare Loch Measured Mile (Approximate):

Skelmorlie markers:

Arran Beacons:
North beacons Corloch:

Mid beacons Laggantuin:

South beacons Sannox Bay:

St Abb's measured mile Admiralty poles:


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