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What’s in a Word

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There’s been interest around the Fleet recently in the origin of maritime terms. Captain David Wharington has been doing his research and here he tells us . . . 

WHAT IS A GASKET?

Since man first built boats and ventured out onto the sea, he has had to turn his hand to using whatever materials, or objects he had available. Old worn out rope was unlaid into rope-yarns and platted up into sennit. Commonly used flat sennet used five or seven yarns, and square sennet used eight. Falconer in 1815 describes it as “a sort of flat braided cordage used for various purposes….”. It was commonly made up into short lengths used for simple lashings. A major use was as a gasket, which Falconer describes as ”a sort of platted cord fastened to the sail-yards of a ship, and used to furl, or tie up the sail firmly to the yard……..”  

When sailing ships were in port alongside a berth, cargo was worked by topping up a yard and hoisting the cargo in or out, using a rope reeved through a block at the yard-arm. Animals, often donkeys, were used on the wharf to pull on this rope.   At a later date, as boilers and steam engines became more common, a boiler & steam winch was mounted initially on the wharf, and still later on the ship’s deck. This boiler became known as a Donkey Boiler, and the person who operated the system was known as the Donkey-man, a term that exists in steamships to this day. He is the Engine-room equivalent of the Bosun.

These early boilers were made of cast iron and filled with sea-water. If a potato would float in the boiler-water, it was too salty and needed changing. The boilers required regular cleaning to remove the hard crust of salt that quickly built up inside, and boiler failures and even explosions due to the insulating properties of the salt crust were not uncommon. In the early days of steam, the boiler’s manhole door was made pressure-tight with rust, created by steaming in a mixture of fine metal turnings, sal ammoniac and water. (See British Steam Tugs, by Thomas)   Breaking this manhole seal when boiler cleaning was next required, was clearly not an easy task.

An easier way to seal this joint was developed by an enterprising seaman, who wound a length of this same rope gasket that was used for countless other purposes, in and out around the numerous studs that held the manhole cover in place. It was then used for sealing the cylinder cover in the same way. The square sennet form of gasket was also used as a packing to seal the glands around oscillating or reciprocating shafts such as the piston rods, and rotating shafts such as propeller tail shafts. The name of the ubiquitous item, first hand-made by a lowly seaman, was carried over when gaskets became a stock engineering item.

Eventually as steam pressures and temperatures became higher, sheets of flat material were used on the manholes and cylinder covers, but the name “gasket” was still retained for the item. The eight strand square sennet form of rope gasket remained in use for the stuffing boxes around rotating, oscillating and sliding shafts and took on the name “packing”, as they were packed into the confined gap around the shaft. Kent’s Mechanical Engineer’s Handbook, 1950 edition, describes “square packing” as “a form of gasket”. The Blackwoods Catalogue still includes under Gland Packings “Greasy Hemp – Style No. 30. Suitable for water, saltwater, marine and hydraulic applications. Low to medium pressure.” The Catalogue also has the exact same square sennet made up as gland packing, using more modern and sophisticated materials for the higher pressures and temperatures in use today.

References

A New Universal Dictionary of the Marine, 1815:                    W.A. Falconer

Blackwoods Catalogue, 16th Edition                                             J. Blackwood & Sons, Ltd

British Steam Tugs, 1984                                                                 P.N. Thomas

Illustrated Marine Encyclopedia, 1890                                        Captain H. Paasch

Kent’s Mechanical Engineer’s Handbook, 12th Ed, 1950        Colin Carmichael, Editor

The Ashley Book of Knots, 1944                                                     Clifford W. Ashley

The Young Sea Officer’s Sheet Anchor, 1819                              Darcy Lever

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This entry was posted on 22/07/2016 by in General, Sydney Heritage Fleet.
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