Philip Dixon Hardy wrote in The Northern Tourist, or Stranger’s Guide to the north and north west of Ireland: including a particular description of Belfast, the Giant’s Causeway, and every object of picturesque interest in the district referred to William Curry, Jun and Co, Dublin 1830:
The river Lagan, although of very considerable breadth in the immediate vicinity of Belfast, and running nearly thirty miles, is yet by far too inconsiderable to be of any great advantage to the town in the way of trade or commerce. By its means, however, a regular communication is kept up between Belfast, Lisburn, and Lough Neagh. Since the year 1755, upwards of £100,000 have been expended in forming a canal, by the assistance of cuts in various places along the line of the river, where it was found too shallow for lighters to pass.
The Lagan Navigation Company have now the direction of the entire line, and have made such judicious improvements, as materially to promote the desired object — a speedy transit of goods and merchandise. This, however, can, after all, be only partially accomplished, as, from the circumstance of the Company not being able to have a horse-track-way along the entire line, nor to introduce steam power, the journey can be performed in a much shorter space of time by waggons and drays going direct. On Lough Neagh there is a small steam-vessel, by which the goods taken up in the lighters are rapidly conveyed to the different towns which lie in various directions round that extensive sheet of water.
W A McCutcheon, in The Canals of the North of Ireland David and Charles, Dawlish 1965, confirms the point about the trackway:
As a result [of various improvements in the early 1800s] traffic greatly increased, though water supply problems remained, and there was a horse-towing path for only part of the length of the navigation.
He gives no details, though, so I don’t know why the trackway was incomplete, how lighters travelled on those stretches that had no trackway or when and how the deficiency was remedied. My guess is that those stretches were along the river rather than the artificial cuts and that the riparian landowners were unhelpful, but I would welcome further information.
McCutcheon does not mention the steamer on Lough Neagh. However, D B McNeill mentions it in Coastal Passenger Steamers and Inland Navigations in the North of Ireland Belfast Museum and Art Gallery Transport Handbook No 3 1960:
The first steamer on the lough was the Lagan Navigation Company’s Marchioness of Donegall. She was built by Ritchie and MacLaine of Belfast, her engines were obtained from David Napier of Glasgow and she was launched at Ellis Gut in November, 1821. She was the first inland navigation steamer in Ireland and was used for towing the Lagan canal boats across the lough. When new, she was reputed to have had a speed of two knots. She was uneconomical and her owners tried to sell her in 1824, but there were no buyers. It is believed the Marquess of Donegall used her occasionally as a yacht. She was broken up sometime about 1840 and her engines were stored in Belfast.
In his Irish Passenger Steamship Services Volume 1: North of IrelandAugustus M Kelley Publishers, New York 1969 he says that the Marchioness was a wooden paddle steamer, built in 1821 and broken up in 1843, 73′ long with a beam of 16′, with a simple single-cylinder engine. He says that the engine cost £1,400, provided 30hp and gave her a speed of 6 knots. A passenger service was considered but never provided, but picnic parties could charter the boat for five guineas a day.