The new canal, although a considerable improvement over the earlier ones, imposed many restrictions on design, and the "Canaller" is the result of the compromise between these restrictions and the cargo-carrying requirements.
The canal locks in the three main sections vary slightly in dimensions, those of the Soulanges section being a little wider and longer than the Lachine and Cornwall - Lachine and Williamsburg sections. The controlling lock of the whole system, as far as ship dimensions are concerned, is No. 17 at Cornwall. This lock is nominally 45 ft wide at the waterline but since its completion the masonry walls have moved and the breadth at the bottom of the lock is now only 43 ft 8 in. At a point about 4 ft above the lock bottom corresponding to the upper turn of the bilge of the canallers, the width is 44 ft.
The maximum breadth of canallers is therefore strictly controlled by this lock and is generally 43 ft 7 in. extreme at the bilge. Many ships have a slightly wider deck, the extreme breadth being 43 ft 11 in. The accompanying midship section, Fig. 19, of an early postwar canaller, shows this.
To avoid possible fouling of the lock walls by the topsides, canallers generally have tumble home on all structure above the upper deck. This enables the ships to pass through the locks without touching the walls even if slightly heeled by cargo or other conditions.
The normal depth over the sills restricts the draft to 14 ft and most canallers are designed to operate at this draft when canalling. The scantlings, however, are usually arranged for a draft of 16 ft 6 in. which allows the canaller to carry a much greater deadweight when clear of the canals and the ships are built to comply with the requirements of the Canadian Board of Steamship Inspection for a certificate for Home Trade Class I or II.
A Class II certificate is required for trading in the Gulf of St. Lawrence and down the Eastern Seaboard as far as New York, this area covering the Gaspe and St. Lawrence north shore pulpwood trade and the ore terminal at Seven Islands.
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This paper was presented at a meeting of the Society of Naval Architects and Marine Engineers and is reproduced with permission.