Mr. C. S. Smith, Member:
This paper gives a comprehensive picture of the St. Lawrence canaller, covering the subject thoroughly from the historical beginning through to its present development and with some projection of the possibilities this vessel has for the future. To many of us it is the future of the canaller which is of particular interest and it is to that part of Mr. Gilmore's paper that I would like to direct most of my comment.
The principal dimensions of full canal-size vessels generally run in the vicinity of 250 ft in length by 43 ft 6 in. beam by 22 ft 6 in. depth and, with a vessel having conventional forecastle and raised quarter deck aft, will usually obtain under the Great Lakes Load Line Regulations a geometric freeboard corresponding to a draft of approximately 18 ft, plus or minus a few inches depending on superstructure details, sheer, and other particulars which affect freeboard. In view of the limiting 14-ft canal depth, however, many of the canallers have been designed for scantling drafts which will not permit minimum freeboard. The advent of the St. Lawrence Seaway will tend to accent this aspect of the canal vessel and the canallers able to take advantage of the deeper draft will, of course, have a considerable advantage, particularly so for any possible lengthening, which the author has touched upon. Any consideration as to lengthening of these vessels, however, will bring out certain design limitations.
The Great Lakes Load Line Regulations for vessels under 325 ft in length and the International Load Line Regulations for all vessels specify that the length-to-depth ratio shah not exceed 13.5 for the standard of strength given in the Regulations so that the maximum length permitted for a vessel 22 ft 6 in. in depth would be about 300 ft, or an increase of only 50 ft in present length of the fullsize canal vessel unless deepening is to be considered. Generally, however, for conventionally designed vessels of this length, proportions of up to 16 depths to length for Great Lakes and 14 depths to length for ocean service have been accepted.
It might be worth mentioning here that a rather simple but effective method of deepening many canal vessels has been carried out over recent years by raising the main deck to the height of the aft raised quarter deck and this has had the effect of increasing the vessel's cubic in association with deeper permissible draft, the latter being a valuable consideration for operation in sectors away from the restrictive depths of the canals.
Increasing the length, however, also has the effect of increasing the other required minimum scantlings dependent on the length such as shell thickness, deck area, and longitudinal strength in particular. Deck area and longitudinal strength can often be brought up to an acceptable minimum by fitting of deck doublers and longitudinal stiffening, but raising minimum shell thickness is quite another matter and often in itself is not economically feasible. A reference to the American Bureau of Shipping Rules indicates, for example, that for a vessel of 300 ft in length in this service a minimum thickness of shell plating of 0.41 in. is required. Corrections in required shell thickness to compensate for increase over Rule frame spacing of 24 1/2 in., or for draft in excess of 15 ft might increase the required shell thickness to as much as 1/2 in. With many canal vessels having bottom and side-shell plating substantially below this figure throughout the midship half length it will be appreciated readily that the shell thickness alone might be a critical factor in any proposed lengthening of a canal vessel.
It is a matter of record, as covered in the author's historical review, that many of the canal vessels which are currently privileged to trade from ports on Lake Superior, eastward to Newfoundland and even beyond, in limited coastwise operation were not, at first, considered for such an extended scope of operation. This has imposed a number of problems on the owners and other interested parties who were faced with the need of augmenting the design of a vessel, originally constructed to handle cargoes between St. Lawrence River ports and Lake Erie, to permit operation far beyond either end of the originally intended limits of navigation. The eastern boundary of the Great Lakes Load Line Regulations which is a line in the Gulf of St. Lawrence from the tip of the Gaspe Coast to the western end of Anticosti Island and thence along the northern shore of the Gulf of St. Lawrence eastward to Havre St. Pierre, has done much to confine many of the canal vessels to this limited operation since vessels under the Great Lakes Load Line Regulations are permitted slightly more draft in association with modified requirements for longitudinal strength and other considerations such as reduced coaming heights and protection to openings in the freeboard and superstructure decks.
Notwithstanding this fact a number of the older canal vessels have been fitted out for coastwise service, many having been converted for such operation during the last war emergency period. Apart from the extra protection fitted on these vessels to the openings on deck it became necessary, at that time, for a number of the canallers in American Bureau Class to be fitted with longitudinal deck doubling and, in addition, the bottom shell and tank-top longitudinal frames and stiffeners which had been sniped clear at their ends were required to be attached at the double-bottom transverse bulkheads.
The nature of the seasonal operation of the canal fleet which provides winter lay up of these vessels, similar to that experienced by Great Lakes vessels generally, has led to their being considered by the Canadian Government authorities and by the classification societies on much the same basis as the larger upper Lake vessels in so far as periodical survey requirements are concerned. With particular reference to the author's description of classification of these vessels it should be pointed out that the British Corporation originally included the designation "Limited" in association with "Gulf of St. Lawrence" service and this was considered to be a time limitation to cover the annual lay up of the vessels. Great Lakes survey requirements permit dry-docking and tailshaft examinations at the Special Survey due dates rather than on the more stringent basis required for full ocean vessels. In itself this appears rather lenient for vessels which might operate a substantial amount of time in salt water. However, it has proven to be a reasonable and satisfactory treatment over the years and possibly one reason for this is the fact that canal vessels, because of their frequent transit of the canals themselves and of other restricted waterways are of necessity drydocked often enough to permit frequent examination of the underwater body. A study made a few years ago of the canal vessels in class with the American Bureau indicated that the average dry-docking interval of these vessels as a group was just slightly in excess of 18 months.
The fact that the canal vessel is constructed for salt-water operation, plus the added fact that many canallers already have been converted or otherwise fitted for ocean or coastwise service indicates that many of these vessels can still enjoy a number of productive years in operation after the St. Lawrence Seaway becomes a reality, particularly to ports where shallow drafts or limited cargo-handling facilities will exclude the larger vessels. While the days of construction of the canal vessel may now be terminated the fact so many canal vessels have been built within recent years, even with the Seaway nearing a reality, lends considerable credence to the belief that, if the demand for tonnage holds up, the St. Lawrence Canaller will be able to enjoy its share of continued operation, in the near future.
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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.