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A Lock Is Not Just a Lock

One would think if anything were certain about C&O Canal construction, it would be the size and design of the 74 lift locks. The truth is, however, that despite the decisive nature of most statements on C&O Canal lift locks, there are many uncertainties concerning them. In fact I am reluctant even to write about this issue, but I decided to do so in the hope that all those with relevant information or opinions will jump into the fray and help to clarify some of the murky areas of C&O Canal engineering.

I’ll begin by recognizing four major lift lock designs used on the C&O Canal when it closed in 1924: (1) That of the first 25 locks; (2) that of locks 28 through 75 excepting those in the next two classes, (3) the 13 composite locks (58-71—excepting 65 that was not built), and (4) the locks extended in 1876–1883. A good number of locks had additional changes that make them anomalous and each lock can be viewed as unique in a variety of ways.

The initial 1828 design seen in locks 1 through 25, is distinguished by the placement of the upper mitre gates on the breast wall. (The height of the breast wall from the lock floor to its top determines the lock’s lift, or the altitude variation between the level of the canal prism below and above the lock [Unrau, p. 208].) This design placed the upper gates outside the usable chamber of the lock and allowed them to be shorter than the full-length lower gates. Locks 1–27 (excepting lock 13) were further distinguished by the use of culverts in the lock walls—rather than bypass flumes around the lock on the berm side—to help maintain the flow of water to the level below the lock.

Those familiar with locks 1–27 today will recognize that bypass flumes now exist around many of these locks (1–4 in Georgetown, 14, 23 and 24 excepted) and none of the lock wall culverts still function although remnants of that system remain in some lock structures. While Lock 20 in front of the Great Falls tavern appears not to have a bypass flume, it merely puts it under the plaza. In 1830 the lock design was changed to make the upper mitre gates full length and to include them in the lock chamber directly in front of the breast wall (rather than on top of it). This inevitably meant lengthening the lock chamber to allow for the upper gate pockets (that allow open gates to fit flush with the lock wall).

This brings us to the sticky issue of the length of the locks and the chamber length practically available for boats. In January 10, 1850, Chief Engineer Charles B. Fisk advised a Baltimore boat builder that “the distance from the upper side of the lower mitre sill to the upper side of the upper mitre sill, or from point to point of lock gates . . . is 100 feet.” As the ends of the boats were not designed to fit the angle of closed gates, this did not represent the usable chamber, which was closer to 90 feet. Indeed, for practical purposes I believe we must assume that the actual length of the boats could not have exceeded 90 ft. This is supported by Davies’ documentation of Lock 36 (now filled in to prevent its collapse), which he describes as having been 89 ft. 11 in. long and the only C&O Canal lift lock less than 90 ft. in length. Because of its shortness it was “most troublesome to the boatmen.” (Davies, p. 219. Also see note)

The composite locks were built along a 26-mile stretch from Fifteen Mile Creek to Oldtown due to the lack of stone appropriate for the ashlar masonry locks in that region. This part of the canal was in the final fifty miles from Dam 6 (just above the mouth of the Cacapon River on the opposite shore of the Potomac) to Dam 8 at Cumberland. Contracts for this final section began to be let in 1837, but due to the many difficulties that arose, including financial and labor problems, many contracts were abandoned and construction faltered. By June, 1839, even Chief Engineer Charles B. Fisk, who had been so confident that adequate stone could be provided for the structures in this section, was accepting the fact that this was not so.

Admittedly, the Canal Company’s inability to provide high quality stone for the structures in the Paw Paw bends region was partially due to the decision not to build Dam 7. Fisk’s insistence that there would be coping and facing stone for the locks in that area had been based to a great extent on his assumption that once the Dam 6 to Dam 7 section was opened, stone could be carried up the canal in boats from Hancock area quarries. Abandoning plans for Dam 7 meant the final 50 miles had to be watered from Cumberland’s Dam 8 and that the entire 50-mile section could not be opened until the whole was complete.

Land carriage of large amounts of stone from Hancock through the rugged Potomac Valley terrain to the Paw Paw bends region was financially impossible even if the practical problems of transport could have been solved. And even if Dam 7 had been built, significant stone transport on land would have been required to build the locks on the Dam 6–Dam 7 section. However, above Dam 7—once it was built—slackwater navigation in the river would have facilitated transportation to the locks still to be built in the stone-poor region above the dam.

In any case, a plan for composite locks was offered by Principle Assistant Engineer, Ellwood Morris, based on the use of rubble stone masonry “laid in full beds of pure cement mortar grouted with pure cement grout.” (Bearss, 13, quoting from a letter from Morris to Fisk, Aug. 18, 1839). Fisk, however, preferred a design used on New York’s Chenango Canal. This involved building drywall locks faced with a watertight lining of timbers and planks that could be replaced, when necessary, during winter shutdowns. This plan was eventually used for Locks 58 through 71. During the post-Canal Company era when the canal was operated by a court appointed receivership (1890-1924), concrete was extensively used on these locks, entirely replacing the plank lining in some cases.

The fourth significant lock design is that of the extended locks. The idea of increasing the length of the locks to accommodate longer boats appears to have been the brainchild of Canal Company President Arthur Pue Gorman (president June 1872–August 1882) who took advantage of the canal’s most prosperous years to engage in extensive repairs and improvements. Gorman clearly saw the need for enlargements if the canal was to remain a competitive carrier and in June 1875, Gorman proposed in his report to the stockholders that the chamber of the locks be increased by removing the breast walls, extending the chamber, and using a drop gate at the upper end. Gorman points out that such lengthening would allow boats that could carry ten tons more than the present boats without any additional power or labor. (Unrau, p. 87) He proposed that this be done to all 74 lift locks during the upcoming winter suspension of navigation.

This 10 ft. lengthening was an interim solution only, however. Gorman envisioned eventually doubling the length of all the locks to allow for boats with a capacity of more than 230 tons—twice the tonnage of the current C&O freighters. These longer boats would be built in two sections that could be separated for passage through locks not yet extended. When operated as one long boat it was anticipated that four mules would be required to pull them and the time to lock through the extended locks would be increased to 25 minutes. However the human labor needed would not be greatly increased, although the Canal Company would have to provide assistance at the short locks where the boats’ sections would be disconnected for passage through the locks. It is worth noting that there is no indication that any sectional boats were ever used on the C&O Canal.

During the winter of 1876–1877 only three locks, numbers 5–7, were lengthened in accord with Gorman’s “interim length” plan that extended the locks ten feet and put a drop gate at their upper end (Unrau, p. 88). In May 1881, Gorman’s report to the stockholders was again proposing the more ambitious lengthening of the locks, now specifying an increase of 100 ft. for section boats that could carry 240 tons. (Unrau, p. 88-89) As in 1876, Gorman cited the experience of the Pennsylvania canals with such a lengthened-locks and section-boat system.

On June 5, 1881, after significant debate, the stockholders approved this plan and in January 1882 civil engineer Leslie Duvall produced plans for lengthening the upstream end of the locks with crib type walling and drop gates. However in March 1882 President Gorman reported to the stockholders that only fourteen locks had been extended in this way. In August Lewis C. Smith would replace Gorman as President and in June 1883 Smith reported that only two more locks had been extended the previous winter. (Unrau, p. 94) The June 1884 annual report issued under President L. Victor Baughman indicated that a total of sixteen locks had been extended, and it refers to two locks being extended the previous year. Interestingly the 1885 annual report listed $208.96 spent on lengthening—certainly not enough to complete the work on a single lock, given that the average cost to lengthen a lock in 1882 was nearly $5000.

So one of the mysteries about the C&O Canal concerns exactly how many and which locks were extended. Additionally it is clear that not all were extended on the upper end. Unrau states in a footnote on his study of C&O Canal locks (p. 95) that

the Canal Company records do not indicate which locks were lengthened other than locks nos. 5–7. However physical evidence indicates that [the] locks lengthened were Nos. 25, 27, 29, 30, 31, 32, 33, 37, 38, 43, and 60. See USDI, NPS, “The Chesapeake and Ohio Canal: A Physical History,” by Miele (1968), pp. 22–54.

These eleven locks together with the first three extended locks (5–7, which, however, were likely only extended by 10 ft. as called for in the original and interim plan of 1876) would represent a total of fourteen, agreeing with the 1883 report. If indeed two more were extended later in 1883 the total would have been sixteen as indicated in the 1884 report—although this leaves the Unrau/Miele listing short by two locks. Hahn also indicates that the total number of extended locks was fourteen (not sixteen) and that eleven were extended on the downstream end and only three on the upstream end. (p. 64) No source speaks to the fact that locks 5–7, with their merely 10 ft. extensions, could not have passed the 240-ton sectional freighters in their intact configuration and thus they should not have been included in lists of the fully-extended locks.

Although it may seem but a matter of physically surveying the locks to see which were lengthened, such on-site evaluations are not always definitive. Lock 68, for example, was extended on both ends, according to Hahn (p. 207), who states that the downstream extension was done to permit passage of the longer boats but the upstream extension was “to allow greater depth of water.” If a definitive list of fully lengthened locks exists, I would love to know about it.

Note: While the locks were intended to be 15 feet in width, the tendency of the locks to bow inwards (especially the upper ranks of stone near the center of the lock) resulted in an actual width often several inches less than this. The issue of lock width was discussed in my article “Those Incredible Shrinking Locks” in the September 2000 issue of Along the Towpath.

-- Karen Gray

Bearss, Edwin C. The Composite Lock: Chesapeake & Ohio Canal National Monument, Division of History, Office of Archaeology and Historic Preservation, March 31, 1968
Davies, William E. The Geology and Engineering Structures of the Chesapeake and Ohio Canal: An Engineering Geologist’s Descriptions and Drawings (1999, C&O Canal Association)
Hahn, Thomas F. Towpath Guide to the C&O Canal, 10th Edition, 1992
Unrau, Harlan D. Historic Structure Report, Historical Data, The Masonry Locks, Chesapeake and Ohio Canal National Historical Park, Maryland/District of Columbia/West Virginia, June, 1978, Denver Service Center, National Park Service, U.S. Dept. of the Interior, Denver Colorado.

The source of this article is the C & O Canal Association’s newsletter, Along the Towpath, Vol. 35, No. 2, June 2003.

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