Building the Scale Model of the DeTour Reef Light Crib


By John Covell

Sometime during the late 1920s, the Lighthouse Service determined that the lighthouse at DeTour Point would need to be replaced with an off-shore facility. The St. Mary’s River is the only shipping link between northern Lake Huron and Lake Superior, and the DeTour Reef lurks only 21 feet below the surface, a hazard for all St. Mary’s traffic. At the time, accurate navigation around the reef was not possible, and so the new lighthouse would be located on the reef itself, almost a mile from the nearest land. Here it would serve to guide ships in upper Lake Huron to the mouth of the St. Mary’s and the DeTour Passage.

General foreman for the project was to be John Sellman. Sellman had been working for the Lighthouse Service since 1909, and had been in charge of the Stannard Rock and Martin Reef projects, and he had an experienced crew available. The new light on DeTour Reef was to be anchored on the reef itself, using an underwater structure called a crib.

The crib for the new lighthouse was to be similar to the crib built for the lighthouse on Martin Reef. For purposes of clarification, the term “crib” applies to a wooden lattice work structure used as a containment for the concrete mass, supporting the pier upon which the lighthouse would be built. The crib would be built at Watson’s Coal Dock, a site just north of the present day DeTour Marina. When finished, it would be floated out to the reef and sunk into place. Here a concrete pier would be built upon it, and upon the pier, the lighthouse. In service since 1931, DeTour Reef Light still stands today, a monument to the men who designed and built it. This is a short story of the building of the crib that supports DeTour Reef Light.

Before I describe what the crib was to be, I need to note what it wasn’t. There are several misnomers in current usage today. An example might be the practice of confusing the word “cement” with the word “concrete”. “Concrete” is a word that describes a mixture of sand, gravel and water, bonded together by “cement”, a heavy grey-colored powder. When the cement takes up the water in the mixture, it once again becomes hard, like the rock from which it was made. Another point of confusion is the practice of using the terms “caisson” and “crib” synonymously. To simplify matters, a caisson or coffer dam, is a structure used to provide a relatively dry work area below water level. Once firmly in place, the water is pumped out, leaving an empty space. Here such things as bridge piers may be erected, and then anchored in concrete. A crib, on the other hand, although water tight, is not pumped out. Concrete is placed by means of the tremie method. The mix is delivered by large sealed tubes or pipes, to the underwater surface of a reef, lake, or river bottom, displacing the water as it fills the prepared chambers of the crib. This system is ideal for constructing smaller structures, such as a lighthouse pier. The crib can be built off-site, floated to the site and sunk into place. The method is very cost-effective, an important consideration in the 1930s.

No one really had any idea that what they were undertaking in 1930 was to become an historic monument, after an extensive restoration, some 80 years later. There was no diary of events kept during the construction that we know of. The restoration committee had the architectural drawings and some fine photographs showing various stages of development, but what was lacking was a step-by-step schedule or plan by which the crib was put together. Also, the restoration effort was confined to that part of the lighthouse that was above water level. Only part of the steel plating of the crib is visible today. The restored lighthouse was to be opened for guided visitors, but there was little that could be done to show visitors just how the lighthouse was supported on a reef, almost a mile from the nearest land. It was decided that what was needed was a model that could be displayed for our visitors.

The idea of a scale model was the brain child of Dr. Chuck Feltner, historian for the DeTour Reef Light Preservation Society. While looking for someone to do the actual work of building the model, this author stumbled in and took the bait. It was a task that looked straight forward enough, once I had studied the plans and photos. Model builders can often buy kits that include all the necessary materials, and plans containing specific instructions for assembling the model. Lacking an instruction manual, I decided that the best way to accomplish my task would be to adopt the same set of procedures used by the workers who built the actual crib, back in 1930.

But, where to start? At the bottom, of course, but how? A lot of study and research followed. Consultations with Dr. Feltner produced some answers, but also led to more unanswered questions. We both agreed that the best we could do would be to proceed on a plan of reasonable assumptions. As it turned out, we found out that we were right on the mark, but more on that later.

The real crib was basically a lattice work of heavy Douglas Fir timbers, 60 feet long and one foot in cross section. Such timbers do not exist in nature, so plans were made to join them together using bolted scarf joints. The ends of the timbers were dove tailed into the outer walls of the crib, also made of the same materials. The outer walls were caulked and water-proofed. Reinforcing the dovetail joints were vertical steel angles, bolted into place, and rising about 21 feet above the bottom of the crib. The interlocking timbers formed a network of contiguous chambers, each about 10 feet square and 20 feet tall. The 16 inner chambers were isolated from the outer chambers by a wooden plank wall. Below the inner chambers, a heavy wooden floor provided a means of containing the rock ballast that was to secure the crib to the reef, while the pouring of the concrete fill was underway.

We knew that the crib was assembled in the water, but we had to discount the idea that it began there. In the drawings, bolts were called for, fastening the first two tiers of timbers together, and it was there- fore logical to think that some primary assembling began on land, while final assembly took place afloat in the water. As it turned out, our assumptions were correct, but verifications of that came later after our model was finished. Logic also told us that the flooring would, of necessity, be installed as one of the very first steps in construction. Gradually the picture of how things were done in 1930 was formed. Once the entire wooden works was completed, it would be crowned with half-inch steel plating, eight and a half feet tall. This was to protect the upper part of the crib from ice damage during the winter months.

This, then, would be the crib under DeTour Reef Light. Noteworthy were the four spud timbers which served as a set of retractable table legs. These could be lowered down to the surface of the reef, keeping the crib in a fixed location until enough rock ballast could be placed to secure the crib to the reef. The reef itself was a sunken rocky promontory. It had been leveled as much as possible by hard-hat divers, providing a 75 foot square bed for the crib. Once the crib was filled with ballast and concrete, tremie tubes were used to pump concrete into the space below the floor of the crib. This was a point of interest, as tremie tubes were not evident in the Martin Reef crib.

When the model was almost complete, a most remarkable book came to light. This book was the work of John J. Sellman. Mr. Sellman was a lad of ten years when his father was the chief engineer on the Martin Reef Light project. Young John J. joined his father each day on the job, and his recollections of those days spawned the basis for his book.

More importantly, Mr. Sellman included photographs of the Martin Reef Crib, in the early stages of construction, and it was these photos that confirmed that our assumptions about the work at DeTour Reef were correct. One of the most striking of these photos shows the tender MARIGOLD, or possibly ASPEN, in the act of towing the infant crib from the skid way, where it began its existence. We knew then that the same procedure must have been in use at Watson’s Coal Dock, where the DeTour Reef Light crib was born. Provided with this information, we can now offer our visitors and weekend keepers on DeTour Reef Light a much more complete picture of the crib beneath our lighthouse.