: Yes, the contest has been around for as long as I can remember. So,
: there must be some valuable leasons to be learned for civil
: engineers, Pardon my rant. :)

I went SCUBA diving in 1971 at a (usually) closed lake in Danville IL. The park rangers opened it a fw times a year so local divers could get familiar with the bottom, just in case they needed to call on volunteer divers to recover a body from a drowning victim. When i surfaced I was in the middle of the annual concrete canoe competition between the University of Illinois and Purdue. Danville was about midway between the campuses and the colleges took advantage of the one day that the lake was available.

I had never before seen a concrete canoe on the water, but I recognized these things immediately. As i swam to shore i did some mental calculations. During my previous summer of canoeing I had gathered the information from a 17 foot Grumman aluminum canoe's ID plate that it had a capacity of 900 pounds. figuring the weight of the paddlers at just under 300 pounds I calculated that the canoes must be a bit bigger--maybe 18 feet-- and would weigh around 600 pounds. At the time I thought they would be pretty heavy, but at that weight they would certainly float.

About a decade ago this topic came up on this board and there were links to college teams from (as i recall) Kentucky and Michigan. The boat design had evolved to include sealed floatation chambers--which in some case doubled as the canoe seats and cross bracing, replacing of thwarts. Putting a deck on these designs helped with the floatation chambers and structural strength. It also allowed them to float lower in the water without swamping. about that time some of the colleges were making some extremely light boats from modern "concrete" mixes. I read here about a concrete kayak which weighed under 20 pounds, but i was not able to confirm that elsewhere. I think it might be possible to do something that would weigh about the same as a rotomolded plastic kayak, or roughly 45 to 70 pounds.

Rob's comments about using fiberglass fabric as a reinforcement, rather than a steel mesh, seems like a sound idea. I'd worry about the fabric flexing and the concrete flaking off--but that can be resolved by using small sections of fabric surrounded by stiffer bracing. think of a typical SOF with a space of 6 to 10 inches between the stringers in some places. Add chines between the existing stringers to reduce the unsupported space the fabric spans to 3 to 5 inches and you reduce the amount of flex the fabric will have. So the solution would be simple--just add more chines.

In the 1980's I got a book from the library on concrete boats. Sorry, but i can't remember the title. The author was mostly concerned with larger commercial and sport motorboats and sail boats, but he included a story of a rowboat he built for a summer cabin he had. As i recall the story, he brought 3 bags of high strength cement to the beach by his cabin and mixed this with sand from the beach. The mold for the boat was made from a pile of beach sand (think about the sand castles built on the beach and imagine an ugly one which looks like an upside down rowboat). Over this mold he put 3 or 4 layers of metal screen, tying the layers together with twist ties of iron/steel wire. When he had the form completed he used a squeegee and plastered the frame with his concrete mix. The build took a day, and he kept the plastered shell on the form, watering it for a week so the concrete would cure to its proper strength. After that he flipped it over, fitted seats to the inside and oarlocks. At the end of the summer he sank the boat so the concrete would simply stay wet and unfrozen all winter. the next few years he would refloat the boat and enjoy it.

I think the low cost and minimal upkeep would make concrete canoes and rowboats interesting camp projects--but I can see a lot of concern for safety issues.

PGJ