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September 1, 2001 Issue
September 15, 2001 Issue
September 1, 2001
The Advantage Of Resonance In Concrete Canoes
(From an Internet printout received from reader Don Stucke)
The idea of a concrete canoe may sound like a contradiction in terms, but how about one whose material is geared to be outer-space worthy, and whose conceptual design is so unconventional that it was once incorrectly applied to a bridge that consequently sank?Yep, this is no ordinary canoe. In fact, the most pedestrian thing about it is the concrete part. Concrete canoes are not new; universities throughout North America have participated in concrete canoe competitions for at least 14 years. But there's never been a successful one built designed to achieve its natural resonance, and that's leaving many a structual engineer completely floored.
A lot of people would say "You're nuts," said Robert Vaughan, a structural engineer at Marshall Space Flight Center. Structural engineers are taught to avoid building anything that may come into contact with a matching natural resonance. To do so is to invite disaster. Natural resonance describes the minute vibration frequency that every object has. If you get two objects sharing an exact natural resonance, it can lead to those vibrations being excited into stronger ones.
A famous example of this gone wrong is the Tacoma Narrows Bridge in Washington state. The bridge was inadvertently designed with a natural resonance equal to the vibrations created by the wind gusting through the narrows. On November 7,1940, the wind blew with a fluctuating force that was exactly in resonance with the frequency of the bridge. ne equal vibrations of the wind and the structure of the bridge caused the bridge to roll, buckle and ultimately collapse.
Some may be wary of getting into a canoe, concrete or not, if it were designed to operate when excited in this way. "It's operating on a paradigm. The prevailing concept is turned completely backwards," Vaughan said. But according to Dr. John Gilbert, faculty adviser at the Universitv of Alabama in Huntsville. where the canoe is being built: "Half the great ideas people have come up with have come from people not thinking in the normal way.
To achieve resonance, without failing apart, the canoe, known as Survivor, has to be made from concrete. The concrete is made up of a mix of Portland cement, glass microbeads (microscopic hollow spheres), latex, acrylic fortifier and water. Mix these in the right proportions, allow the mixture to dry for 12 hours and presto, you have concrete so flexible that it will bend and snap right back with nary a crack.
"Our biggest claim to fame is that our concrete just doesn't crack," Gilbert said. "We can get more flexibility from this material than they can get in the aerospace industry." With this flexibility, the team hopes to push the 22' canoe to its natural resonance of 6Hz (six vibrations per second). "If our boat reaches this, it'll start to flex and the side walls will bend in together and then apart, like butterfly wings," Gilbert said.
"What we try to do is attain this natural resonance and then utilize the energy it creates and turn it into forward propulsion," Gilbert said. "The boat bends and deflects with very I ittle energy input," Vaughan added. "You can cause something to move with very little energy input and then use the energy produced for something positive. It's a very innovative and bright approach."
The canoe, which weighs 76lbs, took six months to build and cost $1,200, is built around a mesh frame made up of strips of graphite fiber an eighth-of-an-inch thick. The cement is thinly applied over this mesh, "a little thicker than the diameter of a pencil," Gilbert said.
Gilbert admits that he still has a long way to go with the canoe. "We still need to do a lot of engineering and testing. I'm not saying that we are there yet. It's virgin territory but the underlying value of the technology is evident. It opens new horizons."
Despite Gilbert's reservations, Survivor has fared well in competition, finishing first against 24 other teams in the 2001 ASCE/MBT National Concrete Canoe Competition held last month in San Diego. "We won because we utilized the boat's natural resonance. The other teams had not looked into using this, although I am sure they will now," Gilbert said.
Gilbert is also very confident of the future of the canoe. "Before, it was thought of as ridiculous with no benefits at all but I believe it's going to be the boat that will make the difference on who gets silver and who gets the gold at the Olympics," he said. "Our boat can travel up to 14 feet per second. This is lightning speed compared to a regular canoe, which can go about 8 feet per second. An Olympic race canoe can probably go one-half foot per second faster than us," Gilbert said.
Others are not so confident of the canoe's Olympic prospects. "If we raced them over a straight-line course, his boat would be left for dead," said Charles Luckman, sprint program director for USA Canoe/Kayak. "It's a great project but it's primarily an engineering project. We have years of research in hydro-dynamics behind us," lie added.
Canoe designer John Winters agrees. "They are not likely to replace conventional canoes because they are not light enough and are quite fragile," he said. "Once the conapetition is over they often end up in the landfills."
September 15, 2001
Scallop Hunting at Anclote Key
By Hal SchmeizerThe lower limit of the area where it is legal to take bay scallops in Florida is currently the Suwannee River. When I was living in Palm Harbor in the late 1980s it was legal to take them down off Anclote Key, just west of Tarpon Springs. I read about the scallop season in one of those breezy articles they run in the back of the sports section of the Tampa Tribune. I thought, "Why Nor?"
My SOD, Andy, and I got our snorkels and masks out of the closet and found we didn't have a dive flag. I got out some red, ripstop nylon left over from another project and we took over the kitchen table on a Friday night to make a diving flag. I hand stitched around the edges, set two grommets in the corners, and used a strip of sail mending tape to make the white stripe. All out of my sail mending kit, bigger, and a lot cheaper than the store bought plastic flags in the boat stores.
We got up early on that July Saturday and hooked the car to our 20'fiberglass sloop, Jean Marie, that lives on her trailer in the side yard. I had topped the gas tank the night before, all six gallons, and we put the ice chest with lunch and the jug of frozen water in the cabin and off we went. The trip to Pop Stansell park on Sutherland Bayou takes less than five minutes and we have the little park with its sand ramp and wooden fishing pier all to ourselves. I take the time to rig the mast and hank on the jib. We plan to motor up to Anclote Key, but like all rag baggers, I have been betrayed by my outboard before.
This time the four horsepower Evinrude Yacht Twin with its long shaft starts on the third pull of the recoil starter. We use the outboard spun into reverse to back away from the fishing pier that doubles as the boat dock. The sky is now clear blue and the sun is coming up over the land as we motor out of the bayou past the mangroves and the oyster bars. The temperature never drops much below 70 degrees in the summer in this neck of the woods. We can see the huge homes built on stilts off Seaside Point with the glass doors closed and the air conditioners running full blast. Andy rigs the bimim top up over the cockpit and we sort out the extra cushions until we are comfortable. The water is shallow around here and I keep the swing keel up. With the keel up, the 20', 2000-pound Montego, built in St. Petersburg, draws about 18". The rudder has a kick-up blade of fiberglass and has been patched on the edge a few times.
We clear the end of the bayou channel, slip easily into St. Joseph Sound, and turn north toward Anclote Key and the wily bay scallops. Off to port are a series of small party islands labeled "spoil" on the chart. They were pilcd up when the inlracostal waterway was dredged. The islands have sand beaches, small coves, Australian Pines, and mangroves. The interior of each is littered with beer cans, broken glass. and old campfire remains. Farther off to the west is the green backside of Honeymoon Island. This is a great island state park with a causeway leading to it. The south end ofthe island is developed with the picnic areas and bath houses. The park rangers keep it safe and clean for families and tourists. The norlh end of the island is mangroves with small patches ofbeach reached after hiking through the woods with tall pines and palmetto palms, The fishing is good off the grassy flats on the eastern, protected side of the island. As we motor north we can see a long, curving, sand island that is covered by tall waving grasses. The place is called Three Rooker Bar and is a favorite anchoring spot for the big power cruisers that blast up the intracoastal from Clearwater and points south. From time to time several small ultralights fly out and land on the long sand beaches, Andy and I have seen schools of Tarpon with their tails and fins showing in the two mile pass between Three Rooker Bar and Honeymoon Island.
We keep our eyes peeled as we purr north with the outboard at half throttle. This pushes our little sloop at bull speed and only uses one half gallon per hour. We have found that this boat with its cockpit shaded by a bimim top, the stability of the 500 plus pounds of keel, and the open cabin top and fore dock makes a great fishing platform. Sometimes we fish and sometimes we just sail, but always we look at the astounding variety of sea life.
St. Joseph Sound is just at the end of the intracoastal and despite the continuous building and population growth the marine life is still present. We have sailed up on huge green sea turtles basking on the surface and then watched in awe as they rocket off to the bottom. How can something so big and slow looking move so fast? The porpoise are very much in evidence and we have had them swim off our bow and pace us. The pelicans and the seagulls and the diving ducks come and go without even looking at us as we get closer to Anclote Key. The Sea Pearls were built near Tarpon Springs and there is a covey of them that moor off Klosterman Point. Chasing Sea Pearls with their tan bark sails and open cockpits is great fun and they really dress up the area.
Anclote Key is a state park and has an abandoned red lighthouse on the south end. Anclote Key also guards the entrance to the Anclote River that leads right into downtown Tarpon Springs. We get to the green flashing buoy number 41 that marks the end of the intracoastal waterway and start looking for a place to start the scallop hunt. We see quite a few small power boats anchored in the grass flats with diving flags waving from their radio antennas. I throttle back the outboard to a mutter and we glide quietly through the anchored boats and swimmers. There are a lot of people in the water with the orange tips of their snorkels and the round bulging of swim suit bottoms as they dive down to the bottom. The water here is bath warm and crystal clear. The bottom is waving brown grass with white sandy patches. Occasionally a long clear streak shows where someone blasted through the grass on a low tide with a fast prop. Andy ~oes forward and drops the anchor and chain. lAle keep the anchor and line Lip On the bow pulpit in a piece of white pvc pipe banded upright. It works well and keep the anchor and line out of the way when we are sailing
I rig our rope and wood ladder oft' the backand we jump off the stern into the water. Heaven.
The sun is well up, its about 9:30 in the morning and there is just a hint of breeze from the northeast. We have short sticks to stir in the grass and net bags to put the scallops in. The scallops are there, but it takes some effort to find one hiding in the top of the grass. If you are not careful with the draw string on your bag, the scallops will swim off. It is amazing to see a shell that looks like a gas station sign swimming off by pumping water through its shell.
Stingrays are in the white sand patches and leave swimmers alone. If you step down on one they lash around with that nasty tail and the barb gets you. No troubles today as we give them a wide berth. After we swim around for about an hour we get used to them and quit worrying. Getting back on the boat is a real chore. Even with our salty looking wood and rope ladder it is work. I resolve to look into a fixed ladder on the stem.
We sit in the shade of the bimini top and drink cans of icy cold soft drink and it's great. We don't get more than about two dozen sea scallops, but that's all right. The thunder clouds are building up for the afternoon deluge off to the east over the land. The air is hot and the metal parts of the sloop are too hot to touch. Welcome to boating in the Florida summer.
The ride back is uneventful and the ramp is clear for a quick retrieve to the roller trailer. I get the mast down after the boat is on the trailer. I keep one eye on the clouds and hustle getting the mast down. We lose lots of boaters every year from the lightning. Last month a young man taking down the mast on his Hobie Cat on the causeway to Honeymoon Island was struck and died before he could get to the hospital. Back at home we back the trailer in and hose down the whole rig with fresh water. I have built a huge wooden gate/fence in front of the boat to keep the home owners association happy. We close up the gate and go in to clean our catch.
The scallops are small and not too many. I shell and clean the white meat portion. We sautee them in butter on the stove and stand around in our bare feet and swim trunks eating them off forks. The shells go into my wife's sea shell collection, and the trip goes into Andy's and my memories.
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