At the rail of the Duda was French underwater archaeologist, Franck Goddio—the same energetic man who has been made internationally famous in Discovery Channel specials. Franck welcomed us to the team. Our three crates of heavy equipment had traveled much farther than us to reach Alexandria—they were now on the main deck of the Duda. As we off-loaded them onto a smaller crane boat, antiquities were being carried up the dive ladder or hoisted by crane onto the main deck at an amazing rate. Our mission, as Goddio and the Smithsonian Institution's Dr. Jean-Daniel Stanley, reiterated, would be to collect about 40 sediment Goddio, with a Bronze Age pot recovered from the submerged city of Herakleion, Egypt


vibracores using our P-3 Rossfelder System. The cores would be driven at key locations in the areas of ancient Herakleion, Menouthis (both in Abu Kir Bay), and in Alexandria's Eastern Harbor (home to Cleopatra's Palace, and possibly, the lost Pharos Lighthouse). All three areas have one common trait, they are submerged under the Mediterranean and have been for a thousand years.

Goddio team diver, American, Eric Smith, worked with us to accurately position (DGPS) and anchor the vessel over each sampling point. Eric would then don his Scuba gear and dive to survey the sea floor, minimizing the possibility of making a direct hit on or into a priceless antiquity with our vibracoring equipment. During this process, Eric found what may be a small sphinx, several building foundations and cobbled streets—all areas we carefully noted and avoided.

The sediment cores we collected will be studied by Dr. Stanley's scientists at the Smithsonian Institution. Cores will be X-rayed, each strata carbon dated and physically analyzed to try to unlock the mystery as to what caused this massive area of northern Egyptian coastline to become submerged under 30-60 feet of water and sediment.

Working with our sediment coring tools to aid in an international archaeological mission was a first for us, as well as having our work filmed by the Discovery Channel. We are looking forward to working with Franck Goddio on other missions and to seeing our equipment at work under water, as it advances through the sediments of time on the Discovery Channel.

We would like to say "thank you" to Dr. Stanley and Franck Goddio for giving us this unique opportunity to be part of this important archaeological mission and to diver Eric Smith, who so vividly transferred his finds on the sea bottom to those of us on deck— "There is a cobblestone street below the vessel; if I were to take off my fins, I could stroll down it."

Among the three basic types of vibrators—pneumatic, hydraulic and electric—pneumatic piston vibrators were the early favorites because they can work underwater with very little adjustments and don't involve the undersea use of electrical current, long considered risky. While they were extensively utilized for many years and still are, these vibrators have a basic limitation: they work on compressed air, therefore essentially against the ambient pressure. Air consumption increases so rapidly with depth that pneumatic vibrocoring is only applicable to shallow waters; also it requires a cumbersome compressor and the hose becomes an impediment in swift or choppy waters.

Hydraulic vibrators may appear more attractive because the fluid flows in a closed circuit in balance with the surrounding environment, but we encounter here again the two drawbacks of pneumatic vibrators—the need for a hydraulic power plant and for an umbilical hose. We shall note however that high-frequency air-ball or hydraulic vibrators have a niche in sub-aerial "resonant" vibrocoring as later noted.

When considered in terms of force/weight ratio, all included from the power source to the vibrohead, electric vibrocorers readily appeared to be the most attractive choice, particularly when the energy source is already part of the vessel's system. From our experience in handling electrical instruments at sea during many years of exploration in the surf or spray zones of the Pacific atolls and in view of the rapid development of a wide variety of safe underwater connectors, we concluded that electric drive was simply the best choice.

A main consideration in developing our vibrocoring systems was the "Rule of Deployment" that every oceanographer knows by experience—the cost of an operation is related to the size of the vessel which is related to the size of the draw works which is related to whatever hangs at the end of the cable. This concern led us to minimize the weight of the individual parts of our models while maximizing their overall force/weight ratio so that they could be handled with limited manpower from small vessels and even from inflatable barges. We similarly developed our patented underwater "buoyant frame" to replace the bulky bottom-standing rigid frame ordinarily used for stabilizing and guiding vibrocorers. In this arrangement, which is very easy to deploy, the vibrocorer is guided vertically between two taut lines connecting a weightstand and a float package.

Many other improvements can be and have been applied to vibrocoring. Some important improvements are also the simplest, e.g., a free-flowing water escape, a tight check-valve and a good seal at the top of the coretube—which can all be incorporated in a special plug, and also an acceptable, if not perfect, core-catcher at the core nose. Others are more difficult to develop into a reliable design, such as an efficient positively-closed core-catcher. Some procedures intended to increase the penetration are very valuable but are not always easily implemented in open sea: e.g., incremental coring either performed with straight-through water-jetting or with reverse-circulation in a casing. Or they may involve some relatively complicated systems where, for example. the vibrohead is mounted on restoring springs in a "vibro-hammer" design in order to increase the energy delivered downward, or, for another example, compressed air is injected inside the coretube at a pressure slightly above ambient in order to eliminate the water column and to improve the core recovery ratio and its quality.

The tradeoff between standard vibrocoring and these more elaborate designs or procedures generally relates to the cost, efficiency and practicality of the improvement with due regard for the support vessel, the available manpower and the operating conditions.

André Rossfelder, D.Sc.
ROSSFELDER Corporation
www.rossfelder.com

Under the NED contract, ASI will be providing Battelle with on-water services such as vibracoring, hydrographic surveys, and current studies. In addition, ASI will provide sediment water column and benthic solid phase toxicity testing services as well as bioaccumulation studies to Battelle in support of this contract.

The P-12 will augment ASI's already extensive line of vibracoring equipment. We expect that the P-12 will now allow us to provide clients with sediment, sand and gravel vibracoring services. Rossfelder is the manufacturer of the premier line of electric vibracoring equipment. ASI currently owns six complete Rossfelder vibracoring systems, and provides vibracoring services worldwide (e.g., we used our Rossfelder P-3 unit for coring in Egypt).