There are basically two kinds of power systems for tethered underwater remote operated vehicles (ROVs). One type of ROV has a power cable running down the tether, and the ROV gets the electricity to run its motors, operate its lights and sensors, etc., from a shore station, either a large battery pack or an electrical connection. The other type of ROV carries its power supply internally, generally in the form of high-capacity rechargeable lithium battery pack.
For some specialized missions, an ROV powered from the shore has its uses. However, for most types of ROV operations, a battery-powered ROV like the Aquabotix Endura or Hydroview Sport has the clear advantage. There are three main factors that make running an ROV from battery power the better choice.
First, battery power is portable. A battery-powered ROV can be deployed anywhere the ROV can be carried to, and the lightweight ROVs made by Aquabotix can be carried by one person to almost any location on Earth. Battery-powered ROVs can be deployed from the beach, from a small boat, from an oceangoing ship, from an offshore platform – if a person or vehicle can get there, then a battery-powered ROV can go with them and engage in missions from that spot.
Second, battery power is compact. The person or team deploying a battery-powered ROV does not need to carry a bulky generator with them to remote areas in order to send the ROV on missions. They can carry the charged ROV to the entry point and work from there without needing any expensive and heavy infrastructure. This makes a one-off mission even in the remotest areas simply a matter of putting the charged ROV in a vehicle (or even a backpack) and heading out.
Third, because radio waves do not carry well underwater, all non-autonomous ROVs use a tether to provide control and communication with the operator. In an ROV that relies on shore-based power, this tether also carries the electrical power the ROV uses for its operations. That means the tether must be much thicker for a shore-powered ROV. For example, a typical power-carrying cable might be [X – Beats me <g>] millimeters in diameter, while the tether for an Aquabotix ROV has a diameter of only [X] millimeters. Of course, a thicker tether is also a heavier tether – 250 meters of standard power-carrying tether weighs [X] kilograms, while the same Aquabotix tether weighs only [X]. This makes moving and deploying the battery-powered ROV much simpler and easier.
Battery-powered ROVs are simply easier to deploy, easier to carry, and able to operate in places that powered ROVs cannot.
Fish farming in the ocean and off the coasts has become an enormous business. Declining wild fisheries and an insatiable (and growing) global appetite for fish have created tremendous opportunities for the development of oceanic aquaculture. Local cultures have conducted aquaculture (generally in lakes and river systems, rather than the ocean) for thousands of years, but modern aquaculture has become a globally important food source. The UN’s Food and Agriculture Organization estimates that about half of the world’s food fish come from aquaculture, and the sector continues to grow at an astonishing rate – five to six percent annual increases in production are the norm. Total aquaculture production is over 80 million tons per year of fish, crustaceans, mollusks, and aquatic plants.
There are two basic types of oceanic fish farming. Coastal farming involves shallow-water farms located on the coast, along rivers, or in lakes. Open ocean farming involves deep-water farms that are not tied to a specific coastal location. There are important differences in these two approaches to oceanic aquaculture.
Coastal fish farming is the predominant form of oceanic aquaculture today. In a coastal aquaculture facility, pens or fish cages are deployed along the coastline, often in a protected bay or inlet. Most crustacean and mollusk farming is done inshore, using racks on which the food animals are grown. Depending on the species being farmed, the nutrients for the farmed food animals might come from the water itself, from the provision of forage fish, or from the addition of nutrients into the water in soluble form.
There are advantages to farming fish along the coast. Because the facility is located near the shore, storms are attenuated by the proximity of the landmass, and both workers and shipping infrastructure are close at hand. Operators can bring in supplies and export product from the convenience of local railheads and ports. Because the water is generally shallow at the coastline, it is also possible for operators to use ranch-style techniques, building habitats on the sea bottom for desirable fish such as abalone, and then simply catching the fish in the normal fashion without needing to closely manage the population.
Coastal farms have a number of significant disadvantages as well. Coastal areas are subject to intense competition from other uses such as recreational activities, fisheries, ports, and renewable energy development. Fixed-site aquaculture also has fairly severe environmental impacts on the delicate coastal ecosystem. Fish farms produce large quantities of waste and excess nutrients, which settle onto a fixed location on the sea bottom. This can utterly disrupt or even extinguish the local benthic ecosystem, causing repercussions to fisheries and tourism. Disease among the fish stocks is also a major problem, and because coastal fish farms can be close to one another, a disease which decimates one population can spread to other operations, even crossing species barriers.
Offshore fish farming, or deep-ocean aquaculture, cuts the ties to the shore, although not to the sea bottom. Generally, an offshore facility is tethered to the bottom and anchored to buoys, so that cages can move up and down in the water column but are still at a fixed location in the ocean. An offshore aquaculture can be sited almost anywhere, and does not have to compete with pleasure boating or fishing fleets. In addition, the much greater area (and stronger currents) available for dispersal of waste products and excess nutrients means that the environmental impact is significantly reduced or eliminated. Disease transmission is less problematic, and experimental offshore aquaculture operations have found that parasitic infestations are much more easily managed in the relative isolation of an offshore facility. Offshore locations are also more able to coexist with other uses of the same area of the ocean; since the cages can be moved deeper into the water than is possible in a coastal area, other uses such as boating can be accommodated.
Offshore aquaculture has its own set of problems, however. The expense of building cages that can withstand the storms and currents of the open ocean is considerable. Because the environmental conditions are more rigorous in the open sea, fish escapes are more likely to occur, which has ramifications both in terms of cost and in the potential for the introduction of invasive species to ecologically vulnerable areas of ocean. In addition, the laws and regulatory environments that apply close to shore (within the three-mile limit, for example) become more complex further out to sea; for this reason, off-shore aquaculture in the United States has primarily developed only in areas of the ocean that are unambiguously under Federal jurisdiction so that operators can have a predictable legal environment in which to do business.
Despite the potential issues and problems that arise in both coastal and offshore aquaculture, it is a certainty that these areas of economic activity will continue to grow and expand. Fish are a vital part of the global food infrastructure and aquaculture is rapidly becoming the dominant way in which this sector produces its output.
Underwater cave diving is one of the most interesting, fascinating, and dangerous types of underwater exploration, and offers divers the relatively rare opportunity to explore genuinely unknown territory. From the cenotes of the Yucatan Peninsula to the submerged coastal caves of Mallorca, underwater caves are beautiful, archeologically important, but perilous to untrained and trained divers alike. The dangers of underwater cave diving have led to the development of strict protocols and training regimes for underwater cavers, which ironically have made the actual death rates from such diving fairly low.
Unlike open-water diving, where a diver in distress can simply head to the surface, cave diving is a type of penetration diving. To leave the dive zone, the diver must swim back out of the cave, as far as he or she has already penetrated, reversing an often difficult navigational process and requiring enough air to reach the surface. Caves can have strong currents, both of inflow and outflow varieties, and some cave systems have inflows to one egress and outflows from others, meaning that a diver can easily underestimate the amount of time it will take to retrace a route. Visibility can vary wildly from perfect to zero within the same cave. In addition, there is a possibility of getting lost in a cave of any significant size.
All of these factors mean that cave diving is out of reach of casual divers (or should be), and cave exploration thus left to a relatively small cadre of extremely well-trained divers. However, the development of inexpensive and easy-to-use ROVs has changed the balance in cave exploration. ROVs can be sent into the water by people with zero dive experience to explore caverns, caves and cave systems in perfect safety. Modern ROVs have high-resolution video camera systems and powerful lighting systems which permit incredibly detailed views of the underwater environment, efficient electric motors that allow hours of underwater time, and long tethers which permit explorers to penetrate hundreds of meters into underwater cave systems. In addition, a small ROV can be packed overland to inaccessible inland underwater caves, such as the deep cenotes in the Yucatan, or easily deployed from a small boat in coastal locations.
ROVs are also a useful support tool for experienced divers who are exploring difficult or unknown cave systems.
ROVs can be used to ‘scout’ unfamiliar passages or to check whether there is a passageway between two tunnel systems, without putting a human diver at risk. Because ROVs have a much longer dive duration than a human diver, a single scouting mission with an ROV can open up large areas of new caves for the human divers to follow up on. ROVs can also find the most interesting areas for human divers to explore, allowing the limited human dive times to be spent in the most enjoyable or most important areas of the cave system.
Although many underwater cave explorers are motivated purely by recreation or the challenge, there is also considerable scientific interest in exploring underwater caves. ROVs have been an enormous asset to scientists and archaeologists in exploring the cenotes of the Yucatan Peninsula in Central America. Cenotes are large sinkholes that open onto groundwater from an underlying aquifer. There are thought to be more than 2,500 cenotes in the Yucatan area alone, and many of them are of great archeological significance because they were used as ceremonial sites by the Maya civilization. Although many large cenotes have been at least somewhat explored by archeologists in the last century, many remain untouched or even undiscovered. Researchers and explorers have been using ROVs since the early 2000s to explore and map the Yucatan cenotes, as well as the extensive underground cave systems that many cenotes connect to.
As in most areas where ROVs are deployed, ROVs used in cave exploration serve to greatly extend the range and effectiveness of human divers, and also open up new possibilities that simply would not exist without these useful tools.