World's fastest Personal Submarine

SeaBird is claimed to be world’s fastest personal submarine – and it doesn’t even have a motor

If the amount of personal submarine stories crossing our desks in recent years is any indication, recreational submarines are a burgeoning market. While most personal submarines, such as U-boat Worx's offerings, employ electric motors powered by a rechargeable battery pack, US-based company AquaVenture has taken a different approach to create what it says is the fastest personal submersible available. This is because the SeaBird doesn't pack a propulsion system of its own, but is instead towed through the water by a surface vessel.

AquaVenture says the patent-pending tow system used on the SeaBird essentially delivers the power of an internal combustion engine to an underwater vessel. Pointing out that the fastest personal subs currently available are limited to speeds of less than 10 mph (16 km/h), the company says the SeaBird will be certified to travel at speeds of up to 22 knots (25 mph/40 km/h), both above and below the water's surface.

The SeaBird can be towed on a cable of up to 400 ft (122 m) in length, which allows it to operate in a large cone behind the towing surface vessel. Up to two SeaBirds can be towed from the one surface vessel and AquaVenture says the vehicles can operate to depths of 150 ft (46 m) - however, this can be doubled to 300 ft (91 m) for "certain (non tourism) customers." The SeaBird also provides a habitable atmosphere for 24-72 hours.

Controlled via a side-mounted joystick and rudder pedals, the SeaBird is guided by an electrically-actuated 6-hydroplane control system, which AquaVenture says allows it to perform rapid 360-degree rolls, and climb and dive steeper than most roller-coasters. The company also offers the option of a single center-mounted 3-axis control stick in place of the side-mounted joystick and rudder pedals. The electrical system is powered by 24-volt hot-swappable batteries that can swapped out in around five minutes.

The SeaBird's pressure section is constructed from ABS certified steel, with the canopies made from ABS certified Plexiglass and the external faring or shell composed of composite materials - primarily fiberglass with Kevlar at the front for impact protection and in the lower portion of the shell for protection from sea-floor impacts. An energy absorbing crumple zone is designed to protect the sub's pressurized section in the event of a collision, while its positive buoyancy means it will automatically surface if the towing vessel comes to a stop or is disconnected from the SeaBird.

The SeaBird also features a sonar system to display potential underwater hazards in cases of reduced visibility and offers optional extras including leather seats, headliner and trim, custom exterior paint job, wired telemetry system offering the ability to transmit video, GPS and other data in real time between the SeaBird and the surface, additional video monitors, upgraded lighting, and additional sensors, such as water temperature, salinity and sea-state.

While a single-seater version is in the works, AquaVenture will initially launch with a two-seater model measuring 21.5 ft (6.5 m) in length, with a maximum diameter of 40.5 in (102.8 cm) and maximum width at the dive planes of 120 in (305 cm) and a dry weight of 6,570 lb (2,980 kg). Without its own propulsion system, the company says the SeaBird will be cheaper than most personal submarines on the market - although you will obviously need to shell out for a surface vessel to tow it if you don't already have one.

Its US$210,000 base retail price includes training for one pilot and a short warranty period that has yet to be finalized. AquaVenture has had the SeaBird in development for over four years and has just recently completed design and testing and begun taking orders.

Huge Breakthrough for Solar

While solar panels are very useful at converting the sun's rays into electricity for immediate use, the storage of that energy for later use is ... well, it's still being figured out. The energy can be used to charge batteries, for instance, but that charge will wear off over time. Instead, scientists have been looking at thermo-chemical storage of solar energy. Last year, researchers from MIT discovered that the chemical  fulvalene diruthenium was quite an effective storage medium. Unfortunately, the ruthenium element that it contains is rare and expensive. Now, however, one of those same scientists has created a new storage material that is cheaper, and is able to store much more energy.

The advantage of thermo-chemical storage in general is that the chemicals can be stored for long periods, without experiencing any energy loss. Suitable chemicals that don't contain the pricey ruthenium, however, have tended to degrade within just a few storage cycles.

MIT associate professor Jeffrey Grossman, who led the research last year, has now developed something better. He and postdoc Alexie Kolpak combined carbon nanotubes with the compound azobenzene, the result being a chemical that is less expensive than fulvalene diruthenium, and that has about 10,000 times the volumetric energy density - in other words, it can store more energy in less space.

Kolpak claims that its energy density is similar to that of a lithium-ion battery. By utilizing different methods of nanofabrication, it is also possible to independently control both how much energy can be stored, and how long it can be stored for.

The system works thanks to the azobenzene-functionalized carbon nanotube molecules, that change in structure when exposed to sunlight, and are capable of staying in that state indefinitely. When a stimulus such as a catalyst substance or a temperature change is applied, however, they revert to their previous form, releasing their stored energy as heat. That heat can be used directly in heating systems, or can be used to generate electricity. The molecules, meanwhile, are ready to be charged again.

"You've got a material that both converts and stores energy," said Grossman. "It's robust, it doesn't degrade, and it's cheap."

The MIT research was recently published in the journal Nano Letters.