Home | Contact ST  
Follow ST



June 2013 Issue

Deep-Diving, Manned Subs: Flipping Vertical Could be the Key
By Karl Stanley

Despite being the only way to personally explore the majority of the planet, manned submersibles have had a diminishing role in ocean science as ROV and AUV technology improves. A primary reason for this is cost; manned subs weigh many times more than their unmanned equivalents, and the ships and handling systems for manned vessels drive up costs to the point where sending in a robot is more cost-efficient.

A look at recent submersible designs demonstrates that the modern designer is well aware of this problem, but the limited utilization of the existing designs show that the costs and logistics are still problematic.

For instance, 'flying' subs offer speed, but this speed is only an illusion of freedom. In order to have an adequate reaction time to obstacles, the pilot must keep a certain distance from the target terrain. Thus, observation is severely limited.

Modern battery technology at first glance seems to lengthen—even triple—underwater range, but this too is a mirage in terms of extending the sphere of influence of a small submersible. Personal comfort limits missions to about eight hours; however, most people prefer half of that. What good is it if the batteries can go all day but the person inside the sub cannot or does not want to?

One engineering answer to cost and logistics problems associated with manned submersibles is to design these vehicles to move horizontally along the surface, then flip vertically to dive. For instance, James Cameron's Deepsea Challenger project will likely be the first of many subs to orient vertically during diving rather than horizontally because of the efficiency of this method.

Examining horizontal versus vertical orientation for diving is important when considering the desired depth of operations. For shallow vehicles, staying horizontal is not a big impediment to movement, but if the goal is to travel for miles through the water, it makes perfect sense to do so in the most streamlined way possible.

In retrospect, it seems amazing that most manned deep-sea dives to date have spent up to half of their dive time in a state of extreme positive or negative buoyancy while descending or ascending. The fact that most deep subs are run by government institutions is a possible explanation for why such a practice, which only makes sense in very shallow applications, has lasted so long.

Cameron not only demonstrated that a vertical design drastically reduces transit times to the seafloor and back; he also showed that it actually improves visibility and maneuverability as compared to that of a similar-sized vehicle that dives horizontally.

Further proof of the advantages of a vertical sub come from nature. Biomimicry has become a hip area of study in the last 10 to 15 years, but people have been looking to nature to solve engineering and other issues for time immemorial.

Nature is a particularly good teacher when it comes to submersible design. To note, all but the shallowest vehicles are some combination of spheres or ring-stiffened cylinders—the strength of which is illustrated in many places in nature (e.g., soap bubbles and bamboo).

Nature also has many examples of animals that flip vertically in order to dive deeply. Sperm whales and human freedivers would not make it even a fraction of the depth that they are able to reach if not for streamlining themselves by orienting vertically. Additionally, many deep-sea animals, such as oarfish, squid and frostfish, spend most of their time in a vertical position.

A submersible that travels to the dive site in horizontal mode, then flips vertically as it begins its dive, would dramatically extend its sphere of influence without the necessity of a large, dedicated mother ship. The time that traditional deep subs spend sinking and floating back up could instead be spent towing at 5 to 7 knots from the nearest port via a small boat of opportunity, and the passengers could be loaded at sea 15 to 20 miles away from port. The range of deep waters within 20 miles of the nearest port would be several factors higher than the 1 to 2 miles to which a sub is currently limited without the help of a mother ship.

A design that flips vertically would not only tow faster, but be much safer to load in various sea conditions because of its larger size and greater freeboard. A typical 6-to-7-foot diameter, three-person sphere would translate into 30 to 40 feet overall length. This would allow for larger-than-normal main ballast tanks and higher freeboard. This additional size would not matter much while underwater, because it would only take up space overhead—a maneuvering liability only in caves or under overhangs, places most subs already avoid.

An additional benefit lies in the simplicity of the thruster arrangement. With one large fixed thruster in the tail and two rotatable thrusters midship, the sub would not only have complete maneuverability in either vertical or horizontal mode, but also the ability to steer a course in the event of any one of the three thrusters failing.

Another benefit of this thruster arrangement is that the tail motor would be the thruster of choice for vertical adjustments while underwater, and its position far from the sea bottom would virtually eliminate silting issues.

In summary, a manned submersible that is elongated and capable of traveling on the surface horizontally, then flipping vertically to dive will have a greater sphere of influence, improved visibility, increased maneuverability and reduced operating expenses compared to traditional manned subs.

Karl Stanley has spent more than 4,000 hours exploring the ocean in submersibles he designed and built himself. A book he read at nine planted the seed, and by 15 he was constructing his first sub, the Controlled by Buoyancy Underwater Glider (C-BUG) that paved the way for Idabel. With Idabel, he offers tours to the public, scientists and filmmakers to depths of 2,000 feet. It is the longest-operating and deepest diving operation of its kind.


-back to top-

Sea Technology is read worldwide in more than 110 countries by management, engineers, scientists and technical personnel working in industry, government and educational research institutions. Readers are involved with oceanographic research, fisheries management, offshore oil and gas exploration and production, undersea defense including antisubmarine warfare, ocean mining and commercial diving.