Undersea Control Systems Design

Named after Greek god and Messenger of the Sea, the all-electric Triton silently glides among coral reefs, putting explorers face-to-face with denizens of the deep. Triton's designers pride themselves in the craft's intuitive operation, savvy implementation of controls and a few unexpected options befitting the $2-3 million acquisition price. These include developed-for-marine science robotic grippers, fish feeder and laser-guided spear gun.

Billed as the "world's first luxury deep submersibles designed for yacht-based operation," Triton 1000/2 belongs to a family of four, ABS (American Bureau of Shipping)-classed, one-atmosphere civil submarines. Each turnkey vessel from the Triton 1000/2 (1,000 ft-rated, two-passenger vessel) to the deep-sea Triton 3300/3 (3,300 ft-rated, three passengers) features such exclusives as direct launch and recovery from mega yachts and real-time, Ethernet controller-to-iPhone monitoring.

Patrick Lahey, Triton Submarines LLC president and vice president of operations for U.S. Submarines, explains that the hand-built Triton goes beyond one-upmanship among yacht owners.  "Many yacht owners love being on the water and they love diving," he says. "So it was hard to not imagine them wanting to go down deeper, for longer periods of times and do it safely."

Lahey added that most mega yachts feature helicopter pads - so outfitting a yacht with a crane for submersible launch and recovery is "not a big stretch."

Ethernet Goes Undersea

After two weeks of U.S. Submarine's training, virtually anybody can safely pilot Triton. The craft's ease of navigation is enabled by an intuitive graphical user interface (GUI) tied to Wago's programmable fieldbus couplers (PFCs), which enable real-time, controller-to-iPhone monitoring. Per ABS regulations, all manned submersibles require mechanical analog instrumentation. However, because Triton's spherical acrylic pressure hull (passenger compartment) emphasizes an outward and down view, analog instrumentation is arranged behind the captain. This frees space for an F-16-style joystick (navigation/propulsion), GUI and unobstructed views.

Earlier Triton designs used large PLCs to communicate all mission-critical navigation, propulsion and HVAC information. However, packaging all the systems in the craft proved difficult and the existing HMI (human-machine interface) was considered "too industrial."

"The biggest challenges were making everything compact and aesthetically pleasing, as well as streamlined for maintenance," Lahey says. "For example, the panel can't look like a squirrel cage of wiring, especially at a $2 million price point."

At a tradeshow, Lahey saw a GUI from Vessel Monitoring Inc. (VMI) and immediately wanted it for the Triton.

VMI replaced the Triton's existing PLC and HMI with three Wago 750-842 Ethernet TCP/IP PFCs and a Panasonic Toughbook-19 touch screen tablet PC. Data transmission is Ethernet-based, with just four conductors among PFCs. A Moxa Wi-Fi access point provides data transmission to above-surface equipment.

"Thanks to the PFC monitoring, you look at the GUI and know instantly what everything means," Lahey says. "VMI configured the gauges to feel similar to a car's."

The GUI enables toggling between units of measurement for all displays, as well as mixing-and-matching of graphical, analog-style and purely digital outputs.

Tri-Zone Triton

Triton models are divided into three PFC-equipped zones: acrylic passenger hull, internal electrical junction box (IEJB) and external electrical junction box (EEJB). Within each zone, the PFC controls, monitors and sends alarms for gases, environmental systems and machinery. Lahey says the Wago PFC-based monitoring and controls system does not control any safety system, as all safety is mechanical-based. Instead the PFC controls funnel all pertinent data into the GUI.

Data from the PFCs are used for pre- and post-dive operating reviews and to view battery current and digitally store all data. Remote-monitoring is also possible via PFC to streamline any troubleshooting, as well as enable software updates.

In Triton's Zone 1, the passenger hull, a Wago PFC replaced what Lahey called the "lump under the passenger seat" to control digital instrumentation and environmental gasses including temperature, humidity, high- and low-pressure oxygen, reserve oxygen and air, as well as the A/C set point. Zone 2's IEJB controls lighting, external HID (high-intensity discharge) lamps and related 24V switching. The high-voltage EEJB in Zone 3 houses contactors that activate thrusters and handle the main 120V and back-up 24V batteries.

For protection from extreme thermal cycling, and 1468.5 psi resulting from cruising at depths up to 3,300 ft, all control components were placed in pressure-resistant vessels. Each was outfitted with moisture sensors, backfilled with nitrogen, vacuumed and filled with dry nitrogen. 

Compact size, modularity, marine approvals (such as ABS, GL, LR, DNV) and Cage Clamp spring pressure terminals are among the reasons why Matt Youney, VMI president, specified Wago technologies for the Triton. For him, operating conditions for the Triton were a good demonstration of the need for reliability. "If it works reliably at 1,000 ft below the surface of the ocean, it'll work in a typical factory environment," he says. This comparison to industrial systems is appropriate, considering that Triton's development was approached like the design for a typical decentralized, industrial control project replete with SCADA, PC software and multiple PFCs.

With the Triton "you have a very small footprint, yet full-blown decentralized monitoring system," says Youney.  "For instance, we use wireless sonar, which is a serial device connected via a serial-to-Ethernet bridge. We also have a wireless Doppler velocity log. Since the GPS in the Toughbook will not work after submersion, the Doppler velocity log tracks the sub wirelessly and communicates the position via a serial-to-Ethernet bridge."

Lahey views the PFCs as "amazing tools" that enable data tracking within submarines roaming the globe.

PFC-to-iPhone Monitoring

Non-man-rated cranes launch/recover Triton, and passengers wait while crane and crew guide Triton into the water. There it undulates with the waves while mission-critical and life-support systems activate. This includes moisture detectors to monitor propulsion battery pods for water intrusion - crucial if an
O-ring was pinched or a vent was improperly sealed prior to launch. Environmental systems are also monitored, including humidity, percentage of carbon dioxide and oxygen, as well as absolute cabin pressure and even A/C set point.

Previously, the crane operator had to physically hold the PC to monitor all systems as Triton geared up. The PC was then handed to passengers after boarding. But once the craft is in the water, it's not the best idea to be handling a PC controlling mission critical systems over saltwater. "It's a dicey prospect," Youney adds.

To address this issue, Lahey tethered his iPhone to the system during test dives, so that Youney could deliver a real-time iPhone app that monitors all water alarms, as well as the status of electrical, mechanical and environmental systems.

"I tied the iPhone's integrated Wi-Fi to Moxa," Youney explains. "I had already written the ModbusTCP stack in Cocoa (Apple's development language) for another application."

Click here to watch a video of Triton on a dive in the Bahamas.