The “Jetyak”—Autonomous Kayak Performs Shallow-Water Surveys
Boaters in the Connecticut River estuary, Connecticut, were puzzled by a seemingly driverless vessel last summer, when scientists from the U.S. Geological Survey (USGS) Woods Hole Coastal and Marine Science Center in Woods Hole, Massachusetts, and their partners from the Woods Hole Oceanographic Institution (WHOI) conducted pilot surveys with an autonomous kayak nicknamed the “jetyak.” The jetyak is a relatively inexpensive vehicle that can execute various scientific missions in coastal waters. In August 2013, the scientists used it to map the floor of a shallow cove in the Connecticut River estuary with both downward-looking and sidescan sonar (see image below) and to measure current profiles (current velocities at various heights above the seafloor) with an acoustic Doppler current profiler (ADCP).
The idea of developing an inexpensive autonomous surface vehicle began with ocean engineers Hanumant Singh and Peter Traykovski in the Applied Ocean Physics and Engineering Department at WHOI. They developed a prototype jetyak that was used to measure freshwater flow at the front of calving glaciers in Greenland in July 2013. The second-generation jetyak was built in summer 2013 with help from Sara Goheen, a USGS WHOI Summer Student Fellow coadvised by Traykovski and USGS oceanographer Chris Sherwood.
The core of the jetyak is a commercially sold gas-powered kayak built in upstate New York and marketed mostly to fishermen and hunters. It has a roto-molded polyethylene hull and an air-cooled 7-horsepower four-stroke engine. It is propelled and steered by means of a water-drive. The stock boat costs about $5,000, is 11 feet long, weighs 165 pounds, draws 3 inches, and has a payload of 360 pounds. Full speed is around 20 miles per hour, and the boat will run for 8 to 10 hours on 3 gallons of gas at survey speeds of 2 to 6 knots. Newer versions of the stock boat break into three pieces that nest together and can be transported inside an SUV or floatplane.
Modifications to make the jetyak autonomous draw on contributions from the hobbyist community. The two manual controls (throttle and steering) are replaced by servos—automatic devices that use error-sensing feedback to correct performance, such as those employed in remote-control airplanes and satellite-tracking antennas. The servos are run by an onboard computer developed for aerial drones. This computer, a modified Arduino, costs a few hundred dollars and includes Ardupilot software and a special circuit board that provides interfaces for the controls, radio, and Global Positioning System receiver (GPS). The only other modification is installation of a centrifugal clutch, which allows the engine to idle without moving the jetyak. With this setup, a “mission” (sequence of navigational waypoints) can be downloaded by radio from a laptop computer, and the jetyak will follow that mission autonomously. The boat can also be driven remotely by radio control.
The jetyak is rugged, has no propeller or other dangerous parts, and can run aground without damaging itself. The biggest operational problem is occasional clogging of the jet-drive intake with trash or weeds, which slow the boat down but can be easily removed. The simplicity that makes the vessel so sturdy and reliable, however, does have a drawback: the jetyak is not very smart and cannot, on its own, recognize or avoid hazards or obstacles. For this reason, it must be closely supervised while on a mission, particularly when other vessels (or swimmers) are in the area.
The jetyak is ideal for work in areas that would be dangerous for humans, such as the calving glaciers in Greenland; for repetitive and (or) protracted surveys that can be performed more precisely by autonomous systems than by human operators; and for data collection that increases the efficiency of field scientists conducting complementary tasks as they monitor the jetyak.
Sherwood, Goheen, Traykovski, and USGS technician Jon Borden used the jetyak to survey Hamburg Cove in the Connecticut River estuary from August 13 to 16, 2013. This cove is an important settling basin for sediment but was too shallow to be included in a survey conducted in fall 2012 from the research vessel (R/V) Raphael—a 26-foot survey vessel operated by the USGS Woods Hole Coastal and Marine Science Center. (See the related USGS Field Activity page.) During the August fieldwork, the team found that they could run the jetyak from their 16-foot skiff (the R/V Knob) with great efficiency. They programmed jetyak missions on the fly using Google Earth images in the Mission Planner software and easily modified the mission as conditions changed. Both vessels were equipped with relatively inexpensive sidescan sonars with integrated GPS, and thus the team had dual-vessel survey capability that could be conducted by two people. They sent the jetyak across the shallow regions while surveying the deeper parts from the skiff. In the crowded moorage basin, they drove the jetyak by radio control and enjoyed the shocked looks when the unmanned kayak motored past folks enjoying lunch on their yachts.
The jetyak has a generous capacity for batteries and scientific equipment. Over the course of summer 2013, it was deployed with various instruments, including a sidescan sonar, a 1200-KHz ADCP, a high-resolution pulse-coherent ADCP, and an RTK GPS. A scientific computer running Windows was mounted inside the jetyak and used to log data from some instruments, such as the ADCPs, using software from the manufacturers. This computer was accessed via wireless network. The prototype jetyak used by WHOI in Greenland was equipped with a davit, winch, and profiling CTD (conductivity, temperature, and depth recorder). For USGS studies, it would be easy to mount instruments to measure water-quality parameters (turbidity, pH, oxygen, chlorophyll, nitrates, and so on).
The jetyak’s shallow draft makes it the ideal vessel for surveying in marshes and back-barrier lagoons. Its speed and stability allow it to operate easily in strong winds and currents. It was tested in summer 2013 in Woods Hole passage (between Woods Hole village and the Elizabeth Islands), where it surveyed supercritical flow (flow that is faster than waves can travel) with current speeds of more than 4 knots and a vertical drop in water-surface elevation of about 1 foot over a distance of about 300 feet, or about 17 feet per mile (fpm). (This is an impressive slope in the ocean; the average gradient of the Colorado River in Grand Canyon from Lees Ferry to Lake Mead is 9 fpm, and the maximum is 35 fpm.) The vessel is quite stable and runs comfortably across boat wakes and 2-foot wind waves. The autonomous navigation software is robust and surprisingly precise: the jetyak can repeat cross-channel transects with better precision than boat operators, and can do it for hours on end without a lunch break. Additionally, it is remarkably inexpensive. Total cost for the jetyak, modifications for autonomous use, and survey equipment was less than $10,000.
As this article went to press, the third-generation prototype was being built for the USGS through our research cooperative agreement with WHOI and was scheduled for missions in February 2014.
in this issue:
Autonomous Kayak Performs Shallow-Water Surveys