It's summer, and some of you may be boating while on vacation. Boating is one of my personal leisure activities (check out www.boatme.fun
), so I thought I would talk about a few exciting boat technologies for a change. Most of what I describe in the rest of this article is relevant to either powerboats or sailboats. The audience of this newsletter's edition is probably boat aficionados and general roboticists.
Introduction
Like any ground or flying machine, marine systems can be decomposed into a propulsion subsystem, a sensory and localization subsystem and a guidance subsystem. Communication technologies are also of prime importance (you are operating a machine out in the wild). Let's review some of the key technologies for each of these areas.
Propulsion systems
Nowadays, sailboats are hybrid systems that can be either propelled by engine(s) or wind through their sails (powerboats are defined as not having sails). The main propellant sources of energy for these two classes of machines are wind, gas, solar, hydrogen, and electricity.
- Gas (or diesel) engines: boat engines are ~5x less efficient than their car counterpart in MPG (assuming the same vehicle weight). Water friction is actually more penalizing than air.
- Wind: the annual worldwide wind force potential is estimated to be in thousands of terawatt-hours. Mankind is currently only able to capture a fraction of this potential, partially because (1) it's intermittent energy and (2) the cost to capture, store or redistribute wind energy is often not cost-efficient. Yet with sailboats, you strive to go where the wind is and, in many cases, worst case, you don't go as fast as you had planned to, but you are still moving and for "free".
- Solar: the surface-to-generated-energy ratio doesn't really work to propel boats, so the solar panels you see on boats are often relegated to charging non-propulsion systems (i.e., it remains a key source of energy redundancy for emergency systems).
- Hydrogen for boats: It's coming and is "CO2/planet friendly" but not as cheap to produce as fossil-derived energy. Noteworthy is the fact that the vast cargo freighters that convey goods between continents still burn cheap "crude" or "bunker" oil (as opposed to more refined oil). The availability of salty seawater to help with the process of generating hydrogen is one argument being put forward, as hydrogen is an excellent solution to propel large boats (like with trucks, in the cargo industry, a key metric is the ratio between the energy-cost-per-ton versus the dollar-per-ton-of-good shipped). Although hydrogen is more expensive than gas, its density may compensate for the value of the good it is asked to move... (hydrogen-based airplanes are going through the same analysis).
- Electricity: pure electric boats are coming, but they are seldom. I don't think they'll enjoy the same level of commercial success as cars. Why? (a) water and electricity don't mix well (b) corrosion issues (part of (a)) (c) lack of charging/recharging infrastructure for boats except for slow charging at marinas (d) weight: water creates a lot more friction than air (this is why all the new F1/GP sailboats have foils, to lift the entire hull above water). Foils need steady speed and energy to lift floating structures above water, so even with foil technology, a good part of a boat's life is to have emerged in water. So, a good amount of energy will still be needed for a continuous operation, which cannot just be electric and gasoline has a much better energy-to-weight ratio than lithium-ion batteries for example.
Sensor and Localization
Other sensors and systems exist on modern boats:
- In terms of localization technologies, a few typical technologies are found on boats: AIS (for Automatic Identification System) allows one to transmit or receive GPS coordinates (including speed, heading type of boat) via a simple VHF radio. Some solutions include a collision warning and an "off-boat" feature to notify a captain of a potential collision or boat drift when no one is aboard. Very often, AIS is paired with digital graphical chart plotters, enabling one to pinpoint the location of other vessels on a map. AIS is optional for small boats but typically mandated for larger ones. AIS range is limited to VHF radio range, typically 20 miles or ~30km. Since AIS precision is based on GPS technology, the position is accurate (normally less than 100 meters). AIS isn't a "multi-hope" technology in that AIS signals received by one boat aren't retransmitted to another radio (this typically allows for increased range).
- Even when anchored, a boat can drift, or an anchor can detach, which can have severe consequences. Using geofencing, it is possible to set a maximum drift area and emit an alert in case of excessive drift. This is particularly useful if a boat is empty or when the occupants are asleep. Some phone apps already offer this feature. Advanced chart plotters also offer this feature.
- Marine Radar technologies are the rotating antennas or sometimes domes you see on boats. They emit microwaves (in the S or X-band) and can pick up surface reflection from other boats or objects miles away (typically ~50 miles or ~80km). Contrary to AIS, they don't require other boats to be equipped with an emitter. Both radar and AIS work even in dense fog.
- Speed sensors: When navigating, there are a few sets of significant speeds: boat speed, wind speed (and direction), and current speed. Boat speed is typically measured using GPS or via a device that measures incoming water flow (by a paddle wheel that converts the rotation of the paddle into electricity that can be measured or a pitot tube that covers water pressure into air pressure that can be measured). Wind speed and direction are typically measured using an anemometer, which also converts an air-propelled paddle into an electrical signal that is measured. A digital wind vane measures the wind direction. Current speed is often measured by static buoys and relayed to real-time chart plotters through various means of communication. It can also be deducted from a boat's GPS speed (absolute) and the incoming water-flow measurement (relative). Similarly, "True Wind Speed"/TWS can only be measured when a boat isn't moving (that is, propelled by current or its motors). Therefore, TWS typically accounts for the estimated speed induced by motors and sometimes the current speed.
- Fish finders use ultrasound emissions (in water, sound travels at the speed of 1500 meters per second, 5x time faster than in air). Some fish finders are combined with GPS to help with the marking of possible fish/fish school locations. Some fish finders implement "CHIRP" techniques, which allow the echo of multiple soundwaves at different frequencies to increase resolution and penetration. Recreational fish finders have a range of ~200 meters. Sonars also use ultrasonic waves and can be used to locate fish in all directions of a vessel (simple fish finders only detect objects directly below the hull).
Guidance systems
- Electronic chart plotters have decreased in price and can now be found on many boats. The most basic ones integrate a GPS and a small screen, while higher-end ones integrate radar, sonar, and AIS functionality and tend to offer a bigger touch screen. Nautical maps can often be updated through a side channel (wifi/Bluetooth connection to a phone or an SD card slot). Some chart plotters integrate cellular connectivity as well. Tablet-based and smartphone-based chart plotter apps are also now widely available - typically offered as a paid-for app with a renewable subscription. Some of these apps integrate weather/tide forecasts and can even display AIS traffic or water current information through cellular connectivity (since cellular is typically only available near shores, some features may not be available, and many boaters continue to prefer having a basic chart plotter attached to the boat).
- Auto-pilots typically use a GPS, a compass and a gyroscope to keep track of boat movement and heading and make the necessary adjustments to a pre-plotted trajectory. Some advanced systems can even avoid dynamic obstacles (e.g., other boats) and re-course in real-time while keeping the overall desired plotted trajectory. On sailboats, modern auto-pilots are able to implement specific maneuvers like tacking (turning sideways against the wind), maintaining a constant angle to the wind or holding a heading despite current and lateral wind forces. These features are convenient when navigating alone and dealing with various lines and sails.
Communication technologies
- The most basic type of communication on boats is a 2-way VHF radio, which can be a fixed or handle device). Several reserved channels are used and codified (for example, channel 16 is reserved for emergency messages or to initiate vocal communication before switching to another channel).
- Cellular reception is typically unavailable far from shores but can work surprisingly well at sea a few miles from populated areas.
- Satellite communication is also often used (e.g., with portable emergency locator beacon devices) and typically uses one of the Inmarsat, Iridium or Argos networks. Cruise ships initially used these systems to upload or download essential amounts of data (to benefit their guests or own operation) - with high network access costs. Elon Musk's Starlink system (which works very well on my RV) is now offered to the marine world with a cost/bandwidth structure that is way more advantageous than Iridium.
Conclusion
There is an interesting overlap between ground, air, floating machines, and the disciplines of robotic systems and underlying technologies. Modern boats are just another form of robots, and in fact, more and more designs are unmanned like military drone boats or exploratory boats mapping the ocean floor (check out the Saildrone startup for example).
Happy summer vacation, and if you are in the San Francisco Bay Area, this coming Bastille-day weekend is hosting the grand final edition of the SailGP season 4 race (where France and other countries are represented). Check it out here: https://sailgp.com/races/season-4/grand-final-san-francisco/overview/
; these amazing boats can exceed 100km/h!
#boattech #sensors #engines #ais #sonar #radar #starlink #fishfinders
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