Just look at any maritime drone on the market. They don’t look like regular ships. Drones are different. That translates into different challenges, new design quirks. How do we handle these differences? What are the secrets to designing a drone?
Autonomous Surface Vessels (ASV), Unmanned Surface Vessels (USV), or just drones for short. How do we design one? Just look at any drone on the market. They don’t look like regular ships. Smaller. No place for people onboard. Strange antennas on top. Drones are different. That translates into different challenges, new design quirks. How do we handle these differences? What are the secrets to designing a drone?
We start by understanding the application. The main advantage behind ASV’s lies in their low cost. Drones work best on simple, single purpose missions with a long timeline. For example, drones found a niche in survey work. Over 72% of the ocean remains unmapped. [1] Because it’s really expensive to operate a 300 ft long ship full of crew, scientists, and research equipment. All just for the boat to run its sonar and slowly troll across the ocean? For the cost of a single NOAA research vessel, we can afford an entire fleet of survey drones. It’s nothing more than a sonar, propulsion, and transmitter to beam the information back to land.
Drones achieve more than just run sonar. They can measure water currents, collect water samples, perform visual reconnaissance, blow up destroyers (military applications), aid in aquaculture, and more. (Figure 2‑1) The common theme for all drones: we keep them small and simple. Ideally, the drone only performs a single mission at a time. This simplicity was the key to keeping drones cheap, and cheap is the main advantage behind a drone.
Figure 2‑1: Ukrainian Military USV (Unconfirmed) [2]
Stability: how do we keep the ASV upright? Better question: do we need the drone to stay upright? Most of the rules and standards for ship stability derive from protecting the people onboard. We devote a lot of energy to limiting the ship roll. Because when a ship rolls 45 deg, people fall and get injured. Objects go flying across the room and hit people. Bad things all around. It’s all about the people. People break much easier than the ship.
No people means we throw out most of those rules. For example, most ships come with a myriad of openings on their main deck. Doorways for people, And air vents to get oxygen inside for the people and engines. We call these openings downflooding points. Because if they ever go underwater, the ship floods from the top down. Conventional stability invests great effort to ensure those openings always stay above water. But we can build drones more like a submarine. Seal up all the hatches. We can even temporarily seal the engine air vents if they go underwater. Drones truly embody watertight design, which makes stability far less critical.
That said, the small size of a drone presents some new challenges. Your typical drone is only 20 – 30 ft long (6 – 9 m), facing waves that dwarf it on the open ocean. The drone will capsize. It just takes one unlucky combination for the drone to completely flip over. We guard against this by designing most drones with self-righting capability. (Figure 3‑1)
Figure 3‑1: Self-Righting Explained [3]
Self-righting ensures that no matter what, the boat returns to an upright position. No machines required for this. Self-righting emerges purely from careful design of the drone hull shape. We start with a very low center of gravity. But the real magic happens in the reserve buoyancy. The entire hull stays watertight, top and bottom. As the drone rotates around, we include large buoyant structures on the top. These may be a tall, watertight deckhouse. Or a floatation bag on top of an arch. The key principle is to make these structures tall. High up. In normal conditions, these structures stay out of the water and don’t do anything. But when capsized, this extra buoyancy ensures the drone can’t find a stable position upside down. Its only choice is to flip back upright.
Drones don’t naturally tend towards self-righting. We need very careful design work. Naval architects simulate the drone stability and check it on the computer before ever building the real thing. When simulating stability, we often look at graph called the righting arm curve. (Figure 3‑2) Naval architects get a lot of information from this graph. For self-righting, we only need to know if the curve goes negative.
Figure 3‑2: Righting Arm Curve Comparison
Conventional Ship
Includes unstable regions
Self-Righting Ship
No unstable regions
On a conventional ship, the curve starts positive, and at some critical angle the curve goes negative. A negative curve means that the ship wants to be upside-down. Negative stability. If a conventional ship capsizes, it stays capsized. The classical strategy tries to push out this point of capsize’ ensure nothing can heel the ship into that region of negative stability.
With a self-righting ship, the region of negative stability just doesn’t exist. In the self-righting ship, the righting arm curve always remains positive. Over the entire range of heel angles. No matter how far you roll the ship, it always wants to go back upright.
Ironically, the biggest problem with self-righting comes from the machinery. Especially the main engines. Those lumps of metal were designed to work upright. We need several special adaptations to ensure that when the drone flips over, the engine still works by the time we get upright.
In general, the strategy is to shut down the engine if we capsize. Several devices then protect the engine, ensuring we can restart when upright.
Naval architects know solutions to each of these problems. The trick comes from recognizing the problems in the first place. This is why naval architects think about system integration. We look across different disciplines of engineering to understand how self-righting places new requirements on different mechanical systems.
The biggest challenge with drones comes from power. You find plenty of drones on the market that get by with nothing but a battery and electric motor. That works fine for short-duration missions. But for long endurance drones, a battery doesn’t cut it. We can’t just supersize the battery. It adds too much weight. Extra weight drives up the hull resistance, requiring more power for propulsion, which needs even larger batteries. When storing massive amounts of energy, we need to get more creative.
For long duration, we find two major solutions: engines or renewable energy. Engines offer the more predictable option. When it works, the engine always provides reliable power, matching all our needs. We see successful examples on the drones by Chance Maritime. (Figure 4‑1)
Figure 4‑1: Chance Maritime Drone
Example of Engine Powered Drone [4]
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But engines also introduce a lot of complexity. Potential points of failure. We can’t use the engine as the sole source of power. Remember, the computers and controllers on the drone all require power. If we completely lose power, we lose communication, with no way to restart the drone. When using engines, expect a backup power source. Either a generator or large battery setup. Plus, engines require air inlets, exhaust outlets and cooling. Those all lead to thru-hulls (holes) in the drone hull. Every hole is a potential point of flooding. In short, engines work great when they work. But if anything goes wrong, we face limited troubleshooting options from back on land.
The second option is renewable energy. Harvest power from the environment as we go. This tempts with the possibility of unlimited power. But adds a note of warning: the sea rarely cooperates with our power needs. We find three main sources of power on the ocean: wave, wind, or solar. Wave power is the most abundant, but very difficult to harvest. There are no commercial off the shelf options (COTS) for wave energy. Wind is the next option. We see this most often as sail propulsion, with the Sail Drone being a prime example. (Figure 4‑2) This provides both propulsion and electric energy. Many of these drones include a propeller driven by an electric motor. With the sail powering us forward, the propeller acts like an electric generator, slowly recharging batteries. Of course, sails only work when the wind blows.
Figure 4‑2: SailDrone
Example of Sail Powered Drone [5]
Finally, we come to solar power, favored for its mechanical simplicity. But solar power depends on environmental conditions. Your average solar powered drone only contains a battery to last 1 – 2 days without supplemental power. In terms of power management, we require sufficient solar energy every day. How much is sufficient? That depends on the size of your solar panels. In this case, we can’t rely on average solar output. Average means that half of the time, you get less power than expected.
We need to size our panels for the darkest, cloudiest days in the year. If our drone only operates near the equator, those dark days still offer abundant sunlight. But in the northern latitudes, winter brings scant sunlight. In those scenarios, a solar panel only produces 20 – 30% of rated power (depending on environmental conditions). Our location on the planet dictates the viability of solar power.
Every option for ASV powering comes with a list of pros and cons. The regular solution: install a combination of different power options. Engine plus sail. Sail plus solar. Or even solar plus wave. The trick is to find a combination with the lowest cost and lowest weight. (Extra weight adds to propulsion power requirements.) This takes some careful planning, studying the local variability of renewable resources. But when done right, you get a situation where each individual power source is small, but the collective whole offers abundant and reliable power.
If something breaks on a drone, you can’t fix it. You are still stuck back on land. And things do break at sea, all the time. Take the example of the Dali with the Baltimore bridge.
Figure 5‑1: Dali Collapsed Baltimore Bridge
Equipment failure isn’t so bad for a small toy that only trolls in harbor. Worst case scenario, you lost a cheap drone. And small toys can’t do much damage to surrounding property. But for the long endurance drones, we can’t afford to lose the drone. We invested a lot of money into that 40 ft. (12 m) long drone. Fault tolerance becomes critical as we expand into larger and better drones.
Your average ship comes with plenty of fault tolerance. Think about fuses on a ship electrical system. Great idea. Something goes wrong, the fuse blows, protecting the rest of the system and isolating the problem. Now we just need to fix the problem and replace the fuse. Except how do you plan to achieve that fix on a drone? You aren’t there.
Most drones employ redundancy to get around the remote problem. If a system goes down, use the backup. This is especially important with communications. If we lose a communication link, we lose the whole drone. For small electronics, redundancy makes sense. It’s relatively inexpensive to add a 2nd GPS receiver. But for larger systems, this becomes more complicated.
Do we add a second engine? What about the electrical power system. Do we provide a completely redundant power supply, with double the electrical wires leading to every instrument and device? Those system redundancies become very expensive. And complicated. Consider a redundant power system. I need to keep the backup power isolated. Otherwise, whatever fault killed the primary power may do the same to my backup power. Then we need a way to switch from primary to backup power. The switch also needs power. So now I have a tertiary power system just to switch from my primary to secondary. Wow! That’s a lot of switches, wires, and complexity. Means a lot more things that can break.
Most drones don’t come with full system redundancy. If something major breaks, the drone switches to recovery mode. We don’t expect the drone to have full capability or to continue its mission. At this point, we just want the drone to return to safety. Recovery mode might be something simple, like a radio beacon so we can go out and find the drone. Some drones use a reduced propulsion system that allows it to limp home. The details of disaster recovery change with each drone. Currently, drones can continue with one or two minor faults. We run for home if a major fault happens. Beyond that, things don’t look good for the poor little drone.
Admittedly, fault tolerance still needs improvement on drones. The next major advancement I want to see: self-repair. Show me a drone that changes its own fuses. I see nascent signs of this already. Some operators equip their drones with cameras for self-diagnosis. For example, a camera pointing at the propeller can be critical when diagnosing loss of propulsion. Did we lose power, or is the propeller fouled with seaweed? A simple camera solves this problem. I look forward to seeing the next step, when the drone contains its own internal robot for self-repair. I think that capability will enable trust for larger drones and better autonomous operation.
Drones play by different rules. Their small size and challenging power requirements require a different philosophy on ship design. Different problems to solve. And some problems still suffer from imperfect solutions, like fault tolerance. But that’s the beauty of the design process. We try different solutions, which help us to narrow down the exact problem that we need to solve. The strength of human imagination envisions a solution to nearly any problem. As USV’s and drones continue to evolve, their story is the progress of clearer definition behind the problems associated with drones. Each drone is a step towards clarity and progress to the perfect design.
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| [2] | J. Guttman, “How Ukraine Turned a 12-Foot Boat Into a Floating Guided Missile,” HistoryNet, 04 Nov 2022. [Online]. Available: https://www.historynet.com/usv-weapon-ukraine-war/. [Accessed 22 Dec 2025]. |
| [3] | Rafnar Maritime, “How Not to Capsize – Self-Righting Explained,” YouTube, 4 May 2021. [Online]. Available: https://www.youtube.com/watch?v=ggNx7G6i664. [Accessed 1 Jan 2026]. |
| [4] | Chance Maritime, “Fleet,” Chance Maritime, 2025. [Online]. Available: https://chancemaritime.com/fleet/. [Accessed 01 Jan 2026]. |
| [5] | SailDrone, “Revolutionizing Cable Route Surveys with USV’s,” SailDrone, 2025. [Online]. Available: https://www.saildrone.com/missions/meta-cable-route-survey. [Accessed 01 Jan 2026]. |
| [6] | NTSB, “Francis Scott Key Bridge and Cargo Ship Dali NTSB view,” Wikimedia Commons, 28 mar 2024. [Online]. Available: https://commons.wikimedia.org/wiki/File:Francis_Scott_Key_Bridge_and_Cargo_Ship_Dali_NTSB_view_(cropped).jpg. [Accessed 07 Jan 2026]. |
| [7] | J. Turner, “Sea Hunter: inside the US Navy’s autonomous submarine tracking vessel,” Naval Technology, 3 May 2018. [Online]. Available: https://www.naval-technology.com/features/sea-hunter-inside-us-navys-autonomous-submarine-tracking-vessel/?cf-view. [Accessed 22 Dec 2025]. |
| [8] | Wikipedia Authors, “RSDS wiki,” Wikimedia Commons, 04 July 2022. [Online]. Available: https://commons.wikimedia.org/wiki/File:RSDS_wiki.png. [Accessed 06 Feb 2026]. |
