Speed, Bow Shape, & Ultrasonics, Electrification & More Will Reduce Marine Shipping Fuel Requirements

For thousands of years, humans have been building boats and ships powered by wind and oars. For about 240 years we’ve been building powered ships. You would think that with those millennia of exploration, we’d know the best way to make them by now, and that the standard approach would be the most efficient.

Alnic MC, Liberian registered chemical tanker with a bulbous bow, image courtesy US NTSB

And yet, that’s not true. The bulbous bow, what looks like a fat sausage protruding at the water line on many ships, only entered service 110 years ago, and many recent ships don’t have them. There are retrofits adding them to existing ships today. These bulbous bows increase fuel efficiency by up to 15%, reduce pitching in rough seas and allow ships to sail faster. They’ve been understood for over 100 years, yet many ships still don’t have them, even the ones which could take advantage of them, hence ongoing retrofits.

This is relevant as we move forward in decarbonizing global shipping. In late 2021, I’d started my assessment by projecting global shipping in megatonnes through 2100. The aha moments out of that analysis were that 40% of deep sea shipping was for coal, oil, and gas, and that these massive ships truly consuming enormous quantities of fuel were going to go away over the coming contracts. Further, another 15% was raw iron ore shipped from countries that mined it to countries that turned it into steel. With increases in shipping costs, economics would make more local processing more economically viable more of the time, so I projected a reduction there as well. Obviously COVID-19 caused a substantial reduction in shipping, something I projected to rebound through 2030 before climate actions started reducing fossil fuel and iron ore shipping. Container shipping would increase slowly through 2100, but my thissis was that we might have reached peak shipping in 2019.

Earlier in 2022 I returned to the analysis to attempt to assess what greenhouse gas emissions implications there would be for electrification and climate action of shipping through 2100. I adjusted my projection for 2030 megatonnes upward, as feedback and thought indicated I’d been too aggressive in reductions in that time frame. I broke the model down into inland, short-sea, and deep-water shipping, a standard — if poorly differentiated — structure. That enabled me to scale the average ship for those categories, assess freight tonnage, fuel usage, and trip duration. That led to the assertion that all of inland shipping, and two-thirds of short-sea shipping, would be electrified by 2100, leaving the longest short-sea shipping and deep-water shipping as the challenges. Due to the truly enormous amounts of fuel used in deep-water shipping, this still left a lot of marine fuels being consumed.

And so, to the next step in the analysis, marine shipping projections. My latest model had a significant reduction in consumption for the average ship starting in 2030, something that in retrospect was also too aggressive. The basis for that was mostly slower shipping, something that’s being applied operationally today. Ships are subject to drag, and drag increases with the square of velocity. The bigger the ship, the greater the drag penalty of velocity. Slowing ships, per a substantive assessment from 2009, from 22 knots to 19 knots increases fuel efficiency by roughly 40%. Slowing further to 17 knots increases efficiency gains to roughly 60%. I had seen but not assessed impacts of other efficiency approaches, including X-Bow hull designs, ultrasonic defouling systems, and eddy-disrupting post-propeller systems purported to reduce drag further.

X-Bow on cruise ship Ocean Victory

X-Bow on cruise ship Ocean Victory, picture by author

Enter the Ulstein X-Bow. This is a fairly radical ship design transformation, brainstormed by the Norwegian ship building firm Ulstein in the early 2000s. It inverts the bow, putting the point at water level and having smooth sides moving up and away from that point. Effectively, it extends a pointier bulb to be the entire front of the ship. The image is from Vancouver’s harbor in April of 2022, the first one I’d seen in person, and I snapped a picture from a float plane’s cockpit. Ulstein’s material indicate that it’s on over 100 ships globally already.

The bow design has multiple advantages. First, it slices through waves instead of bashing through them or riding up and over them. This substantially increases efficiency and speed in heavier seas, and smooths the ride, something crew and passengers appreciated deeply, hence its initial adoption by ships with many passengers and crew, such as the cruise ship above. It also lengthens the water line, increasing the hull speed — the top efficient speed of a ship — without increasing over all length, which allows more efficient operation. It reduces white water over the bows by pushing more green water higher and around the high bow. Bow thrusters can be further forward as well, enhancing maneuverability. There are other advantages for crew and passengers, but the concern of this article is freight shipping.

For container ships, the X-Bow allows a far-forward bridge and crew quarters with significant room for containers behind it stacked above the height of the bridge. This is being assessed for smaller container ships of up to 34,000 twenty-foot equivalent (TEU) ships suitable for short-sea shipping at present, but I expect it has strong potential for deep-water shipping as well. It has all the advantages of a bulbous bow for efficiency and additional advantages as well, suggesting in the range of 20% efficiency gains as it spreads to more and more ships.

And for conditions where running ships in reverse, something apparently a common requirement in offshore windfarms, Ulstein has developed the X-Stern as well, allowing ships to run in reverse almost as rapidly as they move forward.

Of course, X-Bows will only be built on new ships, not retrofitted to old ones. As 0lder ships are retired and new ones enter service, this type of technology will be rapidly adopted, by shipping standards, but will still take decades to be dominant. The average age of ships is 20 years, and older for general cargo vessels, after all.

Fouled ship hull

Fouled ship hull image courtesy California State Lands Commission

Fouling of hulls is a very significant efficiency problem in marine shipping. It’s remained challenging as the ‘best’ anti-fouling paints and formulas have been found to have significant environmental downsides, unsurprising for what is, after all, paint that’s toxic to living things. Even minor fouling can reduce efficiency by 10% to 16%, and major fouling can reduce a vessel’s speed by over 80%. This is a $36 billion annual expense between drag and defouling for the US alone.

Enter ultrasonic — sound waves above the hearing frequency of humans and also above the hearing frequency of the vast majority of sea life — hull anti-fouling projectors. High-intensity ultrasonic sound projectors attached to the hull create sounds waves and micro-bubble cavitations that disrupt microscopic sea life — a green slime of tiny animal and vegetable matter — and macroscopic sea life — barnacles and larger plants — from attaching to metal under the water. The sound intensity is very high, around 200 dB at peak, which requires a comparatively high amount of energy, but vastly less than that required to push fouled hulls through water. That 200 dB is, once again, ultrasonic, so while intense, it diminishes rapidly with distance. There are some concerns about noise-masking for ocean life, but compared to the major low frequency noise of the engines and massive screws on ships which is also high intensity and propagates much further underwater, this appears to be a minor concern, especially compared to anti-fouling paints, and amenable to easy operational changes. (Ocean biologists who have studied this, reach out to confirm or refute my assessment please).

Studies are showing very significant value, and there are multiple vendors on the market. This isn’t to say that ultrasonic is a magic bullet for fouling, but it’s definitely a major cost saver both in fuel and services to defoul hulls and apply anti-fouling paints. One of the studies asserts that roughly 50% of ships at any time globally are suffering significant efficiency losses due to fouling, so widespread application of ultrasonics, and less toxic and more effective anti-fouling agents, has a significant value proposition. This one is low-hanging fruit, requiring very little in the way of effort to install or operate, so should spread rapidly.

Sankey diagram for ship energy

Sankey diagram for ship energy courtesy M. Dumitrescu

To return to an early point, much of shipping will be electrified. That’s non-trivial in and of itself. And it’s already more advanced than most realize. Just as the vast majority of freight train locomotives are diesel electric hybrid drives, with the diesel engines acting as generators for electric motors driving the wheels, most new ships are already some form of electric drivetrain run off diesel generators. Just as hybrid electric cars are more efficient than internal combustion cars without electric motors and battery buffering, so to be ships more efficient and higher torque with electricity generated by generators that run at their most efficient speeds to generate electricity required for ship propulsion and onboard systems .

For the segment of shipping that can easily shift to battery-electric, the 54% of thermal losses mostly goes away, raising ship efficiency into the realm of other electric vehicles. But simply adding significant batteries to buffer a diesel generator running electric motors has benefits, as does using electric motors. The simplest forms of this aren’t fully baked into the shipping ecosystem yet, and so efficiency gains will be seen even in the segments of shipping that can’t fully electrify.

Of course, there are several smaller innovations which are in the works as well. While defouling until recently was something human divers did at a cost of $450 per square foot of hull, now there are multiple hull-cleaning robotic vehicles available, for both large and small boats. Automation has come to hull cleaning just as it did to living rooms. There’s also still optimization available in screw design, as a brief dive into the subject made clear to me, so propulsion systems will be reducing the 14% of propeller losses as well.

Marine shipping megatonnes fossil fuels before refueling

Marine shipping megatonnes fossil fuels before refueling, chart by author

The point being that the average ship is going to become a lot more efficient at using energy over the coming decades. In a large part this will be because their traditional dirt cheap fuel — resid aka the burnable waste from oil refineries — will be carbon-priced, not to mention being in shorter and shorter supply as the rest of the transportation shifts off of petroleum for. While traditional fuel becomes more expensive, alternatives will remain more expensive. Physics doesn’t allow for miracles when it comes to fuels, and nothing is going to be cheaper than digging up higher energy liquids, refining them a bit, and treating the atmosphere as an open sewer.

With higher fuel prices for shipping comes an every increasing economic driver for efficiency that will force most of these techniques to be applied. A lot more ships will run in the 17 knot range, possibly the majority, while few will make sense to run in the 22 knot range. Five days slower delivery will be more salable. More ships will be more electrified. More ships will have better anti-fouling and spend less time and money on defouling and fuel costs as a result. Time may be money, but fuel is money too, and the balance will shift.

Now that I have a reasonable forward projection of demand for high-energy density fossil fuels through 2100, the next step is to evaluate the alternatives. Green ammonia, green methanol, and biofuels are all potential candidates. Which will dominate?


 


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