# Moving a Heavy Ship with Relatively Small Sails? **URL:** \ **Category:** Factual Questions\ **Created:** [February 23, 2021, 4:43am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521 "2021-02-23T04:43:37Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [February 23, 2021, 4:43am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/1 "2021-02-23T04:43:37Z")
I recently read this article: > **[Wallenius Wilhelmsen reveals wind-powered ro-ro vessel](https://www.automotivelogistics.media/finished-vehicle-logistics/wallenius-wilhelmsen-reveals-wind-powered-ro-ro-vessel/41604.article)** > > Wallenius Wilhelmsen has presented Orcelle Wind, a concept for a primarily wind-powered pure car and truck carrier (PCTC) vessel that the finished vehicle logistics provider is confident could be on the water in 2025. In normal operation, it is... And frankly my gut reaction is that the sails shown are too small to move this heavy a vehicle. Why am I wrong? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 23, 2021, 6:02am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/2 "2021-02-23T06:02:19Z")
I don’t have an answer, but here’s a similar ship that will travel at about 11 kts, which is essentially the same as the 10-12 kts claimed for that ship: > **[Michelin to ship tires by sail in effort to reduce emissions | CBC News](https://www.cbc.ca/news/canada/nova-scotia/michelin-to-ship-tires-by-sail-in-effort-reduce-emissions-1.5919025)** > > French multinational Michelin Tire has signed up to ship some of the tires it makes in Nova Scotia across the Atlantic to France on a cargo vessel powered mainly by sail. ---
**Author:** ![GreenWyvern](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/greenwyvern/32/2834_2.png) [@GreenWyvern](https://boards.straightdope.com/u/GreenWyvern)\ **Post date:** [February 23, 2021, 6:23am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/3 "2021-02-23T06:23:32Z")
They are wingsails, aerodynamic rigid sails that provide far more power than an equivalent area of conventional sails. They operate on the same principle as aircraft wings.   > **[“Wing Yacht” Evidence: Compelling Case for Wingsail - Megayacht News](https://megayachtnews.com/2017/11/wing-yacht-evidence-compelling-case-wingsail/)** > > Sailing cats have plenty of fans. Sailing superyacht catamarans have their fans, too. The VPLP design studio sees room for more among the latter thanks to technological advances with wingsails. Evidence, a concept it created, combines the advantages... > The dimensions of the sail may surprise you if you’re familiar with sailing technology. In fact, it may seem too small. However, _Evidence_ has no need for a big rig. In fact, Van Peteghem explains, “Given that it is twice as powerful as a traditional rig, you get the same level of performance for half the surface area.” ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 23, 2021, 2:49pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/4 "2021-02-23T14:49:48Z")
Also going to comment about they are wingsails and use different airflow/air pressure differences for propulsion than conventional sails. Look at the blade area of a modern wind turbine vs the old style dutch windmill to see the difference. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [February 23, 2021, 4:28pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/5 "2021-02-23T16:28:49Z")
> [@GreenWyvern](#): > > They are wingsails, aerodynamic rigid sails that provide far more power than an equivalent area of conventional sails. They operate on the same principle as aircraft wings. That may be true, but I’d like to use this opportunity to point out that (many, not all) conventional sails, too, operate on the same principle as aircraft wings. There’s a common perception that sails function by the boat being “pushed forward” by the wind blowing from behind. That is true only for some conventional sails, such as spinnakers. Most conventional sails, such as lateens and square rigs, work best with wind coming from aside rather than from behind (on beam reach, in nautical terms). The wind flows along the sail, and the profile of the sail creates a pressure differential between the two sides that propels the sail forward. It follows the same principles as the creation of lift by an aircraft wing. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 23, 2021, 4:40pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/6 "2021-02-23T16:40:35Z")
True. But the effective area of those foils far exceeds that of conventional sails. Much of the cloth sail is used to form the shape of a foil without providing much lift. The term ‘lift’ is often used for sails and keels because it is the same function provided by aircraft wings even though used for horizontal movement. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [February 23, 2021, 8:12pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/7 "2021-02-23T20:12:12Z")
I expect that a lot of sails spend their time in what would be called a stall on an airplane. Stalls don’t decrease the lift to zero, they just decrease it over the maximum due to the flow separation on the top of the wing–what would be the leeward side of a sail. An airfoil sail should be able to achieve true lift, with both surfaces contributing to the motion. A more normal sail design might be able to achieve lift some of the time, or over part of the surface, but with limits on the angle of attack. A square rig might gain efficiency with the wind coming from the side but it’s probably going to have fully separated flow on the leeward side, so not really achieving lift in the normal sense. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 23, 2021, 9:48pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/8 "2021-02-23T21:48:22Z")
Another point is that you can tolerate low thrust, if you’re not in any particular hurry. Cars aren’t going to go bad if you don’t get them to their destination quick enough, so if using sails rather than diesel engines adds a week to the trip, that might be acceptable. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 24, 2021, 2:14am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/9 "2021-02-24T02:14:21Z")
> [@Dr.Strangelove](#): > > I expect that a lot of sails spend their time in what would be called a stall on an airplane. The tell-tales on the sail will tell you if the sail is stalling, so that you can adjust your sail. Lots of sails don’t have tell-tales, because any competent sailor will have some idea what the most efficient sail angle is. But from sailing with tell-tales, I would say that, unless it’s gusting, most of the time most of the sail is not stalling on either side. It’s just not an efficient airfoil shape. Actually getting an efficient sail shape from a stitched piece of cloth is impossible, and the more stitching and shaping you do the more it costs, but given whatever you’ve got, you still try to run it without stalling any more than a tiny amount of the sail. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [February 24, 2021, 9:52am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/10 "2021-02-24T09:52:31Z")
> [@Melbourne](#): > > I would say that, unless it’s gusting, most of the time most of the sail is not stalling on either side. It’s just not an efficient airfoil shape. I defer to your experience. I guess my thinking is that you don’t always have a lot of choice in the matter, and if you’re simply headed downwind then the sail is going to be in drag mode. And probably the same for any heading not too far from downwind. But then, that’s not an efficient way to sail, so why do that? Sailboats don’t have the problem that they have to support their weight on their wing, so they have a lot more flexibility in managing their angle of attack. ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [February 26, 2021, 3:45am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/11 "2021-02-26T03:45:56Z")
> [@Chronos](#): > > Cars aren’t going to go bad if you don’t get them to their destination quick enough … But it definitely is costly to build a shipload of cars, then keep them from the hands of consumers for an extra week. There’s also the point that a slower-moving ship (and its well-paid crew) can carry less freight in a year than a fast one. The point being that time is money in much the same way fuel is. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [February 26, 2021, 3:53am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/12 "2021-02-26T03:53:01Z")
Fuel is probably around $15,000 a day though. I agree that the economics of sail may well not stack up, overall, but saving fuel isn’t insignificant ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [February 26, 2021, 3:53am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/13 "2021-02-26T03:53:48Z")
> [@Melbourne](#): > > Actually getting an efficient sail shape from a stitched piece of cloth is impossible … Difficult, yes … But the Americas Cup boats now racing in Auckland have achieved notably efficient sails by using two cloth surfaces - with some fairly fancy cloth and rather sophisticated schemes for actively tuning its shape. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [February 26, 2021, 3:57am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/14 "2021-02-26T03:57:31Z")
> [@Princhester](#): > > Fuel is probably around $15,000 a day though. I agree that the economics of sail may well not stack up, overall, but saving fuel isn’t insignificant Fuel is billed to the charter customer. Capital costs come out of the owners pocket and at the owners risk. Will the customers be willing to pay higher fixed costs to offset uncertain lower fuel costs? What if the price of fuel continues to go down? ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [February 26, 2021, 4:44am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/15 "2021-02-26T04:44:51Z")
Sure. Charterers take into account tonnes of fuel per day in their current chartering decisions. Owners already consider more fuel efficient designs when ordering newbuilds with an eye to gaining a competitive advantage in winning charter business. So it’s all possible in theory. I suspect that actually this sort of vessel is far more likely to be built for a particular trade, after taking into account prevailing winds, speed, etc and vertical integration is more common in that sort of trade ie more likely that owners are building something for their own use. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [February 26, 2021, 12:52pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/16 "2021-02-26T12:52:43Z")
> [@PastTense](#): > > And frankly my gut reaction is that the sails shown are too small to move this heavy a vehicle. Why am I wrong? Looking at the picture in the OP reminds me of _Flettner Rotor Ships_, another case where the mechanism for the propulsive force looks woefully small (and vertical). Only in that case the mechanism itself is unusual: > **[Rotor ship](https://en.wikipedia.org/wiki/Rotor_ship)** > > A rotor ship is a type of ship designed to use the Magnus effect for propulsion. The ship is propelled, at least in part, by large powered vertical rotors, sometimes known as rotor sails. German engineer Anton Flettner was the first to build a ship that attempted to tap this force for propulsion, and ships using his type of rotor are sometimes known as Flettner ships. > The Magnus effect is a force acting on a spinning body in a moving airstream, which produces a force perpendicular to both the di... > **[Flettner rotor](https://en.wikipedia.org/wiki/Flettner_rotor)** > > A Flettner rotor is a smooth cylinder with disc end plates which is spun along its long axis and, as air passes at right angles across it, the Magnus effect causes an aerodynamic force to be generated in the direction perpendicular to both the long axis and the direction of airflow. The rotor sail is named after the German aviation engineer and inventor Anton Flettner, who started developing the rotor sail in the 1920s. > In a rotor ship, the rotors stand vertically and lift is generated at righ... [https://www.sciencemag.org/news/2017/09/spinning-metal-sails-could-slash-fuel-consumption-emissions-cargo-ships](https://www.sciencemag.org/news/2017/09/spinning-metal-sails-could-slash-fuel-consumption-emissions-cargo-ships) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 26, 2021, 1:10pm UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/17 "2021-02-26T13:10:58Z")
When the sails are combined with conventional propulsion that ship could travel with remarkable fuel efficiency. I expect many more ships to add sails. They don’t have to sit adrift and wait for a breeze, and whenever the winds are favorable they’ll be saving on fuel without sacrificing travel time. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [February 27, 2021, 4:34am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/18 "2021-02-27T04:34:04Z")
The elephants in the room though are (off the top of my head) reliability, maintenance, air draft, interaction with loading infrastructure and low crew numbers. There may be more. Everything deteriorates at sea and needs a lot of maintenance. On deck mechanical systems are notorious. The opportunities for maintenance for a hard-working ship are limited. So it will need to be reliable, low maintenance, and not require many more crew to operate and keep in good repair. Also, high masts will give trouble at a number of ports due to low air draft (from bridges). And a lot of loading and discharging infrastructure require, ideally, unimpeded access above the holds. None of these issues are insurmountable but they will mean that owners will be cautious about leaping into the purchase of new and untested technology of this nature. As mentioned above, what I can see happening is purpose-built sail assisted ships being used for a very specific trade, where it is known what the routes will be, what prevailing winds will be, and which (potentially customised) berths the vessel will be calling at. Knowledge gained from that sort of limited exercise could then (as the technology matures) be seen as a lower risk proposition for more general trading vessels. ---
**Author:** ![GreenWyvern](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/greenwyvern/32/2834_2.png) [@GreenWyvern](https://boards.straightdope.com/u/GreenWyvern)\ **Post date:** [February 27, 2021, 6:07am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/19 "2021-02-27T06:07:15Z")
> [@Princhester](#): > > Also, high masts will give trouble at a number of ports due to low air draft (from bridges). And a lot of loading and discharging infrastructure require, ideally, unimpeded access above the holds. It’s clear that you haven’t even bothered to find out the basic facts. **The wingsails are retractable.** They can be retracted at the touch of a button for bad weather and going under bridges. Since it’s a Roll-on/Roll-off vehicle carrier, _not_ a container ship, it’s not loaded and unloaded by cranes above the holds. This vessel hasn’t been designed by some tech whiz kid, but by a major shipping corporation, which has been in business for 160 years. Their subsidiary Wallenius Lines owns a fleet of 40 RoRo vessels, and they control far more vessels than that through partnerships. We can assume they know what they are doing. > **[Wilh. Wilhelmsen](https://en.wikipedia.org/wiki/Wilh._Wilhelmsen)** > > Wilh. Wilhelmsen Holding ASA (WWH) is a Norwegian multinational maritime group, headquartered in Lysaker, Norway. The group employs more than 21,000 people and has operations in 75 nations. The Wilhelmsen group operates the largest maritime network in the world, with over 2200 locations worldwide. > The WW group was founded on 1 October 1861 in Tønsberg. The company's first vessel was the barque Mathilde in 1886. Halfdan Wilhelmsen was forward thinking and realised that steamboats were the futur...   Here’s their web page about the wind-powered vessel, including a 45 min video: > **[Orcelle - Wallenius Wilhelmsen](https://www.walleniuswilhelmsen.com/news-and-insights/highlighted-topics/orcelle)** > > Orcelle Wind is a new design concept for a wind-powered RoRo vessel that will achieve up to 90% reduced emissions compared to today’s best vessels. ---
**Author:** ![GreenWyvern](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/greenwyvern/32/2834_2.png) [@GreenWyvern](https://boards.straightdope.com/u/GreenWyvern)\ **Post date:** [February 27, 2021, 7:35am UTC](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521/20 "2021-02-27T07:35:11Z")
I watched that 45 min video, and I have to say it’s very impressive. These are serious, intelligent, capable business people, who are not playing games. They are thinking through all the issues in great detail, and planning carefully. They have built a prototype, done wind tunnel tests, etc. They are are considering all the financial and practical implications, and drawing on a long, successful history in the shipping industry. [Next page](https://boards.straightdope.com/t/moving-a-heavy-ship-with-relatively-small-sails/933521.md?page=2)