Air lubrication for shipping - Introducing the Silverstream® System 

Many thanks to Silverstream for the cooperation and professionality during ther Princess Regal project held on Palermo fincantieri Shipyard. Looking forward to continue the cooperation for other projects. RM Marine Team

Viking ships and Norwegian traditional boats have this effect mixing air and water under the hull giving less friction

ver the past eight years, the Michigan team has investigated a variety of techniques to cut friction drag. First it looked at injecting slippery polymers into the water at the boundary layer. "Near the injector, drag was reduced by 70 percent, but the polymer degrades in the turbulence and just diffuses away," Ceccio says, "which means it needs constant replenishment, so we turned elsewhere." The researchers next shot bubbles-a millimeter or less in diameter-into the boundary layer. They got an 80 percent drag decrease for six feet (two meters) or so, but again, no satisfaction; the bubbles refused to cling to the hull surface long enough to have a significant effect on overall efficiency. If one injects enough gas, however, the bubbles eventually coalesce into a buoyant film that can sit (at least for awhile) between the horizontal hull and the water, which is what Ceccio's team is working on now-air layer drag reduction. In this concept, the bubbles typically would leak sternward and out from under the hull. New air would be injected forward to constantly refill the lubricating air pocket. Scientists speculate that more effective drag-lowering systems using smaller "microbubbles" might be possible if someone could come up with a low-cost way to make the sub-millimeter bubbles. Winkler says that his company is working on a "super-microbubble generator" that would enable existing ship hull designs to be retrofitted with such technology. These systems would also require the installation of surface cavities in the hulls. The big issue then becomes maintaining stable coverage of nearly the entire hull surface so that rough seas do not simply wash away the bubbles. Continuous, maximal coverage is the key to success; every millisecond that a section of hull contacts water directly contributes to drag. This means ships might have to be equipped with radar and laser sensors that detect oncoming waves, which could permit constant adjustment of air flow in time to compensate for rough seas. Although the costs of this air-carpet technology have not been fully worked out, Winkler says that adding relatively simple air cavity systems into new ship construction would add 2 to 3 percent to building costs.ggggAir lubrication: Only big bubbles do the trick Date: September 2, 2016 Source: University of Twente Summary: Blowing bubbles underneath a ship’s hull, causes them to be pushed against the surface. In the surface layer between the ship and water, these air bubbles cause less friction: it’s also known as air lubrication. In practice, friction can be reduced 20 percent, with a huge impact on fuel consumption and carbon dioxide emission. The precise mechanism is still unknown, as the local water flow is complex and turbulent. As scientists demonstrate, the size of the bubbles make a big difference: tiny bubble don’t have a net effect at all. This may seem counterintuitive, but large bubbles that can be deformed easily, give the strongest effect. Share: FULL STORY Blowing bubbles underneath a ship's hull, causes them to be pushed against the surface. In the surface layer between the ship and water, these air bubbles cause less friction: it's also known as air lubrication. In practice, friction can be reduced 20 percent, with a huge impact on fuel consumption and CO2 emission. The precise mechanism is still unknown, as the local water flow is complex and turbulent. As UT scientists now demonstrate, the size of the bubbles make a big difference: tiny bubble don't have a net effect at all. This may seem counterintuitive, but large bubbles that can be deformed easily, give the strongest effect. For investigating the effects, the University of Twente has a unique 'Taylor Couette' setup, capable of generating fully developed turbulent flow. This machine consist of two large cylinders with fluid in between. When the inner cylinder is turning fast, injected bubbles will be pressed against the surface, just like they do at the ship's hull. At the surface of the cylinder, they start influencing drag. This setup enables the scientists to search for the relevant parameters in efficient air lubrication. With four percent of air in the water, a reduction of 40 percent is feasible in the experimental setup, using large, millimeter size bubbles. By adding a tiny amount of 'surfactant', the scientists were able to vary the surface tension between bubbles and water, and they could vary bubble dimensions. The other properties, like flow speed and density, were kept the same. What was the result? On average, the bubbles get much smaller, because the surfactant prevents bubbles getting together, coalescing, forming larger bubbles. Within the turbulent flow, the bubble have a uniform distribution and moreover, they will not be pushed against the surface. With, again, four percent of air that is in microbubbles now, there is four percent reduction: there is no net air lubrication at the ship's hull. Ruben Verschoof: "From previous experiments, we knew that deformable bubbles work well, but in no way we expected a dramatic difference like this. By doing the experiments in real life turbulent flows, and not in the simplified situation of slow and laminary flow, the outcome of this research is directly applicable in the naval sector. For reducing drag in pipelines, the experiments also provide valuable new insight. The research has been done in the Physics of Fluids group of Professor Detlef Lohse. This group is part of UT's MESA+ Institute for Nanotechnology. Research is funded by Dutch Technology Foundation STW and Dutch Foundation for Fundament Research on Matter (FOM).

So it's like the Prairie/Masker system? Brilliant.

This dates back to 1960-70's in racing boats so nothing new , also Deep heavy grit sanding allowed higher speed boats to hold the small bubbles thus reducing drag even more as more air next to hull, but then more ideas I have to make hull so slick and few they have not thought up yet LOL

nice to see

Air Lubrication was tried on Atlantic Conveyor, prior to her loss in Falklands. In extensive tests, including Arran Measured Mile runs, no increase of speed or reduction of resistance could be detected. Maybe the only way the system could be effective is on a ship with large proportion of flat bottom area (which Atlantic Conveyor did not)

How is this system installed on ships with sea chests installed in the bottom shell? Are there additional air ports aft of the sea chest?

Why am I watching this? How did I get here?

could it prevent hull biofouling?

I wonder if the US and Russian naval architects have considered this for their navy vessels. I guess that if they have, then it would be classified information. Sounds like a great way to get a bit of extra speed when necessary. Perhaps the Gerald R. Ford class aircraft carriers have this? If they don't, then why not?

They should have collector ports at the stern to collect the compressed air, so it can be recycled without much additional compression.

Submechnaphobia nightmare

this is impossible because it destroys the air lifting force, which means that the ship will be more fuel-consuming and more fuel-consuming (I hope I have written it in an agreeable manner)