Silverstream – increased interest in bubbles under the hull

Nov 19 2020

Silverstream reports a growing interest in its technology which injects air bubbles into the boundary layer between a vessel’s hull and the water, to reduce frictional resistance and in turn reduce fuel consumption.

Silverstream Technologies, based in London, reports that it has received “a lot of orders” over Spring 2020 for its technology, which injects air bubbles into the boundary layer between a vessel’s hull and the water, reducing frictional resistance.


The bubbles are sent from beneath the vessel’s bow (front), so the whole vessel can ride over them. It has been described as an “air carpet”. 


For tankers, it can typically achieve 7-8 per cent savings in deep draft and 10-11 per cent in shallow draft, the company says.


When the vessel is laden and in deep draft, the bubbles have a smaller effect as a percentage of all fuel use. But the fuel saving in monetary terms can be higher, because more fuel is being used. 


As a rough estimate, the technology will pay back within 2-4 years, says Noah Silberschmidt, founder and CEO. But there are many factors affecting this.


The 2-4 years is based on the vessel steaming for a large proportion of its operational time, and based on an oil price of around $50. Tankers are typically steaming 250 days a year, LNG carriers around 300 days a year at high speed. 


The costs will be different if the technology is fitted when the vessel is being built, or if it is retrofitted later. The bigger the fuel consumption, the faster the payback. 


“We are addressing the segment with big fuel spends,” Mr Silberschmidt says.


Silversteam offers shipping companies an engineering study for about £100,000, where it will assess in detail how much savings its technology could achieve for a specific vessel and what the payback time would be. This fee is deducted from the price of a system, should it be ordered. 


Such studies are underway “with a variety of oil and gas majors,  and the leader in container shipping, the leader in cruise shipping, the leader of an ore business, and LNG vessel owners,” he says.


The company is hiring another 10 people.


How it works

The technology works best with big flat bottomed vessels, with at least 20 per cent of the area of the submerged part of the hull consisting of flat bottom. 


Tankers typically have 40 per cent of their submerged hull area flat, cruise ships typically 25 to 28 per cent, Mr Silberschmidt says.


Larger flat bottomed vessels can see 8 to 10 per cent net fuel saving from the system.


The system’s generators require power to run, so Silverstream quotes net savings rather than the higher gross potential. 


As a different way to understand the fuel costs and benefits, a vessel with 40 per cent of its total submerged hull flat bottomed will typically use 25 to 30 per cent of its propulsion power overcoming frictional resistance, and the air bubble system can halve the amount of frictional resistance.


The fuel saving can be immediately verified, just by switching it on and off. When switching it on you see an immediate drop in shaft power, followed by an increase in speed, he says.


The air bubbles are sent out from an air release unit, or recess, created at the fore (front) of a vessel’s hull. You might need 8-10 air release units for a small vessel, 16-18 for a VLCC, or 22 for a 22,000 TEU container ship. 


The number required depends on the width of the vessel not the length, because the air bubbles flow under the whole length of the ship.


Some space is needed on the vessel to install the compressors. This is generally easier to find on merchant vessels than cruise ships, he says.


The technology works independently of weather conditions.


The additional cost of installing the technology can be very low if it is planned as part of the vessel design before it is built. “Just a few more pipes and a few more cables,” he says.


On a newbuild vessel, the technology could be fully integrated into the propulsion chain, so customers would specify “a propulsion system together with air lubrication”. 


For a retrofit, the work requires installing the air release units under the hull, which is a major work package, involving dry dock. The work on MR1 tanker “MT Amalienborg” took 14 days.


Getting support behind the technology

For a shipowner to invest in the technology, they are likely to want to have a clear idea of the savings. They need to find a shipyard that can build it, and see support or commitments from charterers, he says.


“The owner needs to be comfortable they are able to maintain and service it, the yard needs to be comfortable they can accomplish what is needed,  the charterer wants to know how much he is going to save.”


Investors, including pension funds, are another factor. They are increasingly concerned about ESG and “don’t want to invest in companies that are not trying their hardest,” he says.


The technology would have relevance even in an era with vessels running on zero CO2 energy, such as ammonia or batteries, because of the savings in propulsion costs - with zero CO2 energy likely to cost far more than conventional fuels. 


Trials and orders

The company started a sea trial with Shell in 2014, including with a Shell funded retrofit on a MR1 tanker, MT Amalienborg, owned by the leading Danish Shipping company Dannebrog Rederi.


The trials verified by the Lloyds Register Ship Performance Team showed net [fuel savings minus additional energy costs] average energy efficiency savings of 4.3 per cent and 3.8 per cent for the vessel in ballast and laden conditions respectively.  The retrofit took 14 days to complete. The tests were made under a series of 52 single runs under ballast load conditions (6.9m draught)


A subsequent laden condition trial conducted on a constant heading (at 10.6m draught) was completed six months later, due to operational restrictions.


The trials procedure for both was specified by Lloyd’s Register.


This led to the first commercial order with Norwegian Cruise Lines in 2015. It was a commercial new build vessel, Norwegian Joy, at the time one of the largest cruise vessels in the world. 


In 2017 the system was retrofitted on Carnival Corporation’s Diamond Princess. This system is now used all the time when the vessel is in propulsion, except when it is manoeuvring into port, he says. 


In 2018 it signed a deal with Grimaldi Group for the system to be installed on 12 ro-ro vessels, anticipated to be the “cleanest, most pioneering in their class”. These are being built at Jinling shipyard in Nanjin, China, with the first already commissioned. 


Silverstream has a framework agreement to fit an unspecified number of LNG carriers in Shell’s fleet. It also has a license agreement with maritime power company Wärtsilä, which plans to offer the system to customers integrated with its propulsion solutions.


The company

Noah Silberschmidt founded the company in 2010. He previously worked in investment banking, including the role of managing director at Bank of America Merrill Lynch from 2007 to 2010, and started out in the supply and trading department of Shell from 1992 to 1994. 


The company provides shipping companies with a package of engineering work and equipment ready to be implemented, as well as a license to use the technology and design.


The system includes the air release units, the compressors, an automation system, piping and cables. Silverstream does not directly supervise the implementation.


The company defines itself as an “IP and design company”. It has “9 families of patent in 40 different jurisdictions,” he says.


The technology is also available through Wärtsilä. Wärtsilä offers service agreements, so any customer has access to Wärtsilä’s engineering staff around the world. 


There are framework agreements with 3 large engineering companies – including Houlder Ltd, a UK marine engineering and technical consultancy firm. Silverstream is collaborating with Houlder on design and integration procedures for both newbuild and retrofit installations of the system.


Another joint development agreement with shipyard SWS (Shanghai Waigaoqiao Ship Building Co Ltd) was announced at Marintec, China, in December 2019.


The company reports that it has recently doubled its staff count to 22 people, and is currently recruiting for 15 further staff mainly in technical roles. 


Global Industry Alliance

Silverstream is also part of an organisation called Global Industry Alliance. It is described as “a new public-private partnership initiative of the IMO under the framework of the GEF-UNDP-IMO GloMEEP Project that aims to bring together maritime industry leaders to support an energy efficient and low carbon maritime transport system.”


Members include vessel operators Maersk, Grimaldi, MSC, Royal Caribbean, Shell, Stena; engineering and equipment companies ABB, Ricardo, Silverstream and  Wärtsilä; class societies Bureau Veritas, DNV GL and Lloyd's Register; and a mix of others - Total Marine Fuels, Marine Traffic, Panama Canal Authority and the Port of Rotterdam.


“We try to figure out how to best affect public and private [activities] to make changes in how things are done,” Mr Silberschmidt says.


For example one project is working out the best way to run a sea trial and validate vessel performance technologies. 


There are many technologies which only provide savings of under 3 per cent – and gathering evidence for small savings can be very hard, he said.


Ensuring real savings

Air lubrication for vessels is a 160 year old idea, first suggested in 1860 by English engineer William Froude, who also worked with Brunel on the Bristol to Exeter railway. There were a number of further attempts at air lubrication in the 20th century.


But the systems all ended up requiring too much energy to operate. If the 

amount of energy required to squeeze bubbles of air out of the hull is more than the system saves, it has no value.


So the technology innovation from Silverstream can be more precisely defined as finding a way to do air lubrication of vessels with a low energy consumption from the system itself.


Today, a number of yards are starting to say they offer air lubrication systems, but “to my knowledge there’s no third party proof,” he says. 


“We are very open about who is testing the technology and how we are doing it.” 


Mr Silberschmidt says he would be happy for the Silverstream solution to be tested directly against other air lubrication systems, so the market can see which is better. 


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