Technology

A few postings ago, I reported on a new trend, the ASV or Air Supported Vessel, that seems to show some positive results. Here is a follow-up sent to me by Ulf Tudem, the General Manager of Effect Ships International AS, the Norwegian company that along with several others, including U.S.-based Axcell, appears positioned on the forefront of the next trend in propulsion efficiency. I’m going to follow this technology and hopefully, will be getting aboard several of these new boats in the near future.

Amazing results from testing of 65’6″/20m ASV Mono demonstrator.

Effect Ships International AS (ESI), the Norwegian company behind the innovative Air Supported Vessel (ASV) technology, reports truly spectacular results from resent testing of their fully instrumented 65’ test- and demonstration ASV prototype.

The ASV concept test and demonstration vessel:
The 65’6″/20m ASV demonstrator with a beam of 17’7″/5.4m offers class leading interior space. From an operational point of view, the novel concept sets new standards in efficiency, and low consumption for operation in the 15 – 35 knots speed range. Whereas 30 knot+ conventional vessels with shaft drive of this size normally require between 2,000 and 3,000 HP for propulsion,  the ASV Mono has only 2 x 435 HP and uses two small series 1 Volvo Penta IPS 600 drives.

The difference in overall system weight between the two alternatives, including engines, gearboxes, prop system, auxiliary systems, tanks and required fuel (to obtain an acceptable range) for a vessel of this size can represent as much as 5 tons or more. When medium to high speed is required, weight is always an issue for reducing consumption. ESI will combine market leading ASV low hull resistance with high-efficiency pod propulsion and lightweight construction. The ambitious goal is to cut fuel consumption by a staggering 50% in the 15 to 35 knots speed range.

On the ASV test vessel a Volvo Penta D3 engine is supplying power to the lift fan system. The D3 is located in the main engine room, and power is distributed to the lift fan in the bow of the vessel via a Bosch Rexroth hydraulic system. In series production, power to the lift fan could alternatively come from a PTO on the main engine(s). Electric powering of the lift fan is also possible.

From the outside, an ASV Mono will resemble any semi-planing conventional vessel. The only element distinguishing an ASV from the mainstream boats is the air intakes high up on either side of the bow. Talking about bows, an ASV can be configured with all common types, including “Wally type” and various variants of bulbous configurations, giving most boat builders freedom to combine their use-, design- and image-criteria with the ASV hull technology principles.

The small and compact engine/pod propulsion package is another major ASV Mono benefit, allowing more of the volumes down below to be utilized for accommodation space. The double inlet, single outlet centrifugal fan system is located far forward in the bow, and the duct down into the air cushion chamber will normally be arranged with outlet to the air cushion chamber underneath the forward VIP cabin double bed.

The patented ASV Mono concept combines the principles of air cushion support, planing surface areas and buoyancy volumes, where each element is contributing to ultra low resistance, efficiency, performance and safe handling of the vessel at different speeds and operational conditions.

The air cushion chamber is covering a major part of the vessels water foot print. When filled with pressurized air, the air cushioned section of the hull is completely separated from the water, reducing the total wetted surface of the vessel substantially. The air pressure on the test vessel is between 3.5 and 4.5 kPa depending on vessel loading. Although the fan system has the capacity to deliver almost 15 m3 of air pr second, the volume flow and lift fan power requirement during normal calm water operation is very low. In waves the ventilation from the air cushion increases, and somewhat more volume flow and fan power is required.

The height and volume of the cushion chamber are related to each ASV hull form and targeted operation. On each side of the air cavity, the vessel has a propulsion body, a planing hull section designed partly to generate lift at speed and to house the pod propulsion unit. These bodies will remain wetted and will secure green water to the propulsors.

In the aft of the air cushion chamber an air cushion enclosure flap arrangement is located. The main function is to seal the cushion to prevent excess ventilation. On the demonstrator the flap is controlled with special air valves, enabling the operator to adjust the setting- and damping of the flap during different operational conditions. A Humphree interceptor system may also be fitted, and will give the operator added options to fine tune the vessel trim, during different loading, as well as assisting in giving the vessel the targeted response and lateral trim in a turn.

Operating the vessel:
Inside the harbor an ASV will be operated without the fan system running, and will behave very similar to any conventional “wet” hull. The underwater hull-elements are gripping the water as least as efficiently as a conventional V-shaped hull giving low sideways drift when operated at low-speed and heavy wind. The wide separation of the pod propulsors, combined with joystick maneuvering make the vessel a joy to handle, and eliminates the need for bow (and stern) thrusters. The vessel responds quickly and controlled in most situations and will go sideways and up wind if required.

When engaging the air cushion enclosure flap to seal of the cushion chamber, and then starting up the lift fan system, the vessel will, even with no forward speed, hover effortlessly out of the water almost instantly. In this situation some 70 – 80% of the vessels weight is supported on a cushion of pressurized air. The feeling resembles standing in an elevator when the elevator starts up. The actual rise of the test vessel, from dead in the water to up on the cushion, corresponds to some 15.7″-19.7″/40-50 cm. On the cushion, the vessel will accelerate swiftly forward, still with almost neutral trim, picking up speed rapidly.

Another noticeable difference with a conventional boat is the lack of “hump” and typical struggle to overcome the “hump”. The wake wash from standstill, through the transition phase, cruise speed to flat-out is remarkable modest. The general comment to the wake wash is “almost no wake wash at all. People having tried out the ASV concept all note the obvious low hull water resistance, and the fact that the vessel stays on top of the water, rather than trying to force its way through the water.

When taking the vessel at 30 knots into a fairly sharp turn, the vessel rides with almost neutral lateral trim, not banking in as most comparable conventional vessels will do. The turn is felt safe and predictable, and the speed loss is minimal. Pushing on at 30 knots or more, and suddenly turning off the lift fan system completely, results in nothing more than a very soft deceleration. The speed is dropping to 18 – 19 knots and the vessel is then continuing in an “off cushion” mode.

In a sea state, the air cushion will act as a motion damper, soften the ride, and reduce slamming. Due to the underwater hull form, in some ways resembling a catamaran, the vessel has much less roll motion. The ride feels safe and predictable. Depending on planned use, ESI may offer several hull variants, including a variant internally denoted “ASV Soft Motion Mono Hull”, designed to handle a though sea conditions at high speeds with reduced onboard motions and improved passenger comfort.

Performance and fuel consumption:
The ASV concept demonstrator is equipped with instrumentation for logging various operational data, including powering and fuel consumption. The ASV test team has recorded systematic fuel and speed readings throughout the full speed range. During these tests the lift fan system has been adjusted for optimum overall efficiency of the vessel. The tests have revealed very interesting results. So far tests have been carried out at three “design” loads: 19, 21.5 and 22.5 tons. In addition tests have also been completed with 27 tons, a significant overload over design weights. At 19 tons and 9.2 kn the total consumption was .8gal/3.06 l/NM. At 13.4 kn, a typical hump speed for a comparable conventional hull, only 1gal/3.76 l/NM.  At 24 – 28 kn the fuel consumption was still remarkably low, 1.02gal/3.89 – 1.15gal/4.38 l l/NM. At 31.4 knots still below 1.2gal/4.6 l/NM. At 21.5 tons, the fuel consumption of the main engines were virtually the same as with 2,5 tons less, the lit fan engine consumed somewhat more to support the higher load.. At 30.5 kn the consumption was still below 1.3gal/5 l/NM (4.95) only some 0.9gal/0.36 l/NM more than at 19 tons.

The test vessel will, in the near future, also be  with evaluated with even higher loads to assess and document the effect of excess loading to performance and fuel consumption. A max speed of 33 knots was recorded for all load alternatives; with main engine RPM of around 3600 RPM, indicating that the propellers most likely could have had somewhat higher pitch. At 27 tons the vessel still reaches 32 knots, and the fuel consumption is only a little over 1.6gal/6 liters/NM even at speeds close to 30.

Comparisons with market leading contenders having conventional hull and shaft propulsion:
Comparing statistics and tests of fuel consumption for conventional 60 – 65 feet vessels reveal that at 25 – 30 knots, consumption values between 2.6gal/10 and 3.2gal/12 liter/NM is the norm. The fact that an ASV consumes less than 1.3gal/5 liter/NM at same speed is quite astonishing and represents a technological shift. Not only is a cut in refueling cost of more than 50% something to applaud, smaller engines and systems represent also less initial investments. Environmental impact, including emissions to water and air, from use of larger pleasure boats, will undoubtedly be given higher priority in the years to come. With ASV technology at least 50% reduction can be achieved today.

Plans for exploitation and dissemination of the ASV technology:
Effect Ships International AS, plans to license access rights to use the ASV technology, IPR and patent to selected yards, yachts and pleasure boats builders constructing vessels from 12 m upwards to 100 m and more. The new ASV concept, patented in all major marine markets around the world won the “European Motor Boat of the Year 2011 – Innovation – Award”, at the Dusseldorf Boat Show in Germany end of January. This award and splendid feedback from all that have tested the boat certainly boost the confidence for the new technology.

With the ASV demonstrator in the water, yards and boat builders are invited to come and test the vessel and discuss commercial arrangements related to exploitation of the new, environmental friendly concept.

If you would like to know more about Effect Ships International and its ASV technology, contact Ulf Tudem, General Manager: Phone: + 47 334 65 650; Fax: + 47 334 65 610; Mobile: + 47 908 51 311; Skype:       ulf.tudem; e-mail: ulf.tudem@effectships.com; or at the company Website: www.effectships; www. seseu.com