An Icon of a Sustainable Future is For Sale

To find out more about the sale contact Shuttleworth Design

Reflections on the Design and Performance

By John and Orion Shuttleworth - 2019

After seven years of cruising and 60,000 miles on the log, this multi-award winning yacht has become established as an iconic design, representing a new vision of style and incredible fuel economy.

Adastra represents a joint dream between the owner Anto Marden and Shuttleworth Design to create a truly sustainable yacht that would be a showpiece of what is possible using modern technology to help address climate change. Our hope was that the design would come to represent consciousness of the environmental issues facing mankind and give hope and impetus to changing attitudes towards the urgent need to reduce carbon emissions and reduce fossil fuel consumption.

In 1982 we designed a 45 ft sailing trimaran for Anto, using principles for the shape and engineering that we called integrated structure, he still owns the yacht today and sails her regularly out of Manila. Exactly 30 years later we launched Adastra, a 42 metre power trimaran that has redefined what is possible in styling and fuel consumption for a luxury superyacht. Adastra uses one seventh of the fuel of a conventional 42 metre superyacht demonstrating what is possible if the focus of design is changed radically to fully incorporate and use technology to reduce the impact on global warming. Her iconic appearance and phenomenal efficiency stands as a beacon for others to follow suit, not just in yacht design but in all aspects of development.

All the ambitions that the Mardens had for the boat have been met, and more. Anto has called Adastra "an ocean greyhound" and he and his family have used the boat extensively for cruising all over the world. Based in Hong Kong, they have visited Thailand and Singapore, cruised through the Indonesian islands including Raja Ampat, then across the Pacific via Fiji, Tahiti and the Panama Canal, into the Caribbean, stopping in Columbia and up into the Caribbean islands. They have made several Atlantic crossings and cruised most of the Mediterranean.

Adastra-Kas-small.jpg Click on image to enlarge.

Adastra in Kas, Turkey.

Adastra has weathered 50 knot storms and extremely rough seas. After one particularly bad storm just north of Venezuela, the captain said that he would not have wanted to be on any other boat in those conditions, helping to justify the statement made by the judges of the Showboats Superyacht awards, "that she would perform better in more sea states than any of the other 19 superyachts shortlisted."

As the designer's it is interesting to reflect on what we hoped for in the design and what we know now. Before the launch in April 2012 we did not know how successful all the ideas we had would be, and it is surprising how quickly we became used to the performance and success of the design and forgot the excitement and nervous anticipation of the launch and sea trials.

The first thing to happen after launching is the engine manufacturers hook up their computers to the vessel and go out and check that the propeller size is correct. This means that the propeller has to load the engine correctly throughout the speed range. In a boat like Adastra, which had no comparable vessel in existence, it was probably the most nerve wracking moment, however all our calculations and the skill of the propeller manufacturers proved to be correct, when they pronounced it perfect. They then surprised us by saying the fuel consumption was 17 litres per hour at 10.5 knots, a figure that was one seventh of the amount used by a conventional 42m superyacht.

Early on in the design process, we built a 2 metre motorised scale model and filmed it driving at various speeds and angles to the scale equivalent of 2 to 2.5 metre waves. The model tests were helpful in showing the motion in waves, but we did not know for sure how the outer hulls would interact with the main hull in real conditions. There are three main elements to the outrigger design, they need to be long enough to give low drag at the design speeds, they need enough buoyancy to stop the boat rolling in big seas and they should not be too long and buoyant so they start to drive the pitching movement. After the launch John Shuttleworth was invited to do a trip from Hong Kong to Manila aboard the boat when it encountered 2 to 4 metre waves. They were on the beam for a time and then on the aft quarter, he was able to film the water flowing over the outer hulls through the portholes to observe how they were working. They did in fact perform very similarly to the model, the hull volume was not high enough to make them lift at each wave, but instead they pierced and drove through the crests, becoming nearly fully immersed at times. Meanwhile the centre hull remained reasonably upright and just followed the large wave fronts, regularly surfing up to 22 knots. This easy surfing action meant that even though the throttle was pegged to give 14 knots in flat water, she actually averaged 17 knots for the trip, but using the fuel she would have used at 14 knots without the wave action. This meant she was able to gain 20% in performance from the force of gravity.

In the image below the six shots show how the outrigger drives through a 2.5 metre wave at 16 knots. Note that the hull barely moves vertically or in pitch, so the whole boat is barely rolling. The outrigger can cut through the waves without driving the motion of the boat, and the streamlined deck shape also means that drag does not increase enough to slow the boat, so surge and yaw is also cut to a minimum. This has a huge effect on the comfort of motion at sea.


Outrigger bow penetrating a 2.5 m swell, without rolling the boat.

The outriggers were immersed by 300 mm when at rest to damp rolling and that has proved to be excellent. There is a small cost in efficiency but that is more than compensated for by the comfort of the vessel when underway and at anchor. The long thin centre hull slices easily through the water and makes the going relatively easy upwind in a rough sea, avoiding that shuddering slowing feeling that large vessels with wider bows experience when driving into waves. At anchor she is "as stable as a rock", according to the owner.

Turning the boat on its own axis makes docking easier and safer. The usual method is to have bow and stern thrusters, but these are heavy and leave large holes in the hull bottom, which create drag. In a trimaran the outriggers are spaced far enough apart to use a small engine with a folding prop in each outer hull. This has proved to be a good low drag solution and provides full manoeuvrability.

Great attention was paid to saving weight, including moulding the toilets in carbon fibre. The fact that she launched at 49 tonnes is a credit to the engineering and the build quality of McConachy in China. The vessel's light weight, and a fuel capacity of 30,000 litres means that she can go halfway around the world at 10.5 knots without refuelling.

The Mardens always wanted to cruise the world and have spent at least three months a year on board, mostly with the whole family. After fulfilling all their aspirations for the boat they are putting Adastra up for sale and it's now time for someone else to enjoy this extraordinary vessel.

For more information please contact Shuttleworth Design.