How can superyacht efficiency be improved to reduce impacts on the environment?

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West Nautical’s Technical Manager David Ormston takes a closer look at how different areas within the construction and operation of superyachts can be optimised to reduce environmental impact. 

Commercial Yachts of 400GT and above currently in operation should be reviewing their Ship Energy Efficiency Management Plans on an annual basis. This is a great opportunity for Yacht Captains and Engineers to review the way in which their own yacht is operated.

Weather routing

The review can include weather routing for yachts sailing globally, with companies specifically employed to provide passage plan guidance that will provide options giving the most fuel efficient, quickest, comfortable and safest passage, often between continents.

Main Engine fuel curves and efficiency

The engine ‘fuel curves’ should also be analysed. Each engine installed into a yacht is provided with ‘fuel curves’ and form part of sea trials prior to delivery. These curves not only provide the fuel consumed at maximum speed but also provide information of the most fuel-efficient speed the yacht can operate at. This is often known as the ‘sweet spot’, and whilst it is not always possible to operate within this range due to charter requirements operating at efficient powers should always be factored in wherever possible such as overnight cruising or repositioning voyages between charters.

Optimum ballast

For yachts that carry ballast, this is often required for changing trim in heavy weather for example, the effect of additional ballast not only makes the yacht heavier it can also change the trim of the hull, such as pushing the bow down further into the water. This can have a dramatic effect on the way a yacht performs whilst underway, increasing the amount of power required by the engines and therefore increasing fuel consumption, making the yacht less efficient. The ballast onboard should be continually reviewed to ensure the yacht is performing at its optimum for the conditions.

Auto pilot and steering

Cruising yachts commonly rely on the auto pilot function when sailing between destinations and can free up a Deck Officer to carry out other navigation functions. Care must be taken to ensure the autopilot and feedback from the steering flat are set correctly otherwise the rudders may move more than is necessary, this action can cause an increase in power on the engines and reduce their fuel efficiency. Corrections to the steering will also increase the distance the yacht travels between ports also increasing the fuel consumed unnecessarily.

Hull Maintenance

An important part of yacht efficiency is the underwater hull condition and whilst its critical for the yacht aesthetics that the yacht superstructure and upper hull area has that gloss finish, it is equally important for efficiency that the underwater area is clean, painted and free of any marine growth as this will cause friction and drag on the hull reducing the yacht performance and increasing fuel consumption as the engines try and maintain the yacht’s required speed.

There are a number of products available to assist the underwater hull maintenance including prop speed for example a coating applied to a polished propeller to help retain its polished finish. Anodes and on larger yachts impressed current systems are installed to stop the hull corroding.

Above all however is the underwater anti-fouling paint which has been in development  for over 100 years, with paint companies now supplying biocide free self-polishing coatings (SPC). An alternative and possibly more environmentally friendly option are the silicon based paints that are too slippery on the surface for growth to adhere to.

Fuel quality

The regulations recently changed in January 2020 reducing the allowable sulphur content if fuel to 0.5%, of course yachts already more than comply with this as they generally burn low sulphur gas oil with a sulphur content of 0.1%. However regular testing of bunkers taken, by independent laboratories is recommended, particularly where fuel is not taken from a regular supplier or at an unknown port or marina.

The Future

It is unlikely in years to come we will be installing marine diesel engines, into the majority of yachts as the primary mode of propulsion for several different reasons.

Emissions and fuel efficiency

Even with cleaner fuels there are still significant emissions released to the atmosphere, damaging the environment combined with relatively poor fuel efficiency, whilst not only making cruising a costly exercise, it also restricts the distance many yachts can cruise for at speed until having to refuel.

Space

Space is a valuable commodity onboard a yacht and on many of the 30-40m range of Superyachts a large amount of space aft is taken up by engines and exhaust systems.

Removing the need for large engines located aft to drive propellers, allows designers and Naval Architects far more freedom to develop additional guest areas such as Beach Clubs and spas as examples in the location the engine room would have once been positioned.

Noise and Vibration

Recent studies have highlighted how much underwater environmental damage is caused to marine life due to the noise and vibration created by propulsion plants on bother commercial ships and yachts. Removing the source of much of this, the diesel driven main engines, provides a significant reduction in the noise and vibration transmitted. Not only that but the guests also experience a far more comfortable experience whilst cruising particularly where there are shallow drafts such as the Caribbean.

How do we manage this?

Already in operation are a number of diesel electric options, where the propellers are driven by electric motors rather than diesel engines. Diesel engines are still required but as smaller units that can be located around the yacht in much smaller sound proofed spaces supplying the electricity for the motors.

A further development of this idea are hybrid systems that are still in their design stage and will become more common over the next 5/10 years. The generators combined with solar panels will be used to maintain the charge on the batteries with the batteries driving the electric motors. The advantage this gives, is smooth almost silent running when cruising at low speed, providing a second to none experience for guests.

Finally sail, by far the oldest and most tried and tested method of yacht cruising and with the delivery of Sailing Yacht A, may well pave the way for similar designs and the development of sail even further.

West Nautical’s Yacht Manager Tony Hildrew contributed on the matter:

“When entering port and connecting to shore power there are a number of ways superyachts can be a little more environmentally friendly and reduce the amount of power that they consume, things like reducing the number of air conditioning compressors running, keeping exterior doors closed and harmonising guest and crew meal times to reduce the length of time the galley equipment is running can all have an impact on the power a modern day superyacht consumes whilst sat in port.

A few little adjustments can make a huge difference when looking at the bigger picture, if every one of the 10,000+ superyachts worldwide made the little changes then the steps in helping to move yachting towards a more environmentally friendly industry would be great!”