The evolution of environmentally friendly superyachts

21 January 2015 • Written by Dudley Dawson
The De Voogt Breathe concept uses black-and-white stripes to create air flow across its decks and superstructure.

Is it possible for a large motor yacht with minibus-size internal combustion engines to legitimately be called 'green', or is 'the green revolution' in yachting just media and marketing hype meant to prey on the guilt of environmentally conscious owners, or assuage the suspicions of some segments of the general public and regulators who see the sport as a wasteful recreational pastime of the affluent? The likely answer is yes and no.

What is undeniable is that marine engines and systems are gradually becoming more efficient, and thus, greener. With fuel costs ever rising, governments cracking down on emissions and owners becoming more sensitive to the impact their yachts have on the fragile ocean environment, designers, engineers and power plant manufacturers are beginning to employ novel approaches to improving the efficiency of existing marine power and explore new angles on alternative fuels. If not so much a green revolution, we are at least seeing a green evolution.

Perhaps no more familiar visual symbol of eco-friendliness exists than the recycling logo of three canted arrows arranged in a triangle. Few are aware, however, of the meaning behind the symbol, particularly that recycling is the last and least important step in going green.

The three arrows in the logo represent 'Reduce, Reuse, Recycle', and the order is deliberate. Being green starts with reducing our waste of products, materials and energy a process that should begin long before an owner ever sees his yacht. The owner and his design team, working in conjunction with the builder, are the individuals who can have the greatest and longest-lasting effects, simply by making the reduction of waste a priority.

Reducing construction materials

Sparkman & Stephens, one of the most venerable American design firms, is on the cutting edge in this regard. Their designs are now conceived with low-impact construction in mind, and include procedures for incorporating the building frames as part of the yacht's structure, rather than using separate jigs that are later scrapped. Not only does this reduce the amount of material used initially and the amount that is thrown away, it can also reduce initial costs in some cases.

Yacht builders and their subcontractors, such as the Dutch engineering firm Vripack, have almost universally adopted 'nesting' techniques to get the greatest number of parts from a given sheet of steel, aluminium or wood. Computers are used to plan how to cut parts from a sheet of metal or wood, to maximise the amount of the material used.

The resulting pattern uses as much of a sheet of material as possible, with the remainder often looking like a piece of lace filigree. Even that isn't wasted, as steel and aluminium are easily recycled, and wood scrap often finds other uses around a shipyard.

Royal Huisman installed a hybrid propulsion system in Ethereal.

Builders of fibreglass and composite yachts, occasionally scapegoats for their reliance on petroleum-based construction materials, also have ways of reducing their environmental impact during construction.

Resin infusion and other closed moulding methods reduce the amount of material used and the quantity of chemicals (volatile out-gassing compounds, or VOCs) released into the atmosphere. Also composite pre-preg materials reinforcements with the resin or epoxy binder already incorporated, waiting to be activated by heat curing allow unused materials to be stored for later use rather than discarded.

The inclusion of higher-strength reinforcements such as Kevlar and carbon fibre can result in substantial weight reduction, which has measurable and lasting benefits once the yacht enters service.

This reduction of consumables in service, along with its attendant reduction of environmental impact, is one of the most important areas for attention during design, during construction and during operation. It starts with a professional design by a team that is focused on the issue.

We've seen remarkable examples of such efforts in recent years, with the 45m motor yacht Marco Polo, built by Cheoy Lee, and the 58m sailing yacht_ Ethereal,_ built by Royal Huisman, as prime examples. Both are from the boards at Ron Holland Design and include good examples of what can be done, even though not everyone might be ready to include all the bells and whistles found on these two yachts.

Marco Polo's hull is designed to enable the yacht to use a relatively small engine and one propeller.

_Marco Polo _is long and lean, not as extreme as the commuter yachts of the Roaring Twenties, but employing a longer waterline length and narrower beam to create the same interior volume that would normally be found in a shorter, wider yacht these days.

Using his expertise in sailing hulls, Holland gave her a fine displacement hull form, so the extra length allows an increase in her hull speed. It also results in a higher length/beam ratio for a lower hull resistance per tonne of displacement. That allows her to use a smaller engine, yet still keep up with yachts in her class, and a single screw another feature that reduces weight and improves efficiency.

Ethereal, on the other hand, appears fairly typical for a sailing yacht, but when you look under the skin, there's a lot of innovation designed and built into her mechanical and electrical systems. She incorporates a hybrid system, in addition to her sails, for propulsion.

Her system uses electric propulsion motors that can be powered from either batteries or diesel generators. While the hybrid moniker is fairly new, the heart of the system a diesel-electric propulsion system is tried-and-true technology, used for years on everything from submarines, tugboats to locomotives.

It is a bit surprising that we haven't seen hybrid systems on more superyachts. Diesel-electric propulsion systems are particularly appropriate for them, as the at-sea propulsion loads are closely matched to their in-port electrical loads, also called 'hotel loads'.

Such a system was installed on the Lürssen-built 96m motor yacht Limitless about 20 years ago, to good advantage.

Planet Solar's completed a circumnavigation, but solar power is still impractical for commercial yachts.

Electrical yachts

New advanced battery systems and their controls are what make hybridisation practical. These systems, while not perfect, continue to improve, and other energy storage systems to replace batteries, such as large-scale capacitors, are also in development.

Other hybrids, particularly those intended for only sporadic use, have special gearing so that both electric motors and diesels can be connected to the propeller shaft. In either case, hybrid systems do not, by themselves, make for a greener yacht.

The difference with Ethereal, as it should be with any yacht being considered for such a system, is that the hybrid propulsion is not just a trendy afterthought. It's part of a total energy-conservation package that includes additional thermal insulation to keep the climate at bay, thus allowing the use of smaller heating and cooling equipment. There's also low-energy LED lighting specially developed to replicate the soft glow of daylight, while dropping the toll of kilowatt-hours and reducing unwanted heat output.

Most important, though, is the advanced control system in the hands of a well-trained on-board engineering team.

The crew factor

It's that latter factor a capable crew that can help any yacht, regardless of age or equipment, achieve a greener profile.

The simple act of leaving port to meet the owner or charterer in another locale, for instance, is more efficient and friendlier to both the environment and the bank account, when done early enough to allow slower steaming. Fifteen hours at 10 knots is more economical than 10 hours at 15 knots.

Additional savings are also possible with weather routing, and other techniques in day-to-day operations can further improve the green factor. Little things, such as switching from harsh chemicals to bio-friendly cleaning agents, can make a big difference for very little effort or cost.

Arcadia's superyachts incorporate solar cells into their superstructure to provide a green, free power source.
Custom-made propellers can increase the efficiency of a yacht's propulsion system, leading to reduced fuel use.

Advantages of custom propellers

Recent years have seen the implementation of both the best and the worst of features regarding operational aspects. The best feature, by far, is the availability of advanced custom propellers for yachts of all sizes and types.

Keep in mind the simple truth that engines don't push boats through the water, propellers do. The water never sees anything other than the hull and propeller, not caring a bit what's inside the hull.

Model tests or computer analyses are used by naval architects to optimise the hull form for a given yacht, and one of the results is a determination of the effective horsepower (EHP), the range of power required to push that hull at various speeds.

The total shaft horsepower (SHP) provided by the engines is considerably more than the EHP required to propel the yacht. The ratio of EHP to SHP, called the overall propulsive efficiency (OPC), is determined by the gear ratio and propeller characteristics.

For many years, the installed SHP would be roughly twice the required EHP, yielding an OPC of 0.5 or 50 per cent, meaning that only half of the engines' power was being utilised to push the yacht.

Ill-advised owners sometimes demand generators that are too big, to avoid any possibility whatsoever that peak demands may tax the system's capability.

Modern custom propellers have raised that number considerably, often to 70 per cent or more. It's a remarkable improvement that, coupled with engines that are more fuel efficient, delivers an increase of up to 50 miles to the litre/gallon.

Clearly, the additional cost of modern engines and custom propellers is well worth the extra investment, both for its continuing benefits to the environment and for its dramatic savings in fuel over the years.

Also mentioned was the worst feature, environmentally speaking, of recent years, and that is the inclusion of electrical load banks on yachts.

Load banks are essentially huge water heaters, using excess generator capacity to warm the ocean. Ill-advised owners sometimes demand generators that are too big, to avoid any possibility whatsoever that peak demands may tax the system's capability. It is a very expensive solution to a very remote possibility, one that can be handled by that capable crew we mentioned earlier.

Installing too much equipment, carrying too much weight, burning too much fuel, and warming the world, all in the interest of convenience, are the very definition of environmental incorrectness.

De Voogt concept Aeon uses green power sources such as biofuel and solar energy

Reusing and recycling

The second arrow in the 'eco' logo is reuse.

Yachts, with afterlives of charter service, of being repowered, refit, lengthened and having cockpits added, enjoy an extended life that is unparalleled by any other consumer products.

In our age of 'throw away and replace', there is a healthy fleet of yachts approaching their 100th birthday, with a few even having seen that milestone in their wake.

And that brings us to the third arrow in the logo: recycling. This is so seldom an issue with yachts that there is little to say. When scrapping is in order, steel and aluminium are perhaps the ultimate recyclable materials, with demand high and recycling facilities plentiful.

Composites are more difficult, but even there, creative uses have been found for scrap that mitigate the amount of material finding its way to the landfill.

On the regulatory side, activity by national and international agencies will continue to affect the green factor of yachts. Already this year, we have seen emission control areas (ECAs) come into effect along the US and Canadian coastlines, and they will soon be implemented in the Caribbean as well. Similar ECAs already exist in the North and Baltic seas.

For the foreseeable future, diesel will remain the power source of choice. It will be implemented in new ways, with diesel-electric and its sister, hybrid, leading the way ahead

For large seagoing vessels subject to certain provisions of MARPOL, the ECA treaty mandates the use of low-sulphur fuel to reduce sulphur oxides (SOx). Other requirements relating to nitrous oxides (NOx) and particulate matter (PM) are in effect or anticipated in numerous areas.

Engine builders are continually improving their products to meet such requirements both ashore and afloat, and secondary suppliers are introducing auxiliary equipment that allows yachts to run cleaner than ever.

Solar, wind, fuel cells and liquid natural gas (LNG) power all have found markets some niche, some mainstream in shore-side applications. Research continues for such applications afloat, but only LNG is currently showing any significant promise, and that only in specialised trades or specific geographical venues where the infrastructure exists to support refuelling.

For the foreseeable future, diesel will remain the power of choice. It will be implemented in new ways, with diesel-electric and its sister, hybrid, leading the way ahead, particularly for the larger superyachts, and with improved equipment burning less fuel and doing so more cleanly.

Originally published: Superyacht Owners' Guide to Propulsion 2012.

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