People often ask about the GHG emissions from superyachts and the ‘Fourth IMO GHG Study 2020’ provides some indicators for each year from 2012 – 2018 represented in the graphic.
Due to a variety of reasons the data is a little incomplete e.g. Automotive Gas Oil (AGO) and shore-power are not included. This means once AGO and upstream emissions from marina electricity is included, the CO2 emissions could be significantly higher, especially as the data suggests yachts are, on average, at sea only 71 days a year.
The extended trendline suggests that there is a possibility with ‘business as usual’ (BAU) a DOUBLING of CO2 by 2030 compared to 2018.
Fortunately, it does not have to be BAU as there is plenty of technology and operational changes that could help flatten and reverse the trendline. The incentive to make these changes is another matter!
Rather than rely on sources unfamiliar with yachting, it would help if the industry took it upon themselves to gather the data – available from most professional management companies. Emissions and reductions could be measured and validated, and more accurate trendlines projected so that we could demonstrate to the wider World we are working towards reducing CO2 and ensuring the sustainability of our industry.
There has been much talk about reducing CO2 emissions from superyachts and apart from incremental changes that may be possible through technology such as hybrid propulsion, batteries, digitalisation and efficient hull design, the uncomfortable truth is it will not be sufficient to reach the goal of zero-carbon yachting.
The only way to achieve that goal is to move from fossil fuels to alternative fuels or energy carriers that are suited to the operational profile of the vessel. In the shipping industry batteries and Hydrogen are seen as viable solutions for coastal vessels where refuelling can be done regularly but, other fuels such as Methanol and Ammonia (very challenging on storage and safety) are seen as more practical for ocean going vessels.
The main problem with Hydrogen and batteries is the volumetric energy density compared to fossil fuels – this can be seen in the diagram below.
This is certainly a consideration with superyachts where space is at a premium. Requiring more volume for fuel, ancillary equipment, and associated safety systems, will either compromise the interior, significantly reduce the range, or both.
Apart from bio-diesel such as 2nd generation Hydrotreated Vegetable Oils (HVO) the most promising fuel may be Methanol.
What is Methanol
Methanol (CH3OH) is one of the four basic chemicals used to produce all other chemical products such as formaldehyde, acetic acid, and plastics.
It is a colourless water-soluble and biodegradable liquid at atmospheric conditions with a mild alcoholic odour. Energy density is approx. 14MJ/l compared to diesel which is 34MJ/l. It boils at 64.6 C and has a Flashpoint of 11 so requires additional precautions for use, storage and handling but, these are well understood.
It burns cleanly with no particulates, does not contain sulphur and the combustion of Methanol emits a very small amount of NOx. Engines using Methanol can be Tier III compliant without exhaust gas after treatment.
Methanol is mainly produced from natural gas or coal and, according to the International Renewable Energy Agency (IRENA), annual production is around 98Mt and accounts for about 10% of the CO2 emissions from the chemical and petrochemical industries.
With all alternative fuels it is important to understand the GHG emissions along the whole value chain, including production, storage, transportation, and final use. Methanol does emit CO2 when combusted and in the reforming process for Hydrogen but, importantly, it can be carbon-neutral depending on the energy and feedstocks used in the production of the fuel.
Production methods include: –
• Bio-Methanol from bio-mass such as agricultural waste, bio-gas, sewage, municipal solid waste and black liquor from the pulp and paper industry.
• E-Methanol from Green Hydrogen and, either CO2 from direct air capture (DAC), or carbon capture and storage (CCS).
Currently only about 0.2Mt of Green Methanol is produced. Studies suggest this is forecast to grow to 2Mt by the end of this decade. It is one of the easier fuels to scale as the technology is well understood and much of the infrastructure, such as storage and distribution, is already in place.
Like all alternative fuels this is a challenge, and much will depend on demand and the scaling up of production and bunkering infrastructure.
Shipping companies such as Stena and Maersk are already driving maritime demand, and the chemical industry will require Green Methanol to reduce their CO2 emissions. This increasing demand will provide the producers the confidence to invest in production and improving availability – it’s likely there will be more demand than supply in the early days.
In the meantime, Grey and Blue Methanol that use natural gas, carbon capture and renewable feedstocks, could be a suitable pathway until such time Green Methanol is more widely available.
According to the DNV Alternative Fuel Insight, Methanol is already available in 117 port terminals around the World, including Algeciras, Tarragona, Genoa, Livorno and Trieste. It can also easily transported by truck.
A major benefit is Methanol, unlike Hydrogen and Ammonia, can be carried in structural tanks – the same as diesel. It does require additional barriers, double walled piping, ventilation, and inert gas, but there is wide experience in its transport and use. The IMO have produced guidelines for its use as a marine fuel under the IGF Code – Interim Guidelines For The Safety Of Ships Using Methyl/Ethyl Alcohol As Fuel (MSC.1/Circ.1621).
It can also be used in diesel engines and reformed to produce Hydrogen for Fuel Cells.
Diesel engines are a mature technology with some engines around 45% energy efficiency at optimum power. Overall efficiency can be further improved by using hybrid systems, waste heat recovery and power management to optimise engine performance and electricity generation. In addition, they are well suited to running on alternative liquid and gaseous fuels.
In a recent White Paper titled “The Future of Internal Combustion Engines” Rolls Royce maintain combustion engines will continue to play an important role but, with a steady transition away from fossil fuels to sustainable fuels. And, as well as new engines optimised to run such fuels, they also see the need to offer conversion kits for existing engines.
As an example the Stena Germanica, operating in an Emissions Control Area (ECA) between Germany and Sweden, was successfully converted in 2015 to burn Methanol in its engines.
AP Molller Maersk believe in the fuel for shipping and have signed a contract for 8 x 18,000 TEU container ships to be delivered in 2024 with engines running Green Methanol.
ScandiNAOS has produced a diesel engine with power outputs from 150 – 450kW that runs on Methanol for propulsion and genset applications. Approved by Lloyds and DNV.
Image: Courtesy of ScandiaNAOS
There is no doubt that in the coming years we will see most engine manufactures launch new engines to run on alternative fuels such as Methanol, as well as upgrade kits for their existing engines.
Most Fuel Cells require Hydrogen, and Methanol is a great source of Hydrogen.
Unfortunately, whether Hydrogen is stored as a liquid or a compressed gas, it has low volumetric energy density. You need about 7 – 10 times more volume than for the equivalent amount of diesel, whereas Methanol requires about 2.5 more volume.
Methanol can be reformed into Hydrogen onboard for use in the Fuel Cell. And, interestingly, there are reformers that use a blend of di-ionised water to achieve 30% – 40% more Hydrogen, compared to using pure Methanol.
This and the other characteristics of Methanol, make it an ideal fuel for Fuel Cells.
Lurssen have announced they are building a 100m+ yacht that will use reformed Methanol in a Hydrogen PEM-FC as part of the energy mix.
Feadship, with the ‘Pure’ concept, have engineered different solutions that will allow for a phased transition from Diesel – HVO – Methanol by including this pathway in the design and build. Partial or full conversion to Fuel Cells may also be a possibility.
Though the above are large yachts, the Fastwater Project has recently shown how it can be used in a smaller vessel. They successfully converted a Swedish Pilot boat to run on Methanol.
The idea that electrification of superyachts via hybrid or diesel electric will ‘Future Proof’ a yacht misses a critical component, the fuel. Claims of this type need to be treated with caution.
It’s one thing to swap out a diesel engine for a Fuel Cell, but it’s a totally different matter to convert a yacht for a fuel that is higher risk and less energy dense. Apart from the high cost, it is unlikely to be practical without significantly compromising space and/or range.
Building a yacht ‘Methanol Ready’ by including the extra tank capacity, cofferdams, ventilation, piping and, later inert gas system, would be one way to ‘Future Proof’ a yacht. And, like ‘Pure’ It would allow the yacht to initially run on MGO or HVO and, in the future, covert the engines to run on Methanol and allow hybrid solution that includes Fuel Cells in the mix.
The evidence suggests that Methanol is a serious alternative to diesel fuel that would significantly reduce a yachts GHG emissions and improve overall air quality.
There are still some challenges to overcome such as the availability of Green Methanol, though Grey and Blue Methanol could help with the transition.
A limiting factor at present is the availability of engines and/or conversion kits. The indications are that we will see more these in the next few years, and with the power required by superyachts. And, although PEM-FC are relatively mature, combining reformers in a maritime setting in MW scale, is less so, and may restrict earlier adoption. However, a hybrid solution using Methanol engines and PEM-FC could certainly be a viable solution in the near term.
Methanol clearly has advantages over many of the alternative fuels. Given the available build slots and projected launch dates, a forward-thinking owner might be well advised to consider the use of Methanol in their next superyacht to not only protect the environment but also protect the future value of their investment.
There is a growing body of evidence that suggests a large percentage of the microfibres in our oceans is the result of washing clothes in automatic machines. Many of those microfibres are from man-made fibres i.e. plastic. It is suggested that up to 30% of the micro plastic pollution in our oceans may come from this source.
One such study detailed in the report “Me, My Clothes and the Ocean” by Ocean Wise and sponsored by the Canadian Government, revealed a surprisingly large variance in the amount of microfibre textiles shed in a single wash; ranging from a loss of 9.6 mg to 1,240 mg, or an estimated 9,777 to 4,315,371 microfibres, per kg of textile washed. Factors include the type of machine, wash cycle, type of fabric, fabric finish and age. Amongst the worst products are fleeces made out of man-made fabrics.
Just think how many kg of clothing a yacht laundry handles on a daily basis!
Various countries are starting to take this plastic pollution seriously. Within our European waters France has already introduced a law (LOI n° 2020-105 du 10 février 2020) that will require manufactures to include microfibre filters in washing machines sold from 2025 and, in the UK, an all-party group of MP’s are trying to introduce similar legislation, and have produced their first report.
But what has this to do with superyachts?
Unless your yacht has an Advanced Wastewater Treatment System (AWTS) that processes black and grey water, laundry effluent – including the microfibres – is discharged straight into the sea, often at anchor or in port.
Even if an AWTS is installed, the microfibres will end up in the residual sludge that is eventually discharged in compliance with MARPOL at least 12nm offshore. It is not being prevented, just displaced by time and place and still finding its way into our oceans.
So, whilst the industry has been focused on reducing plastic onboard, we may have been ignoring what happens below the waterline. Along with other pathogens, contaminants, and organic matter – see my previous article “What Lies Beneath” grey water is perhaps having a more profound effect on the ocean and marine life than stopping the use of plastic straws or bottled water onboard, especially in the coastal waters where yachts congregate. After all, we play in that water and may also consume seafood that may have been harvested from inshore waters.
Until microfibre filters are installed as standard then the only real solution is to fit external filters to the waste discharge from washing machines.
In a 2020 Bloomberg article, PlanetCare who produce an external washing machine filter, mentioned their filter can fill up in about 20 laundry cycles, after which they are sent back to PlanetCare where the fibres are collected, repurposed and the filters recycled. That would be a day’s use in many superyacht laundries – though they have commercial solutions as well.
Superyachts will require a more practical solution with easy access for cleaning and procedures for storing and disposing of the waste.
With the right filter the superyacht industry has the opportunity to help protect the marine biota and improve sea water quality by removing microfibres before they enter the grey water tank or AWTS and preventing their discharge into the sea.
There has been a lot written about ‘Hybrid’ yachts, often with some hype about being eco-friendly, having green credentials, etc., but with very little information of substance to support the claims.
Hybrid, in the context of motor yachts, just means there is more than one system capable of providing propulsion and/or electrical power.
Apart from a couple of innovative examples, all these systems rely on burning diesel fuel (MGO/MDO) as the primary energy source. This is sometimes glossed over where batteries are concerned.
Hybrid motor yachts and tenders have also been compared to Hybrid vehicles, but completely ignore the fact that they generate power from coasting or braking to increase their efficiency – something not available to yachts.
So, in this piece, I take a more in-depth look at Hybrid systems in an effort to provide some much-needed clarity on their benefits. I also question whether it is a transitional technology, or if it will be here for the longer term?
No Standard Operation
When it comes to superyachts and their operation, this is true. It’s what makes optimising the propulsion and electrical package challenging.
Main engines (ME) must be able to deal with variable speeds e.g. manoeuvring, cruising, maximum speed.
Generators (GEN) must handle variable loads and the ‘cycling’ of equipment that is dependent on the operational mode e.g. underway, guest-on, guest-off, in port or at anchor.
Given the variability of speed and load it can be difficult to size the main engines and generators for their best performance. This matters, because running engines at optimal load increases efficiency, reduces fuel consumption and emissions such as CO2; this is where ‘Hybrid’ can help…but, more on that later!
A Little History
Traditionally, superyachts used diesel main engines to provide propulsion power, and diesel generators to provide the electrical power for auxiliary and hotel loads – independent systems.
Fig 1. Traditional – ME to drive the propellors and GEN’s that power the hotel and auxiliary loads.
Although Diesel Electric has been used in shipping for many years it was not until the launch of M/Y Limitless in 1997 that it started to receive attention in the superyacht industry. And, in 2005 we saw the launch of M/Y ICE a Diesel Electric yacht that also used Azipods – interestingly both were built by Lurssen.
The story goes that many shipyards were reluctant to adopt Diesel Electric due to the complexity, engineering risks and the associated costs of developing a new platform – concerns that still apply to any new technology. However, their benefits, and the demands from yacht owners and their technical team saw a steady increase in use – especially on the larger yachts.
Fig 2. Diesel Electric – GEN’s provide electrical power for propulsion through Permanent Electric Motors (PEM’s) and the hotel and auxiliary loads.
Diesel Electric has many benefits. Having a number of generators (can be different sizes) that can be brought on-line for propulsion, and the hotel and auxiliary loads, meant the engines could run at optimal loads with better efficiency. It also provided a high degree of redundancy, greater flexibility in the technical layout – no longer limited by shaft lines – and, reduced noise and vibration which improved comfort.
You could say Hybrid is a mix of ‘Traditional’ and ‘Diesel Electric’ systems, combined with batteries (BAT) and sophisticated Power Management System (PMS) to optimise engine performance and efficiency.
The diagram below is an example of a Hybrid system.
Fig 3. ‘Hybrid’ Arrangement
Propulsion can be driven by ME’s, PEM’s or both (Boost), electrical energy can be generated from the ME and/or GEN’s and stored in batteries. The PMS takes care of managing the loads for propulsion, hotel and auxiliary systems.
The 83m Feadship, M/Y Savannah, delivered in 2015, is often cited as the first Hybrid motor yacht; though, just like Diesel Electric, it was not new to shipping. Since then we have seen am increase in its use across a variety of different sized motor yachts.
As mentioned, although diesel fuel is the primary energy source, there are some examples of innovative Hybrid motor yachts that use ‘Alternative Energy’. These include Artifact that uses solar, and the recently announced Lurssen project that will use Methanol in the energy mix.
No doubt the use of alternative energy will increase over time as the industry strives to reduce its carbon footprint.
It’s All About Efficiency
There are different types of marine diesel engines, two-stroke, four-stroke, slow speed, medium speed and high speed, each with their own performance characteristics. We use four-stroke high speed diesels on superyachts for both main engines and generators.
Whilst diesel engines are the most efficient internal combustion engines (ICE) at approx. 45% energy out vs. energy in, there are challenges to improve this – we may be close to the max with modern engine designs and materials.
What may not be so obvious, is that diesel engines have an optimal load; a point where the power generated requires the least amount of fuel. For many marine diesels this is at or near the Max Continuous Load and can be found from a table or graph of Load (kWh) vs. Specific Fuel Oil Consumption (g/kWh) in the engines test/technical file.
The example below is the SOFC for fixed speed 340 kW generator.
Fig 4. SOFC for 340kW GEN
The lowest fuel consumption 205 g/kWh is at 100% load. As the load decreases fuel consumption increases at a shallow and near linear slope until about 40% load, where it starts to rise exponentially.
The effect of running at or near optimal load on fuel consumption can be seen in the below.
Fig 5. Using one GEN at 80% load instead of two at 40% load can reduce the fuel consumption by approx. 9%.
Providing the generators are sized correctly it is unlikely they would run at less than 40% load – a point to bear in mind when looking at fuel efficiency claims for ‘Hybrid’ systems as they may be based on the more extreme ends of the SOFC curve.
This is also relevant to main engines though because they are able to run at variable speed, the difference is less pronounced – one of the advantages of variable speed generators as fitted to Artifact.
In the example below of a 3600 kW main engine, the SOFC slope is shallow and near linear from 100% load down to 25% load, where it starts to rise exponentially. There is about a 5% difference in fuel consumption between 25% and 100% load – a much wider load range and lower fuel saving compared to the fixed speed generator.
Fig 6. SOFC for 3600 kW ME
Unless ME’s are significantly over-sized to eke out that extra 0.5 knot of top speed, the only times when running at less than 25% load would be whilst maneuvering and/or motoring at sub-optimal speeds – you can determine this by comparing power/speed graph with SOFC.
What About Batteries
Batteries are just one form of Energy Storage System (ESS) others include devices such as capacitors and flywheels but, they all need an external energy source to charge them e.g. generators, solar, shore power.
Batteries perform a number of functions in a Hybrid system.
Buffer and avoid start/stop of additional generator
Backup for running generators
Fewer generators needed online
Improve fuel efficiency and reduce emissions
Reduce engine hours and maintenance
Instant power on demand
No startup delay
Each of the above helps to improve performance and efficiency of the yachts systems by keeping the engines operating at their optimal load, reducing fuel consumption and CO2 emissions.
Batteries with sufficient capacity can also power propulsion and/or the hotel and auxiliary loads for short distances or time.
Engine Free Operation
Whilst it is clear that batteries are an integral part of a Hybrid system – though not essential as I have sailed on a Hybrid yacht without batteries – whether they offer significant benefit when used for ‘Engine Free’ operation is another matter.
Engine Free, often described as ‘silent’ or ‘zero emissions’ mode, is perhaps a little more nuanced than might be suggested.
One reality is that emissions are not really reduced or prevented, they are merely displaced by time and location and do nothing for the overall CO2 footprint of the yacht – you still need to burn diesel fuel to generate the electrical energy stored in the batteries.
When it comes to noise, I also found that on larger yachts that with proper isolation, sound insulation and dry stack exhausts, it was difficult to tell if a generator was running in the guest areas. It was often the air-conditioning that emitted the most obvious noise and shutting down the a/c often resulted in an eerie silence, even with generators running.
With the above and, given the known issues with Li-ion batteries, from their production and imbedded emissions, to safety, life-cycle and recycling, I think the use for Engine Free operation needs to be carefully assessed. The current battery technology does not provide sufficient capacity for any reasonable level of autonomy without significantly impacting the interior space and weight.
In addition, if installing large battery banks for Engine Free running, you may need to upsize the generators as the total amount of energy required is not diminished, it is just generated over a shorter period of time. You may also lose some efficiency gains due to the power required to keep the battery banks at optimum temperature.
A Hybrid Solution
The following example provides flexible modes of operation.
Fig 7. Fully Integrated Solution
A. Stationary – Hybrid GEN/BAT for electrical loads
B. Low Speed – Propulsion and electrical loads from Hybrid GEN/BAT
C. Cruise – Mechanical propulsion, Hybrid GEN/BAT electrical loads
D. Performance (Boost) – Combined mechanical and electrical propulsion/loads from Hybrid GEN/BAT
The main purpose of these modes provides operational flexibility to ensure the optimal engine load, performance and efficiency.
Fuel Saving and CO2 Reductions
Whilst we now know fuel can be saved by running diesel engines at optimal loads, the more difficult question to answer is; by how much?
One DNV study ‘Electrical Energy Storage For Ships, published in 2020’ suggested that the ‘fuel saving potential’ for yachts was around 5 – 10%. Engine manufacturers and yacht builders tend to be a little more “optimistic” with the potential savings and benefits often using emotive words to describe their benefits.
Where you measure the ‘delta’ from matters, as using the extremes will result in significant differences in SOFC, but may not reflect the real-World use – the time the engines spend at least efficient load may have very limited effect on overall consumption.
It is important not to focus on the headline figure, but to evaluate the potential savings across a range of speed and load scenarios that are expected with the yachts use. The engines technical files will help identify the real savings.
Is It Worth It
The evidence confirms that a well-designed ‘Hybrid’ system can have a positive impact today in terms of more efficient yachts and reduced fuel consumption. According to the IMO fuel coefficient, every ton of MGO/MDO emits 3.206 tCO2. So, on that metric alone, the answer would have to be yes.
Unfortunately a ‘Hybrid’ yacht will be more expensive which no doubt affects more widespread use. When viewed purely on a cost/benefit basis, it may be hard to justify the extra cost against the potential fuel savings, and reduced operational costs due lower engine hours and extended maintenance intervals. Depending on use, the break even point may be a many years away and lay outside the envisaged ownership timescale. So as long as it’s an ‘option’ from builders cost will probably trump environment.
In the evaluation process, it worth considering the cost of diesel fuel may increase in the future due to carbon tax, and renewable fuels such as HVO (drop-in diesel) will be significantly more expensive. So, the additional cost today, may be sound investment for the future?
Finally, whatever energy is used in the future, it will likely be less energy dense than diesel fuel, and certainly more expensive. This means power management and efficiency will become even more critical and Hybrid technology will remain a fundamental component, especially in mixed energy solutions.
There have been several concepts, and a good many articles and discussions relating to the use of solar panels on superyachts. And, as a zero-emissions energy source, this would seem to be an ideal technology to reduce or replace a yachts reliance on fossil fuels. You could have large arrays of panels on the superstructure or build them into sails to provide all the yachts energy…but could you?
Like many alternative energy solutions, away from the sensational headlines, it’s only when you look at the details do you begin to understand whether they are practical solutions or not.
In this piece I will shed some light on the use of solar panels on superyachts.
Using a 65m yacht as an example, I will assess the energy required from generators for a 24 hour period and the area of solar panels that would be required to generate this energy.
Sunlight As Energy
Studies suggest that the amount of sunlight that strikes the earth surface in 1.5 hours is sufficient to handle the Worlds entire energy consumption for 12 months. It is important to understand that although this solar radiation bathes the entire World it is dependent on time, date and location.
This is the monthly variation due to the sun’s declination, but there is also the diurnal variation due to the elevation of the sun from sunrise to sunset, as shown below.
Of note, the total radiation (Global) is based on Direct and Diffused radiation e.g. reflected.
Taking the monthly figures, the average daily amount of energy is therefore:-
July 6.6 kWh/m2
January 1.56 kWh/m2
Much like a stabilised VSAT or TV antenna depends on pointing directly at the satellite for the best signal, the same is true for solar radiation; the highest levels of insolation are when the sun’s rays are perpendicular to the plane – hence the improvement in solar cell performance with systems that track the sun both in azimuth and elevation.
For those projects that have suggested using solar panels on sails, the angle of the sails relative to the sun’s rays will impact heavily on the energy generated. Underway, the wind is unlikely to allow for the most optimum angle and, at anchor if windy, you would need a method of ‘stalling’ the sails to achieve the best angle.
Solar Panel Efficiency
But I have seen powerful solar panels rated at 500-550Wp!
This is true they are available, but panels of that power are approx. 2.2m2 and power rating is the peak performance based on the Standard Test Condition (STC).
The STC is based on horizontal solar radiation of 1000W/m2 at an internal cell temperature of 25°C. Efficiency is measured by how much of the solar radiation is converted into electrical power and currently the best panels have an efficiency rating of 21%.
This means under STC conditions the best 1m2 panel would produce 210Wp but, of course, as can be seen from the graphs above, solar radiation is not constant. And, along with seasonal and diurnal variation, a solar panel is also affected by angle of incidence and other factors that can reduce efficiency, such as system losses, contamination on the surface and temperature.
Air temperature has a major effect on the cell temperature, and higher or lower cell temperature will either reduce or increase the power output by a specific amount for every degree above or below 25°C (STC). This is known as the power temperature coefficient (PTC) which is measured in %/°C.
As an example, monocrystalline panels have an average PTC of -0.38% /°C, while polycrystalline panels are slightly higher at -0.40% /°C.
In general, cell temperatures run approx. 25°C above the ambient temperature. So, on a summer’s day with air temperature of 30°C you could see an approx. 11% reduction in efficiency of a Monocrystalline panel.
Daily Solar Energy Example
Knowing the efficiency of a solar panel enables us to do some basic calculations on daily energy produced from a 1m2 solar panel in July and January for Monaco.
Average daily solar radiation is 6.6kWh/m2
Total energy produced 1.39kWh/m2 per day
Average daily solar radiation is 1.56kWh/m2
Total energy produced 0.33kWh/m2 per day
How Much Energy is Required?
Taking a 65m yacht fitted with 200kW generators and, assuming with ‘guests-on’ will require around 4500kWh/day for the non-propulsion such as air-conditioning, stabilisers, water-makers, refrigeration, galley, laundry, water heaters, av/it., etc. This will be less ‘guest-off’ with good power management practices employed by the crew.
On this yacht the flat surfaces available for solar panels is approx. 407m2.
From the above, in Monaco in July, if you wanted to generate the energy from solar panels alone you would need approx. 3,240m2 of panels – approx. 8 x available area.
In addition, you would need and a battery bank of approx. 2.8MWh (only 80% useable due to battery cycling) for the hours when the sun is not shining.
This is assuming maximum efficiency and does not include any de-rating due to shade, cloud, rain, contamination on the panel surface or high air temperature, all of which impact efficiency and final energy generated.
And, in January…well you can work that out!
The Potential of Solar Panels
As can been seen given the variables that effect energy produced and the large surface area required, it would not be a practical solution to replace diesel generators with solar panels – not for large yachts anyway. However, they could be used as a part of a hybrid solution to reduce fuel consumption and CO2 and other exhaust gas emissions.
With the above example 407m2 x 1.39kWh/m2 = 565kWh or approx. 3 hours of generator use. This is a useful saving especially if combined with batteries and power management systems that can use that energy to help with generator efficiency. But, don’t forget, season and location will have a large effect on this number.
The challenge on any superyacht will be finding sufficient flat surfaces and the issue of heat and efficiency. New panel technologies are in development with higher efficiencies, possibly up to 50% and this will help the adoption of solar panels in the energy mix but, by themselves, do not offer a replacement of fossil fuels on superyachts.
Although the primary environmental concern challenging our industry is C02 and other emissions generated from burning fossil fuels, there are other vectors such as sewage and grey water that can also have an impact.
Whilst on the larger yachts the new treatments plants take care of both, producing effluent that can be clean enough to use as wash down water, smaller and/or older yachts may not be so well equipped, or have inadequate black/grey holding tanks. Grey water is often simply discharged overboard.
For those of us who have had the ‘pleasure’ of sticking their head into a grey water tank, we are only too aware of the odious and putrid soup that is contained within, in fact, I suggest many crew would rather inspect a sewage tank than a grey water tank such is the assault on the senses. And, given these sensory observations, and the impact grey water can have on tank coatings, why is grey water treated essentially as a harmless liquid?
Whilst the discharge of sewage (black water) is mostly regulated under the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex IV and other national legislation such as United States Environmental Protection Agency (EPA) Clean Water Act (CWA) grey water from ships and yachts is discharged untreated directly into the sea. On yachts, this is very often in close proximity to the coast, beaches, ports and marinas, where there are swimmers or other recreational water users and where it has the potential for the greatest impact on the marine ecosystem.
So what is grey water?
*If using mobile phone, swipe or rotate screen to see the full table.
Grey Water Definition
Annex V Reg 1 Definitions
4. Domestic wastes means all types of wastes not covered by other Annexes that are generated in the accommodation spaces on board the ship.
Domestic wastes does not include grey water.
1.6.1 Dishwater means the residue from the manual or automatic washing of dishes and cooking utensils which have been pre-cleaned to the extent that any food particles adhering to them would not normally interfere with the operation of automatic dishwashers.
1.6.2 Grey water means drainage from dishwater, shower, laundry, bath and washbasin drains. It does not include drainage from toilets, urinals, hospitals, and animal spaces, as defined in regulation 1.3 of MARPOL Annex IV (sewage), and it does not include drainage from cargo spaces. Grey water is not considered garbage in the context of Annex V.
*Note: if in-sink macerators drain into grey water tanks, then the contents and discharge of that tank will need to comply with Annex V.
Clean Water Act, 33 U.S.C. 312(a)(11)
Galley bath and shower
Coast Guard regulations, 33 CFR 151.05
Drainage from dishwasher, shower, laundry, bath, and washbasin drains and does not include drainage from toilets, urinals, hospitals and cargo spaces.
So, whilst grey water is well defined, what is less well understood is that untreated grey water contains many undesirable pathogens, organic matter, chemicals and micro plastics (the microfibres that are shed during washing of man-made fabrics) often at levels that can be higher than domestic effluent from sewage treatment plants, and can have an impact on human health and the marine ecosystem.
One of the largest studies on grey water was done by the EPA following a petition in 2000 from Bluewater Network who represented 53 environmental organisations who wanted the EPA to take regulatory action on cruise ship pollution. The report – Draft Cruise Ship Discharge Assessment Report (EPA842-R-07-005) – was published in 2007 and covered sewage, oily bilge water, solid waste, hazardous waste and grey water. And, whilst there are significantly more crew/passengers on cruise ships and waste volumes greater, the sources and treatment are very similar to the superyacht industry.
From that study they list common sources and characteristics of grey water in the table below.
Automatic Clothes Washer
bleach, foam, high pH, hot water, nitrate, oil and grease, oxygen demand, phosphate, salinity, soaps, sodium, suspended solids, turbidity
Note: recent studies also suggest micro plastics from man-made fibres are also contained with the waste water.
Automatic Dish Washer
bacteria, foam, food particles, high pH, hot water, odor, oil and grease, organic matter, oxygen demand, salinity, soaps, suspended solids, turbidity
Sinks, including kitchen
bacteria, food particles, hot water, odor, oil and grease, organic matter, oxygen demand, soaps, suspended solids, turbidity
Note: if food waste from in-sink macerators is draining into grey water tanks this changes the grey water to food waste and therefore discharge must comply with MARPOL V.
Bathtub and Shower
bacteria, hair, hot water, odor, oil and grease, oxygen demand, soaps, suspended solids, turbidity
Source: ASCI 2001
Of course, the quantity and quality of grey water varies considerably depending on many factors, such as the number of crew and passengers, the various types of detergents and cleaning products used, personal grooming and hygiene products used by the crew and passengers, and various filters and fat traps if installed.
The EPA study, combined with findings from a previous study by the Alaskan Department of Environmental Conservation – Alaska Cruise Ship Initiative in 2001, found a range of readings of various analytes. A sample of which are found below.
Untreated Domestic Water
10,000 – 100,000
Biological Oxygen Demand (BOD 5 day)
110 – 400
Chemical Oxygen Demand
250 – 1,000
66.9% between 6.0 and 9.0
Between 6.0 and 9.0
Totals Dissolved Solids (TDS)
Total Suspended Solids (TSS)
100 – 350
Ammonia – Nitrogen
Total Kjeldahl Nitrogen
20 – 85
*MPN – most probable number
Untreated grey water contains many pathogens and, in addition to those listed above, can also include, Salmonella, shigella, hepatitis A and E, and gastro intestinal viruses (national Research Council, 1993). Pathogens can pose danger to human health by contact or ingestion of contaminated water, or by consuming shell fish which feed by filtering water.
The 1986 EPA Quality Criteria for Water, commonly known as the ‘Gold Book’, references pathogen indicators and has defined water quality standards based on two activities of import to yachting: marine water bathing and, shellfish harvesting.
From the samples of untreated grey water analysed in the study, the average fecal coliform contamination exceeded the standard of 43 MPN/100mL for shellfish harvesting and, the average enterococci contamination exceeded the standard of 35 MPN/100mL for marine water bathing.
Although not a major indicator in this study, chlorine is used on yachts in a variety of applications including sanitising fresh water tanks, the discharge of which is generally pumped overboard, often via the grey water tanks, so levels must be carefully controlled so they do not exceed recommended limits.
Studies have found that chronic affects to the marine biota such as poor reproduction and health can be observed at concentrations above 230mg/L with acute effects, severe illness or death, at concentrations exceeding 860 mg/L.
Organic matter from the grey water acts as food for water borne bacteria. The more food available, the greater the number of bacteria decomposing the waste and using oxygen in the process. Nitrates and phosphorous also contribute to high oxygen demand by providing nutrients for plants and algae to grow quickly, contributing to organic waste when plants die and decompose.
Reductions in oxygen level can be harmful to aquatic species and can, in extreme cases, create ‘dead zones’ where no fish or other organisms can live.
Suspended solids can affect the clarity of the water and in turn adversely affect the photosynthetic activity of marine biome.
This is a more recent and topical concern relating to plastics entering the food chain, consumption by humans, and the longer term environmental and health impacts.
A number of studies have shown that during machine washing of man-made clothing significant numbers of tiny fibres are released into the waste water; and, in the case of yachts, into the grey water tank and eventually into the sea.
One such study is ‘The release of microplastic micro fibres from domestic washing machines: Effects of fabric type and washing conditions’ (Elsevier: Imogen E. Napper, Richard C. Thompson).
This study examined the release of textile fibres during machine washing of clothes from three commonly used fabrics; polyester, polyester-cotton mix and acrylic. The results showed that laundering 6kg of synthetic material could release between 137,951 – 728,789 fibres per wash, ranging in size between 20 𝜇m and <5mm. Given the load on most laundries and, composition of the fabrics washed, one can see the potential for a significant number micro plastics being discharged into the sea on a daily basis.
It is important to note that when grey water is discharged into the surrounding sea it mixes with the sea water and dilution takes place. This effect can be affected by factors such as discharge rate, salinity, water temperature, wind, currents and, of course, a yachts movement.
The Alaska Department of Environmental Conservation (ADEC) concluded that dilution factor would range from approx. 5 to 60 and occur between 1 and 7 meters from the ship (ADEC, 2004). The EPA report suggests that the initial dilution estimated by ACSI and ADEC for a vessel at rest would not likely be great enough for untreated grey water to meet the ‘Gold Book’ standards for fecal coliform and enterococci
From tests conducted by the EPA, it was shown that the dilution effect, due to the movement of a vessel and the mixing by their propellers, for a ship underway between 9.1 and 17.4 knots was a factor of between 200,000:1 and 640,000:1 immediately behind the vessel and, based on those results all ‘Gold Book’ standards for water quality, apart from fecal coliform, would be met.
From this it can be seen there are significant benefits in only discharging when underway and away from the near shore.
Apart from yachts that have advanced waste treatment systems that treat both grey and blackwater compliant with MARPOL IV 9.1.1 and the guidelines in MEPC.227(64) most yachts will be discharging untreated grey water from their holding tanks, often with food waste contrary to MARPOL V, whilst static, directly into the sea. The effect of this can be observed in busy marinas and crowded anchorages on windless days when there is little water movement or seabed disturbance and the water takes on a milky and/or scummy appearance – the difference in water clarity around Cala de Volpe in and out of season is quite striking.
Furthermore, the grey water has the potential for human health risk – depending on contamination levels – especially for those engaging in activities such as swimming, jet ski, wake-boarding, or any other activity where they may ingest seawater or have contact via an exposed scratch or wound. There are also short and long terms considerations related to the marine ecosystem such as algae blooms, bacteria in shellfish, and the introduction of micro plastics into the food chain.
Whilst the issue surrounding grey water applies to commercial shipping as well, due to their sailing and trading patterns they tend to have little impact on inshore waters – as can be seen from dilution effect underway. For cruise ships, if they do not have suitable onboard treatment of grey water, the Cruise Lines International Association (CLIA) members voluntarily agreed to limit the discharge of untreated grey water to when they are underway at not less than 6 knots and at least 4 nm from the nearest land and not to discharge grey water when in port.
What can we do?
I outline some of the steps could be taken to reduce the impact of grey water discharges.
As per CLIA, no grey water discharge closer than 4nm from nearest land, underway at not less than 6 knots
No discharge of grey water in port if facilities available – marinas have work to do here?
Where available, discharge grey water to suitable reception facilities e.g. barge or ashore
On new builds, increase size of holding tanks to more practical sizes based on ‘practical’ use of yachts, so discharge can be better managed – including smaller yachts
Install filters to remove micro fibres from washing machines
Use ‘environmentally friendly’ cleaning and personal hygiene products – not just ‘ECO or Green’ labeled as these are often-abused and misleading descriptions – carefully scrutinise such claims and check if they have been independently assessed and verified
On new builds specify and install only black/grey water treatment plants
On refits, consider updating your treatment plant and include grey water
Consider dosing grey water with additives that reduce pathogens and/or organic matter
Avoid using in-sink macerators if the pulp discharges directly into grey water tanks – instead, bag, store and dispose as per MARPOL V
Installation of fat traps
Some of the above does not require major expense, just a change in operational procedures and, of course, education costs nothing.
The quality of our oceans, and its health are fundamental to yachting – it is the ‘playground’ from which we experience so much pleasure. With our intimate connection to the to the sea we have a responsibility to minimise our environmental impact, protect the long term health of our oceans, and to ensure that future generations get to experience the same pristine seas and diverse marine life that we have all enjoyed.
The reason for this question is that it doesn’t take much to realise that being able to switch your yacht from fossil fuel to green fuels in the future will have a positive impact on use, cost, and asset value.
Whilst these concerns and the transition away from fossil fuel seems to be far away, the impetus is growing and the reality is that when you take into account the design and build cycle along with the lifetime of a superyacht, you begin to understand why this may be an important consideration for anyone investing in a new build today.
Indeed, Lurssens recent announcement of a project using methanol and fuel cells may represent a paradigm shift for the industry. Though there are still questions about the availability of green methanol and storage and bunkering, this is probably the only superyacht in build that has the potential to adapt to a zero emissions future.
From discussions with other shipyards, it is clear that the environment is becoming an important consideration for some owners, and the pressure to act will only become more intense in the coming years.
The current narrative seems to be that ‘hybrid’ or ‘diesel electric’ (propulsion from electric motors) will allow you to simply remove the generators, replace them with a stack of fuel cells and then load up on green energy. On the surface these seems to make sense, however I think reality may be a little different.
When you look more deeply at the how, the challenge will not come from the replacement of the generators, it will come from the availability and choice of the green energy carrier that replaces the diesel fuel.
Currently hydrogen, methanol and ammonia seem to be the leading fuels in the drive to zero emissions shipping. LNG and biofuels also provide a useful pathway that helps reduce emissions but are unlikely to be the long-term solution.
The production of green ammonia or methanol, also known as ‘e’ fuels, require hydrogen produced via electrolysis using nuclear or renewable electricity and synthesis with air (e-ammonia) or CO2 (e-methanol). It is a very energy intensive process and methanol also depends on the supply of green CO2 e.g. biomass or direct air capture (DAC).
Due to the amount of energy required to produce these fuels and supply chain costs, these fuels are likely to be more expensive than today’s diesel. Technology and innovation in all its forms will still be necessary to reduce energy consumption.
Worth noting is that hydrogen, ammonia, and methanol, can be used in internal combustion engines (ICE). For example, the Ro-Ro/Pax carrier, Stena Germanica was successfully converted to run on methanol. This could provide another pathway for us; though I don’t know if these ‘gas’ or ‘dual fuel’ ICE’s are suited to superyachts? Maersk has also announced the building of a ship to run on methanol, whilst acknowledging that they are not entirely sure of fuel supply or infrastructure – I think it demonstrates a leadership that may help break the supply/demand impasse and drive change.
The major challenge with all these fuels for yachts, where space and aesthetics – a cryogenic hydrogen tank on the aft deck would not be ideal – are major factors, is that they are less energy dense than diesel, require more volume for the same amount of energy, along with special storage and enhanced safety due to the nature of the fuels e.g. flammable and toxic.
More information an be found in The International Maritime Dangerous Goods (IMDG) Code, International Code of Safety for Ship Using Gases or Other Low-flashpoint Fuels (IGF Code) and IMO MSC.1/Circ.1621 Interim Guidelines For The Safety Of Ships Using Methyl/Ethyl Alcohol As Fuel.
This excellent diagram of Volumetric and Gravimetric energy of various fuels from DNV-GL – Comparison of Alternative Marine Fuels, Report No: 2019-0567, Rev. 3, clearly highlights the energy differences.
Energy densities for different energy carriers (inspired by /49/ /72/ and /73/ of the report). The arrows represent the impact on density when taking into account the storage systems for the different types of fuel (indicative values only)
Hydrogen, due to the storage requirements, compressed or liquid, probably excludes its use directly as a marine fuel on superyachts though, as with shipping, it may be well suited to coastal cruising. Much more likely, as with the Lurssen project, is that methanol or ammonia is used as the energy carrier and converted back into hydrogen using reformers onboard if fuel cells are used.
The resultant hydrogen would then be used in Proton Exchange Membrane (PEMFC) or High Temperature Proton Exchange Membrane (HT-PEMFC) fuel cells. HT-PEMFC are less critical on the purity of the hydrogen and the heat can be used to improve the overall efficiency – though, to date, as an industry we have not been very energy efficient with the use of waste heat from engines or generators.
Although solutions for the storage, ventilation, safety and bunkering of methanol and ammonia will no doubt be found – it’s already carried onboard ships either as a fuel or cargo – how this is integrated into the hull of a superyacht may have some significant impacts on space, layout and, of course, range.
I think some caution is required before promoting the use of ‘hybrid’ or ‘diesel electric’ as ‘future proof’ solutions. We need to be able to demonstrate how this would work, the practicalities and impact on cost, safety, use, space and range to name just a few considerations. This will be crucial to the future growth of the industry as yacht owners and their advisors will need to weigh these factors in their decision-making process.
Finally, Lurssen and their visionary customer, may have found one pathway that helps answer the question. That is a real benefit to the future of the industry.