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.
It could be suggested there is too much information available on COVID-19 and the pandemic; including, an almost infinite number of articles and commentary on the internet, numerous Circulars and Guidance from the IMO and, publications from the International Chamber of Shipping (ICS) such as Coronavirus (COVID-19) Guidance for Ship Operators for the Protection of the Health of Seafarers (version 3.0 29th September 2020).
This excess of information can be confusing and, also as suggested in Tom Nichols book “The Death of Expertise” result in a tendency to trust in the internet to make us ‘experts’ in all manner of subjects and, resist or even ignore, advice from those with a deep understanding and experience of the subject matter, including COVID-19 – this can lead to poor outcomes.
With the absence of a collective response from the industry, it has been left to individual yacht management companies and/or captains and crew to wade through the mass of information, try to assess its quality and efficacy, and then develop and implement their own protocols and procedures in response to the virus. And, whilst some of these are well thought out and effective, others on deeper analysis, are perhaps like the ‘Swiss Cheese’ risk assessment analogy, have holes for the virus to pass through.
So, it was a great relief to come across the “Recommendations from the Healthy Sail Panel.” This is the first document I have seen from a related industry with a well-researched and holistic approach to the prevention, protection and mitigation of COVID-19, in an easy to follow format.
The Healthy Sail Panel is a collaboration between Royal Caribbean Group and Norwegian Cruise Line Holdings Ltd who put together a panel of World leading experts to help inform and find a new pathway back to the “new normal” of sailing. The resulting research and recommendations are broken down into 5 key focus areas, with over 70 recommendations, many of which are applicable to yachting.
The key focus areas are: –
Testing, Screening and Exposure Reduction
Sanitation and Ventilation
Response, Contingency Planning and Execution
Destination and Excursion Planning
Mitigating Risks for Crew Members
It is well worth downloading and reading. I suggest you also follow up on some of the footnote references.
COVID testing is one of the subjects with references in the footnotes. Further reading clearly highlights the value of testing for screening and diagnosis but, like the use of electronic aids to navigation, you have to be aware of the limitations, errors and accuracy.
I was certainly confused by the various tests; Rapid Antigen, PCR, Antibody, etc., their effectiveness for screening, diagnosing present and past COVID infection. The US CDC footnote reference in the Healthy Sail Panel certainly helped my understanding, along with the infographic below – found on the Nature website in their article “Fast coronavirus tests: what they can and can’t do.”
It became clear that, amongst other factors, the timeline of infection has a big effect on the various tests and why caution is required – especially with the Rapid Antigen tests that may be used by yacht crew.
Indian Ocean and Caribbean Passage
As many yachts and crew are readying themselves for passages to the Caribbean, Indian Ocean or further afield, I thought it was also worth considering this in the context of COVID-19 and posing the following question: –
“Should you self-isolate the yacht and crew and test before departing?”
Clearly, the time taken in transit is likely a suitable quarantine period for destination arrival purposes. However, the reason I pose the question is that given that most yachts will be departing from countries/areas with high rates of infection, and crew will have been enjoying shore leave and their time in port, what happens if a crewmember is infected, but tests negative (if tested) and is asymptomatic prior to departure?
Once underway and symptoms present, not only would there be concerns of further infections amongst the crew, and medical treatment if severely affected, there would also be concerns about at the port of destination; would the port allow the yacht to berth and what are the reception and medical facilities for any infected crew?
The same goes for ‘crossing crew’ do you bring them in early and quarantine (onboard in single cabin) and test prior to departure?
Clearly, no captain wants to restrict well-earned shore leave but, then again, it is important to avoid any crewmember being infected and becoming a medical emergency and/or a vector for further transmission, especially on a long sea voyage, so it makes sense to try and prevent this outcome.
I’d be interested to know how yachts and management companies are dealing with this. Some considerations:
What methods are in use for mitigating the risk of infection prior to departure
Has the port authority of your arrival destination been contacted and what is their policy in the event of an infected crewmember on an arriving yacht
Do the hospitals have the facilities and capacity to handle a COVID-19 patient
Are there any additional medical supplies and PPE above ‘Medical Scales’ that may be recommended to carry
The above, departs slightly from the main reason for this post but, for those about to embark on a lengthy passage, it’s something worth thinking about?
As always at OnlyCaptains, or goal is to share knowledge and help inform. Hopefully, the Healthy Sail Panel offers some useful information on COVID-19 that may help with your own procedures. And, perhaps it might be used as a reference by industry associations such as MYBA, LYBRA, IYBA, in a collaborative effort to create our own yachting recommendations. These would not only be of value to captains, crew and yacht management, they would also help to instil confidence in owners and charterers through the knowledge that industry accredited measures were in place to protect them whilst onboard.
Last week, I attended the Yacht Cub de Monaco: Capital of Yachting Experience. It was a very well organised and attended event, with some very interesting presentations and discussions.
It was also the launch of the Yacht Club de Monaco Superyacht Eco Association (SEA) INDEX. Supported by Nobiskrug and Credit Suisse, this is an important initiative with a goal to benchmark yachts in terms of their CO2 environmental performance. And, whilst there are other emissions, CO2 is by far the largest greenhouse gas (GHG) of importance and the one most visible in the public eye.
The principle is that it uses the IMO’s Energy Efficiency Design Index (EEDI) formula with a few changes to make it more specific to yachts.
The SEA INDEX is the first tool designed to assess and compare the efficiency of a yachts design and its environmental impact in terms of CO2, with a transparent and easy to understand rating system. Stars are awarded from 1 (lowest rating) to 5 (highest rating) depending on where a yacht sits above or below the rating bands relative to the baseline of sampled yachts.
Image: Courtesy of the SEA INDEX
The data from approx. 130 yachts of various length and displacement was sampled and their data entered in order to develop the initial baseline – there are now over 200 yachts.
It uses max power and speed, which may seem excessive, but a metric was required and, if you consider this as the ‘maximum emissions potential’ of a yacht, by using the same set of data points for all yachts, it provides a ‘standard’ for comparing their designs. For example, on comparable sized yachts, a more efficient hull will require less power for the same speed, and more efficient HVAC and hotel systems power management, will require smaller generators, both of which will result in reduced emissions and a higher INDEX rating.
And, as new designs and engineering innovations are introduced into yachting, the SEA INDEX will help highlight the improvements being made.
Of course, actual emissions depend on many variables that are affected by an owner and the operational profile of a yacht – these are hard to assess in any consistent or meaningful way. If we had recorded all yacht activity and consumption over the last 10 or 20 years, we would be able to draw a curve of standard deviation and have an idea of what might be described as ‘average use’ on which to make comparisons. Unfortunately, we don’t have this information, and this is perhaps the flaw in all such tools, so the only true account of a yachts CO2 emissions has to be calculated from their fuel consumed.
The factor the IMO use for CO2 emissions from MGO is 3.206, this means for every 1,000t of MGO used, 3,206t of CO2 is generated so it is easy to calculate your CO2 from fuel.
Any design efficiency gains, and improvements that can be made in the operation of the yacht, such as running at lower speed, managing power, switching off unused lighting and equipment, etc., will reduce the power required, fuel consumed and emissions.
In combination with efficiency gains, Carbon offsetting is one way to mitigate a yachts emission. Though, as I have written in a previous piece Superyacht Carbon Offsetting great care is required to select one that is fit for purpose.
But, it’s not just the amount of CO2 that is an important consideration. Looking to the future, it is very likely that shipping, like other industries, will be impacted by Market Based Mechanism’s (MBM) to drive forward the transition to a greener future, and these will have cost implications.
The IMO by 2023 will introduce their new framework for the reduction of GHG emissions from shipping and it could include a carbon tax. The EU in a recent plenary session of parliament, agreed that shipping should be included in the EU Emissions Trading Scheme (ETS) possibly in 2021and include vessels less than 5000gt. Trafigura, one of the World’s largest ship charterers, published on 25th September “A proposal for an IMO-led global shipping industry decarbonisation programme” calling for a $100 – $200 tax per ton of CO2 on shipping as the only way of driving the necessary industry change.
As further evidence of the direction of travel for CO2 emissions for business, Swiss Re made this announcement on the 15th September 2020:
“Swiss Re steps up its internal carbon levy to USD 100 per tonne as of 2021 and will gradually increase it to USD 200 per tonne by 2030”
Any such taxes or levies imposed on CO2 emissions will increase the cost of yacht ownership.
On top of that we have Environmental Governance and Sustainability (EGS) targets that are becoming ever more prevalent, especially in investment and finance. The Poseidon Principles is just one initiative, launched the 18th June 2019, “major shipping banks will for the first time integrate climate considerations into lending decisions to incentivize maritime shipping’s decarbonization” their goal is to work towards the IMO 2030 and 2050 reductions in GHG by ensuring that their loan books are aligned with those targets – finance will become harder for vessels that fail to meet efficiency improvements and GHG reductions.
Could similar lending rules apply to yachts in the future, how would that affect the value of older less efficient yachts?
Whilst it is not yet clear how taxes and regulations will be imposed in the future, what is clear, is that yachting is unlikely to escape their embrace. And our intimate connection to the sea and the environment places additional responsibility on the industry to protect the health of our oceans and planet. The SEA INDEX is the first of many important tools, including those from the Water Revolution Foundation, that will help us to understand our environmental footprint and drive the necessary change that puts us on a pathway to a sustainable superyacht industry.
Like any instrument that is reliant on data; the more yachts that participate, the more refined and accurate the SEA INDEX will become – I would call upon all Captains to get involved.