Cressall Resistors Ltd - Experts & Thought Leaders

Despite an Indiana University study showing a luxury superyacht produces around 7,000 tonnes of carbon dioxide each year, the vessels are exempt from many maritime emissions regulations. While efforts to reduce their environmental impact have progressed in recent years, the industry is still far from sustainable. Mike Torbitt, Managing Director of marine resistor manufacturer - Cressall, explores the progress the yachting industry has made, and what more can be done to improve its environmental credentials.  Annual CO2 emissions A superyacht’s annual carbon dioxide (CO2) emissions, which campaigners claim are 1,500 times greater than that of a standard family car during the same period prove problematic. With an estimated 10,800 yachts afloat in 2022, around 5,400 of which are superyachts of over 30 metres, the combined CO2 emissions will have a significant impact on global temperature increases. It’s not only CO2 that presents a problem for the yachting industry, however. Diesel-powered yachts IMO legislation brought in during 2021 that limits NOx emission levels has threatened the viability Diesel-powered yachts produce high levels of nitrogen oxide (NOx), known to cause respiratory problems and acid rain. International Maritime Organization (IMO) legislation brought in during 2021 that limits NOx emission levels has threatened the viability of superyachts in recent years.  Moving away from fossil fuels Other marine vessels such as cargo ships use selective catalytic reduction (SCR) to convert NOx into water and nitrogen. However, since this method requires high exhaust temperatures to decompose the exhaust fluid, it has been less successful in yachts due to a lower average engine load.  To ensure a thriving and sustainable future for yachting, it is time for the industry to move away from fossil fuels. But how can this be achieved?  More sustainable sailing Industry decarbonisation has seen some promising developments in recent years Industry decarbonisation has seen some promising developments in recent years, with the number of electric boat listings more than doubling between 2021 and 2023, according to boats.com data. This includes an increasing number of tenders using electric propulsion systems to transport passengers between the port and the yacht. While decarbonising the yachts themselves presents a greater challenge due to their size and range of onboard facilities, there has been significant progress on this front with the development of solar-powered yachts.  Solar energy With a predicted market value of 2.4 billion USD by 2031, solar energy charges the lithium-ion batteries used to power this ship and its facilities. Some recent models have seen Li-ion batteries replaced with hydrogen fuel cells, which offer improved energy density and range. However, these recent innovations are not without issues. Although a solar yacht can fully benefit from sunlight when on open water, the position of other boats can block light from the vessel while it is docked. Additionally, during rapid acceleration or deceleration, hydrogen fuel cells’ power output increases gradually to a point but then begins to oscillate. This fluctuating power output can cause reliability issues.  Increasing reliability with resistors  DBRs ensure that the positioning process is safe and precise, by dissipating the excess energy Dynamic braking resistors (DBRs) can help to tackle both problems. To maximise solar efficiency, it is beneficial to place the panels on the ground or sides of the boat so that they can be motor controlled to follow the sun’s position throughout the day. DBRs ensure that the positioning process is safe and precise, by dissipating the excess energy generated as the motors decelerate. As a result, more solar energy can be converted to power the yacht.  Installing fuel cell DBRs can also be used to overcome hydrogen fuel cells’ reliability issues and fluctuating power output. To make sure the yacht’s power requirements are always met even in the case of output oscillation, it is possible to install a fuel cell that exceeds these requirements. However, this option also requires a DBR to dissipate the excess energy when it is not needed.  Cressall’s EV2 DBR Cressall’s EV2 DBR offers an ideal solution, as its modular design means that several units can be combined to fulfill power requirements of up to 125 kW.  As a water-cooled solution, it does not require fans to dissipate heat, making it lightweight and compact. Renewable yachting innovations With ten kilowatts (kW) of power per cubic decimetre (dm3) and 9.3 kW of power per kilogram, it avoids increasing the yacht’s load.  The yachting industry’s long history of excessive emissions once made the idea of sustainable yachts seem like a paradox. However, supporting renewable yachting innovations with resistor technology will finally make high-performance, low-emission yachts a possibility. 

Covering over 70 percent of the Earth’s surface, the oceans are a vital element of our planet’s ecosystem. However, for the millions of vessels that cross them, the aquatic environment can present a problem. Vessels are increasingly using electrical systems to power across oceans, but a component’s design must account for these extreme conditions. Here, David Atkins, project director at marine resistor manufacturer Cressall, investigates offshore resistor design. Importance of dynamic braking resistors Whether for main propulsion propellers, crane or lifting systems, or cable laying, electrical drives can be found at the heart of many marine operations, offering increased control, reliability, and mechanical simplicity. Dynamic braking resistors (DBRs) are an essential part of an electric drive system that remove excess energy from the system when braking to either dissipate as heat if the system is not receptive to regeneration or if the system is receptive, but energy level goes beyond the system limits, so needs to be removed. Engineers tasked with designing resistors must consider material choice, structural stability, and cooling method Material selection When designing electrical components for offshore applications, material selection is key from the start of the process to guarantee that equipment will perform under harsh conditions, including saline atmosphere, high wind loadings, and corrosive seawater. Engineers tasked with designing resistors for marine applications must consider material choice, structural stability, and cooling method. Corrosion-resistant materials Seawater and the saline atmosphere is corrosive, which could leave equipment inoperable. Due to this, stainless steel, combined with special paint systems, is typically used for the enclosure metalwork for resistor elements. With materials containing at least 10.5 percent chromium, stainless steel reacts with oxygen in the air to produce a protective layer on its surface to prevent corrosion if not painted. There are many grades of stainless steel that can offer high corrosion resistance, which can be further enhanced by the addition of extra elements. For below-deck applications, 316 and 304 stainless steel contain nickel to broaden the protective layer created by the chromium and can be used in unpainted conditions. Using resistor enclosures Cressall’s resistor enclosures for the EV2 resistor terminal cover boast at least an IP56 ingress protection rating However, for above-deck components, 316 stainless steel has a higher nickel quantity and added molybdenum, so the resistor unit’s metalwork receives optimum protection against the marine atmosphere, but in some conditions, the painting will also be required. Cressall’s resistor enclosures for the EV2 resistor terminal cover boast at least an IP56 ingress protection rating, certifying that seawater cannot enter the unit to cause harm. In addition to the exterior, it is important that the resistor’s element can withstand harsh conditions. For these applications, Alloy 825 sheathed mineral-insulated elements are less vulnerable to atmospheric corrosion. As the element is encased within the mineral insulated sheathing, the sheath is at earth potential, so if water or high humidity is present this will prevent accidental contact with the live element, making them a much safer choice for marine applications. Structural stability Weather at sea is unpredictable, so vessels must be able to withstand the large variance in the wind and harsh sea conditions found worldwide. Many offshore structures such as wind turbines are located in areas with high winds, so if the system requires resistors to help provide stability to their electrical components these considerations must be considered within a resistor’s design. Considering the impact of a vessel’s rotational motions, its side-to-side motion, or pitch, and its front-to-back motion, or roll, is crucial. Design engineers need to ensure that there is enough mechanical support in the structure to stabilise the resistors for safe operation when it is subjected to these forces. Finite element analysis FEA allows design engineers to predict a product’s performance in the real world, then see the impact of forces Cressall can conduct finite element analysis (FEA) to help ensure structural stability. FEA allows design engineers to predict a product’s performance in the real world, then see the impact of forces and make changes accordingly. This ensures the resistor performs well in potentially extreme weather conditions. It’s also important to consider the size constraints of marine applications. In contrast to onshore units, offshore electrical components must fit into a compact area, so the size of the unit’s support structures must be minimised without compromising durability. Forced Cooling method An essential part of a resistor is its cooling system. Since the resistor dissipates excess energy as heat, the cooling system is responsible for cooling the resistor element to ensure continued operation. Depending on the layout and resources of the system, resistors can be naturally or forced air or water-cooled. Air-cooled resistors come in two types — forced and naturally cooled systems. Forced cooling systems use a fan to dissipate heat in a compact space. These units are suitable for deck mounting and can be secured using anti-vibration mounts. Natural cooling offers a higher power rating and can be mounted in machinery spaces Natural cooling method Natural cooling is the most common in marine applications, offering a higher power rating and can be mounted in machinery spaces, protected environments or on deck. For machinery spaces or protected areas, consideration should be given to how the hot air released from the resistors should be evacuated to ensure other equipment mounted locally does not overheat. Chilled water system Alternatively, the cooling system can use the vessel’s chilled water system, which circulates cool water for air conditioning and equipment cooling. If the chiller system uses seawater, titanium-sheathed elements with super duplex steel metalwork can be incorporated, for continuous use in acidic, tropical seawater and downgraded to 316 stainless steel for freshwater systems. The ocean is a valuable asset for energy, transport, and trade. Ongoing development of electric drives for marine applications can be challenging, but taking these conditions and energy savings into account makes them a viable and advantageous option for powering vessels and for use in offshore structures.