| Written by Michal Wozniakowski-Zehenter

A huge boom in offshore wind energy proves the world's shift to green, renewable energy. Offshore wind farms have grown as a result of the urgency to fight climate change and reduce the usage of fossil fuels. Wind power can be harnessed more efficiently and consistently on these installations than it can on land. Wind farms can pose some logistical challenges because they're huge and often remote. A key solution to these challenges is Crew Transfer Vessels (CTVs), specialized boats that bridge the gap between shore and offshore. Offshore wind farms can't function without different vessels and CTVs play a key role in maintaining and operating them. Those wind farm boats get a lot of attention in this article, as we examine their significance, design, and functionality, as well as their challenges and the innovations that will shape their future. In our effort to transition to a greener, more sustainable energy future, CTVs are crucial to harnessing wind energy at sea sustainably, so we want to emphasize their importance.
Wind Farm Boats

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The majority of CTVs have been designed to be efficient and effective and built to work in the sector. Aluminium catamarans usually hold 12 passengers and have a top speed of 15-25kn, but some have a top speed of 30kn. About 25% of CTVs drive with fixed-pitched propellers, and 14% have controlled-pitched propellers. Water jets are also used. It's about 25% of the fleet has jets because they are super manoeuvrable and shallow draft. This is critical for some sites. On board, passenger comfort is a top priority because technicians need to feel well when they transfer to the field. Most vessels come with individual suspension seats that minimize travel fatigue and stress caused by vessel motion. They also have kitchens, televisions, and entertainment systems. Crew members can use one or two berths when on extended operations.



Typically, CTVs have two or three linked hulls, called catamarans or trimarans, because they're steady and use less fuel than a single-hull boat. It's really important to have a steady vessel when you're working around wind turbines in the ocean, which is pretty wavy all the time. They also have a special bumper system that's made to safely move people onto wind turbines; this system uses a rubber or sometimes a springy front part that touches the turbine's starting piece softly, so workers can walk right on the turbine's bottom part. It's very important that this design cuts on hard bumps and sticks well when the sea is rough to make sure everyone moves across safely, especially when it's windy and wavy. Those wind farm boats have extremely good engines, waterjet or rotating engines, which make them move very smoothly and get close to turbines without bumping into them; these vessels can stay put while people get off, which is good when the weather conditions are not the best. Being able to move around quickly and tightly is important for making sure these wind farm boats do their job right and safely.

A CTV's seats and safety belts need to keep the crew comfortable during the bumpy ride; this careful planning keeps workers from being too beat to do their job on arrival. The ships also have great maps and talk systems, so things run smoothly. Everything you need in case of an emergency, like lifeboats and vests, is easily accessible. With the wind energy industry trying to be eco-friendly, CTVs are starting to use cleaner energy, partly substituting propulsion engines with powerful batteries, and they're working to be quieter to eliminate noise pollution. Many of these things show the industry cares a lot about keeping nature safe and sound. There's also the need for TVs to be able to do more than just carry crews but also brief them. Boats can haul stuff, tow light things, or lift things with cranes. Many of these skills are needed for the lifetime of wind farms, including fixing, building, and coming to the rescue when things go wrong.



In transferring from a vessel to a turbine foundation, one of the problems is that the structure is fixed to the seabed, so the vessel moves relative to the foundation. In most cases, transfers are done using the 'bump and jump' method, where the boat pushes on the bow first toward the 'j-tubes' on the outside of the ladder. Using enough thrust, the vessel remains stationary at the point of contact with the foundation, so personnel can step onto the ladder.

The turbine access ladder is set back from the j-tubes by 450mm so that no one on the ladder will be crushed should the vessel move during the transfer process. On occasion, large waves can cause the ship to lose its position, especially if the side is strong. Generally, most transfers aren't allowed in sea conditions above 1.5m significant wave height. Wave frequency length and current also affect accessibility. The marine coordinator makes operational decisions daily. Several 'walk to work' systems have been developed to expand the transfer window. They have a heave compensating bridge mechanism that attaches to the j-tubes or ladder on the vessel. As the bridge stays stationary relative to the turbine, personnel can walk to work, even on high seas. You can find systems like Ampelmann, Macgregor, Maxcess, and Houlder TAS on the market. These systems are only compatible with larger vessels than CTVs. Systems for smaller crew boats have been developed, but they haven't proven viable yet.

Here is more about walk-to-work offshore systems.



In wind turbines, crew vessels depend a lot on the weather, so that's one big problem. If the wind is too strong, the sea is too bumpy, or you can't see well enough, CTVs have trouble getting people to and from the turbines. There's a lot of downtime when there's bad weather, like in winter or places with hard seas. As wind turbines get built farther out in the sea, the weather gets rougher (learn more about EHS Risk Management).

Wind power is supposed to be eco-friendly, so CTVs have to think about that too. It's hard for them to find the right balance between doing their jobs well and safely and being more environmentally friendly. They have to cut back on things like pollution, loud noises, and disrupting sea life. To fix this, they're making CTVs with better hulls, using new technology to move around, and exploring different fuels--but that takes time and money. Wind farms need to work efficiently because they have to make money and a lot of energy. The CTVs play an important role in wind turbine maintenance and repair; they face issues like cutting down travel time, being available more often for crew moves, and sticking to strict maintenance schedules. If a boat gets stuck, the turbines can't work as much, so there's less energy.



In order to handle tough issues, the offshore wind power scene has turned to bigger boats known as Service Operational Vessels. These excellent boats are built to hang out in the ocean for a while; they keep the repair teams and their gear on the water. For a bunch of reasons, SOVs are way better than CTVs; they can take more people, can handle rough seas better, and have a place for the crew to sleep. With the boats cutting down travel time, the team can work more effectively, even if there's bad weather. They've got very advanced propulsion systems and positioning systems that let them hover near windmills without anchoring; they have this moving bridge thing so they can swap to the windmills even when the waves are really strong. In other words, SOVs can go deep in the ocean and keep everything running smoothly without having to return to shore for a day.

However, the adoption of SOVs also presents new challenges. These vessels represent a significant investment compared to CTVs, with higher operational and maintenance costs. Additionally, the deployment of SOVs requires careful planning and coordination to maximize their utilization and cost-effectiveness. For nearshore wind farms or those with less demanding maintenance schedules, CTVs may still represent the most economical and flexible option.

Learn more about HSE offshore.



What are the types of wind farm boats?

Different vessels are used for offshore wind turbine work, and each has its job. Boats called Crew Transfer Vessels (CTVs) carry small groups of people back and forth to the wind turbines for short visits, fixing related matters, and maintaining them; these boats are usually either supply goods and services offshore or carry passengers under 3 cubic meters. Most of them are made of aluminium and have two hulls. They're pretty fast, going up to 20 knots, and they have seats for up to 12 people.
Then you have Service Operations Vessels (SOVs), which are knowledgeable enough to stay in one location on the water all by themselves and save on fuel; they let workers stay out at sea in the field since they have beds and things and are used for fix-up jobs and tuning up the wind turbines; these boats can host more than 40 people; they get decked out with walking platforms that adjust in wavy water, little cranes, and sometimes smaller boats to scoot around within the wind farm itself.
Feeder Support Vessels (FSVs) are responsible for bringing over big things, the actual wind turbines and their blades, to where they need to be built; they can also fit upwards of 50 people on board. Wind Turbine Installation Vessels (WTIVs) are focused on setting up and building the wind turbines; they can work in shallow water because they can raise themselves or act as floating cranes in deeper spots, and they have enough room to stay and store gears for more than 50 workers.

Last but not least, Field Development Vessels (FDVs) have an important job in stretching cables throughout these offshore wind spaces and hooking these big structures to the land. This is how they make sure electrical power gets from out there on the sea back to our homes.



The maintenance and operations of offshore wind farms face several challenges, such as weather dependency, environmental concerns, and lack of operational efficiency. However, there is a potential solution to these issues in the form of SOVs. Those wind farm boats complement CTVs and can address many of the challenges faced by offshore wind farm operations. The future of offshore wind farm maintenance and operations will likely involve a strategic mix of both CTVs and SOVs, which will enhance the reliability, efficiency, and sustainability of offshore wind energy production.

Walk-to-Work Whitepaper

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