As the wind generator components are becoming bigger, the challenges for the transport contractor are also becoming bigger. Where the blades used to measure 18 – 24 mtr and could be transported on extendible trailers, they can now measure over 100 mtr and require some serious engineering and logistics. However, not all blades are this long and some are even suitable to be transported in pairs (Figure 1).
When the blades become too long to be transported from origin to destination, or the surrounding infrastructure simply does not allow for such a long load, there is an alternative transport method available in the market. Various hydraulic platform manufacturers have developed a so-called “wind blade adapter”. Rather than placing the blade flat on a trailer, the blade is now “stabbed” into an adapter similar to the way it is “stabbed” on the hub during erection.
During transportation, the blade can be kept horizontal as if it were transported on an extendible trailer. When corners are getting tight or obstructions are in the way, the blade can be tilted up by around 25 degrees. This allows the tip of the blade, or the tail swing of the transport combination, to move over street furniture, or trees, or buildings. Figure 2 shows a medium length blade raised so that the tip of the blade rises and swings over a 3-storey office building.
As this adapter is placed at the end of the transporter, it is possible that a counterweight is required to warrant transporter stability. This, however, depends on the weight and CoG of the individual blade.
The challenge with transporting a tower section is two-fold. They are long (although generally not as long as the blades), and for the tall towers the diameter (read height) can become an issue during transport. Diameters of 4.5 – 6.5 mtr are not uncommon and with the height of the trailer or transporter the overall transport height reaches close to 7.5 – 8.0 mtr. This can become problematic when transporting on the public road.
Here also the manufacturers have recognized the opportunity and need for specialized equipment to aid in the ease of transporting the tower section. Tower sections vary in diameter depending on the height of the entire tower. In addition, each section tapers, meaning that the diameter on each end is different. The tower adapter can cope with all these variables, and more.
The tower adapters come with two more advantages: first, no crane is required for the loading of the tower section, this is obviously a huge cost savings. When they are properly laid out, the truck with adapter can simply back up against the tower section and the securing by means of bolt connection and/or hydraulic clamping can be done. Secondly, once the tower section is delivered to site, the front and read adapter can be connected and can be returned to the loading facility as one transport combination. There is no need for a second truck to return the rear transporter. (Figure 4).
Nacelles, specially the bigger ones, have three drawbacks: they are oversized, heavy and awkwardly shaped. The oversize aspect can create a situation where, when the nacelle is positioned on a trailer, the overall height becomes too much for the route. The solution here is similar to the tower sections - to hang the nacelle between a front and a rear transporter and keep it as close to the ground as possible. The awkward shape of the nacelle, which is different for each manufacturer and often for each model, makes a nacelle adapter a tricky design.
This is worked out between the manufacturer of the nacelle and of the transporters by a template design that fits, on the one side, to the tower adapter. On the other side, this template fits the nacelle. The adapters are designed for a certain maximum weight and as the tower sections are generally lighter in weight than the nacelle, not all nacelles can be transported in this manner. (Figure 5). Furthermore, loading of the nacelle does not require a crane and both transporters can be pulled back to the loading facility by one truck.
The transport starting point is often similar to other heavy and oversized cargo, a port facility of a factory. At some point, the transport leaves the public road and continues on temporary (often makeshift) roads that are solely constructed for the purpose of mobilizing the wind generator components and the crane to lift these components. A well compacted dirt road may be just fine for the job. However, it is important to understand what forces are imposed onto these roads.
The transport equipment manufacturers have designed some clever adapters and features as described above to help ease the project execution. The crane manufacturers have not stayed behind either. We all know that crawler cranes are a common appearance on windmill erection jobs due to the ease of moving them from one lift pad to the next while (near) fully assembled. One of the drawbacks of crawler cranes are the wide tracks; 12 – 15 mtr is common for the large capacity crawler that are used for windmill jobs. Hence, the approach road to the lift pad needs to be this wide as well. Knowing that the transport of the wind generator components often requires less than half of this width, it becomes apparent that a narrow-gauge track crane would be cost-effective for the civil works. (Figure 6).
However, one can imagine that when a crane’s stability base is reduced from 12 mtr (40 ft) to 6 mtr (20 ft), the stability of the crane becomes questionable. For this reason, when transporting a crane in narrow gauge track configuration, outriggers are used to guarantee the crane’s stability. These outriggers, however, are off the ground or only slightly touching the ground. They bear no load during the transport unless the crane starts leaning. Leaning can occur due to an unlevel road surface, slight settlement on one side of the road, weather conditions such as rain, wind etc. This is an unwanted situation as leaning will have to be countered by “pushing” the crane back using the outrigger stroke. Secondly, when the crane starts leaning, the pressure underneath the track on the side of the lean reaches extreme values rapidly. It can easily take 70 to 80% of the total weight of the crane. The road needs to be able to withstand these pressures and should not cave in or sink. When this happens, the outrigger will not be of much help. It can push the crane back, but a void will appear under the track. Narrow gauge track cranes are cost-effective and useful, as long as they are used with caution.
About the Author:
Marco J. van Daal has been in the heavy lift & transport industry since 1993 starting with Mammoet Transport from the Netherlands and later with Fagioli PSC from Italy, both esteemed companies and leading authorities in the industry. His 20 year plus experience extends to 5 continents and over 55 countries and has resulted in a best selling book “The Art of Heavy Transport” which is available at www.the-works-int.com. Marco has a real passion for sharing knowledge and experience, the prime reason for his frequently held seminars all over the world. He currently resides in Aruba, Dutch Caribbean, with his wife and two daughters.