Yoke for Single Blade Installation on Offshore Wind Farms

The objective of the project is to develop a blade yoke Blade dragon 80+ (BD80+), which solves an

upcoming issue in the offshore wind industry. As the size of the wind turbines grows (blade length exceeds

80m), the install method ‘Rotor installation wouldn't anymore be reasonable on wind turbines placed

offshore. At Rotor installation, all 3 blades are assembled to the hub, before installing this to the wind

turbine.

For large wind turbines ‘horizontal single blade installation’ isn’t desirable if not impossible (is impossible

for wind turbines without gearbox). At horizontal single blade installation, the blades are all installed

horizontal, where the hub is turned between the installation of each blade (only possible for wind turbines

with a gearbox). Furthermore, when the blade length exceeds ~65m, the gearbox would be dimensioned

by the loads arising when rotating the hub, with only 1 blade mounted, and not by the loads arising during

normal operation. This makes the gearbox more expensive than necessary. A yoke making single blade

installation possible, without turning the hub, is of these reasons strongly demanded by the wind industry.

Liftra has already developed and produced a yoke for single blade installation, which can rotate the blade

250degree, making it possible to install blades in all angles within this range. The above issue is thereby

solved. This yoke can handle a 56m blade.

However, even though the existing yoke has proven to work, the interested parties want documentation

showing that the larger yoke (BD80+) is theoretically possible before ordering it. The reason for their

reticence is the step from handling a 56m 20ton blade to handling a 80m+ ~40ton blade. The major issues

for Liftra are:

1. The weight of the product must be below 75 ton. This is 36% more than the first BD. However, the

weight of the blades to be handled is about doubled and the wind loads on the blade, and BD, is increased

with 200-300%.

2. Due to changed orientation of the blade in the yoke, and size of the blade, the torque required to rotate

the blade is increased with about 500% compared to the first BD. The solution is assumed to be a

combination of stronger structure and considerable design modification of the turning mechanism.

3. Development of new integrated tagline system, used to rotate the yoke and blade in the horizontal plane

(on the first BD, customer was responsible for the tagline system).

The BD80+ will be capable of installing blades on 6MW+ wind turbines. According to EWEA report, more

than 20 turbine manufacturers have launched or are going to launch prototypes and products in size of

6MW+ for offshore. These are all considered as potential customers to one or more BD80+. Liftra are at

the moment leading in delivering blade installation equipment and are at the moment to our knowledge the

only company that can deliver a blade yoke where the blade can be installed in all positions up to 56m and

20 ton.