Fastening Points

Composite panel fastening for off-shore power

20 Jun 2022

bigHead Bonding Fasteners frequently works together with clients to provide Special designs for composite panel fastening.  The Core and Extended product ranges are able to cover many applications, but innovative designs often require bespoke solutions. By their nature, our special designs differ from one another but our ‘Specialisation’ page  gives a flavour of the issues we address.

Some years ago Siemens Wind Power investigated the use of more composite materials for the nacelles on its 6 MW offshore wind turbines. A particular focus was improving the assembly and disassembly of the nacelle panels. Steel panels were traditionally fastened in place with standard nut and bolt fixings, the removal of which was complex and time consuming. Making the nacelle panels out of composite materials opened up better ways of fastening which could simplify the operation, improve safety and reduce costs. and designing the optimum composite panel fastening became a key project focus.

Design review:

Early in the process bigHead worked with the composite designers and fabricators in the Siemens supply chain. This ensured that all the various elements of the design, manufacturing and final assembly steps were considered.  This is particularly important for multi-material fastening where many stakeholders play a part and where many variables will influence the outcome and there are no standards or guidelines to rely on.  bigHead’s 50+ years’ experience and collaborative approach makes a vital difference in ensuring the key details are captured and understood.

Key application requirements for composite panel fastening

As an outcome of the design review, some key application requirements were agreed:

  • Assembly access from one side only
  • Sealing against water ingress
  • Discrete appearance, with colour matched to nacelle panels
  • Additional protection from a harsh offshore environment
  • High load and torque-up performance

Several pre-production prototypes were trialled to make sure the key application requirements were met.

Materials and process expertise:

As an outcome of the collaborative design process, a bigHead design, joint configuration and installation method were all finalised for Siemens:

  • bigHead surface bonding fastener product featuring M16 thread size, and marine grade 316 stainless steel construction
  • Polymer over-moulding and encapsulation of the Head component, colour matched to the nacelle
  • Creation of serviceable assembly connection points using the bigHead product with a threaded-stud fixing functionality in a through-material configuration
  • Adhesive bonding installation of the bigHead product into composite components

bighead bonding fastener


Attention to detail:

Due to the heavy weight of the M16 bolt, special packaging was created to protect the threaded part from damage in transit and before installation:

BigHead bonding fastener with netting

Good outcomes:

The nacelle panel can be easily secured or removed by a single person from the interior of the structure. Despite using a through-bonded configuration, the bigHead composite panel fasteners were colour matched over-moulding ensures the fasteners are discrete, as well as safeguarded against lightning strikes.


BigHead bonding fastener

The solution has been thoroughly field proven throughout the world.

Like all bigHead’s produced at its UK factory, every production batch is tested and documented as part of an ISO 9001:2015 certified Quality Management System.

Siemens Wind Power

Top image is an iStock wind turbine image