Sea mines are used more and more, and need to be removed to ensure safe water ways. That's when mine hunting vessels like the Alkmaar-klasse Mijnenbestrijdingsvaartuig (AMBV) of the Royal Dutch Navy come in. They search for the mines and send diver teams or equipment to destroy the mine in a controlled procedure. Of course, this should be done with great caution to avoid the mine to detonate prematurely. The vessel is therefore constructed of non-magnetic composites to reduce the signature of the ship.

The propellers however are still made of bronze. When the ship was designed the state-of-the-art didn't allow composite propellers to be used. Still today it is challenging to develop composite propellers: the laminate is very thick, up to 8 cm, and the blade is highly loaded especially at the root, these loads need to be handled within the limited space defined by the hydro-mechanical shape, and the shape of the blade needs to be very accurate after manufacturing.

In this project we have solved all these issues, and invented a new solution to attach the blade to the bronze foot. We also developed an adequate resin injection production process to make sure we get an accurate outer shape and full impregnation of the laminate. The laminate is a hybrid design of glass- and carbon fibre, and every ply is separately designed to fit within the shape of the propeller. None of the more than 180 plies that make up the product  have the same contour.

During development the structure has been thoroughly tested to validate the strength and stiffness as defined during the design. Five blades for the first propeller have been manufactured, and will be mounted on an AMBV vessel and tested during operation. A test campaign will be carried out to measure the signature of the ship and evaluate the difference made with our composite propellers.

This project focused on minimising the signature of the blades, but composite blades also improve the efficiency of the propeller, reducing the fuel consumption of the ship. In a follow-up project we are working on optimising the design of the blade further, to both reduce signature and improve efficiency.

For more informatio, feel free to contact This e-mail address is being protected from spambots. You need JavaScript enabled to view it , Managing Director of Airborne Composites.