Each platform is moved by four winches, making a total of twelve winches on the slipway. Each winch is equipped with a 90 kW E-motor. The total capacity of the installation is therefore more than 1 megawatt. All twelve slipway winches are controlled from one central operating position which is located in the control room. The energy released when a ship is launched via the slipway is absorbed by large braking resistors and each winch has its own braking resistor. Because the weight of the ship is slowed down by the winch, regenerative energy is released which must be absorbed. Because the winches are operational in Kenya, we opted for external braking resistors; these only convert the released energy.
The electrically driven slipway winches each have their own starter box with frequency converter. Along with the E-motor, they are built into a container, or a housing, which we have mounted on the winch and all winch foundations have such a housing. Because we have built all electrical components in a container, they are better protected against weather influences.It also makes it easier to carry out maintenance.
Reliability and safety are very important in these types of applications. We faced several challenges in that regard. The biggest challenge was that power failures in Kenya are the rule rather than the exception. The issue is that slipway winches are equipped with a fail-safe brake.This means the brakes are activated as soon as the energy supply is lost. However, especially during the launch of a ship, it is dangerous to apply the brakes suddenly, because there is a chance the ship will fall off the platforms. Therefore, it is important to bring a ship to a controlled stop. That is why we have supplied a separate emergency power supply for each winch. In the event of a power failure, the batteries of this emergency power circuit ensure the ship is brought to a safe stop.
Another safety measure is that all winches are designed with excess capacity. This means the other three winches can finish the job if one winch fails.
Top cradle system
In addition to the slipway winches, DMC has supplied two winches for the top cradle system. Via this system, a ship is moved to one of the repair units or parking spaces as soon as it has been lifted up the slipway. These are also electrically powered winches, controlled by a frequency controller with local controls and a capacity of 90 kW.
What makes these winches so special? The fact that they are mobile. Various fixing points have been installed in the concrete at the shipyard. If large or heavy ships need to be moved, the two winches can be coupled with these fixing points to double the capacity. DMC has supplied a special coupling bar for this.
Lastly, DMC supplied two capstans including controls for this project. These are mounted at the end of two catwalks located at either end of the slipway. They are electrically driven capstans with 10 tons of pulling power.
An extensive and appealing assignment, with which we have made a valuable contribution to a reliable and safe shipyard for our customer.