Precise procedure

Over the next few years, six Daring Class Type 45 anti-air warfare destroyers are being assembled, launched and outfitted for the UK Royal Navy at BAE Systems Surface Fleet Solutions Govan & Scotstoun shipyards in Glasgow, Scotland.

The bow sections, masts and funnels for all six ships are being built in Portsmouth, UK. The destroyers will have an overall length of 152.4 meters (506 feet), including space for a crew of 235, a displacement of 7,350 tons, a top speed greater than 27 knots and its range greater than 7,000 nautical miles. The first one will be christened the HMS Daring and is set to enter service in May 2009.

The ship's hull is manufactured in sections or “blocks” in a fabrication shop adjacent to the berth and slipway. Five blocks are moved in total to build one ship. The heaviest block weighs more than 1,400 tons.

Finding a solution

Each block is transported to the slipway and aligned longitudinally to the slipway on multi-wheeled transportation vehicles. During this procedure, the slide-tracks on the slipway are removed so that the vehicles can drive the blocks into position.

The solution for this process was the Enerpac Synchronous Lifting System, which is used to lift the block free from the transport so that they can be driven away. During the lifting procedure, the 16 points PLC-controlled synchronous lifting system operates within strict load and stroke constraints to ensure that the desired load paths into the ship's hull structure are maintained. With the transport removed and the hull segments supported by the hydraulic system, the blocks are weighed with the synchronous lifting system to confirm the design calculations.

The next step is the slide-track installation. The slide-tracks on the berth's slipway can then be re-installed. The block is lowered synchronously and the load is transferred on to the slide-tracks. The hydraulic lifting system permits the manipulation of the blocks prior to welding to the adjoining section. This manipulation, lifting, lowering and rotation, is a PLC-controlled hydraulic movement.

Accuracy counts

In the use of hydraulics in heavy lifting projects, application knowledge and expertise are very important. Accurate lifting, lowering, pushing or weighing has a significant effect on structures. Very accurate manual control and monitoring is complex and time consuming. And moreover, accuracy is more important than speed. The advantage of PLC-controlled integrated hydraulic systems is enormous. Every step of the lifting process can be monitored via the display of the PLC control unit. Apart from the very accurate and stress-free movement of steel structures, concrete segments, and the like, Enerpac provides a safe, cost-effective and labor saving solution. The Type 45s weight must be optimized and consequently the hull skin is relatively thin when compared with acommercial ship. Therefore when lifting and lowering, the load paths must be strictly controlled. This would be almost impossible with manually controlled systems. Controlled hydraulic movement brings safety to the structure. The second advantage is the increase of productivity where hundreds of man hours were saved against traditionally controlled lifting methods. Moreover, this versatile lifting system is employed on various other lifting and weighing operations around the shipyard.