Turnkey stern tube assembly speeds installation

Blohm + Voss Industries has developed a turnkey stern tube solution called FlexiTube which features fast and uncomplicated installation together with a flexible forward mounting.

Installing a Blohm + Voss Industries (BVI) FlexiTube takes no more than eight working hours, says the company, and is supplied with all of the required bushes and sensors together with a sealing package. It only needs to be fitted into the ship, aligned and, following acceptance by the classification society, cast in epoxy resin and permanently fixed in place. Additionally, experts from BVI will be on hand to supervise the installation at the shipyard.

Installing a complete turnkey solution saves time and therefore money in comparison with a sterntube constructed by the shipyard, says BVI. Because the sterntube is supplied as a complete assembly, the shipyard does not have to press the bushes into the tube. This ensures that, during this often time-critical construction phase of the ship, damage does not occur that could delay completion.

The FlexiTube name is derived from the forward mounting of the sterntube inside the ship – which is of a flexible design. Should a temperature differential between the water and the sterntube cause the sterntube to expand, the FlexiTube is able to compensate for this due to its sliding fit forward mounting point. This means that the ship’s hull structure will not suffer stress cracking.

On-going operation of the ship also benefits from FlexiTube’s machined production, because the tube can be manufactured with significantly greater precision leading to an optimised volume of oil. In many cases just a third of the oil volume that would otherwise be required is sufficient. Should it become necessary, the temperature sensors can be changed from inside the engine room. The perfect alignment of the bushings also contributes to lower operating costs, says BVI.

The FlexiTube is the first turnkey sterntube solution that has reached the market, claims BVI, and is suitable for installation in practically all types of ship. It is available for shaft diameters of 200mm to 1,000mm and lengths of up to 25,000mm.

Another turnkey solution offered by BVI for diesel-electric propulsion systems is high-load thrust bearings. Fit the complete bearing, align it with the shaft assembly, bolt it to the structure, and there’s nothing more to do, says Mathias Rusch, head of the shaft components division at BVI. The special design of the bearing makes it possible to complete the bearing unit as a single assembly at the factory, which means that it only has to be fitted in place at the shipyard. The protracted procedure of assembling the bearing inside the ship is no longer necessary, the inner surface of the bearing cannot become contaminated during installation and the component is already accepted and certified by the classification society upon delivery to the yard, says Rusch.

The bearing features tilting thrust pads. These are a specially-designed shape that forms an optimum lubricating gap at every operating point. This gives the bearing a particularly high load bearing capacity, even allowing it to transfer the thrust from high-power drive systems to the ship. If necessary, they can be easily inspected or replaced through a cover in the bearing housing without first having to remove other components.

“The idea behind this product is to provide a complete and comprehensive carefree system,” explains Mr Rusch. “Customers should only have to install the bearing once and then never have to worry about it over the whole service life of the ship.” For this reason the company also supplies a matching lube oil unit with the bearing. This unit is capable of cleaning up to 60 litres of oil per minute and bringing it to the correct temperature cooling or heating it as required. It also automatically feeds the correct amount of oil to the bearing that is required for lubricating purposes. The size and type of this unit can be matched to the conditions in the ship and to the customer’s requirements.

The Simplex high-performance thrust bearing is available as standard for shaft diameters of 225mm to 630mm. Other sizes are available on request. In addition to a pure axial bearing for large cruise ships, combined axial-radial bearings are also available for other types of vessel such as yachts, ferries or mid-sized cruise ships. The BVI range also includes a special version of the bearing for the naval sector that fulfils the special shock requirements for naval vessels. The bearings can also be manufactured using Simplex seals, making them compliant with the SOLAS Safe Return to Port regulations.