Of UPS and HPUs

The hydraulic power unit (HPU) used with a davit system can feature separate or integrated power packs, while electric motors can be mounted as standard on top of the tank, or ‘submerged’ inside. In either case, the preferred solution represents a straight choice and the market is split roughly but firmly 50/50 between the options.

User preference and experience influence the market share each solution commands, but it is always worth asking how the benefits of any ship’s equipment are shared between the vessel’s operator and its shipbuilder. One owner will prefer a submerged electric motor, for example, due to the superior protection it offers the HPU against weather and corrosion. Another might conclude that, since electric motors fail without warning, a top-mounted motor offers better access for maintenance.

Decision Making

These decisions are clearly for owners, irrespective of yard of build. However, a third decision facing specifiers is closer to first principles: choosing a dedicated power unit or drawing power off the ship’s hydraulics involves a clear divergence in approach. Shipbuilders far prefer the latter but, in what is no longer a suppliers’ market, perhaps it is time for shipowners to ask themselves whether yard preferences should continue to hold sway.

Vestdavit recommends separate HPUs

In most cases, Vestdavit supplies separate HPUs to work with our davit systems and, while we don’t say it’s definitively the superior option, what we can say is that those choosing this option show a very strong preference. A standalone unit is configured to supply hydraulic power to the specific davit, and is more likely to be up and running if there’s a man overboard or if there’s a problem with the main ship, they point out.

More significantly, any ship’s hydraulic system is likely to feature sizeable pumps and, while that means plenty of power to work the system, there are several “users” fighting for the same hydraulic power from time to time. Also, there may be issues with high pressures and the risk of overload. Our recommendation is for davits to be fitted with HPUs working at pressures of around 250 bar.

Also, working in the standalone solution’s favour is that some launch operations require stealth; some of our customers need to ensure that noise levels are no more than 80 dB in the engine room, let alone anywhere else. Our customers may be keeping quiet on the benefits of the separate HPU; but as experts in safe boat handling for life, there’s no reason we should.

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Comfort and constant tension

The perpetually changing sea has often brought the best out of poets, but its constant motion is of more than romantic interest. For their own safety, seafarers must move beyond SOLAS and learn to work with the elements day by day, rather than against them.

As an expert in safe boat handling for life, Vestdavit’s equipment is being deployed in harsher conditions and on ship designs of greater variety than ever before, yet the safety of boat lifting and lowering operations cannot be compromised.

Ensure personnel safety at sea

A slack hoisting wire caused by the wave uplift of a boat being prepared for hoist, for example, represents a hazard for personnel and equipment on board. Again, personnel being transferred on and off ship have no appetite for swings, sways or jolts to be part of their daily routine.

It is for both safety and crew welfare reasons, then, that we are increasingly being asked to deliver davits that include Vestdavit’s innovative wave-compensation solution, achieved via our constant-tensioning system.

Constant-tensioning system – How does it work?

The self-tensioning system can only be active when a boat is waterborne where it is activated by the operator using a straightforward push-button, then joystick controlled to pull the boat towards windward and bring tension into the wire. With tension in the wires, the boat can rise and fall with the waves, up to a maximum applied tension pull of up to one third of the davit’s safe working load (minimum tension pull app. 300 kg). The operator can then judge the best time to hoist, which will be at that moment when the dynamic forces and the pickup force are as low as possible. In general, Vestdavit does not envisage using the self-tensioning system in the boat launching mode.

Preference for the solution is a result of customers seeking wider operational windows and greater scope of duty for the boats being handled in harsh conditions, while also satisfying the need to maintain the highest possible safety standards. If the self-tension function were to be actuated before the boat reached the sea, an override would kick in to disable its operation.

Innovative solutions designed for optimum performance

The self-tensioning principle may not be new, but Vestdavit is unique among boat handling specialists in the way it continues to refine its innovative solution. Most recently, we have improved the system by building more features into the winch block, reducing the amount of piping, and the number of valves so that Vestdavit’s self-tensioning solution is more reliable and robust with less maintenance requirement. Today, we recommend wave compensation at all times where crew safety and comfort are prerequisites, and the Vestdavit system is designed for optimum performance up to sea state 6.

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