Promas comprises of a twisted full-spade rudder with bulb that is smoothly connected to the propeller hub by a hubcap, and is adapted and optimised to the propeller design.
A well-designed twist adapts the rudder to the rotation of the propeller slipstream and reduces the local angle of attack on the rudders leading edge.
This gives a more efficient rudder with lower drag and better recovery of rotational energy from the propeller slipstream.
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Conventional design and construction together with simple installation means the payback time for the Promas concept can be surprisingly short. Other benefits include:
- Propeller and rudder are designed together as a single unit for optimum propulsive efficiency.
- Propulsive efficiency is increased by typically 3-6%.
- Improved low speed manoeuvrability.
- Improved possibility for low pressure pulse / low noise propeller designs.
- Simple and robust design.
- Almost as easy to install as a conventional propeller-rudder system.
The best results are achieved on blunt single screw vessels with a block coefficient of 0.75-0.85 and a design speed in the 14 to 16-knot range. Here the efficiency gain can be as much as 6-9% compared with conventional solutions.
For faster and slenderer single or twin screw vessels such as car carriers, efficiency improvements of 2-5% can be expected.
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Real efficiency gains
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The diagram shows a test comparison for a medium size chemical tanker. A conventionally designed propeller and rudder is compared to the Promas system. The rudder blades are of the same size in both cases and the propellers are designed to be comparable from a pressure pulse point of view.
The reduction in power consumption recorded was 4-5% for a ship speed range of 14-16 knots. A small investment to improve propulsive efficiency during design will save money through out the vessels life.
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Promas Lite – the ultimate upgrade to improve vessel efficiency
Promas Lite, a simplified version of Promas is ideal for vessel upgrading. The vessel’s existing rudder is retained, but is fitted with a prefabricated bulb, while the propeller is equipped with a special hubcap and new blades.
The propeller is designed to utilise the fitted bulb and is matched to the vessels current operational profile, which may have changed since the vessel was built. Installation of a complete Promas Lite upgrade kit can normally be undertaken within a normal 7-10 day docking period.
Recent Promas Lite installations on twin screw cruise vessels demonstrate efficiency improvements up to 20 per cent can be achieved, giving a payback period of well under two years. For these vessels the propeller designs were not only adapted to the Promas Lite system but also for the vessels current operational profile.
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The Promas integrated propulsion system for ships with conventional shaftlines has shown good results in newbuilds and also in Promas Lite form as a conversion for existing vessels.
A useful improvement in propulsive efficiency is achieved and numerous ferry and cruise vessel Promas Lite upgrades show valuable fuel savings and short payback times.
Now the Promas range is being extended, with the introduction of Promas with Nozzle, which is aimed at vessels that need a strong pull at low speed but also a high efficiency at transit speeds, such as offshore anchorhandlers (AHTS), tugs and other specialised vessels.
![[Image] A useful improvement in propulsive efficiency is achieved and numerous ferry and cruise vessel Promas Lite upgrades show valuable fuel savings and short payback times.](/Images/promas_nozzle_450x253px_tcm92-47351.png "[Image] A useful improvement in propulsive efficiency is achieved and numerous ferry and cruise vessel Promas Lite upgrades show valuable fuel savings and short payback times.")
Existing features of the Rolls-Royce Promas system – the optimised propeller, hubcap, rudder bulb and twisted leading edge rudder - are combined with a new design of nozzle.
These elements work together to optimise the water flow in and around the nozzle and so improve efficiency. Savings in operating costs can be substantial, with an increase in bollard pull of 5-8% or more and a fuel consumption reduction in transit by 15-20% for AHTS.
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