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Marine Propulsion & Auxiliary Machinery

Marine Propulsion & Auxiliary Machinery

How does oil market volatility affect vessel efficiency?

Thu 19 Jul 2018 by Paul Gunton

How does oil market volatility affect vessel efficiency?
Foreship’s operability analysis uses CFD to calculate bow wave heights, as here, as part of its fuel consumption prediction (credit: Foreship)

Foreship head of hydrodynamics Janne Niittymäki explains how uncertain fuel costs prompt vessel efficiency considerations

What is behind the oil price volatility?

A moderate rise morphed into a three-year high in April on the threat of shortages from Iran and Venezuela before Saudi Arabian and Russian offers to turn up the taps prompted a 7.5% decline.

These circumstances present a challenge to shipowners that believe they can pass on fuel surcharges to cargo owners and charterers after IMO’s 2020 global cap on 0.5% sulphur content comes into force. This cap will have implications for availability, while low-sulphur HFO quality may vary from different sources. Both factors are drivers of price.

After a three-year taste of lower fuel bills, the Global Shippers Forum pushed back hard in May against ‘emergency’ US$120-140/FEU levies to cover rising oil prices.

Are there benefits from cleaner fuel?

Cleaner fuels may be more expensive, but they are also more energy efficient than HFO. They do not need heating up and are less corrosive, making more energy recoverable from them.

How does consumption vary with speed?

At 18 knots, the average daily fuel consumption of a 13,000-TEU capacity container ship is around 90 tonnes, according to a 2015 study published by the National University of Singapore*. At June 2018 bunker fuel prices, that would cost US$40,680/day. At 16 knots, the same ship would consume 70 tonnes/day, costing US$31,640.

But that paper showed that, between those speeds, consumption can range between 60-100 tonnes/day, depending on factors including weather/sea conditions, displacement and trim. Fuel use can increase dramatically when a ship faces strong bow waves, for example, so maximising efficiency is about more than slow steaming. It includes running engines at optimum load and avoiding excessive speeds to ‘guarantee’ on-time arrival.

How can design improve efficiency?

At Foreship we use a software-driven methodology called ‘operability analysis’ to consider design attributes. It draws on our project database to model the performance of different design options and operating conditions.

Using computational fluid dynamics (CFD), its ‘in-wave’ analysis factors real sea states into hull-form optimisation and has supported a case for the superior performance of vertical stems over bulbous bows at lower wave heights than was previously acknowledged.

CFD has also contributed strongly to propulsion efficiency. A modern design could expect to use 10% less propulsion power than considered hydrodynamically excellent a decade ago. Operability analysis also relies on established ship design and construction software that has been augmented to introduce data such as voyage route planning at an earlier stage than is customary.

Voyage simulations should be made port-to-port, scheduled as starting on a given day at a given time and having a target arrival date and time. Realism is added to our model by using hind-cast environmental data of the wind, waves and currents on the actual route.

Can different ship types be compared?

Operability analysis allows, for example, cargo shipowners to evaluate whether innovations in the cruise ship market can make an impact on optimising cargo efficiency.

As an example, since 2011 Foreship has developed an air lubrication system, Foreship ALS, originally for cruise ships. The projected net fuel saving is inferred from the percentage decrease in the braked power used for propulsion when the system is in use. In the cruise ship applications, net fuel savings equivalent to 7-8% have been achieved.

A detailed feasibility study has been undertaken for a large ropax ferry, showing it to be suitable for ferries operating at <20 knots featuring high propulsion power. Most recently, Foreship conducted a promising feasibility study to use ALS to optimise fuel consumption on a container ship, which has a very different hull shape from a cruise ship. Our simulations indicate that 5% savings in fuel consumption are achievable at operating speeds from 12 knots upwards.

Does such technology give a negotiating benefit?

When shipowners are aware of what is – and is not – realistic from design variables, they are more informed and thus in a better position than they would otherwise be to discuss the vessel’s performance specification. They will also be more able to negotiate any bonus scheme for surpassing expectations!

*Budgeting the fuel consumption of a container ship over a round voyage via robust fuel optimisation (http://bit.ly/FuelPaper)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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