Bigger Is Not Better…It’s Worse!
The design of a ship must necessarily be supervised by a classification society. The design criteria are dictated by standards aimed at ensuring the safety of seafarers and achieving optimal performance under the worst prevailing conditions.
The equipment is selected in order to enable the ship to operate at full power under these conditions. But, what about the day-t0-day operating conditions?
It’s obvious that the equipment is oversized. Yet, one of the foundations of energy efficiency is selecting equipment based on actual needs.
How can the standards be met and the ship still be energy efficient? A different design approach must be used right from the start.
When this is not possible, such as when the ship is already in operation, its existing design must be re-examined, and energy-intensive systems and components must be modified while still remaining in compliance with the standards and approval requirements of the classifications societies.
For obvious reasons, essential equipment on a ship must come in pairs. The problem then arises that the ship is fitted with two pieces of equipment that are already twice too large. For example, it would be more advantageous to install 3 pumps having 50% required capacity design than installing 2 pumps having 100% of the capacity. Redundancy is maintained and, with the addition of a variable speed drive on one of them, flow rates can be adjusted in accordance with actual requirements.
An oversized generator will see its specific consumption significantly increased if it is operated at less than 50% of its rated power. Even more of a concern with large equipment are the maintenance costs.
Among the large producers of energy (utilities), it is well known that the economic profitability of a generating station is based on being able to produce the maximum amount of energy with the equipment in place. This reduces the cost of energy produced in $/kWh. The cost of producing energy lies in the price of fuel per unit of energy, but also the purchase and maintenance costs of the equipment.
The same rule should apply when designing a ship. Sizing three generators to produce a maximum output of energy during the unloading period is not economically cost-effective if this period represents only 5% of the ship’s operating time and parasitic energy consumption (house load) represents at most 40% of the capacity of a single generator. The solution lies perhaps in installation a smaller size generator to meet 80% of the needs while the ship is at sea. Each ship is different and a comprehensive study must be carried out in order to make the right environmental and economic choices.
One thing is certain, shipyards and classification societies cannot be asked to do this kind of work. This is not within their mandate and their prerogative is different. It’s up to the shipowner to put in place the teams that will properly address this aspect during the design phase. The impact on the ship’s design and operating costs will be significant for years to come.
In general, there is a tendency these days to cut back on engineering work. Designers will always have a tendency to oversized equipment in order to reduce their risk of errors. That being said, efficiency is often found in the margin between overreaching safety and undersized equipment. It is worthwhile investing a small amount of money during the design phase so that a team of dedicated experts in energy efficiency can review the concepts and challenge the designers and classification societies in order to ensure that things are done differently and better. Energy efficiency often lies in innovation.
Well sized and properly instrumented systems, flexible control logics, and scrutinized automation processes are all methods that enable shipowners to boost their ships’ efficiency and performance.
GHGES Marine Solutions has the expertise necessary to help you in this and many other areas.