The Measures Landscape: Five Families and a Sceptic's Checklist

7 min read

What you'll take away Sort any efficiency measure into one of the five families and interrogate its savings claim for baseline, measurement method and net-versus-gross honesty.

Efficiency hardware is a crowded market. Every vendor arrives with a percentage, every percentage sounds achievable, and a superintendent who tried to evaluate each gadget on its own terms would do nothing else. The working skill is not encyclopaedic knowledge of every device: it is a filing system for measures, and a short checklist that exposes what any savings claim is actually made of. This lesson supplies both.

The five families

The most useful map of the territory sorts measures by where in the energy chain they act. DNV's catalogue of efficiency measures: the best single reference of its kind, with savings potentials and implementation guidance for each entry (the report is free after registration), organises them into five families:

Operational measures change how the ship is run: trim optimisation, weather routing, port-call timing, hull and propeller maintenance discipline. They cost attention rather than steel, which is why they come first, and why this academy gives them a course of their own.

Hull and propulsion measures reduce what the ship demands from the engine: coatings, hull cleaning, and the energy-saving devices around the propeller that lesson 5 dissects.

Machinery and waste-heat measures improve how fuel becomes useful work: engine tuning, shaft generators, and recovery of the heat that would otherwise leave through the funnel: lesson 6.

Energy-consumer measures shrink the electrical bill: variable-speed pumps and fans, LED lighting, HVAC control.

Energy-harvesting measures bring new energy aboard from outside the fuel tank: wind-assisted propulsion and solar. A rotor sail does not reduce the hull's demand; it supplies part of the demand for free.

The five families, placed where they act fuel energy machinery: engines, boilers shaft and propeller hull through the water cargo delivered energy harvesting: wind, solar machinery and waste heat energy consumers: pumps, fans, lighting hull and propulsion operational measures: trim, routing, port timing, maintenance: act on every link
The five families sorted by where in the energy chain they act: machinery measures work on conversion, hull-and-propulsion measures on what the ship demands, consumer measures on the electrical load, harvesting brings energy in from outside the fuel tank, and operational measures touch every link. Measures sharing a link usually share a pot of loss: the interaction lesson 8 turns into arithmetic.

The families matter because they predict interaction. Two measures in the same family are usually drawing on the same pot of loss, so the second one works on whatever the first left behind. Keep that in mind now; lesson 8 turns it into arithmetic.

The sceptic's checklist

Three questions strip any claim to its load-bearing parts.

Percentage of what? A saving is a comparison, and the baseline is half of it. Five percent of which ship, at which speed, at which draught, on which route? A device tested on a slow, full-bodied bulker will not repeat its number on a fast container ship, because the resistance it attacks is a different share of the total. A percentage quoted without its baseline is an advertisement, not a measurement.

Measured how? There is an evidence ladder. CFD and model tests predict; a dedicated sea trial measures once, in chosen conditions; normalised in-service data measures what the ship actually experiences across seasons and loading conditions. Each rung costs more and proves more. "Verified by CFD" means a modelled estimate: legitimate, useful, and not the same thing as a measurement on your ship.

Net of what? Many devices have an appetite of their own: compressors, drive motors, control systems, added weight or windage. The gross figure is the physics; the net figure, gross minus the measure's own consumption and off-design penalties, is what reaches the fuel bill. If a brochure quotes only gross, ask why.

It also pays to convert percentages into tonnes early. A 5% saving on a ship burning 30 tonnes a day is 1.5 tonnes a day: multiply by fuel and carbon prices and days at sea, and the brochure number becomes a business case you can argue about. The Korean Register publishes a selection guide that frames measures exactly this way, as candidate responses to a ship's EEXI and CII position (the guide is open), a useful second opinion when a proposal lands on your desk.

Where the course goes

The next lessons take the families in turn: wind-assisted propulsion in two parts: the technologies, then the harder question of proof; air lubrication and its compressor arithmetic; the energy-saving devices around the propeller; the machinery room and its waste heat; and shore power, the measure that works only when the ship is not moving. The final lesson returns to this map with money attached: how to choose, stack and verify.

One habit to carry through all of it: whenever a percentage is quoted, ask of what, measured how, and net of what. Most brochures do not survive all three.

Check yourself

1. A rotor sail belongs to which family of efficiency measures?
2. A vendor claims 5% savings. What is the first question to ask?
3. A saving is quoted as 'verified by CFD'. The honest reading is…
4. Which family typically delivers savings with the least capital expense?
5. Net saving differs from gross saving because…
6. Which of these belong to the machinery and waste-heat family?

Select all that apply.

7. Two measures saving 5% each will reliably save 10% together.
8. A measure saves 5% on a ship burning 30 tonnes per day. How many tonnes per day is that?
t/day