1. Cruising speed – the strongest lever on board
On a displacement vessel, power demand rises with roughly the cube of speed: traveling just 10 % slower than full cruising speed often saves 20–30 % in fuel – at a manageable loss of time. Planing hulls, by contrast, should avoid the inefficient transition zone between displacement and planing mode. Logging your boat's consumption curve once at different engine speeds reveals the most efficient cruising point – looking at liters per nautical mile (instead of per hour) makes it visible.
2. Hull & fouling: resistance you cannot see
Even light fouling – a rough film of algae – noticeably increases frictional resistance; heavy barnacle growth can push consumption at the same speed up by 10–20 % and more. Regular antifouling or hull cleaning is therefore not cosmetics but one of the most economical measures of all – in commercial shipping, hull and propeller care is a fixed part of efficiency management.
3. Propeller & drivetrain
A dented, fouled or wrongly sized propeller destroys efficiency: even small edge damage costs noticeable thrust. Checking is worthwhile if the engine fails to reach rated speed (pitch too large) or over-revs (too small). The shaft, bearings and a smoothly running gearbox are also part of the efficiency chain. Rule of thumb: propeller care and correct sizing together deliver up to 10 %.
4. Trim & loading
A stern-heavy boat pushes a mountain of water ahead of it. Correct weight distribution, properly set trim tabs or drive trim, and doing without unnecessary ballast (full water tanks, unused equipment) reduce consumption noticeably – especially for planing hulls in the transition zone.
5. Engine maintenance: filters, impeller, injection
Boat engines often run few but hard hours – and sit idle for long periods. Old filters, tired impellers, coked injectors or fuel that has aged over the winter season measurably degrade combustion. The seasonal service is therefore also a consumption measure; for diesel engines, fuel quality (think diesel bug, water in the tank) belongs on the list too.
6. Fuel optimization with a retrofit system
As on land, combustion itself can also be optimized on board: the Fuel Eco Tech (FET) system is integrated into the fuel line – after the filter, before injection – and works without intervening in the engine management. For vessels, the profile is particularly favorable: long, steady passages under constant load are exactly the scenario in which the highest figures were measured in the published laboratory test – up to 15 % savings at constant speed (diesel, standardized test; in the WLTC cycle on average up to 6 %).
A practical example from shipping can be found under References: the motorsailer Thalassa. The test reports on the laboratory test are available under News & laboratory test.
Context: the figures for speed, fouling, propeller and trim are experience-based benchmarks from boating practice and commercial shipping; actual results depend on hull shape, waters and usage. The FET figures come from published tests.
Conclusion: reduce resistance, optimize combustion
The order of play on the water: first reduce resistance (hull, propeller, trim), then choose your speed wisely, then optimize combustion. Combining all three levels cuts consumption significantly – and extends range and engine life along the way.