Case study · Bulk carrier

The same ship, the same speed —
a different trim

How much power does trim cost? For a handysize bulk carrier of about 30,000 DWT at 14.5 knots and 9.5 m mean draft, the vessel's own data gives a clear answer: about 4.8% less brake power at 2.0 m by the bow than at even keel, and up to 50% more when trimmed heavily by the stern.

Result

Brake power versus trim

Required brake power at each trim, relative to even keel, computed from the vessel's resistance and propulsion data at 13 trim conditions. Calm water, no wind or current.

−4.8%brake power at 2.0 m by the bow vs even keel

≈220 kWless power at 14.5 knots

≈1.0 t/dayfuel at an assumed SFOC of 190 g/kWh

+50%power penalty at 4.0 m by the stern

Example vessel (main particulars rounded): handysize bulk carrier · DWT approx. 30,000 t · LBP approx. 170 m · loaded displacement approx. 37,000 t at 9.5 m mean draft. Vessel identity is kept confidential.

Change in brake power vs even keel

Handysize bulk carrier (~30,000 DWT) · 14.5 kn · mean draft 9.5 m · hover a point for its value

Show as table

Trim (m, + = by the bow)	Brake power vs even keel
-4.0	+49.6%
-3.5	+43.1%
-3.0	+36.4%
-2.5	+29.4%
-2.0	+22.4%
-1.5	+15.6%
-1.0	+9.3%
-0.5	+3.4%
0.0	0.0%
+0.5	-2.0%
+1.0	-2.9%
+1.5	-4.2%
+2.0	-4.8%

Reading the result

What the curve says — and what it does not

Stern trim is expensive. Every half metre by the stern adds power, and the penalty grows fast. Loading and ballast plans that leave the ship down by the stern cost fuel on every sea day.
The optimum sits at the edge of the data. The lowest power is at 2.0 m by the bow, the last trim condition in this vessel's data set. The true optimum may lie further forward. Before giving trim advice beyond that point we extend the data, we do not extrapolate.
This is one draft and one speed. The optimum trim changes with draft and speed, which is why each condition is calculated separately rather than read from a rule of thumb.
Calm-water result. Wind, waves, current and hull condition shift the absolute power. The trim effect is checked against noon reports before it goes into the vessel's operating guidance.
Practical limits apply. Bow trim must stay inside the loading manual, stability, longitudinal strength, visibility and propeller immersion limits. Trim advice is given within those limits only.

Method

From vessel data to trim guidance

For each trim condition, effective power, hull–propeller interaction and the propeller's open-water curve give the propeller operating point and the brake power needed at the chosen speed. Results are interpolated across drafts and trims, and the platform searches for the trim with the lowest power in 0.01 m steps. Our team first delivered trim optimization and energy efficiency studies on 27 commercial vessels in 2013; this case is recomputed with our current web platform. About the platform →

What does trim cost your ship?

Send us your vessel's speed-power and propeller data. We will tell you what can be calculated and what it is likely to show.

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The same ship, the same speed —a different trim