Author Engineer Voyage #39  Raffael Held

If anyone is interested in more charted calculations, please contact us on our office email and we will gladly send you more specifications that Raffael used in his original report.
The conclusion of fuel savings can be found at the bottom of this post. (Mama KWAI). 

01 Phases of the Voyage
Phase no.
Section distance [Nm]
fuel consumption [ltrs]
duration [hrs & d]
average , specific consumption [ltrs / Nm]

abbreviations: HNL – Honolulu CXI – Christmas Island WA – Washingtion Island PEN – Penrhyn PUK – Puka Puka FA – Fanning Island
Ratio time ratio     „sea passage : inter island trade“  „2,12 : 1“ fuel consumption ratio „sea passage : inter island trade“  „1,38 : 1“ distance ration  „sea passage : inter island trade“  „2,04 : 1“
Comment Comparing the ratios it can be seen that although double time was spent during long sea passages the amount of fuel in total in the inter island trades is just a little bit less then in the sea passages: reasons are for sure among others the three running diesel engines (electricity, propulsion during drifting, hydraulic for cargo crane) as well as tough schedules which actually allow the company making profits.
02 Valuation The calculated data shown above is based on sounding measurements of both portside and starboard side diesel fuel oil tanks. Comments to each voyage phase: Phase 01: HNL-CXI, sea passage, main course average 175° Description: The sea passage from Honolulu, USA, to Kirimati/Christmas Island, Kiribati, was determined by 20 kt wind from ENE, NE-trade wind. In the lee of the Hawaiian Islands the main engine was running for the first 2 days, afterwards the ship was propulsed exclusively by the trade wind. Comment: The fuel consumption is mostly influenced by the necessarily running „Lister“, a auxiliary diesel engine for charging the battery systems onboard, average RH / day approximatley  5 h/d.

Evaluation Kwai Voy. 39, 18. March 2017 – 02. June 2017 (77 days: 40,38 days at sea, 36,62 moored)
– 1
Phase 02: CXI-WA-CXI, inter island, main course average 300° / 110 ° (both directions) Description: Starting at arrival a new part of Kwai voyage started: inter island traffic with long lay by times, either moored (CXI, FA) or drifting (WA). During the short sea passages the main engine was running more or less constantly which meant the Lister did not have to run as an alternator was installed at the main engine. During loading / discharging operations an additonal diesel engine, the Cummins was running for establishing pressure in the hydraulic oil system for the loading crane. Comment: The fuel consumption is mostly influenced by the necessarily running „Cummins“, of course the main engine „Detroit“ in the passages from island to island, not to forget the Lister producing electricity during the long lay bys.
Phase 03: CXI-PEN, sea passage, main course average  175° Description: Moving southwards and crossing the equator the wind system changed or paused: light winds came mostly from (south-)easterly direction with a maximum speed of 10kt. Comment: Although the sea passage situation is similar to the phase 01 situation, propulsion by wind was not sufficient for keeping the schedule for Penrhyn, Cook Islands. Main Engine „Detroit“ was running on average 1200 RPM.
Phase 04: PEN-PUK, inter island, main course average 250° Description: Generelly the situation is similar to phase 02 with loading / discharing times and the usage of the Cummins. Caused by shallow reefs the vessel was constantly driftng during the long cargo operations. between the islands there was more or a less a time rush which caused the Detroit running up to 1500 RPM, working running hours is somewhere around 1200 – 1400 RPM. Comment: The high revolutions and long lasting and complicated cargo operations the fuel consumptions comparatively high.
Phase 05: PUK-FA, sea passage, main course average 005° Description: Heading back north to the Line Islands the ME was running up to 1500 RPM due to schedule reasons. Winds came slightly from northeasterly directions up to 10 kt. Comment: Sea levels around 2-4 ft, slight winds and the high revolutions surely are a reason for the high fuel oil consumption.
Phase 06: FA-WA-CXI-FA, inter island, main course average 300° / 110 ° (both directions) Description: Similar situation as descirbed in phase 02, additionally approx. 200 ltrs of diesel oil have been sold and burnt by an external air compressor in a 3 days lasting yard time at Fanning Island. Comment: Caused by the various influenced and jobs during this inter island trade a conclusion cannot really be drawn.
Evaluation Kwai Voy. 39, 18. March 2017 – 02. June 2017 (77 days: 40,38 days at sea, 36,62 moored)

2-Phase 07: FA-HNL, sea passage, main course average 355° Description: Due schedule the ME was running for a couple of days on 1500 RPM. After a few days departing from Fanning Islands we again reached the area of the northeast trade winds. For keeping on track and in time for arrival HNL it was unavoidable running the ME on that high rev‘s. Comment: The high revolutions surely caused a more or less high fuel oil consumption. 03 Savings  / Comment Making a statement on precise fuel savings is not possible in my opinion. The question is what would have been consumed if there would not have been used any sails at all. Taking an average fuel consumption at sea passage from 30 ltrs  / h as a basis following data could be established.
savings: 6911 ltrs.

The difference between original and calculated fuel consumption is equal to 2316 ltrs, which corresponds currently in USA 1528,56 USD (0,66 USD per ltr Diesel Oil) / in Fiji  1690,68 USD (0,73 USD per ltr Diesel Oil). All together there would have been savings:
-in litres: 9227 ltrs -in USD: 6089,82 USD (USA), 6735,71 USD (Fiji)
The calculation is of course influenced by different kinds of errors of measurements (sounding by dipstick, impossibility of evulation of fuel consumption per engine, list during measuring, different sea modes); moreover I think the established data gives an understanding and perspective what alternative propulsion methods can benefit to ship‘s owners and environement.
04 Outlook Saving more fuel is possible in my opinion. More modern ways of propulsion and electricity supply must have been proofed and installed on new constructions. The Kwai is surley performing on its limits, alternatives are hardly to be established onboard due too less space. Better infrastructre ashore would allow proper mooring, which finally would result in less fuel consumption during cargo operations.