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July 15, 2003

Monsoon Weather and Fuel Consumption

 

From the Maldives to Djibouti through the Gulf of Aden is just over 1800 miles. A quite lengthy voyage, although the last 800 miles is sailed within 100 miles of land, it is mostly an open ocean passage. The time of year (February) we were undertaking this passage was during the Northeast Monsoon so we should have favourable winds.

Monsoon climates are typically associated with land weather because of the major influence they have on rainfall. Press reports that 'the monsoon rains have come early/late this year and damaged crops/caused flooding etc.' imply that there is only one monsoon season of the year. In fact the Indian Ocean has two monsoons: the northeast and the southwest monsoons. The southwest monsoon blows winds off the sea onto the land hence it generates heavy rainfall, whereas the northeast monsoon blows dry air off the land and out to sea so is the dry season. For sailors rainfall at sea varies very little between the monsoons. What does vary is the wind direction. That makes the Indian Ocean passage one of the few ocean passages that circumnavigating yachts make which you can cross in either direction at the same latitude, so long as you pick your time right.

For the Indian Ocean, passages from east to west need to be made from December to March, and for an eastbound passage, May to October (the missing months are periods of transition).

We expected east to northeast winds for our passage and that is what we got, unfortunately all under 15 knots and mostly under 10 knots. So it was a slow downwind passage and demanding upon fuel.

Because of the piracy problem in the Gulf of Aden we wanted to be certain that we arrived at the entrance to the Gulf with enough fuel to be able to motor, if we had to, and at a good speed in order to transit the danger area as quickly as possible. Also we had arranged to pass through the danger zone in company with another boat at an average speed of 8 knots. We had a rendezvous with our buddy boat who was coming from Oman at the start of the Gulf of Aden, so we had to make that appointment on time and arrive with enough fuel for the last 800 miles in case we had no wind, as was being forecast.

So 24 hours out of the Maldives with 6 knots of wind from immediately behind, we started to run a fuel log and to calculate speed/distance/fuel consumption ratios. We found that if we motor sailed at low revs we could bring our fuel consumption down to 3 litres an hour (compared to 7 litres at normal cruising revs) and by bringing the wind slightly further forward and sailing a slightly longer course therefore, we could conserve enough fuel to motor at high revs through the Gulf of Aden to Djibouti but also arrive at the rendezvous point on time.

We were glad we had been so careful as we had hardly any wind for the whole trip. Thankfully fuel at ports in the Gulf of Aden is cheap (20 cents Oman, 25 cents Djibouti and Aden) so we were able to refuel in Djibouti without too much pain to our credit card.

As we took fuel alongside the dock a herd of camels was being loaded on a ship. It made a very odd sight to see camels strolling round the deck, looking over the rail like newly embarked cruise ship passengers. By comparison with our fuel issues the biggest 'fuel' problem the ship had was loading enough food for the camels. But perhaps they had the added advantage that they were able to run the ship's engines on methane from the camel waste.

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