This year's idle container ship fleet of above 500 TEUs has fallen to the lowest level recorded since 2011 but there is still a significant amount of hidden excess capacity, according to Alphaliner.

The 500 TEU+ idle container ship fleet averaged only 310,000 TEUs for the first nine months of 2015, or 1.6% of the total cellular fleet. This has sparked a mini rally on the charter market in the first half of 2015 as vessel shortages started to show up in certain segments, triggering charter rate hikes, Alphainer says.

The lower number of idle boxships this year was achieved by much of the supply overhang being absorbed by five key market developments which, between them, have helped to keep to 850,000 TEUs, or 4% of the fleet, employed.

Alphaliner analysis shows that the idle fleet would have increased to as much as 1.2 million TEUs this year in the absence of these five key factors. This would have pushed the year's average idle capacity to 5.1%, or 3.5 percentage points higher than what headline figures show.

This ratio is conservative, since it does not take into account the negative vessel employment effect that a widespread speed increase on liner services, meaning a partial reversal of slow-steaming in the light of more moderate bunker prices, would have had on the idle statistics, Alphaliner says.

The unravelling of some of these factors, as well as the carrier's recent attempts to tackle overcapacity in the container transport market by means of service rationalisations, have resulted in the past weeks' sharp increase of the idle fleet. Continuing this trend, more vessel capacity is expected to become idle in the coming months.