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Adventure of a Thermohygrograph: The Voyage!


Now we get to the business of recording temperature and humidity on a transatlantic voyage in a freight container.Thermohygrograph Trace

Thermohygrographs don't usually get to record an ever-changing environment, but this was the opportunity provided by internationally moving house and having a set of worldly goods being shipped.

There were three Casella thermohygrographs, being shipped in amongst a house-load of stuff, in two 40ft hi-cube containers.

Thermohygrograph 1 was packed in a box inside the old caravan which was in the toe-end of Container 1. Several months went by as the packing continued, and after a while hope diminished on getting any worthwhile results.

Thermohygrograph 2 was packed in a box near to an air vent in Container 2 as one of the last things to be packed. Thermohygrograph 3 was packed in a similar box near to an air vent in Container 1.

It was far from obvious that any of the thermohygrographs would survive the voyage with trace intact, as boxes tend to "settle" on a voyage, and the containers were very full. Also, on the longest time setting, a thermohygrograph like this can record a month's chart, but after that it wraps around. I had to make sure the hardstanding was ready for the containers at the receiving end before I could call for the containers to begin the journey. Also, there were issues about the time to get from the port to the house.

The journey was rough, and on arrival thermohygrograph 3 was found to have its pens crossed over, like crossing your fingers, except for this to happen to a thermohygrograph, it must have been shaken.

Thermohygrograph 2 had suffered an even worse trauma. It had been frozen in the British winter so severely that the temperature pen was frozen off the chart and caught in a groove below the cylinder. Then as the cylinder rotated it hit the bar on the way round causing the machine to be halted.

Thermohygrograph 1 was lost without trace for a whole month after arrival. There was so much stuff, including over two and half thousand boxes, that it was just mysteriously missing. However it was already known to have been running for months and so the chart would by now have become very muddled.

In the end, out of the three, Thermohygrograph 3 produced the best result, and this can be seen here. It takes a bit of explaining, but there are annotations, and here goes...

The containers started in Grantham, Lincolnshire, and were loaded onto trucks on the 27th of February 2012, and were then moved to the docks at Tilbury, to be loaded onto the container ship Bahia Laura to sail on 6th March.

The ship then sailed to Antwerp, and from there, off across the Atlantic. I was following the voyage on ship tracking sites. The route of the Bahia Laura was directly across the Atlantic, to arrive in the Dominican Republic on 18th March, then to Colombia on 21st March, and then Manzanillo, Panama on 23rd of March, where my containers were to be offloaded.

Please note that although the horizontal axis records time, you should disregard the Monday, Tuesday, Wednesday etc in this case, as the thermohygrograph was set to record 31 days per chart, not 7. The Casella de-luxe version incorporates a fine clock mechanism that has dip-switches which can be set to record 1 day, 7 days, or 31 days. The vertical axis is more important, and it's worth noting that the pens do not actually move "up and down" but more along an arc. However, they share an axis in common. There's also an offset in time, which is so the pens avoid collision with each-other.

Here's the trace...

Thermohygrograph Trace

Take a look at position A on the temperature (red) chart. This is the point where the container was being lifted onto a truck, and then after a period of travel, offloaded. The sea-going part of the journey now begins.

Notice how the temperature at sea doesn't vary so much from day to night as it does on land.

As you follow the graph along from A to B, the shipboard temperature across the Atlantic is recorded. As would be expected, it gets more tropical, and the temperature rises day by day.

Following the humidity is less easy, as you can see from the partial trace starting at C and then reappearing at D ... E ... F. Try to ignore the other trace which is swiftly varying in the background. That is what happened a month previous in winter in the UK. The trace C, D, E, F shows an almost dotted line, as if changes in the ship's position on the sea caused the chart-recorder to tilt and record some trace some of the time.

The final smudge at B and F are where the container was offloaded in Panama, after which the shipment went through a variety of traumas such as fumigation, moving to a bonded warehouse and suchlike, before being delivered to the house for offloading.

Whatever traumatic event occurred at G is something to be speculated upon, but it seems to have gone on for a whole day and night, and was quite severe.

The most interesting part of this is the temperature trace from A to B and its corresponding humidity trace C,D,E,F. This is transatlantic thermohygrography.


For thermohygrographs, contact Casella or www.casellacel.com