Sunday, 18 January 2015

LIGHTSHIP CORMORANT / LADY DIXON - Chapter 79




I have found a great deal of  interesting material in the library of the Belfast Harbour Commissioners, the National Archives in Kew and the London Metropolitan Archives. I was hoping that the Commissioners for Irish Lights would also yield something useful. David Ryan has unearthed good photos from the CIL collection in the National Library of Ireland and I hope to find more when I visit this week. However it seems that the CIL Board Minutes and other possibly interesting material is out of reach. Apparently it is not kept in the CIL HQ, but has been stored elsewhere and is not accessible to the public. Also, although the Minutes should be easy to navigate, other documents are not catalogued and would take considerable effort to work through. A heavily over-worked private researcher does have access, but charges 30 euros per hour – definitely outside my budget!
So, back on the ship, Simon would really like to get on and finish off the salon. As hanging very special wallpaper is what he does for a living, it should not be too difficult, were it not for the laws of physics. The structure of the deckhouse includes metal triangular fillets joining vertical beams to roof beams (not sure what they are called but I think in wooden ships they were called ‘knees’). The walls and the roof are now well insulated, but these fillets, or part of them, protrude through by about 16 x 17 x 20 inches (Photo 1). 


 Now they are of course bolted/welded to the metal sheeting which forms the roof and side walls, so they are nearly as cold as the outside. Those of you who paid attention in class will know that when warm, moist air comes into contact with a cold surface, condensation often forms – depending on the Dew Point (I paid attention). It certainly does on these fillets, especially now winter is upon us. Simon does not want water running down his expensive wallpaper, so I am experimenting with ways of preventing this – either by avoiding the fillets getting cold (extremely difficult), or by preventing the moist air reaching the cold metal.

My first idea is to glue an insulating material to the fillets and I am trying rubber at the moment. I bought some 2mm sheet (white) and stuck some to an odd piece of metal, leaving a bare strip which I submerged in ice water (Photo 2). 

Now the worst case scenario is when the room has been cold for a while and whatever heat the fillets have absorbed from the room has been lost by conduction to the outside. When Simon then lights the stove and the room heats up, the warm air (which holds more moisture than cold) will precipitate condensation on any surface colder than the Dew Point.

So I left my apparatus in my workshop (ambient 2°C these days!) for an hour or two and then brought it into the kitchen (ambient 17°C).   After an hour I measured the temperature at various points on the metal and the rubber with a laser thermometer, to see whether the rubber surface stays warmer than the metal and avoids condensation. (Photo 3 – ignore the ice which had all but melted by this time. This is Photo 2 with temperatures added). 

To make sure the emissivity of the white rubber was not too different from that of the dull metal, I stuck small pieces of black tape to the rubber. Impressed? 

There was condensation on the exposed metal below the rubber and this had obviously precipitated before the exposed metal rose above the 0.5°C at which it emerged from the workshop. Doing the test again without the cold start produced no condensation on the metal. There was no condensation on the rubber strips in either case.  Q.E.D.

We must now do an on-site test and I am sending Simon a suitable rubber piece. Of course the answer might be to keep the ship interior heated at all times in cold weather, or to run a large dehumidifier constantly, but until the lower deck space is insulated and some form of heating available down there (or Simon wins the Lottery), such extravagance is not an option.

If anyone out there has had this problem and found a solution, we will be glad to hear from you.
David