CARRIAGE OF FRUIT

Evening Post, Volume CXI, Issue 19, 23 January 1926, Page 7

CARRIAGE OF FRUIT

VENTILATION OF SHIPS' HOLDS

INTERESTING EXPERIMENTB.

(From Our Own Correspondent.)

LONDON, 11th December.

It had already been known from previous observations that carbon dioxide gas leaks in considerable amounts from ships' holds carrying fruit overseas. Indeed, it was because of this leakage that any successful shipments were made when no deliberate ventilation was given. Interesting experiments have been made by the Low Temperature Besearch Station, Cambridge, with the object of determining where the gas leaked out, how it leaked (by mass movement or diffusion), and to what extent the leakage varied from ship to ship, and under different conditions.

Direct leakage tests were made on two vessels with holds of the "unven--tilated" griil type. Carbon dioxide gas • was introduced into the empty holds, and thereafter? by analysing the gas from day to day, the amount of leakage was determined. Experiments were made on two different ships. The first of these boats, A, had only just been equipped for the carriage of refrigerated cargo; the second, B, had been so equipped when originally constructed, and her hatches and insulation showed some signs of wear and tear. One hold of each vessel was investigated. In the former vessel the results indicated a leakage on the average of about 3500 cubic feet per day; that is to say, 3500 cubic feet, of the ".foul air" of the hold escapes, and is replaced" by a similar quantity of j fresh air from outside the hold. In the case of vessel B the Tesults indicated a leakage on the average of between 1300 and 1400 cubic feet of air per day. It will be seen that the leakage from the newly insulated ship, which was expected* to prove more gas-tight, was two and a half times lees than that from the old ship. METHOD OF LEAKAGE. Further experiments to ascertain the method of leakage suggested that the main leakage was occurring through the roof of the bold, producing in this region a stratum of relatively fresh air of fluctuating composition and depth. The exceptionally low and irregular readings of the top centre sample suggested that the leakage occurred by that hatch rather than through the remainder of the roof of the hold. The result* also showed clearly that there was no considerable escape of gas through the I riveted structure of the hold, but that extensive leakage occurred through all the wooden ventilator plug*. Gas passed freely by the bilge limbers into the bilge but did not appear to escape further in this direction. No evidence was obtained of the passage of gas through the metal plate 3of the bulkheads or decks. EFFECT OP STRONG WIND. An attempt was made to measure the wind velocity on the ship's deck and a surprising result was obtained. Although a strong breeze was blowing across the harbour in the direction from starboard to port of the ship, tho air on the ship's deck and immediately over the hatch was moving slowly (20 to 40 feet per minute) in the opposite direction, from port to starboard. Further examination showed that the wind, on striking the starboard side of the Hhip, was deflected upwards. This vigorous upclraught presumably creates! an area of low pressure on the starboard side of the ship's deck, which caused air to bo i drawn over the hatch from pOTt to starboard. Such vigorous draughts as these would have a marked effect on thi! leakage from the holds. The outstanding -fact revealed by the investigation is that the rate of leakage of gas actually observed from the holds in port is very much leas than tho rate necessary to provide for the escape of the gas produced by a cargo of fruit where there are no other means of ventilation. The necessary leakage for successful apple carriage is of the order of -'> cubic feel, of air per day per ton of fruit; such ;i leakage will suffice to keep the concentration of carbon dioxide in the hold at the safe limit of 10 per cent. ' -BSi ?Jf?Jytreet r ;'