LAUNCHED UPSIDE DOWN

Dominion, Volume 12, Issue 46, 19 November 1918, Page 4

LAUNCHED UPSIDE DOWN

SOLVING A CONCRETE SHIP ' PROBLEM. Some of the new concrete ships are built upside down, to make the casting process easier, «ind they,are not turned right side up until they are in the water. 'Phis scheme was first adopted in one of tho Norwegian shipyards that has had most success in building this type of vessel. In constructing a bridge-pontoon, in 1915-claimcd to be the first concrete vessel built in Norway-considerable dillicullv was encountered, as we learn from tin article in "Nature" (London). Especiallv was this the case with tho casting, in which one or two limits had to be remedied. Says the writer:— . ~„, , "It was considered that these difficulties with pontoons having fairly rectangular section would become very pronounced in building vessels of ordinary section, and Mr. Harold Alfsen lias*over-, come them bv building the vessels linttorn uppermost, and using an inner shutter, or onler boarding only, so far aa the vertical sides are concerned. ill is plan was adopted with tho lighter Beton I interior shuttering- only.being used. This vessel is a 200-ton deadweight carrying motor vessel. As she is intended to be seagoing, the reinforcement, was mado !>0 per cent, heavier Ihan in lighters intended for inland waters, rib and girder dimensions were increased, and a fafc concrete mixture of i no to two without cobbles was used. The wall thickness is 1.97 inches. ' "The shuttering was bllilt, on a sledge, which followed the vessel into the wafer at tho launch. On becoming fully watel'-bdrne the vessel is in s)«ble equilibrium, and the turning right side uppermost is accomplished by permitting' the'air to escape from the interior! the vessel sinks in the .\ynter until a'draft is reached for which the equilibrium becomes unstable, mid the vessel then turns over without further aid until the deck is uppermost. , , "The first vessel took about six weeks to arrange the boarding nnd reinforcement, and two days to cast; three weeks wore allowed for the concrete to set. It is estimated that tlw next vessel can be. done in half the time, since the same shuttering can be used again."