From Robert Hill
Reigate, Surrey
One reason for ships not discharging gases underwater (Letters, 12 October, p
49) may be because of the danger of water backing up the exhaust pipe and
filling the engine if the engine stops. A partial vacuum would result in the
cooling of the very hot exhaust gases, the condensation of one of them (water
vapour) and the dissolving of another (carbon dioxide).
It is for this reason that motorists, when driving through floods when the
end of the exhaust pipe could be submerged, are advised to engage low gear to
keep the engine revving as fast as possible.
