WINDSCREENS FOR HARBOURS

Abstract

Big ships may sometimes be prevented from mooring when piers are not shielded against gusts from cross winds. Forces large enough to break the mooring cables can also develop. To prevent these difficulties, a windscreen had to be built in 1947 in Le Havre harbour. It was a plain concrete wall, 240 m long and 21.5 m high, with a curved side facing the most frequent wind. Quite a few wide-apertures were provided across the wall, so as to feed, in a way, the wake downstream from the wall. The question of building a protecting screen has been raised again recently in Marseille, to provide a shield along one of the piers which is open to cross winds (Mistral). I have suggested designing a porous screen, made of a plane thin wall with numerous small holes regularly spaced, as in a perforated plate. I had reasons to believe, and it has been confirmed by experiment on small scale models, that a porous screen could provide a shield as efficiently as a plane wall. On the other hand a porous screen would offer many advantages when compared to a plain wall, as a) reduced stresses from gust effects, b) lighter and simpler structure, and c) eddies in the wake would not be as large.