A vessel moving close to the bank of a river, a cut or a canal will find the stern tends to move towards the bank. This effect is due to the water being squeezed between hull and land, increasing its rate of flow and creating a low pressure area which the hull is sucked towards. I was blissfully unaware of bank effect until I set off from Houston to New Orleans by way of the Gulf Intracoastal Waterway.
In my case, however, it wasn’t the tendency of the bank to suck my little yacht towards it that was the problem; it was the tendency of the huge triple wide ‘tows’ to suck my little yacht towards them – a potentially fatal variation of the bank effect – that had me worried.
This particular stretch of the Gulf ICW is extremely commercial; leisure boats are rare, a minor irritation to the waterway’s regular traffic. One foggy morning we had pulled over to the side of the waterway to keep out of the way of the barges until visibility improved. The bank was grassy and too high to climb but a small sapling overhung the canal and I was able to get a bow line on it – or should that be bough line? The boat lay comfortably against the bank whilst we sipped coffee and waited for the fog to lift.
A booming fog horn indicated the imminent arrival of the morning’s first traffic and shortly thereafter the grey outline of a lumbering behemoth appeared, moving through the gloom some 30 or 40 feet abeam of our snug berth. As the monster triple-wide tow thundered past we found ourselves in the hitherto purely theoretical low pressure area between bank and barge. We were sucked towards the barge at a frightening rate until we were hanging perpendicular to the bank clinging tenuously to our sapling. Oh how I begged that little treelet to maintain its grip on the soil.
As the thousand-foot long iron wall of interconnected barges rumbled past, the sapling bowed and stretched, its immature foliage dipping underwater. Two minutes later, an eternity it seemed, the barge had gone and we settled back against the bank.
Bank effect sucks, I can tell you.