Getting to the bot­tom of black­ing

Canal Boat - - Technical - ROMANYPRIN, TONY REPLIES…

AIs it cor­rect that the bot­tom of a nar­row­boat is not painted when rou­tinely black­ing below the wa­ter­line?

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There are mixed views on this. People who ap­ply the two-part black­ings that are far tougher than tar or bi­tu­men based black­ings ad­vo­cate black­ing the bot­tom. Some people also black the bot­tom with tar or bi­tu­men-based prod­ucts. How­ever, ac­cess to the base­plate can be dif­fi­cult. You also have to make pro­vi­sion to jack up or move the boat on the sup­ports so you can black the parts that were sit­ting on the sup­ports.

It’s said that there is far less oxy­gen in the water at base­plate level so cor­ro­sion is greatly re­duced, mak­ing black­ing un­nec­es­sary and that black­ing will just get scraped off, but I am not so sure. On a mod­ern boat with a 10mm + base­plate, it would take very many years for an un-blacked base­plate to cor­rode suf­fi­ciently to cause con­cern un­less the steel is of very poor qual­ity or you have mains on board with­out suf­fi­cient pro­tec­tion.

Per­haps the best an­swer is to black the base­plate if you can or if you can af­ford to, but re­mem­ber that the small­est punc­ture might tend to con­cen­trate any elec­tri­cal cor­ro­sion into a small area.

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