THE DESIGN OF CATHODIC PROTECTION SCHEMES FOR CANAL CRAFT


INTRODUCTION


Retirement from a long period of active marine surveying in the small craft field has left me somewhat astonished at the amount of misinformation, misnaming, lack of knowledge and excess bar room gossip on the allied subjects of corrosion, anodes and their necessity and use. Over the years, I have given these subjects much thought based on that long and very varied experience together with much scientific and mathematical research combined with practical observation. This paper is the result.


by Eur. Ing. Jeffrey N. Casciani-Wood


First of all, we must be very clear about one point. By a very long chalk, the majority of corrosion found on the outside of the hull is due to the simple process of galvanism NOT the related but different electrolysis, “hot” marinas or being tied up alongside another boat. The second most common source of external shell corrosion was due the actions of the microbes that exist in the water. If you do not believe the last part of that remark, take a look at the photographs of the effect of microbial damage on the wreckage of the rms TITANIC. Over the past fifty years or so, I must have surveyed more than seven thousand steel boats, over 80% of which had some form of shell corrosion and of which I can recall only THREE which could be definitely proven to be suffering from shell damage due to the process of electrolysis. Probably some 40% of them had some form of MIC (Microbially Induced Corrosion). Yes, there are “hot” marinas or other boats with defective electric equipment, but a boat has to be electrically connected to that defective source in order to suffer any form of electrolysis damage. The electricity does not hang about in the water waiting for a boat to moor up near the defective source any more than lightning hangs around in the sky waiting for someone or something to strike. It is fundamental that, for a current to flow anywhere, the circuit it is using must be complete and, if a boat is not electrically connected to the faulty source, she will not suffer from any electrolytic damage caused by it.


104 | The Report • June 2021 • Issue 96


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136