The following notes are applicable to the rigging and use of towing gear on both semi-submersibles and cargo barges.
They are not in order of importance, but all towing gear should be inspected and used only after having regard for the following points which are reiterated because they are vital for success:
1. Is the gear suitably sized to the tow?
2. Is the towing vessel matched to the tow’s gear?
Points to Note:
1. Try and determine the age and usage pattern of tow gear fitted to any particular unit.
Wire rope deteriorates when immersed for long periods and the bridles of semi-submersibles, if made of wire spend long periods hanging unused. The area ‘at the vessel’s load waterline on these wire ropes is liable to suffer severe corrosion damage – not visible until they part.
2. As a general policy, wire rope bridles should be removed from service and thoroughly examined or replaced every two years and after long hard weather towages.
3. Chain bridles and bridle components made up from chain should be inspected at least annually. Chain link/link wear down measured and the whole section rejected if link wear exceeds 10% the link bar diameter.Chain bridles and sections should be installed without twists as far as possible and so far as possible avoid installing joining links except at terminal points.
4. Towing brackets of whatever construction, pad eyes, Smit bracket or lugs should bee thoroughly checked for wear on the whole of pad eyes, weld integrity of connection of the bracket of the eye to the vessel’s structure by means of non-destructive testing, (magnetic particle or ultrasound) and by x ray if doubt exists. This inspection should be biennial.An examination for distortion or damage or deterioration of the primary structure behind the towing bracket should also take place at the same. time as the examination of the bracket.
5. The lead of the tow pennant or bridle leg (chain) from. its securing point to the outboard of the deck should be such as to so far as possible avoid significant side loading on the outboard fairlead. The shoulders. of the fairlead should be smooth, round and undamaged no matter what type is fitted and they should be thoroughly checked as in point (4) above.
6. In every case where a tow bridle leg or two pennant passes through a fairlead from the secure point, the fairlead must be of the closed type that is, there must be either a heavy bar by which the pennant or bridle leg cannot jump out of the lead. In the case of a closed Panama type lead, this obviously does not apply.
7. Where a tow bridle leg or two pennant either chain or wire passes over the outboard edge of the deck of the vessel, the edge should be well rounded so as to avoid a sharp “nip”.This “roller” should be at least three to five times the diameter of the wire or chain which passes over or around – the larger the diameter the better.