Replacement bilge keels should normally be fitted as per the original arrangement, unless modifications are proposed by the owner.
Bilge keels may not be welded directly on the shell plating. An intermediate flat, or doublers, is required on the shell plating.
Below are some comments on the fitting of bilge keels:
Materials
The bilge keel and the intermediate flat are to be made of steel with the same yield stress and grade as that of the bilge strake.
Arrangement
As a general rule, bilge keel ends are not located in the amidships region.
The ends of the bilge keel are to be sniped at an angle of 15” or rounded with large radius. They are to be located in way of a transverse bilge stiffener.
The ends of the intermediate flat are to be sniped at an angle of 15º.
The neck thickness of the intermediate flat is to be equal to that of the bilge stake. However, this thickness may generally not be greater than 15 mm.
Welding
The intermediate flat is to be welded as shell doublers by continuous fillet welds.
The butt welds of the intermediate flat and bilge keel are to be full penetration and shifted from the shell butts.
The butt welds of the bilge plating and of the intermediate flats are to be flush in way of crossings (with the intermediate flat and with the bilge keel).
Butt welds of the intermediate flat are to be made to avoid direct connection with the shell plating, in order that they do not alter the shell plating, by using, for example, a copper or a ceramic backing.
The connection between the bilge keel and the intermediate flat is to be made by continuous fillet weld of throat thickness less or equal to that of the intermediate flat to the bilge strake continuous fillet weld.
The butt welds on the bilge keel are not to extend up lo the flat bar, but to stop on a scallop.
The weld in way of the scallop must be returned and free of defects.
NDE
A radiographic inspection is to be taken, at random, of the wildings of the bilge keel and of intermediate flat.
