Question

a) With reference to the importance of good design and a high standard of workmanship in the fitting and repair of bilge keels.

(i) Describe how the design and method of attachment reduces the possibility

of damage to the shell plate:

(ii) State the authority the must be afforded the opportunity to inspect the fitting and repair:

(iii) State what non-destructive testing is carried out

(b) Explain why bilge keels do not extend for the full length of the ship:

Answer.

(a)

(i) The bilge keels are attached directly in line with internal stiffening such as a girder or longitudinal. On thicker shell plating (such as merchant ships) the bilge keel is made up of a flat bar doubler welded directly to the shell and an offset bulb plate (OBP) with 'scallops' cut in it is welded to the flat bar doubler. The ends of the bilge keels are tapered and if the keels are positioned so that they follow the streamlines at the service speed of the ship, then the added resistance is only about 2%.

(ii) The Authority that must be afforded the opportunity to inspect the fitting and repair is the Load Line Assigning Authority Surveyor (e.g. the Lloyds Register Surveyor)

(iii) The non-destructive testing that must be carried out is either X-ray or ultrasonic.

(b) Bilge keels are not fitted for the full length of the vessel because:

(i) The lever to the ships axis of rotation is reduced at the ends;

(ii) It would be more difficult to make and fit due to the bending and twisting

required:

(iii) It would be difficult lo align with flow along the hull, particularly at the fore end.

The hydrodynamic effect would cause a large increase in resistance and fuel

consumption:

(iv) At the aft end the boundary layer is much thicker and since the keel would not project through, it would have much reduced effect