In shipbuilding terminology, a definition of spigot type is commonly used for the pipe penetration through the bulkhead or side shell.

To understand the meaning of spigot type is necessary because of most pipe penetrations on ship leading to side shell is critical points which may cause delaying the launching schedule due to the wrong design and fabrication.

Initially, in mean of closing appliance, when holes for pipes or duct passages are cut in the wrong place by mistake, they are to be closed. The standard closing methods are as follows :

Insert plate, doubling plate and spigot The thickness of these closing plates is to be the same thickness or more as the cropped plate. In the case of newbuildings, doubling plates are not desirable because the doubling plate projects from the surface with bad appearance.

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a) For longitudinal strength members

When the diameter of the incorrectly cut hole is less than 75 mm, the hole is either to be enlarged to 75 mm and a spigot provided or enlarged to 300 mm or more in diameter and a new plate inserted. After welding external surface beads are to be ground down to a smooth finish.

b) Other members

The diameter of the incorrectly cut hole is to be enlarged to minimum 200 mm and a new plate inserted or a doubling plate applied.

Giving with an example from BV-Rule requirement of pipe penetration to side shell:

As interpretation, spigot passing, mean that the pipe passes through the plate with out gap or  have a spigot passing through the opening. The clearance between the spigot and the edge of the opening is to be uniform for the whole periphery of the opening and is not to exceed 2 mm (max 4mm) as general.

Summary:

From above description, now we can see that the important of spigot passing type which can reduce the failure of structure integrity on strength longitudinal main structures by keeping the gap between hole and pipe as small as possible.