Fishing Craft Technology

Unit 2 - Basic geometric concept of the fishing vessel

2.2. Lines plan
The lines plan is a geometric description of the hull. The hull surface is described by seeries of longitudinal and transverse sections. It is very essential to learn the main parts of a typical ship together with the terms applied to the principal parts. Because at first they are of little interest or influence, super structure and deck houses are ignored and the hull of the ship is considered as a hollow body curved in all directions surmounted by a water tight deck. Most of the ships have only one plane of symmetry called the middle line plane which becomes the principal plane of reference. The shape of the ship is cut by this plane is known as the sheer plane or profile plane.

The design water plane is a plane perpendicular to the middle line plane chosen as a plane of reference at design water line. It may or may not be parallel to the keel.

The planes at right angles to the middle line plane and parallel to the design water plane are called as water planes, whether they are in the water or not and they are usually symmetrical about the middle line. Water planes are not necessarily parallel to the keel.

Planes perpendicular to both the middle line and the design water plane are called transverse planes and a transverse section of the ship does normally exhibit symmetry about the middle line.

a) Sheer plan:
Most of the ships have only one plane of symmetry, called the middle line plane which becomes the principal plane of reference. The shape of the ship cut by this plane is known as the sheer plan or profile.

b) Half breadth plan:
Half water planes are placed one on top of the other, form a half breadth plan. Water planes looked at edge in the sheer are called water lines.

c) Body plan:
Transverse sections are laid one on top of the other, form a body plan. Which by convention because the sections are symmetrical shows only half sections the forward half sections on the right hand side of the middle line and the aft or after half sections on the left.
The sheer, body plan and half breadth plan are collectively called the LINES PLAN or SHEER DRAWING .

d) Buttock line:
These are another set of intersecting planes parallel to centre lines. Each plane intersects the vessel surface in a curved form in the sheer plan in its true form. They appear as vertical straight line in the body plan and horizontal straight line in the half breadth plan.

e) Diagonal plane:
It is an inclined plane; these are inclined to all the above planes. Diagonal planes are usually normal to the surface or nearly so with determining the character of that surface, vicinity more accurately than in a plane sharply inclined to the surface.

f) Bilge diagonal plane:
These planes are inclined line to both horizontal and vertical reference planes, but perpendicular to off ward plane. It appears as a straight line in the body plan and as a curve in the sheer plan and different curve in the half breadth plan. Which is its true shape these are often use because its plane is perpendicular, normal to ship surface at the burn of the bilge.