Molds and other rigid bodies have six degrees of freedom. They can change their position forward and backward (surge), up and down (heave), left and right (sway). Translation in three perpendicular axes, combined with changes in orientation through rotation about three perpendicular axes, often termed yaw (normal axis), pitch (transverse axis), and roll (longitudinal axis).
When setting up the jig it is important that the molds are rigidly fixed in all the six movements movements.
The aluminum profiles take care of the up and down movements and roll.
The lengthwise markings on the aluminum profiles takes care of the forward back position and yaw.
The centerline takes care of the right left movement. The plumb bob takes care of the pitch.
Its good to be careful and make strong hull jig because each plank adds to the pressure on it. There is a concrete flor in my workshop. It is strong.
Below is a picture of the aluminum profiles fastened to the floor.
Click once or twice to enlarge