Reference Planes

Question 1

Baseline Plane (BL)

Answer 1

Lower part of keel, outside of shell plate, through the upper edge of flat plate keel. Vertical dimensions use as a reference.

Question 2

Centerline

Answer 2

Fore and aft (longitudinal), perpendicular to BL, hull shape is symmetrical on either side.

Question 3

Transverse or Vertical Planes

Answer 3

Equal intervals along length called “frame stations.” Not always equal to actual frame locations.

Question 4

Forward Perpendicular (FP)

Answer 4

Frame station Perpendicular to BL, intersects the forward edge of the stem at the designated water line

Question 5

After Perpendicular (AP)

Answer 5

frame station After the edge of the rudder post at designated water line.

Question 6

Designated water line

Answer 6

Where the ship sits in the water at assumed load.

Question 7

Mid-ship

Answer 7

frame station Center of ship longitudinally between FP and AP

Question 8

Length between perpendiculars (LBP)

Answer 8

Measured longitudinally