Hey Bob!

Do you mean the Bow when you say the nose?

"The Foward Perpendicular" generally speaking of course, is the first frame in the "Bow" that meets the designer's waterline... In some circles it is known as the "Extreme Bow" but, that can be misleading in certain circumstances.

Foward Perpendicular: A line perpendicular to the base line and intersecting the forward side of the stem at the designed waterline. Stem: The bow frame forming the apex of the intersection of the forward sides of a ship. It is rigidly connected at lower end to the keel.

A "Ship" or as some of us affectionately prefer to call submarines "Boats" is typically divided into as many as 41 or more evenly spaced "stations".... Planes parallel to the front of the imaginary box or circle running port to starboard are called "Stations"... The first foward station at the Bow is usually labeled station number Zero. This foward station is called the "Foward Perpendicular" (FP).
By definition, the FP is located at a logitudinal position as to intersect the stem of the ship or boat at the (DWL) Designer's Water Line.

Here's another definition: "Forward perpendicular": FP, the point where the design waterline crosses the forward most section of the hull. Now that definition can cause a debate to ensue because of the general vagueness of the definition when it is applied to certain classes of submarines especially when there is no specificity concerning which "Hull" the definition is referring to... In other words, is the definition referring to the outer hull of a certain class of submarine, or is the definition referring to the pressure hull itself which may on certain classes of submarines begin way aft of the same boat's outer hull bow location where one could easily refer to the "FP"?

"The Aft Perpendicular" is generally the last frame that meets the designer's waterline...
The length between these two frames is what determines the boat's waterline length.
Here's another definition: :"After or Aft perpendicular": AP, the point where the aftermost section crosses the design water line (DWL). On commercial vessels, generally located on the vertical rudder post.
However in some ship and "boat' designs, the Aft perpendicular runs thru the rudder post.
But for compartmentation and frame numbering purposes, the first definition is used.

Here's a good website to learn more about Naval Architecture:
http://ntl.bts.gov/DOCS/narmain/narmain.html

this one covers "Ship's Lines and Model Testing":
http://ntl.bts.gov/DOCS/narmain/naintro.html#stab

Here's one of my favorite .pdf's referring to naval architecture fundamentals:
http://www.usna.edu/naoe/courses/en200/ch02.pdf

Her'e a good Naval Glossary of terms:
http://www.history.navy.mil/books/nnv/sz.htm
Hope this helps.

Respectfully,
Henry