: Just so I'm clear, are you saying put one rib in in the direction
: of the dotted line or do you mean two ribs in the direction of
: the solid lines in the picture at:
: http://i33.tinypic.com/sfjj2r.jpg?

Time for some definitions. These are mine.

Think of the keel of the boat as your spine. Now lay on your back and you will understand that the ribs on a boat are aligned like your ribs.

Ribs connect the left gunwale to the keel and continue on to end at the right gunwale. Deckbeams run from gunwale to gunwale, too, but they support the deck and cockpit coaming.
Ribs may be made from single pieces which are bent into shape--frequently steam is used to soften the wood. They can also be made of bent metal. Ribs can be cut from a board or assembled from several boards. They can be cut from sheets of plywood, metal, or plastic.

If you combine a rib and a deckbeam into a single part you call the part a frame. Frames can be made from several boards or they can be cut from a piece of plywood.

Frequently kayaks are designed as a series of frames connected by long pieces of wood or metal. Most fiberglass kayaks start this way. A full-scale wood model is constructed and it eventually yields a mold.

Make a part with the outline of a frame, but with a solid center and you have a bulkhead or bulkhead frame. If you make the bulkheads out of compressible foam you don't need to be too accurate in cutting them. They'll squish in.

If you are building a boat, the plans will describe the shape of the ribs or frames. If these pieces are used in building but are later removed they may be called forms or building forms.
Strips or tubes or rods of wood, fiberglass, aluminum, etc. which run lengthwise may be called longerons, chines, or other names. Frequently they will be named by their location or function. A deck chine is part of the deck. A chine in the center of the floor which runs the length of the boat is called a keel or keel strip if it is on the outside of the boat. If it is on the inside of the boat it may be called a keelson.

The chines that run along the seam between the hull and deck are the gunwales.

: If you mean the solid line I
: am going to have a hard time doing any work much beyond the
: rudder pedals.

The solid lines you've drawn are at the 'sheer' area--the line where the curve of the bottom of the hull connects with the sides. Ribs run perpendicular to these lines.

:If you mean the dotted line would the rib just go
: from seam to seam?

Yes. Basically it would be the shape of the bottom edge, and sides, of a bulkhead at that location. They don't need to be very thick to give strength and support. 1/2" high, or even 3/8" will help a lot. You can glue in strips of wood or lay strips of glass cloth over a piece of vinyl tubing after saturating the cloth with a liquid plastic resin. When the resin hardens you'll have fiberglass ribs which are cast in place.

: Also, not sure that it matters, but I just realized this boat has
: entirely foam bulkheads.

Can I persuade you to make two out of plywood? One would go behind the cockpit opening. The other would go in front of your feet. Make them slightly smaller than the interior at the location where you'll mount them. You don't want them
pushing against the sides. Use a flexible adhesive to mount them.
When the boat is in the water the waterpressure on the hull will try to 'oilcan' it, but those solid bulkheads will resist the squeezing and limit the amount of movement.
They'll also create sealed air chambers. That is less water to bail out if the boat swamps.

PGJ