: 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.

: 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

: 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.

: 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

Foam bulkheads work fine and are watertight too as well as stiffening. This isn't thin foam, usually it's 3" minicell.

Bill H.