Step 2: Making the Station Ribs

Note: Do not cut out any patterns for the ribs or bulkheads until you have read the section on building a Hull Assembly Frame.  First, each station rib needs to have sufficient added height to attach to a frame.  Second, since the bottom of the boat has a curved rocker, each station-rib has to be raised or lowered according to this height disparity, which varies 8 inches.

Undoubtedly, more experienced boat builders will take umbrage with my methods, but the following construction method is easy for the first time boat builder, although it is a little bit more costly due to the extra plywood.  Now that you have the three necessary measurements for each station rib, it is time to cut-out the ribs and place them in a frame so that they remain in their correct position.  Obviously, it is not necessary to add a rib every foot in a thirteen-foot boat.  Instead, the following ribs will be cut out and placed in a form in order to attach the side panels and the bottom panel.  Station-rib #2 remains as a bulkhead..  Place a full rib over the scarf joint on the bottom of your boat. My scarf joint was 4-feet from the transom. Decide where you want your cockpit to end and place your forward bulkhead at theat point. Mine was 4-feet back from the nose of the pram as measured from the top deck, not the bottom. Keep in mind that some of your ribs are only temporary and may be replaced with just the side portion of the rib.

Studying the photograph to the right, you will note that the station ribs also are cut so that they provide support for the side decks and the cockpit.  Here is my dilemma at this point.  If this were a flat bottom boat, it would be easy to construct a simple frame to hold the ribs upside down so that you could screw in the bottom piece, the side panels, the transom and the stern piece.  But the bottom is not flat.  It has an 8-inch rise from the transom to the stern piece.  The easiest solution would be to cut out the ribs later.  In other words, trace the rib on a piece of plywood.  This piece of plywood would have the shape of the bottom and the side panel as well as the side-deck rise.  Each of these "bulkheads" or stations creates the profile or curvature of the boat.  Each piece also allows for easy attachment of the panels to the frame with panel nails and temporary screws.  The disadvantage of this method is that it uses more plywood.  (I used A/C.)

Each station-rib piece is raised or lowered based on the bottom curve or rocker.  This distance can be determined from your full-scale drawing or the table measurements.  The height of your frame must be sufficient to attach each station-rib and allow for the rocker distance.  Before you begin building a frame, draw up some plans for the frame.

 After you have glassed the seams of the hull with epoxy and cloth, remove the screws for any temporary stations.  It is time to sheath the exterior with 6-ounce fiberglass cloth.  (See Devlin's chapter 19, Sheathing the Exterior.)  Be sure to double-check all your measurements to keep the boat true.  When you are finished, flip the boat over and remove the temporary station-ribs.  Because I was working with a female mold, it was easy for me to add the cockpit side supports.  Working with a male-plug, simply screw on some temporary support pieces for the cockpit panel.  Once the deck is in place and the cockpit panel is secure, remove these supports and cut out the ribs.

The small 2-inch by 6-inch piece at the top of each station-rib is used to press the cockpit side panel against.  Screw this cockpit panel directly against these small vertical pieces.  After you have filleted and glued the seams on the outside of the boat, remove the screws, and then cut off these support pieces so they don't press into your back when you are sitting on the floor. Look closely at the photograph below and you can see one of these support pieces. Note that in the third photograph, it has been removed.

Steps for Building the Bitterroot Pram