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A foot block (or bulkhead, same thing) is an essential item. You must have something in the bow to eliminate flex in this area. A combination of the foot block and the knee wedge eliminate the flexing pressure of intense depths. A bulkhead also allows you to flex between your feet and your back to hold you in place solid from scooting foreword or back. This pressure also aids with the knees being engaged more solid in the knee pockets.
The first thing to start with is the centerpiece. Choose a piece of foam that will get from the tip of the boat to your heels with enough pressure still on your heels to hold your back against the back brace. Off of this center piece you can add additional foam for your toes to create the more involved block that you see here. Take the time to get the foam shaped to the contours of the bow as good as you can. The better you can make it, the stiffer this area will be and the less likely it will be for this piece to fall out going down the road. If you do not have a piece big enough to make this center piece, just glue together two or more smaller pieces.
Again the center is the most essential. Make this first and then it will be simple to glue small scraps on the side and contour to the curve of your foot. It is helpful to set the block on top of your boat rather than in it to figure where to make some of the smaller cuts like the one that will be necessary on the outside pieces to follow the contour of the hull.