With the light shining through the hull in picture http://i33.tinypic.com/e5mp95.jpg you can see the outline of the ribs and keel components which were embedded inside the fiberglass construction of the hull.

Considering the location of your damaged area--right on top of one of those ribs--I have to think this manner of construction wasn't adequate for your paddling needs. Burying the ribs inside the glass gives you a clean, smooth interior, but you sacrifice the strength provided by thicker ribs. So, add a few of your own.

I'd sand away the gelcoat over the oilcanned area, and probably go halfway through the fiberglass. draw a circle around the damage, about 2 inches out from the damage on all sides. Sand down through the damage to remove it. If you hit the ribs, you've gone deep enough. All that damaged area has to be removed. It is not giving you any strength there now, so put in something better. Sand a gentle taper from the pit you've created to the circle you drew around it. That gives you a gently tapering area away from the damaged area, blending into the rest of the hull. When you put on a patch it will fill the hollow, and bond nicely to the tapered area, but the patch material will end up above the lines of the hull. Once the patch has hardened you will sand down that excess and smoth the area so the patch matches the original lines exactly, and has a strong bond to the surrounding hull.

Once you've done the outside you can try to get the damaged material out of the inside, but sanding in that area is going to be no fun. Same idea here, though. taper in an area 2 inches away from the damage so you have a good bonding surface area. A patch made this way will be as strong as the original boat.

After that you can put in some internal ribs to add additional strength and avoid a repetition of this problem.

Foam bulkheads work by pushing out evenly against the sides of the boat. The stiffer or more compressed the foam the greater they push out. In this case they either didn't push out enough to resist the external waterpressure, or they were in the wrong place. Since you aren't going to put a solid bulkhead between your seat and your footpedals, you need some other design option for this area. Ribs work, if they are sized right. you may need to do some trials to see just how big they need to be, but start with modest size and only increase them if it looks like you are about to experience a repeat of your oilcan problem.

I favor solid bulkheads. They may not be as good as foam in an impact, but (in my opinion) they are better in general use. I just try to avoid impacts.

Unlike foam they won't continue to compress when subjected to increases in hull pressure from water pressure. They transmit some of that pressure around their circumference, and transfer it to the entire hull and deck. When the hull is pressed in, that pressure is ultimately directed into a force which pushes against the inside of the boat, and tries to stretch it wider. Fiberglass is really strong when it comes to dealing with forces trying to stretch it, so you get the whole skin of the boat helping with resisting the waterpressure. When the hull is in compression, all the parts above the waterline are in tension.

Again, think of how the spokes on a bike wheel transfer loads to the rim and axle. The spokes under the axle are being pushed on, they are in compression, and being really thin wires, they would bend under the rider's weight. But the spokes above the axle are thin steel wires, too, and they are very resistant to being stretched out longer by the tension they are subjected to. So while the pressure of the tire on the road is equal to the weight of the bike and rider, the weight is carried by the tension on the upper spokes, not the compression on the lower ones. Now imagine foam bicycle wheels.With foam you just get more compression on the bottom of the tire. Basically it would look like a flat tire. With foam bulkheads added pressure on the hull from waterpressure compresses the bulkhead below the waterline, but doesn't transmit very much of that added load to other parts of the boat.

I could extend the analogy further and compare a pneumatic tire to an inflatable kayak, but that takes us way off the point.

Good luck with your patching. If you use epoxy you will want to paint or varnish any on the outside of the boat. I'd just paint the patched area this year, and maybe next year fix up a few more spots where repairs have been made. Then, 2 years from now, give the hull a light sanding and repaint it white. Of course, if you like sanding and painting more than I do you can accelerate this schedule. :)

Important safety point.
You will need to wear protective equipment when you sand into fiberglass. Tight-fitting, half face respirator with good particle filters is advised. The flimsy fabric or paper surgical masks are not going to protect you. The sanding dust is a mix of inert plastic with soft edges, and tiny chips of glass fibers with incredibly sharp edges. You don't want these things in your lungs.
you'll cough out the plastic, but the glass fibers will never come out and they'll never get dull or degrade. It is as bad as asbestos, or maybe worse. You can get a good respirator for $20, and really nice ones for a few dollars more. Your health is worth it.
Keep the respirator on until you have finished sweeping up the dust, AND wet mopping the area to pick up any residue.

god luck with your repairs. Now that you know how to do it, send along a few pics of the completed work.

PGJ