You might want to see if the manufacturer/designer has any approved structural repairs for the thing before you get too far into it. There is a good chance the keel is the primary structure for the hull. You also may be able to get the drawings for the machine and figure out if you can ndeed splice in repair pieces for this.
As far as doing real repairs on composites, they are not that hard, you just need the materials and tooling. A great resource for this is
Aircraft Spruce, in addition to the supplies you will need, they also have some good reference materials regarding composite build/repair.