Thank you all, good ideas. I think thaw, drill, drain, dry, and resin. It seems that below about 7inches the keel is solid and will hold. With these added strengthening tips there should be no problems. Do you think that acetone or a like chemical will aid in cleaning /drying the ballast? Thank you. I love the boat and know they are well built, like tanks, as one quote stated. I believe drilling and shrink wrap for winterization may be the way too. Thank you all for the help. I am going to get the boat under shelter and really sing to it. You all are a great help! Now I have a direction, another month and this cold will be pretty much over.
Draining and sealing is good advice.
I would recommend using epoxy resin [not polyester...] with a slow kick hardener to allow time for the epoxy to flow...
Epoxy will adhere to everything in your keel much better than polyester, be much harder, and allow you to do it again in the future if it something else happens.
If the voids don't close-up and become less than ~1/4" after draining, consider adding an appropriate filler to the liquid epoxy before pouring so it fills the void better and is not brittle from being too thick... [The resin manufacturers all have good instructions to follow for using which filler for what.]
You may need a series of drain holes along the bottom of the keel to drain the water. Leave them open to help things dry out and to monitor the resin flow when you pour the epoxy. [i.e., As you pour the epoxy resin, you can wait for it to run out each hole before plugging the hole [temporarily] with good duck tape. This will help prevent entrapped air and confirm the epoxy went all the way to the drain holes.
Once the epoxy is set, you can remove the tape, sand and fair it out, and paint right over it...
It will be better than new when you are finished.
Best wishes with your project.