Really you should only sail the CAL 21 with the keel down and locked. In light airs the boat might be stable enough even with the keel all the way up, but without the keel sticking out you have no directional control (Boat becomes a saucer on hte water with nothing to stop leeway) also, you will need the rudder for steering and it extends down a couple of feet anyway, negating the "advantage" of having the keel retracted (draft about 10").
The CAL 21 was designed so that when you get her in hte water, you lower the keel into position, insert the locking bolt, remove the cable from the keel, insert the keel plug, cover the opening in the cockpit, and sail off in a "semi-fixed" keel boat. If you need to transit a 1/4 mile shoal area (less than 5' of water, boat draws 4'3" keel down) to get out to where you will be sailing, then perhaps the CAL 21 is not the boat for you. You might be better off with a keel/centerboard boat, like an O'DAY 222 or 192 (or O'DAY 20, Precision 21, Quickstep 21, Precision 18, Starwind 19) or a shoal-keel boat like the O'DAY 22 (1'11" draft) or one of the other boats with a shallow wing-keel. There are various centerboard designs too, (O'DAY or Stuart Mariner, O'DAY 19, Sanibel 18). Some of the other retractable-keel boats like the MacGregor-Venture line (17. 21, 22, 24, 25) or the Balboa 20, Ensenada 20, Catalina 22, Santana 21 could be easier to get over that shoal, their keels still are intended to be locked down while sailing, but most still expose enough keel to aid steering with it retracted, although I would still be careful and might still suggest powering until past the shoal.
Alternatively, you could launch the CAL 21, lower the keel part way (about 1/4 to 1/3 down) to provide some control, attach rudder if keel is deeper than rudder, otherwise carefully steer using outboard as you power out beyond that shoal. Once out past the shoal, stop, lower anchor, and then lower the keel down and lock it. Go sailing! Then on the way back in, stop before the shoal and raise keel partway and power back to the ramp. One downside is that it is a LOT easier lowering/raising the keel at dockside than while anchored, especially if you would then be near any waves (or powerboat action) as calm water is very much desired for the operation, specially inserting/removing the locking bolt. Sailing without the locking bolt would not be wise, as the keel will tend to swing a bit fore and aft, and I'm not sure how well the keel plug could be used, thereby allowing water to surge in and out of the cockpit opening of the keel well while sailing, making sailing with dry feet a bit hard.
One final option would be to get a mooring out past the shoal and keep the keel down and locked for the season. That was what we did for the 38 years we had our CAL 21. It had been our intention to keep the boat moored in the cove in front of our house, but it turned out the water wasn't deep enough there, so we rented a mooring at a nearby boatyard which worked OK for us.
I am a tremendous fan of the CAL 21 and can recommend her highly, but I also recognize that she isn't the right boat for everyone. Right now, my sailing budget would not allow renting a boatyard mooring and I've grown too attached to keeping my present boat (1979 O'DAY Day Sailer II) in the cove in front of our family cottage...... so, if I ever realize my dream of a larger boat.... sadly, she won't be a CAL 21.