As a former co-owner of a retractable-keel boat (CAL 21) and current owner of a centerboard O'DAY DS II, I can speak about both types. I haven't sailed a K/CB boat yet (missed out when our late friend Joe got sick) but I really buy into most if not all of the K/CB plusses that O'DAY used to list and agree with most of what their opinion of swing-keel boats said. I do have to note though... that O'DAY did miss one more disadvantge to their K/CB designs..... minimum draft is greater than with a swing-keel design like they describe (our CAL drew 9" if you retracted the keel completely into the trunk, we never did..so that would add enough to equal the 14" draft of an O'DAY 20 or K/CB 22) Many swing-keel boats do not allow the keel to retract totally and so, like the Catalina 22 (24" Keel up), they draw almost as much keel-up as an O'DAY K/CB with the CB up. So the "saucer on the water" is not true of ALL swing-keels.
Now, I must disagree that a fixed-keel boat will "always outsail" a centerboard boat. Alll things being equal, when sailing off the wind you can raise the board on a centerboard (or K/CB) boat part way and thus reduce drag. Our CAL 21 was pretty quick, but on a broad reach I could easily outsail her in my DS II, downwind It might have been a draw, but even with older sails, a CB or K/CB boat will often beat a keel boat. Would love to see a "race" between a fixed-keel Mariner and a centerboard Mariner, or 2 Rhodes 19s. Might be pretty close between the Keel and centerboard. Although I think most racing R19s are keel models, I think that keel and Cb race in the same class.
My feeling on the swing-keel boats is that for a trailerable boat, they work well. You get the deep fin-keel design (keel should have a way to locked in down-position) and advantage of low-down ballast (but most lose some of that advantage due to the ballast being distributed over the full depth of the keel, so a 5' draft swing-keel may not have the center of gravity all that much further down than a 2.5' draft K/CB), with the advantage that when you return to the ramp and winch up the keel, you have the shallow draft of the centerboard boats. For me, I keep my boat on a mooring all summer, with a low-tide depth of 3-4'. I would thus need to lower the keel each time I went out, lock it down (can't be done underway easily), then reverse the process to return. As I say, I like the concept of the swing-keel boats.... but I could keep a K/CB boat like the O'DAY 192 or Precision 18 on my present mooring..... a swing-keel would need to be much farther out from the shore or kept at the local boatyard ($1500.00/year mooring rent) unless I was willing to crank the keel up/down ever time I go out.
I like the CAL 21, but with her keel locked down, she needed 4'3" to float, so wasn't practical to move to my mooring (we had kept her for 37 years at the local boatyard, but although Dad could afford it...... he wasn't using the boat enough to justify the cost, and I didn't want to have to moor out far enough to keep her in hte cove near our cottage (too many powerboat wakes rolling through would wear the keel pivot area out). So, I kept my DS II and we sold the CAL. Dad sails with me now.
The CAL 21 was not a typical "Swing-Keel", in that I consider her to be the only truly "retractable-Keel" boat in her size range. First, the keel had a 360# lead bulb at the bottom and the fin part was a steel-core fiberglass structure. Once lowered into sailing position the keel was locked down by a bolt through the top of the keel fin (above the pivot) and the winch cable was detached and cranked back onto the winch, the winch could then be removed and stowed below and a sort-of plank (Keel Plug) slid into the keel well/trunk to close off the bottom of the slot. This was doen through a large opening in the cockpit sole and a cover was then fitted over that opening. She was now a "fixed-keel". To haul out the process was reversed. Great for our use (launch in Spring. keep her on a mooring for the Summer, haul in Fall), but not so good for daysailing off the trailer, since the process (contrary to the sales hype) took about an hour each way, maybe more. For us it was great, deep, fin-keel when in the water, shallow draft to sit low on cradle or trailer in the winter ashore. We did need to tow a dinghy to go ashore if we anchored, but I think we saw that as just another excuse for our "delusions of granduer" it put us more in line with those with bigger boats!