My brother and I took Alma's Only to the Dry Tortugas, and had a super trip. We departed from Key West in fairly rough, confused , generally following seas, that were predicted to quiet over the next several days. They didn't, and it was fairly windy during our two nights at Ft. Jefferson, and we then took the same water, nose on, for the return. There are some photos of the trip at the following link:
http://www.c-brats.com/modules.php?set_ ... _album.php
I'd do it again in a heartbeat. Although the water was less than ideal, we were able to make reasonable speed, taking turns at the helm. Doing so required constant attention to steering and throttle, and an occasional slam, but nothing that caused any concern. In smoother water, the trip would be a real dream. We left with full tanks of gas (24gal port and starboard), and 20 gal in jugs. We burned right at 20 gal each way, so ended up with 4 gal left in each built-in tank, and a full 20 in reserve. This burn was with considerable throttle changes, and in rough water. You'd do much better in anything that's a little closer to ideal.
While underway, we only saw a few other boats, and those were mostly close to Key West or the Torgugas. But, with nothing else in sight, the DSC went off, with someone sending a distress signal from a VHF which was not hooked up to a plotter. So, there were no coordinates. What was interesting was that the air came alive with calls from other vessels acknowledging receipt of the signal, and eventual relay of that status to the USCG. So, although there was nothing in sight, there were a lot of ears listening. I expect the call was sent by mistake, but it sure gave me a good comfort factor.
The bottom line is that if you plan ahead, the trip can be safely accomplished in a CD 22. The fuel reserve turned out to be most comforting, and I recommend carrying as much extra as possible, since there are a couple of alternatives that might come into play. There's always the possibility of having to turn back to the Tortugas if sudden weather hits Key West during your return leg. We also budgeted enough reserve to allow a diversion to Florida's southwest coast, if returning to the Tortugas or trying to make Key West didn't seem advisable. With those bases covered, we had a lot of flexibility.
I'll be glad to make routes and tracks available to anyone who'd like.
Good luck.