Ok, so "Gonesailing" wants to know some rudimentary information. Instead of verbal abuse, lets look at the question. As a follow-up, what areas do you want to visit? If you have some specific areas in mind, get ahold of nav. charts for the areas. The mean low water levels will dictate where you want to be with regard to draft.
In discussing depth, there are plenty of boats from 30 - 40 feet that (with full keel) would be great offshore boats with 5' draft. 4' is the draft of my Cal 25. I sail the Chesapeake Bay. I've only gone aground once,and that was my own fault for not heeding the depth alarm.
There are plenty of offshore sailors who are perfectly happy with a draft of up to 6 feet.
I think the best bet is to define your scope (where do you want to go) and decide on a draft based on the number of anchorages you can visit. The overall length of the boat can come later.
Regarding seaworthiness, there are several other factors besides keel depth that lead to overall seakindliness/seaworthiness. Look at the boats that have survived it all, like the Westsail 32, Cal 40, Outbound 40 - 44, etc. Things to consider are small self bailing cockpit, small, heavy port/deadlights, bridge deck and small main hatch, sealable dorade vents, sound rudder (attached to a skeg or to the keel). Hull shape that is unstable when the boat is turned "turtle" so she'll right herself, lazarettes that are structurally sealed off from the rest of the boat, heavy through hull fittings with ball valves, heavy hull construction ie: solid glass cloth instead of chop strand matting or "cored" glass hulls. Also, a keel stepped mast, double lower shrouds, multiple bulkheads to prevent oilcanning or twisting of the hull in heavy seas, etc. Of course, these are just my opinions. Every boat has it's own merits. Heck, in 1968 there was a kid (Robin Graham) who sailed a lapworth 24 around the world. Another cruising couple sailed a Cal 25 (like mine) around the world and had 2 or 3 kids along the way. Of course, I'm not recommending this, just commenting that seaworthiness is as much attributed to good planning and heeding weather forecasts/sea states as it is to a solid boat.
There are several good books on picking an offshore boat. One of which (If I can remember the name) is something like "The Seaworthy Offshore Sailboat."
Just remember, there is no such thing as a dumb question. Even the most elementary question leads to others. Isn't this how we build knowledge?
Finally, there are offshore sailing schools, where you learn the basics of navigation, routine maintenance, and successful passagemaking. I believe Annapolis Sailing School has a location in the BVI.
Hope this helps.
Cal 25 #1651 Indefatigable