Have a Kent Ranger 24 ft IOR racer/cruiser boat.
I'm going to use the spinnaker soon. Do I really need a sheet and a guy line on each clew (each side-right and left)? What's the point? They seem to do the same thing.... and I have read that smaller boats just need a single line on each side of the spinnaker.
Do you need two lines both side? Not usually.. but what's the point? The point is that sheets and guys require different sheeting angles so, on some yachts, the sheets and guys are run through different sets of blocks to different sets of cleats. This ensures that the spinnaker can be correctly set from the moment it's hoisted - not some minutes later after the opposition has cruised past..
In that case, usually the guys are thicker line than the sheets, and often a different type (low-stretch) because they're under a lot more strain. Obviously on a smaller boat the spinnaker is smaller, so line thickness and type isn't so critical and, going right down to a dinghy, there often isn't the space for the extra blocks and sheets anyways.
I guess the system you use on your boat will be dictated by how mad-keen a racer you are and how good your crew is.. but on a 24-footer, personally, I would use one line each side.
Would you guys raise it in front of set jib and main? Or would most people drop the jib and just raise it in front of the main?
Most people would raise it in front of the jib, then lower the jib. Reverse for a take-down. This allows the jib to blanket the spinnaker a bit, making it easier to lower in a stiff breeze..
Does anyone sail by spinnaker alone>
Yes. Regularly. It's a great way to get home (down hill, of course) after a long day on the racecourse!