What are we trying to achieve?
Above all, we want to set up a fair test of sailing skills. There's always a degree of luck involved, with changes in the wind, but we want to keep the effect of that to a minimum.
We don't want to favour one type of boat over another. So we want to have a good range of points of sail, particular windward legs, but also reaches and runs.
We want to be able to predict/control the duration of the race.
We want to be able to monitor boats as they complete laps of the course.
What factors do we need to take account of?
Most important is the wind, as it is now, and as it is forecast, for the next hour or so. What is its direction? and how strong is it?
How much of the lake is available to us?
It's convenient, but not essential, to have the start at the clubhouse, and we always like to have the finish at the clubhouse.
So how do we go about achieving it? Preparation
We make sure we've had a look at a weather forecast or three, and then check what it's really like when we arrive at the club. At this point we may decide not to go ahead, or at least to wait and see, if there looks like not being enough wind, or if there's going to be too much.
We form a view of how long each circuit should be, depending on the wind strength. Ideally each lap should take about 7-10 minutes, to help us decide when to finish the race: anything longer than that makes it difficult to hit the duration we're aiming at. So a light wind suggests a short course; you can use more of the lake if there's a reliable stronger wind.
We work out where we would like to put the windward leg(s) (the "beats"), if possible. And we also try to see where there are likely to be dead spots at certain phases of the wind (remember it's changing all the time). If someone finds themselves in a dead spot, they may be there for a long time, while others are still making reasonable progress, and that's not fair, because it doesn't happen to everybody.
Together with the OOD, and taking account of other potential users of the lake (both at the club and around the edges), we discuss how much of the lake we can use, and which areas we need to avoid.
Planning the course
We start with the most important decision: the start line. The first leg needs to be a beat; it should be as long as we can reasonably make it, to allow the fleet to spread out before reaching the mark, and if possible, it should end with a left turn - a port rounding. We set the start line at the beginning of this leg, and it should be square onto the wind (NOT the line to the first mark, if there's a difference). You may choose to set the port end slightly forward, to discourage people from bunching at the starboard end, but you should avoid doing the opposite. And remember: the start line needs to be long enough to accommodate all the boats taking part - at least half a length per boat, preferably more; and you need to have plenty of room behind the line for boats to mill around before the start.
In normal conditions, we'd like to have a second beat. So the second leg would be a reach to the beginning of this second beat. And this time it's not quite so important to have a port rounding at the end of the beat (mark number 3); but it's still desirable.
And then, either way, we need to get back to where we started, so we have one or two reaching or running legs, using up an appropriate amount of the lake according to the conditions.
No matter where you made the start, you should aim to set the finish line at the clubhouse, and the course should go through the finish line on each lap, to allow you to record progress.
Rounding marks
You should check whether your course calls for tacks or for gybes at each mark. There should preferably be a balance between the two types. If you can, you should place each mark so that there's no conflict between boats rounding that one and boats passing by on a different leg. And you should never set a course that requires boats to pass in opposite directions around the same mark.Some special cases
In very light winds, and especially if the wind direction is uncertain, the best plan may be just to set a small triangle in front of the clubhouse (taking care to avoid any wind shadow from the buildings).
And in very strong winds, it may again be advisable to have a simple course, like a triangle, but much larger in this case.
It's sometimes practical to set out an "Olympic" course: long beat to windward, followed by a broad reach to a wing mark, then the opposite broad reach back to the start, then next time round, a "sausage" (simple windward-leeward legs). Or you can skip the sausage and just do triangles.