I need to replace a genoa on a 311. Any suggestions for the sail that will give me the best performance regarding speed?
Lou,
Just remember that you are restricted somewhat because of the rig geometry on the 311...which is to say the shroud base is clear out to the gunwale and the original genoa was designed to sheet inboard (for good sheeting/angle of attack) but this means that it can be NO bigger than about 115% of your L.P. (3.978m / 13.05')
The sail needs to be cut as an all purpose jib in shape, even though it's 'jib' size
We have built overlapping genoas for the 311's...if you're old enough

to remember 'drifters' which are basically a high clewed 150% genoa in 1.5oz nylon which can be 'free flying' or attached to the forestay. These would be a very light air upwindish kind of sail...but you need to think about where it will sheet (spinnaker blocks??) and the rig is still intrusive, so it won't go upwind like a true genoa.
Hope this helps.
Bob Pattison