by tomodda » Wed Sep 02, 2020 1:34 pm
Jenny ALONE? Can you imagine the lee helm you'd suffer? Methinks you'd better raise your main as well.
Anyway, I'm assuming that by Genoa you mean a sail that is hanked to the forestay and is bigger than 100% of the fore triangle, say 110% or so. I've see on this forum and other internet sites where folks are flying asymmetrical spinnakers, but those fly free of the forestay. And foreward of the forestay, usually on a short sprit to keep it clear. So, for a true Jenny, you have a large triangle, with some overlap of the main. You'd have to get it custom made, so really can't tell you re: dimensions... but, roughly speaking, in standard IJP dimensions - I (the luff) continues to be 16 feet, J (the foot) will be 10% or so more than the distance from the forestay to the mast, and P (the leach) is - do the trig.
Hopefully, this answers your questions, but I have a question for you - why? What are you trying to do with a Genoa? It's not necessarily the best solution, I've not seen many true Jenny's for a fractional rig and certainly not on a small boat. Asyms probably make more sense, I've been kicking that around in my own mind for low wind (which I get a lot of)!
Best,
Tom