It might work but it probably won't be "right". You'd have to figure
out what it does to the overall center of effort... If the center of
effort is off, it'll be much less efficient (i.e. a poor sailer). It
sounds to me as though it would shift things up and forward... You
would do better repairing the 15. (IMO)

Ed

JS wrote:
I have two sailboats; a fairly new 13' in good condition, and an old 15'
where everything is about to fail (except the hull, which seems bombproof)

The 15' has a furling jib. Can I use it on the 13'? It would mean moving
the attachment point up about 18", and it would open up past the mast (like
a genoa?); and obviously be bigger than the old jib.

Are there problems that I just don't understand that would make this
impractical? In strong wind the boat handles very poorly with just the
main, but reasonably well with a jib and the main reefed; I am guessing an
oversized jib would be much like the latter case.

Any comments would be appreciated. Is there a good forum for sailing
questions?