Hi Michael,
The answer depends partly on wether or not you intend to gybe your chute. On lazy Pelican (B39) we have a single 10mm sheet, about 1.5x boat length, which works well- we snuff the chute if we need to gybe. We found that the longer length served no usefull purpose and just got in the way.
Incidentally we fitted a short ‘bow sprit’ from which to fly the chute, which makes a huge difference to the way it sets and allows me to leave the tack line permanently rigged.
John
