The last thing you want when the wind comes up is for your mainsail to get overpowered and the purchase system to become so cumbersome that your crew can’t pull it on under load. Don’t underestimate the importance of a smooth-running, low-stretch outhaul; when the breeze is up and the sail needs to be flat, you’ll be thankful for this tweak.
For the gross part of the outhaul purchase, start with low-stretch rope, such as New England Ropes HTS90 or STS-HSR. A low stretch, easy-to-hold line, such as FSE Robline’s Racing Sheet Pro, works well for the fine-tune part of the purchase.
I have found that minimizing the last purchase of the outhaul greatly increases the ability with which it can be eased or trimmed. For example, you could have a 4:1 pulling a 2:1 and then to the sail for an 8:1. Or better yet, you could have a 2:1 pulling a 4:1, for an 8:1 as well. The latter example will ease better in light air. Trust me. I’m a doctor… sort of. We built an outhaul like this on a SC50 with a long boom. We built a 2:1, pulling a 3:1, pulling a 3:1 for a total of an 18:1. I can pull it on upwind in heavy air and it eases well in light air.