If you are outfitting a sailboat for blue water cruising, the two most important items that you can add, in my opinion, are:
- A drifter
- A Monitor Windvane
A drifter is a light air sail cut like a genoa but made out of spinnaker material. This sail will keep you ghosting along on windless days. It even managed to pull us through the doldrums! When choosing your yachts sail wardrobe, be sure to include a drifter (and forget about a spinnaker).
The second important item is the Monitor Windvane. This unit will steer you to a set angle to the wind in all conditions. If the wind shifts, it will change your course to keep your sails trimmed perfectly and prevent them from luffing. While the prospect of changing course might seem bad, when you are offshore it's not a big deal. Your destination is hundreds or thousands of miles away, veering a little to port or starboard for a few hours will not make a difference.
Now, be sure to get a Monitor and not one of the other brands like Hydrovane or Cape Horn. Hydrovane will quickly be overpowered and overwhelmed as the wind builds. Cape Horn works just like a Monitor, but all of the control lines are hidden away making it hard to frequently inspect for chafe.
Now, I can't say which of these two items is more valuable than the other for ocean cruising. Honestly, both items should be carried that way you can move on light days and relax as your yacht sails itself across the ocean with you onboard.