Visualize the shape of your jib

Dave Dellenbaugh, member of the 2025 Class of the National Sailing Hall of Fame, talks about sail shape in WindCheck magazine:

Before we talk about how you can use sail controls to change the shape of your headsail, let’s quickly review how we look at that shape in the first place. Let’s discuss how the various headsail controls affect four basic measures of sail shape: overall depth (fullness), the position of maximum draft, the leading edge angle and twist. Each of these has a large effect on the sail’s total power and performance.

Depth of the sail – The depth (also called fullness or draft) of the jib/genoa is essentially a measure of the sail’s roundness. A sail that is very curved is also quite deep. In general, depth produces power so a deeper sail is more powerful than a flatter one (but also has more drag).

Almost all the headsail controls affect the depth of the sail. Pulling on the backstay, for example, reduces headstay sag and flattens the sail. Moving the jib lead aft makes the bottom of the sail flatter, while more tension on the jib halyard pulls draft out of the sail. – Full report