We have enjoyed the benefits of big roach mainsails for a long time (beginning 50 years ago in cats). In the late 1980s we started putting roach past the backstay on our monohulls. With the Sundeer Series a combination of swept spreaders and rig geometry allowed really aggressive roaches. When Dan Neri moved to North Sails  and made sails for Beowulf in the photo above they were the biggest roached sails – mono or multihull – North had made. The advantages are many:

• First is an increase in effective aspect ratio through reduction in tip losses. Induced drag, what heels you over and makes the keel work, is a function of aspect ratio squared. Changing from a triangular sail to a roached sails results in a huge reduction in this form of drag.
• Sail area can be increased for a given rig height.
• Wind velocity goes up with height above the surface, so sail area up high provides more drive than if it were lower.
• It is easier to have the sail twist off correctly at the top which reduces stalling.

Bottom line is if you trade in your triangular inside the backstay main for something more aggressive, you will go faster and heel less, while reducing weather helm (details in Offshore Cruising Encyclopedia).

A detail from the previous photo. Notice the telltales on the upper two battens. The top telltale is slightly stalled because there is not enough twist for these conditions, but otherwise the sail is looking good. Race boat pressure has taught sailmakers how to build square headed mains now which twist perfectly and have a better planform for even less induced drag and better driving force.

The square headed mains on the RC44s are a good example. Take a look at the twist required sailing to windward.

We could not come close to this with Beowulf’s sails. This is a much faster, and by reason of the reduced induced drag, more comfortable, cruising sail shape.

This year we have noticed quite a few cruising cats with square headed mains.

So we are assuming the sail hoisting issues, with the required top batten at its acute angle, have been solved. If we were buying sails today and could fit a square headed main we would certainly do so.

The conventional shape. Slow, heaps of induced drag, more heel, less comfortable.