Ask Sail: Do Square-Top Mains Make a Difference?

Publish date:
Square-top mains are better for multiple reasons

Square-top mains are better for multiple reasons

Q: I’ve been watching the most recent America’s Cup down in Auckland, which has got me thinking about technology and sails. My question is, how much difference do square-top mains, like those used aboard the AC75 mononulls, really make? In the America’s Cup, obviously every fraction of boat speed counts. But what about on a cruising monohull or Wednesday night beer-can racer? Would that little bit of extra sail area up high be even noticeable? — Mike Stella, 

Brian Hancock Replies

The square top makes a huge difference not only because of the additional sail area, but because of the overall geometry of the sail. You don’t see rudders shaped like triangles, because that would be very inefficient. Same thing with keels and mains. The top third of most mainsails is quite inefficient because of the short chord length, i.e., the distance from the luff to the leech. The resulting lack of power is especially problematic because there is more wind aloft than there is at deck level. Water creates drag on any passing breeze, so the farther away from the water the wind is the faster it is. This in turn means not having a square-top main results in failing to take full advantage of whatever breeze you may have. The problem is the backstay. You can’t have a true square-top main if you have a single backstay. Multihulls can get away without backstays because they can spread their shrouds out wide to support the mast. Not so with a monohull. So you usually end up with a conventional mast, a pesky single backstay and a triangular-shaped mainsail.

Got a question for our experts? Send it to



11th Hour Christens Two IMOCAs, Hits a Snag

This week has been a big one for the American-founded, sustainability-centric ocean racing team 11th Hour Racing. In addition to christening their two new boats, the team also took them out for a quick test ride—against some of the most intense IMOCA 60 skippers in the world. more


Clewless in the Pacific

Squalls are well known to sailors who cruise the middle Latitudes. Eventually, you become complacent to their bluster. But squalls vary in magnitude, and while crossing from Tahiti to Oahu, our 47ft Custom Stevens sloop paid the price for carrying too much canvass as we were more


SAIL’s Nigel Calder Talks Electrical Systems at Trawlerfest Baltimore

At the upcoming Trawlerfest Baltimore, set for Sept. 29-Oct. 3, SAIL magazine regular contributor Nigel Calder will give the low down on electrical systems as part of the show’s seminar series.  The talk will be Saturday, October 2 at 9am. Electrical systems are now the number more


Bitter End Yacht Club Announces Reopening

Four years after being decimated by Hurricanes Irma and Maria, the Bitter End Yacht Club is set to reopen for the Winter 2022 season. Hailed as one of the best anchorages in the Caribbean and built by sailors, for sailors, this island outpost in the BVI has been a favorite with more


Cruising: Bluewater Pollywogs

Bluewater sailing is 25 percent actually sailing and 75 percent learning how to live on a boat at sea, in constant motion and with no chance to get off the roller coaster. I cannot over-emphasize how difficult normal daily functions become at sea, even on nice, calm days. more


Refurbishing Shirley Rose: Part 2

If you missed the first installment, click here. Thankfully, the deck and cockpit of my decades-old Santana 27, Shirley Rose, were in pretty good shape. The balsa core, in particular, was for the most part nice and solid. Nonetheless, there was still a fair bit of work to do. more


Orca Encounters on the Rise

This week’s confrontation between a pod of orcas and the Nauticat 44 ketch Tuuletar which left the boat rudderless is just the latest in a string of encounters with orcas off the coast of the Iberian Peninsula. In fact, over 50 of these encounters have been reported, half of more


DIY: an Antique Nav Station

Ever since the advent of GPS, I have not found much use for the chart table on my schooner Britannia. Most of our passagemaking navigation is done on a Raymarine multifunction display on the helm pod, which is then transferred to a paper chart on the saloon table roughly every more