Catamaran fundamentals : Downwind Sails: the Parasailor

Published on 01 october 2015 at 0h00

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No, the symmetrical spi isn’t dead! Sure, on board our multihulls gennakers sprout from the bowsprits, unfurling and furling in just a few seconds. Close-reaching or with the wind on the beam, they work very well… but not quite so well beyond a broad reach. And this is where the wind usually blows from on our big trips! So the symmetrical spi has lost none of its magic. The Parasailor is simply and evolution: the same sail, but integrating a paraglider wing in its upper section. The idea is to stabilize the sail by creating lift. And it works well on monohulls with their spinnaker poles! On board our multihulls, the bows enable us to position the tack upwind, which is even better. Let’s have a look at how it works!
So how does it work? The upper third of the spi is opened by a gigantic kite wing. It’s a three-fold principle. It’s a question of helping the lift of the sail, of forcing it to spread out properly in a horizontal plane, and also to avoid it collapsing annoyingly (waves or other jolts), by evacuating the air, likely too much of which is stuck in the sail. That’s it for the theory, and it seems to be best adapted to “classic” monohulls. Heavier and generally slower downwind, they are frequently being pushed along when they sail. Not so in the case of multihulls, where the airflow over the spinnaker is almost always laminar, due to their higher speeds, and therefore their higher wind angle. One reason why the famous French sailor, Yves Parlier uses downwind sails with cell-construction… but oriented at 90° to the wing of our Parasailor and better adapted to our cruising multihulls.
We need to go offshore, with a few miles of clear water to run in. All the crew gets the sail ready. For now it’s securely stowed in the forward cockpit of our test boat, a Lagoon. On each side, two lines are prepared. One acts as a guy, passing through a block fixed at the extremity of the bow. The other is the standard sheet. So that’s responsible for the horizontal trimming, which is to say the angle of the sail in relation to the wind. In practice, the four lines are never in use at the time, as you would see on a big monohull. To windward, the guy is under load, but the sheet remains slack. To leeward, the sheet is the main line for adjustment. The guy is more of a downhaul. The setup is very easy, even for a crew unfamiliar with downwind sails. So here there’s no need for either a pole or a bowsprit. That’s the first advantage of a Parasailor: the relatively minimal amount of hardware required. We put in a reef. The aim of this is to encourage the maximum lift out of the headsail. The sock is quickly hoisted, thanks to a continuous line, slowed slightly by the wing. The spi isn’t completely out yet, but is already beginning to fill. Despite the inevitable weight of the wing and its hangers - compared to a traditional spinnaker, the Parasailor shows an undeniable willingness to fill, and remain filled! This behavior is especially noticeable in a ...

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