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I write this as we sail along, midway through a 2000 mile trade wind sail between the Cape Verdes and Tobago - which seems like the appropriate place to write about downwind sailing!

Previously I wrote about the need for boom vangs and barber haulers when sailing offwind; in this article I'll concentrate on headsails and spinnakers. Surprisingly we haven't been using the spinnaker that much. So far it's just been too rough and windy.

Instead we have goose-winged and boomed out the headsail, and have strapped down the reefed mainsail. We don't need the long booming out pole that a monohull would use, instead we are using a short (1.5m) pole attached to the top of a raised daggerboard. We need a pole because Rush has a masthead rig and a big genoa with a long foot.

My similar length Eclipse has a fractional rig and 110% genoa so we can goose-wing without using a pole, as the clew always remains inside the gunwale. If you need to use a pole, the important thing is to have it supported independently from the genoa by a combination of topping lift and fore and aft guys. Only after it's all set up do you unroll the genoa. Of course, if you don't have daggerboards you can always fit a U bolt as the pole attachment point on the gunwale somewhere near amidships.

Even if you normally use a spinnaker, in very light winds you may still find that you will actually sail faster using a masthead genoa/drifter/screecher either goose-winged or set from one bow, rather than a much larger spinnaker. That's because of the apparent wind, or rather the lack of it. It's easy to have a boat speed of 5-6 knots in 8 knots of true wind. Thus there is only 2-3 knots of wind over the deck, and so, unless you steer very precisely (something an auto pilot can't do), the wind angle will vary rapidly which means constant sail trimming to prevent the spinnaker from collapsing. A screecher, on the other hand, will just flap, yet still provide forward drive.

Having said all that, the dream off wind sail is of course the spinnaker.

Most cruisers are put off using spinnakers because of the difficulties they have experienced on monohulls. These difficulties are in part due to the narrow, heeling foredeck, but mainly because of the complications caused by the spinnaker pole. Of course that's why cruising chutes have become popular on cruising monohulls. Even after the spinnaker or cruising chute is successfully set and drawing well, there's still the ever present danger of broaching.

Fortunately a multihull and, especially, a catamaran have none of these problems. Even so, there are a few simple things that make spinnaker sailing easier and more enjoyable.

First you have to decide what sort of spinnaker to have, as there are two distinct types. An asymmetric spinnaker is bigger and has a more efficient shape than a conventional spinnaker, so is favoured by most racing boats. However, it is much harder to use and, especially, to gybe than a conventional one. Over the years I've raced many times with a conventional spinnaker against competition using asymmetrics. Yet it has been only on rare occasions that the asymmetrics have been significantly faster. So my recommendation is that cruisers (especially those with slower boats) use a conventional spinnaker.

Your next decision is how you will hoist and, more important, lower the sail. You can use a spi squeezer to do both, but personally I don't like the spi squeezer as I find it then takes longer to hoist the sail (which isn't good when racing). Also it is very easy to get all the ropes tangled. Lowering is usually straightforward, providing you let the sheets fly first. So I prefer to quickly hoist the sail behind the mainsail (if you needed to winch the halyard you were too slow) and then use a "float drop" or very occasionally "trip" the guy before lowering it. A webbing loop sewn into the foot will give you something secure to grab.

It is OK to keep the spinnaker in its bag until you need it, but don't then hoist it straight from the bag. Instead, stuff it under a triangular canvas panel that's been tied to the forward net (it's easier to tie down a triangle than a rectangle). You'll find it much easier to hoist and stow from there. As I said last time, once the (conventional) spinnaker is set, keep the clews level and "if in doubt let it out". It's very easy to over sheet the spinnaker. If you do, it will still look full, but will provide little forward drive.

Generally, the more wind the easier it is to fly the spinnaker. Keeping the apparent wind high is one reason why it's better not to sail dead down wind; even cruising boats usually reach their destination quickest by sailing at 165-170 deg to the true wind. If you are sailing a fast racing boat, you will be tacking downwind, in which case you don't want to let the apparent wind come aft of the beam until you become overpowered. The simplest and best way to check the apparent wind angle is to use tell-tales tied to the rigging (video tape works great). They are better than a masthead vane or electronic instruments because they are at the spinnaker trimmer's eyelevel.

You'll also find it's VERY much easier to sail under spinnaker with the mainsail lowered. You'll be ½ knot slower, but the auto pilot can cope. It's a great way to sail, but remember that you need to unroll the genoa and/or re-hoist the mainsail before lowering the spinnaker. Gybing a conventional spinnaker is very easy, in fact it's usually harder to gybe the mainsail than the spinnaker. All you need to do is slowly bear off onto a dead run and at the same time pull in the slack in the lazy sheet and guy. Then just bear of a bit more onto the new gybe and as you do so ease the old sheet and guy. The spinnaker should stay full all the time. At the same time, of course, you would also need to gybe the mainsail.

Simplifying gybing is thus another good reason for sailing downwind with the mainsail lowered. In comparison, gybing an asymmetric is trickier. It's best to have the asymmetric mounted on a short bowsprit, as that way the spinnaker is kept well clear of the forestay. Then you can gybe it as if you were tacking a jib. Mind you it's still not that easy as you'll have a lot of sheet to pull in (ball bearing sheet blocks will help). If the spinnaker is tacked straight onto the forward beam then you will have to take the lazy sheet round the outside of forestay and spinnaker and let it fly forward as you gybe. Otherwise there won't be room for the spinnaker to get past the forestay. You'll need longer sheets, and unless you are very fast at pulling it all in there's a good chance the sheet will go under a hull.

On my 10m Eclipse and 9m Sagitta I used a conventional spinnaker pole as a bowsprit when I used an asymmetric or a screecher. In use it clipped to a U bolt on the bridgedeck front and overhung the netting beam about 1m, suitably stayed of course. When not in use it stowed neatly across the aft edge of the trampoline.

Maybe you are now convinced that you want a new spinnaker. So here are some basic guide lines to help you order the right sail:

A conventional spinnaker will have the leeches approximately the same length as the forestay, with a foot approximately 80% of LOA, giving an area of approximately 63% x LOA x forestay length. An asymmetric spinnaker will be about 10% larger. That's just a guide, obviously you need to discuss it with your designer/builder and sail maker. I'd recommend a tri radial cut as it makes a much better reaching sail. At the very least get one with a radial head.

People like spinnakers to be nice and colourful, but there is actually a logic to choosing the colour scheme. To start with, I always have the outer leech panels in different colours, with the foot a different colour again. That makes it much easier to avoid twists when following down the leeches. If you use the spinnaker at night or in bright sun you want a good contrast between the first 2 leech panels, so that you can see the leech collapsing. Thus I use a red (green) panel on the leech itself and then a white panel. I usually use black along the foot.

I have tried buying cheap sails but have found that they are often not well cut. So not only do they reduce the maximum possible drive, but more important they can also be much more unstable. So I much prefer to spend the extra and get sails from a multihull specialist; Dolphin Sails in the UK and Dave Calvert in the USA are my current favourites.

You'll also need some ropes to control your new sail. Sheets need to be at least LOA + BOA in length; the guys can be a bit less. You need longer sheets if you have an asymmetric spinnaker, but obviously the tack strop only needs to be long enough to go from the pole end to the spinnaker stowage area. 6-8mm sheets are suitable for small boats (under 9m) while 8-10 is OK for boats under 12m. I recommend wearing gloves when sailing under spinnaker.

Finally, remember that sailing under spinnaker is potentially dangerous. NEVER cleat the spinnaker sheet when close reaching in a gusty wind. Furthermore, the spinnaker trimmer mustn't be distracted by joining in discussions of race tactics or by being offered drinks or food.

Back to my transatlantic: The article is finished, we now have the spinnaker up, there's bright sunshine and a small swell, we have a steady 9 knots boat speed, with not a hand on sheet or helm - it's the only way to sail!