The Multi Purpose-Spinnaker

Of all the sails developed for the cruising sailor over the past 35-40 years, the multi-purpose spinnaker (or MP-S) is a sail that sits atop the “must have” list for anyone sailing outside the confines of their multi sharbor. 

The MP-S is an asymmetrical spinnaker with the luff longer than the leech. The way these sails are set means the tack of the sail is attached to the boat at all times, unlike conventional spinnakers. MP-S sails are light, large, powerful, and inexpensive. They take up little room for their size and are easy to set and douse. They are a boon to sailing in light to medium airs across the spectrum from 70 degrees to about 130-150 apparent wind angle, depending on a few variables.

The MP-S is often the difference between motoring home in light to moderate air or being able to sail sometimes at the same speed, or more, as motoring, without the engine noise and fumes and so can make for a fine end to a great day sailing.

In very light air, under about 5-7 knots true, the MPS can be carried surprisingly close to the wind, occasionally upwards of 50 degrees apparent wind angle with a bit of attention to steering. They will sail at 60 degrees readily and 70 degrees regularly.

In 10-15 knots of wind they make a fine addition to the inventory when sailing off the wind, deeper than a beam reach. I’ve sailed to Newport from Block Island many times broad reaching in a medium south westerly, with the MP-S set, the boat powered up and stable, (not rolling as with a genoa flapping uselessly behind the mainsail) and sailing fast.

The MP-S is made from lightweight nylon fabric and so can fill in very light wind. It is ideally suited for sailing in winds up to about 15 knots up to perhaps 20 knots true wind speed, depending on the boat hull shape and the degree to which the person steering wants to concentrate. When cruising, there comes a time when boat speed can be maintained and it is a lot more comfortable too, to douse the kite and unroll the headsail. This action also makes it a lot easier on the autopilot.

For boats up to around 33-34 feet and depending on the boat’s displacement, the MP-S is made from ¾ oz. nylon. For heavier/ longer boats (up to 50 feet), we use 1.5 oz. nylon. For even longer and/or heavier boats, we consider a combination of either strategic 2 plying (using two layers of material in high load areas) or 2.2 oz. nylon.

If you’re thinking about an MP-S, there are a few considerations in order to take the best advantage of this useful sail.

I am often asked if you need to have a spinnaker halyard to use the MP-S. Ideally yes, but it can be set on a second genoa halyard as long as some guidelines are followed. Because the genoa halyard is aft of the head stay, or ‘inside’ the fore triangle, the tack is ideally set inside the fore triangle too. In practice, this means the tack is set to a fitting that can often be the on the aft end of the head stay chain plate on the bow. This setup keeps the entire sail “inside” the fore triangle. Having the sail set thus means that it needs to be gybed inside the fore triangle too. As a practical matter for almost all family/weekend sailors, there is a dearth of spare hands so I simply pull the sock down over the sail, gybe the boat and hoist the sock on the new gybe.

If, on the other hand the mast has a true spinnaker halyard that is on top or “outside” the fore triangle, then the sail can be “tacked down” “outside” the head stay. But, this invites a couple of items to pay attention to…

Unless your boat has been designed within the past 10 years, there is a lot of “stuff” forward of the head stay at the deck level. This is most apparent in boats from between the 1960’s up to the late 1990’s. Take a look at the bow of your boat where the pulpit extends out over the end of the bow, there is an anchor and anchor roller, navigation lights, the base of the furler, and all sorts of stuff there, many with sharp edges. Setting an MP-S on the bow with all this hardware is nearly impossible without either breaking something or tearing the sail. It can be done, but needs attention to detail. An alternative that has become popular over the past several years is the retrofit bowsprit.

These are basically tubes of usually aluminum, but sometimes carbon, offered by most of the spar manufacturers in either kits or as semi-custom products. With a bowsprit, the tack of the sail can be located away from the bow and from the minefield of “stuff”. So how much bowsprit does one need? Not much.

To test how much bowsprit you need, you can take a boat hook, whisker pole, fishing rod, your son’s Laser mast top section or a similar 6-8 foot length of something straight and lay it on the deck and push it forward a couple of feet. Where the line, (the halyard, in fact, will serve nicely), from the masthead hits this and clears the bow rail, is all the length of bowsprit you need.

In terms of rigging, the sail needs a halyard, of course, and a tack line. Many folks use only one spinnaker sheet, but this means you need to re-lead the sheet each time you gybe. I think this becomes tiresome as you learn to benefit from the advantages of using the MP-S. It is common today for all the lines to lead aft to the cockpit, but the halyard for the MP-S need not do this. In fact, it is better if it is at the mast, since that is where you will be to connect the lines to the sail.

The sheets don’t need to be super thick or strong, in fact lighter is better, as the sail will not really get the same loads as the headsail or the mainsail sheets and the thicker they are then the heavier they will be when they get wet

Without doubt the sail ought to set in an ATN sock. This is the long grey sleeve like device into which the sail is “loaded” and which allows you to hoist the “sail” while still having it under control. One gets the sail on deck-in the sock, connects the tack halyard and sheets and when ready, you then hoist the sock. The reverse is true when lowering the sail. Ease the sheet, pull the sock down over the sail and if necessary you can tie the sock off at this point to attend to something more pressing. Or you can lower the sock down immediately.

Today there are a variety of free luff “Code Zero” furlers intended to be used in this application. The advantage is, of course, you can furl the sail without leaving the cockpit. This equipment is generally much more expensive relative to the ATN Sock.

If we measure our sailing value by the time spent actually sailing, the MP-S is a very high value sail. They are inexpensive per square foot, don’t take up much space, easily set and doused and cover a wide range of wind angles and speed. Once you have become comfortable shipmates with it, you will wonder how you got along without it.