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Balanced Lugsail Rig on a Multihull

QUESTION: I am interested in the W17 concept but want a cruising boat with shorter spars. I particularly like the Balanced Lugsail Rig and wondered if this could effectively be used on the W17? I consider its ease of tacking outweighs any slight loss of efficiency from having the sail distorted when it is pressed against the mast on one tack and in addition, the compensation from having some sail area forward of the mast, makes gybing far more gentle. The sail is also very efficient downwind with sheets eased. Your comments would be appreciated.—WS, Germany.

ANSWER:
This is a very traditional rig and I grew up sailing many small boats with such rigs back in the 50s. The main advantages are in its ease of handling, safety, and storage, plus, as you say, it's a good performer downwind. But its drag and relative inefficiency as an upwind sail does not really show up when matched with a traditional displacement monohull that has a top speed of say 5–6 knots, and this really makes it a rather poor companion to a multihull that 'demands' more aerodynamic efficiency to sail at speeds of 10 kt and above.

Let's look at the needs and attributes of a multihull, compared to what this rig offers. First of all, a multihull rarely sails directly 'downwind' as it's far more efficient to broad reach and 'tack' downwind, as the much higher boat speed can generally more than make up for the extra distance sailed. Also, due to the higher speeds typically achieved on a multihull, such a boat is effectively 'going up wind' far more often than even a regular Bermudan-rigged mono. Even reaching across the wind while travelling fast, the apparent wind will move so far forward that it appears to come from ahead and the sail will need to be hauled in closer and then, the long leading edge of a tall rig really starts to pay off when comparing 'lift' to aerodynamic 'drag'. It's true that the peak of the typical triangular sail is not very efficient, as the masthead is proportionally too large for the sail behind it. So the ideal is to have an elliptical head, offering comparatively reduced mast tip drag with more area—and the so-called fat-head rigs now lean in that direction. (Here's a sketch of something I dreamt up a few years back, but never tested ;-)

Now on to gybing concerns. Gybing on a trimaran is much easier and safer than on a mono. In most conditions, you can just crank in the main on a nearly centralized traveler, and push the helm over. The boom is controlled by the tight sheeting on the traveller and there is very little slamming and also very little heel due to the inherent high initial stability of a multihull. After the sail gybes, you simply let the traveller run out again on the new tack. A totally new experience after sailing a monohull. It's also done at high speed. In fact, you WANT to be going fast downwind when you gybe, as then the wind force in the sails is less than it would be if you were stationary or moving slowly.


One efficient cruising rig with a shorter mast and small yard that can work well on a multihull, is the Wharram Wingsail seen here. Here the mainsail has a large sleeve that goes around a plain, tubular mast and hauled up with a short yard. Simple and efficient, and typically used without a boom. The sail does not readily remove from the mast though, unless the sleeve were closed with an overlapped lacing or with somewhat unreliable Velcro.

But if a rig is truly sought that has spars not greater than the length of the boat, then the so-called Steilgaffel Rig that was astonishingly developed in the late 1920s for the J‑Class mono, would appear more suitable. This advanced design of gunter rig (see below) is fully battened for better sail shape control (required for higher speeds) and its peak is rounded to the nearly elliptical form that more recent tests have shown to be the most efficient. The rotating mast, laminated gaff and fittings can also be built by a do-it-yourselfer, so this reduces the cost of the rig compared to a rotating wing mast—that would typically be slightly more efficient again.


A drawing of this Steilgaffel gunter sail plan is available from Bernd Kohler for $25 as Bernd matches this rig to his plywood KD 650 catamaran, being as this rig can offer the drive, low drag, lift, and efficiency required for a boat with higher speed potential. Reefing of this sail is possible, but as this requires that the yard be lowered while the halyard still comes from the mast top, the top battcar loses that extra support to the mast, so the track must be strong, the car of high quality, and the yard well reinforced to accommodate this potentially high point load. A 2nd (lower) halyard might be an option to consider here.

So in conclusion, I'd say that the balanced lug sail and others like it, are just not able to do the job for a multihull, and will always add an unnecessary limit to its potential performance.

Mike —2012


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