Hakan,

I have been talking about pure upwind and downwind course as well.

Naturally I also included the more general cases were the crew overstands the mark or a windshift cause them to sail below their highest upwind pointing angle. This latter situation is indeed when the sloop rig is even more favoured. I even included a wide range of sailing craft in my discussion, ranging from slow sailboats to fast landyachts. Basically the comments I made cover the whole spectrum.

Even on a windward-leeward course it is still true that a maxed out sloop rig will be faster then a maxed out uni-rig even on a perfect upwind-downwind course.

Now you are adding a spinnaker to both boats, in addition to a perfect course. Again this reduces the difference between both setups but still the maxed out sloop rig will be faster then the maxed out uni-rig although not by much. Roughly 2 minutes per hour racing windward-leeward. Also, how does adding a spinnaker differ from adding a very large overlapping jib ? Not by very much I say. So basically we all already know how the principles underlaying the sloop rig will make any given boat faster. The ORMA 60 and Ricks Hooter rigs are an intermediate state between this spinnaker and a 25 % jib. The Genua is so too, although more closely related to an actual high aspect jib.

Now Steward goes one step further and introduces the solid wing sails to the mix. Now this the first serious counterargument we had in the whole thread. It is indeed a good suggestion. So how do I disproof it ? Well, as good as all solid wing sails have slots because they found that deviding the total sail area in more narrow slips with slots between them is most efficient in creating drive. The sloop setup of two sails with a slot between them is a rather crude approximation of that, but nevertheless it is. As such the slotted solid wing sails have more in common with sloop rigs then pure uni-rigs (non slotted), it is just that the sloop principles are implemented in a slightly different way.

But there are exceptions. Think of Macquarie Innovation. That craft uses a low aspect solid wing wingsail without any slots; so thatsolid wing may be regarded as a close relative of the pure uni-rig. Does this disproof my comments ? Not really as I had already stated in an earlier posting that very fast moving sail craft like landyachts prevent the effective use of a jib sail because of their speed. For the same reason a slotted solid wing sail will be disadvantaged. I also gave speeds and angle of attacks that would lead to such a situation. Macquarie innovation is doing roughly 50 knots in 30 knots of wind and as such it close to the speed range of landyachts and shares the same angle of attacks. The latter are the real reason that a jib can not be used effectively.

Our soft rig beach catamarans however are nowhere near those speeds and their significantly larger angle of attacts allow the effective use of jibs to increase performance. The same applies to the effective use of spinnakers on our beach cats. On even slower moving sail craft adding a second mast (rig) will improved performance because the angle of attacks are even larger there.

There are also some interesting scientific principles underlaying the sloop rig. For example the jib will produce just as much drive per square meter as the mainsail does but does so at an significantly lower "angle of attack" then it would if it were the only sail fitted. Summerized, it is surprisingly more efficient when it is added to an uni-rig then would be expected. This is because of the interaction between the mainsail and the jib. A compounding effect is that other limits keep the uni-rigs pointing angle rather large and as such it can not make full use of losing the jib. Basically it is the interaction between these two sails (small slot) that makes the whole perform better then what you initially would expect by looking at each sail on its own. If this slot were to be increased to say 2 meters or more then this interation will be lost and with it most of its advantage.

For more info on this read the books by Marchaj and the excellent articles by Arvel Gentry.


The sloop rigs have gotten a bad name over the last decade because of some boat designs and class rules that are made to favour the uni-rig. But this is undeserved. We only need to look at the ORMA 60 tris and 18 foot skiffs to see that a less restrictive sail area limit in the class rules (or none at all) will show the sloop rig to be performing better.

That is basically the whole story.

Wouter