Rig Options - Schooner

As any sailor knows, allowing a sailboat to come to a stop is allowing it to get out of control, because with no water flowing past, the rudder is rendered useless. All Western craft are fundamentally designed with the unspoken assumption that the craft is NEVER to come to a complete halt while sailing. When this does unintentionally occur, the boat is said to be "caught in irons" - a colorful expression that illustrates the Western sailor's dread of the situation.

So along comes the proa, a craft that must become "caught in irons" every time it tacks (I believe this is a fundamental objection that Western sailors have with the proa). Why would anyone sail a vessel that appears to become temporarily out-of-control every time it tacks?

The answer is that a well-designed proa does not NEED rudders, like almost all Western craft do. Proas steer very effectively with only their sails. When a sailing craft is sitting motionless in the water, the only foils that can create a steering force are the ones with fluid still flowing by them: the sails.

Air Rudders - Steering With Sails

Now back to the schooner. It is extremely simple to steers with the sails on a schooner-rigged proa. Sheet in the aft sail or ease the foresail and the boat heads up. Ease the aft sail or sheet in the foresail, and the boat falls off. A schooner sailor has two very large and effective air-rudders at his disposal, and these rudders work whether or not the boat is actually moving through the water.

Though Cheers had rudders, I believe it is entirely possible to sail a schooner-rigged proa with no rudders at all. Imagine the instant simplification this achieves! No rudders to build, or to shift around for each shunt. No rudders to catch weeds, or to hit bottom. Steering a schooner through a shunt is simplicity itself:

• Steer onto a reach, and release the sheets.
• The boat glides to a halt.
• Haul the booms around to the midway position.
• Sheet in the forward sail.
• As the boat accelerates and falls off, sheet in the aft sail.
• Adjust both sails to achieve the desired course.

Note that raising or lowering rudders is absent, as is moving a steering oar around, or even swiveling counter-rotating rudders around to face the opposite way.

Utilizing the steering capability of twin fore and aft rigs is an unusual and elegant solution to the proa rudder dilemma, but it won't give you the razor sharp steering control of a well-balanced rudder — not the best solution for close racing around the cans (not that any proa WOULD be a good solution).

Other Schooners Advantages

• The twin rigs may have a lower CE than the equivalent single-masted rig. This means the schooner can carry more sail area than the single-sticker.
• The sail area is divided into two smaller sails, which are more easily handled by a small crew.
• The twin masts can carry all manner of additional sails, such as spinnakers, screechers, mizzen staysails, even golliackers. The multitude of off-wind laundry capable of being flown is what makes schooners such legendary downwind sailors.
• Flexible reefing options again make the schooner easy to balance, and it makes the proa easy to steer.

Schooner Negatives

OK, schooners make proas easy to steer, what's the down side?

Cost

Schooners require two masts, two of everything. They are considerably more time-consuming and expensive to build. However, if you can subtract the cost of rudders, they pay for themselves...

Efficiency

Mbuli - the CLC proa designed by John Harris.

Splitting the sail area up into smaller sails with more leading edges and wing tips reduces the over-all efficiency of the rig. Putting the aft sail directly in the exhaust of the forward one is also not such a great idea if one is seeking maximum efficiency, and L/D. Exactly how much efficiency is lost compared to a sloop is a matter of debate. I have heard 3% batted about, though it could be much greater.

(According to Tom Speer, a twin masted, or biplane rig can be as efficient as a single masted rig of the same area if the twin masts are kept as tall as the single mast, so that the sails become extremely narrow, high aspect-ratio wings. Two narrow wings have less induced drag than a single, wider wing! Unfortunately, this approach eliminates one of the schooner's main virtues; that of having lower masts and a lower CE).

It appears that the amount of separation between main sails is important, though I haven't been able to locate any data or testing on the subject. Sidewinder, the Kelsall designed Atlantic proa was schooner rigged and notorious for the foresail back-winding the aft sail. The more separation between the two sails, the better.

Handling

Though a schooner will steer a proa easily, if considered separately from the steering aspect, a schooner is a bit more difficult to handle than a sloop, because there are two mainsheets, and trimming the two sails is more difficult than trimming the main and jib of a sloop, at least while close-hauled. This must be weighed against the size of the various sails, so it may be that a schooner is easier to trim than a sloop if the sloop has large genoas that require big, expensive winches.

Many schooners will fly a jib from the foremast, and if that is the case, then it becomes even more tedious to shunt than a sloop, though a schooner could easily get by without the jib if short tacking was the order of the day, and only set the staysails when longer tacks are anticipated.

Schooner Alternatives

Schooners on proas need not follow the traditional Western rig in all the details, of course. Why not a crab-claw schooner? Or a Gibbons schooner?

Free-Standing Spars

Cheers used free-standing masts instead of stays, which greatly simplified the rigging. Freestanding spars also eliminate the problem of mast support in the event of getting back-winded.

Balestron booms

Mega proa concept by Michael Schacht and Dave Culp. Note the free-standing balestron schooner rig.

If the balestron boom can tame the sloop for use on a proa, than why not the schooner? The balestron allows a jib to be flown from each mast, yet without the jib's attendant bother. The balestron is also aerodynamically balanced, which greatly reduces the pull on the mainsheet. Low mainsheet loads means that the mainsheet can be a single purchase and is easily weather-cocked around 180 degrees during a shunt.

Lug Rigs

If you've seen the elegant luggers by Nigel Irens - Roxane and Romilly - you can appreciate the beauty and and utility of this rig. An excellent cruising rig for many reasons on monos, the lug offers these potential benefits to the schooner proa:

• The lug is aerodynamically balanced with a portion of its sail area ahead of the mast. Balance dramatically reduces sheet loads so that no purchase is required on the sheets. It is a low-tech yet highly effective alternative to the balestron rig.
• Thanks to the vanging action of the sail area ahead of the mast, the rig needs no cunningham.
• The rig can have a better aerodynamic plan form than a leg-o-mutton, and since it has no large mast section at the leading edge, will enjoy less leading edge turbulence.
• Lugs are compact rigs, with short mast and spars. Relatively low loads are the result.
• The sail area is kept low, with less overturning moment created.

Comments

• Having turned our 17 ft Klepper folding kayak into a yawl with an outrigger, and having found it a blessing, I can see that a twin-mast proa must be a very good way of getting the best out of the sail area, without undue heeling problems, or loads.

  I can comment on the spacing of the masts, though, that on aircraft the general rule is that there should be at least 2 x the chord (width) of the main wing distance between the trailing edge of the forward wing and the leading edge of the rear, no matter if the forward wing is the main wing, or if the rear wing is the main.

  Sadly the longer the wings are the more do they affect each other, too, as the maximum lift goes up with span length (in our case mast height).

  So in essence, the masts should be as far apart as technically is possible !

  Yours,

  Tord S Eriksson

  Posted by Tord S Eriksson  on  03/13  at  10:34 PM