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ProasRig Options - Schooner
Posted by on 03/02 at 09:21 AM
Cheers, perhaps the most famous Western proa, was schooner rigged. Since she was so successful, you might think that her rig had something to do with it, and you’d be right.
Though the schooner has several good points, the most important one as far as proas are concerned is the ability to vary the fore and aft CE (center of effort) by trimming the sails. This ability cannot be overstated enough, in my opinion. Proas are, by their nature, "rudder-challenged". That is, the necessity of shunting makes operating a rudder a problem. You may think that I am talking about the problem of shifting the rudder from one end to the other during each shunt. Though this is an issue, twin rudders, perhaps counter-rotating, at each end of the hull, can handily solve this problem. No, the bigger problem is that a proa must come to a complete and dead stop for each and every shunt.
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
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:
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
Schooner NegativesOK, schooners make proas easy to steer, what's the down side? CostSchooners 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
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. HandlingThough 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 AlternativesSchooners 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 SparsCheers 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
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 RigsIf 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:
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