harryproa/articles/ About 'U'

Mad About 'U'

Article by Rob Denney
Portions of this article have previously appeared in
the Multihulls Magazine and at http://www.schachtdesign.com


CNB 64AeroRig	Birth of an Idea. A couple of years ago I heard about a development in cruising rigs known as the AeroRig. Consisting of an unstayed carbon mast, with the boom extending forward to the tack of the headsail, this looked to me like a breakthrough in rig handling technology. To determine whether it was as good as it looked, I built one and installed it on a 5m bridge deck catamaran. It was every bit as good as it should have been and I decided to market it in Australia as the EasyRig. I wrote an article about it which duly appeared in most of the local yachting magazines. The response was huge. Overwhelmingly, the inquiry's were positive and indicated that there are a lot of sailors who are less than happy with current rig technology. Generally speaking these are cruising oriented, frequently with wives and kids to consider. There were, however, a number of very negative responses. Some of these were expected, such as those from metal mast and fittings manufacturers. However, there were also a few which were totally unexpected, such as designers and builders who describe themselves with terms such as "innovative" and "leading edge" who without even coming for a test sail or seeing the prototype were extremely disparaging. I corresponded with a couple of these to point out the errors in their thinking and to invite them for a sail. When the correspondence deteriorated to the level of a couple of schoolboys comparing the size of their willies, I gave up. The third group of negatives were performance oriented yachties who, generally speaking were competent sailors but unconvinced that the savings in man power and weight were worth the loss of rig control and the potential for extras. I tended to agree with them, but the longer I thought about it, the more I considered that a racing version might work. The trick was not to replace a conventional rig with an EasyRig which meant that all the beefing up and dead weight was still being carried, but to look hard at the EasyRig, and design and build a boat that would make the most of these benefits.
The Northrop Alpha. Circa 1935.	Airplanes haven't used wires or struts to support their airfoils since the early 1930's. Primagaz at speed. Primagaz formerly held the Best Day's Run record of 534 miles. 18m x 17m x 6 ton trimaran. The "State of the Art". The relevant advantages of the EasyRig for racing are its ease of handling and concentrated loads (all loads are taken by the two bearings) resulting in serious weight reduction.It was obvious that this approach would not work with the rules restricted boats, which eliminated all the monohulls, where even the "unrestricted" classes still require a book of rules. Consequently, I looked at multihulls, where the only rules are safety related and there are a number of designers who have drawn flat out racers. Most of these are of trailerable size, the exception being the Formula 40. I started with the trimaran concept because an essential requirement is to have enough bury (distance between deck and bottom bearings) which was not possible on a cat unless there was a rig in each hull, a concept that I liked and have played with but as it would almost double the cost of the rigs, it was unacceptable. Racing multihulls have made incredible leaps in speed and reliability over the last decade, although not in Australia where six of the seven fastest are over 10 years old. However, speeds have reached a weight related plateau. Even with all the exciting new materials, designers are constricted by the surface area of boat, plus the structure to hold it together. The minimum requirement for a trimaran is three hulls and two beams, all more or less the same length. The hulls have a minimum requirement to keep out the water, and in the case of the main hull, also resist the fore and aft rig loads, which on modern rigs with huge mainsail roaches and tight forestays are enormous. The beams support the rig sideways, and when two hulls are flying, support the weight of the boat. The floats and beams resist the enormous twisting loads generated by a mast well to windward trying to depress the leeward bow. Catamarans are theoretically better off, because they only have two hulls, however, the structural weight required to support the enormous rigging loads generated by a mast sitting half way along a beam mean they are quite similar.The sheer area of these components mean that, for example, an 18m tri is going to displace a minimum of 5 tons, and a 7m tri is going to be doing well to come in under 600 kg. Both then have the same problem. They achieve enormous righting moment, almost to the point of becoming square, and limited only by difficulties in tacking inherent in becoming any wider. They then have to apply enough power to utilize the righting moment.
Primagaz formerly held the Best Day's Run record of 534 miles. 18m x 17m x 6 ton trimaran.	The current crop of 18m offshore tris have masts 30m high (limited now by the rules).However, the spiral of increased power leading to increased righting moment to increased weight and on to increased power has a number of drawbacks.The worst of these is cost. As rig size increases, the cost of all the components (sails, spars, rigging and fittings) rises exponentially, and as the strength required to support the extra power at minimum weight increases, the materials volume and hence cost increases. The increase in rig size also means an increase in the difficulty and cost of controlling it on a small base. Larger winches, more wires, more purchases, and frequently more crew to ensure it is all sailed at peak performance. A second, less obvious drawback is that as soon as a fast boat becomes powered up, the apparent wind increases and moves forward, causing the changeover from powered up to overpowered to occur earlier than for conventional craft. Primagaz sails at 8 knots with 5 knots of true breeze and at 24 knots in 10 knots of true breeze. These give apparent winds of 9.5 knots and 26 knots respectively, at a time when a conventional boat still has it's #1 genoa on and the crew sitting to leeward! Primagaz is powerful enough to fly two hulls in not much more than a calm. Consequently, for almost all of the time she is sailing to windward, she is overpowered and dragging around a huge amount of unused mast and rigging.
	Reversing the Spiral. The problems outlined above (particularly the cost) have interested me for some time, and I have spent a number of quiet watches pondering how to reverse the spiral. That is, have less boat and less drag requiring less power, resulting in less boat requiring less power to go faster. This Less is More approach is against all conventional logic (particularly of those who benefit from selling more), but worth investigating. The first unnecessary thing was all the wires holding the mast up. Airplanes abandoned this approach very early in their development for extremely good reasons. Namely, less drag, and as long as the base of the wing or mast could be sufficiently well supported, the diameter and weight need not be huge. The drawback of this approach is performance. An unstayed rig is not as efficient as one that is rigid, all else being equal. To make all else unequal, it is necessary to reduce weight and drag. Drag by using a pocket luff on a rotating wing section mast and eliminating wires, spreaders, sail track, external halyards and mast fittings. Weight by using a carbon mast and the new ultra strong See Tuff sailcloth. This has the added advantage of being transparent, enabling the rig to sit right on the deck. The savings resulted in a rig that is considerably lighter and cheaper than an alloy extrusion and all the fittings and wires required to hold it up. 26 sq. m of sail area, including carbon battens: 3 kg. 9m mast and bearings: 13 kg, and the box section boom: 10 kg. If the mast flex is known and the sails cut accordingly, a bar tight forestay becomes less necessary and there is no need for all the winches and associated muscle required to achieve it.
The 5m prototype. Click to enlarge.	If the boom is extended forward of the mast with the headsail tack attached to it's forward end, we have a balanced rig with all the loads contained by the mast and boom, and only a single purchase mainsheet required to trim both sails. This eliminates the heavy deck gear and the expensive, in terms of labor, material and weight, beefing up required to reinforce it. Without the wires and the need to attach them to something, the windward hull and beams of the trimaran looked superfluous. Why carry all that weight and windage when it is only working for half the time? Lop them off and keep the leeward side to leeward on both tacks. Then reduce the huge twisting loads on the leeward beams by putting the rig in the leeward float. With an all up rig weight of 26 kg, the righting moment loss was more than offset by the weight saved. The middle hull now had no rig loads and low sea loads so it only needed to be big enough to fulfill Category 2 accommodation requirements: headroom 1.4 m over 0.5 sq. m, 1.8m bunks, toilet, cooker, 5% crash bulkheads, etc. Draw these and enclose them with a minimum surface hull which would go in both directions and when sailed properly, would be either skimming the water or airborne. The minimum size this could be done in was about 5m long, 600 mm wide and 1.4m high in the center. Ugly, but within the rules. For warm water, short course sailing on a small boat, it appeared to be extravagant, given that the bunks would seldom be used while racing. We then slung waterproof bunks under the trampoline, accessible from the weather hull. These are very comfortable and reduced the size of the hull to 2m long x 1.4 high x .75 beam. Even uglier, but minimal: 7 sq. m of surface area compared to 18 previously, and at least 30 for a conventional hull with accommodations. The finished float weighs 10 kg. The float in the pictures is an interim version which is being replaced. So the minimum boat possible was achieved: A Pacific proa with an Easy Rig.
	Proas & Cons. Why would anyone build a proa? If the not inconsiderable problems relating to a boat which goes both ways can be overcome, it is the minimum boat possible in terms of materials and sailing stresses, consequently it is potentially the cheapest, lightest and fastest. The problems are:
The 5m prototype. Click to enlarge.	· First, because there is no hull to leeward of the rig, crew weight, water ballast and judicious use of the sheet and tiller are all that prevents capsize. · Second, it always has the same hull to windward, so it requires a whole different approach to sailing. You don't tack or jibe, you shunt. That is, bear away or luff up to a reach, reverse the rig, steering and centerboard and take off in the other direction. Diabolically tricky unless everything has been designed accordingly, when it is easier than tacking, although not as efficient because you lose the direct to windward gain associated with tacking. · Third, it has to go in both directions, so the hulls, rig, steering and leeway preventer all have to go both ways.
	There have been almost as many solutions to these problems as there have been proas, which, admittedly is not many! Before proceeding with a large proa based on the above theories , I built a 5m prototype, primarily to test the balance of the rig and the shunting/steering/leeway conundrum. A lot of things were tried and abandoned, always tending towards simplicity. The final result works, and is almost idiot proof. The next step was the absolute minimum boat in which a competent, hardy crew could venture offshore. U is 7.5m long (minimum for Brisbane-Gladstone), 5m wide, and weighs 130 kg plus 80 kg of Cat 2 gear, ex crew. Unladen, U is 5% shorter than Cogito (the lightest, most technically advanced C Class cat yet, and winner of the last Little America's Cup), 23% lighter, has 5% less sail and is 25% wider. A little more money, and this could be reduced to 100 kg plus gear. A little more again (spent on stress analysis and testing) and reduce the specification from offshore racer to C Class cat and 86 kg is possible. This is half the weight of Cogito, in a class where 22 kg is worth a minute per mile over the 20 mile course and a huge winning margin is 10 minutes. True, U does not have a high tech solid wing, but it is built for Category 2 racing, so it is probably better to compare it with the Farrier 25C tri at 500 kg or the Grainger Velocity 7 cat at 800 kg. A fairly conclusive indication that the weight savings of an EasyRig are not only in the rig. Innovative Solutions How have we solved the problems? The capsize problem was easy. Keep the rig small, displacement low, and all non-rig weight to windward. If it is overpowered, the windward hull will lift a long way before it's weight is overcome by the weight of the rig. Static tests without crew indicate the point of balance is 70 degrees from the vertical. Add crew and it will be even higher. At this angle of heel, the breeze is blowing almost directly across the sails and not exerting much heeling force. If the trampoline is fairly porous, it would take a severe gust to capsize the boat, and this "should" happen fairly slowly. The first time we flew a hull in a big breeze in the 5m boat, the wind got under the sailcloth trampoline and flicked it over quickly enough to snap the mast. If it does go all the way over, the buoyant mast will not allow it past 90 degrees and another advantage of the EasyRig comes into play. The front of the buoyant boom is lifted, submerging the aft end and flicking the boat upright. This works on the 5m proa in calm water. It will be interesting, but hopefully never necessary, to try it at sea in a gale.
"U" sailing in a light breeze. Click to enlarge.	Having all the weight to windward poses a potential capsize the wrong way problem if you are caught aback. Because the rig is balanced and only has one lightly loaded sheet, the entire rig weathercocks, and you sit quietly until things are sorted out. The other potential capsize mode is stern over bow. The rig is so low, and the main hull so buoyant, that the chances of this are low, but still exist. Shunting is a lot of fun, until the bugs are worked out, when it becomes easier than tacking or gybing. The requirements are reversible everything! The rig is easy. Release the sheet, the mainsail blows out to leeward, pull in the new sheet and off you go. Vastly easier on any boat, not just proas, than flapping sails, winches, changing sides etc. Leeway prevention required a new approach. The center of resistance must be aft of the mast. On the little boat we tried two dagger boards, using one at a time and daggerboards with rudders on the bottom. Neither worked satisfactorily, plus the likelihood of impact damage to daggerboards on offshore boats is very high. There are also the structural problems, weight and drag associated with a hole in the bottom of the boat. We threw the boards away, blocked up the holes and installed a leeboard. An ogive wing section which was mounted on a fore and aft tube allowing it to be slid fore and aft. Easily controlled and in the event of a hit, the lines pull through their cleats. When not sailing to windward it is lifted clear of the water, completely removing all drag. The rudders originally revolved through 360 degrees, based again on the 5m experience. This worked but had drawbacks: Getting the boat sailing in a straight line after a shunt when the windward hull is causing it to luff, the weight and drag of permanent rudders, collision damage (particularly to the bow rudder) and getting back on course if caught aback were all potential problems. Plus, I had to crawl into the very small ends of the hull with grinder and epoxy and bond in the rudder tubes. This evolved to rudders mounted on the ends of the hull with the bow rudder able to be inverted to get it out of the water. This reduced the weather helm, removed the vulnerable rudder and half the drag, was all external and very light. Both rudders, complete with all fixings and steering lines weighed 1.5 kg. I think we can improve the system further by using oar steering. This was tried on the little boat and was successful, but limited by the inability of the helmsman to move quickly to balance the boat. The oar is mounted on a rowlock on the aft beam. Consequently it does not enjoy much mechanical advantage. It is only used to correct the course, the rest of the time it is held clear of the water. The hull is long and skinny, and the leeboard and sail balance infinitely adjustable so it should not be used often. Until either system proves superior, we will play with both. Meanwhile the oar serves as auxiliary power. The steering oar has the same theoretical drawbacks as the leeboard; that surface piercing foils are inefficient. True, but the rudders and centerboards on any powered up multi are clear of the surface more often than not, so the difference is minimal. The advantages of weight, drag, cost and wetted surface saved, structure eliminated and safety are enormous. With the oar, the boat can be sculled in light air or if caught aback. Being able to paddle out of trouble is a welcome relief on a proa! Shunting is simple. Bear away and release the lightly loaded mainsheet, release the leeboard line, and pull it aft (2 m of unloaded rope), flip the 2 kg oar from one side of the trampoline deck to the other, or pull a string to lift one rudder, and a second string to lower the new one, and pull in 2.5m of new lightly loaded sheet. With practice, the boat rounds up to hard on the wind at the same time as the sheet is fully trimmed. No one has had to change places, sail flapping is minimal, no winching; easy. With practice it is possible to go places that conventional boats can't go, such as slowly short tacking between two rows of boats in a marina. The other problem was designing hulls that were efficient in both directions. I designed a bow and repeated it. Not strictly correct according to the theorists, but in reality, for a fast, ultra light machine, the hull shape should not be too critical as long as it is fair. Because the boat is so light, we decided against traditional semi circular underwater sections. They would have resulted in a hull which was too narrow (400 mm) to crawl inside, and far too sensitive to weight alterations. Instead we put a flat bottom on it in the hope that it would plane. The wetted surface is 3.6 sq. m, less than that of a conventional trimaran, and the beam to length ratio is 1:16.
"U" somewhat broken. Click to enlarge.	The First Sail U was launched at Lake Samsonvale, a deserted lake north of Brisbane. This was fortunate as it proved impossible to steer with the oar, and the balance of the rig was so far out of whack that it was a struggle to sheet it in. Before the headsail could fill, the main had blown the stern around until the bow was head to wind. Admittedly, this was in 20 knots (silly, but once it was rigged, the temptation to try it was overwhelming), which made it difficult to experiment with sail and leeboard trim, much less the rudders, but the bottom line is that it did not work, not even a little bit. On the bright side, nothing major broke, the rig was stiffer than expected, the sails are gorgeous, it is very easy to scull with one oar (3 knots by GPS), and we discovered that the crew was able to swim a mile across the lake to get a dinghy to tow us back. The problems were some or all of the following:


Tangled & mangled "U" Click to enlarge if you must.	· Main too big compared to the headsail. The pocket luff on the main did not cause the center of effort to move forward as much as I had hoped and the top of the mast did not lay off so the huge roach on the sail was working in much stronger winds than expected. · Center of resistance too far forward. The leeboard needs to be angled aft and the crew needs to sit towards the back. Difficult when everyone is worried about imminent capsize, and the strength of the trampoline net. This was exacerbated by the temporary nature of light weight experimental boats. There are no cleats or pulleys as you don't know where they are going to go. Consequently, everything is tied with bits of string which are not quick to adjust. · Excessive drag from the weather hull. The plan was/is for this to fly so there is no drag. This will require more movement from the crew than was anticipated.
All in all - a disaster. As it was the weekend, and the temptation was still great, I sticky backed a couple of patches on the main, sewed loops on and reefed it by 25%, making it into a masthead rig. This reduced the headsail/main ratio from 20:6 to 15:6. It worked a treat. The balance was good enough that I could steer by moving my body fore and aft or in and out. The oar steering worked and the rudders were feather light, although I did manage to break the (in retrospect) delicate hinge mechanism. The leeboard, which worked so well on the 5m version was a disappointment. It kept floating away from the hull, and then crashing back into it. The wake was almost nonexistent, except for a huge vortex off the leeboard when it was in float mode. Performance was good, relatively speaking. Shunting time was about 2 minutes and 50m lost to leeward, (less if it was done in the weeds at the lakes edge) tacking angle about 120 degrees and speed about 50% of wind speed. Good, relative to day 1! The sails were designed and built by Gary Martin Sails, but the dimensions were all mine, as was the estimate of the mast's stiffness. The sails are glued together from See Tuff, a lightweight transparent material , and are excellent, as were Gary's sails for the 5m prototype. His enthusiasm, knowledge and willingness to try new ideas, are very handy with projects such as this. Gary resisted the temptation to say "I told you so", and reduced the roach on the main and extended the headsail tack forward. Because SeeTuf is a film, there are no thread lines so this type of addition is relatively simple. I extended the boom by hose-clipping an old piece of dinghy mast to it, and trimmed the battens. I was perplexed by the behavior of the leeboard, so changed it to a "weatherboard" so I could see what was happening and to make adjustments easier. The board pivots fore and aft which is an easy solution and definitely works, but is probably not totally efficient due to increased tip losses. With both rudders up, I can steer within 10 degrees of course by tilting the weatherboard fore and aft. It is absolutely enthralling (to me, anyway) to observe the pressure differences, the flow over the board, and the transfer of loads over the asymmetric foil. I also built new rudders which were retractable and almost got around to painting and polishing the bottom of the weather hull. Importantly, I got patient and waited for a light air day. The rudders retracted, but did not turn, so I stuck with the oar. The rig balance was near perfect, and apart from the time taken to untie and retie all the strings, everything worked well. Shunting time was about 20 seconds and negligible loss to leeward, tacking angle about 90degrees and speed about wind speed. However, all boats are fast on their own in light air, so the next test is to find some competition, and some more breeze. Now that the practice has supported the theory (for a while, I thought it wasn't going to), it's time to get serious about tuning and destruction testing. If all goes well, I then need to install Category 2 accommodation at minimum weight, which should be interesting. I will keep you posted......... Why the odd name? A project such as this requires a lot of thinking and dreaming. This frequently occurred in the presence of my long suffering, ever supportive wife. She frequently asked "What are you thinking about?" I found it diplomatic to be able to answer "U, Dear".

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