Atlantic 47 MastFoil™ Updates
Ready for Prime Time
Our sailing trials last November showed us that there were several ways to make the MastFoil simpler to operate and also pointed to the need to fix a couple of design/construction bugs. To incorporate all the improvements, the best approach was to construct an entirely new MastFoil. This, plus some delays in obtaining imported electronics, pushed the re-launch date from February into March.
A47 #1, christened "Escape" by her owner, is now complete and sailing again. Having just returned from sailing her in Chile I am very pleased to report that all of the improvements are working as intended and the results are stunning.
What did we change and why?
The primary difference between the first and second generation MastFoil is that the foil chord length was increased and the flap chord length was decreased. Sailing trials in November showed us that finding the right trim angle for the foil and adjustable flap was not particularly intuitive. The reason for this is that as the flap angle is changed, the foil angle of attack also needs to be changed in order to get the most drive. How to simplify the trailing edge flap while retaining its clear benefit in providing additional drive to the MastFoil?
Research into various aerodynamic foil/flap combinations yielded an interesting find called a "Gurney flap". This is a fairly small trailing edge flap that is set at a position perpendicular to the foil surface. The flap sets up an eddy at the trailing edge of the foil which "fools" the airflow into behaving as if the foil is larger than it is and that it has more camber. This flap type is very small in relation to the main foil, which greatly simplifies the required flap control mechanism and also reduces the flap weight. In aircraft, the Gurney flap is typically fixed in a full on position. However, on a yacht where we need to reverse the foil to sail on the other tack the flap must be made to switch to the opposite side of the foil.
In experimenting with a full size mock up of the new foil section I discovered that if the Gurney flap was constructed as a "V" section, a very beneficial third flap position resulted. This is the neutral position, where there is essentially a partial flap deployed to both sides of the symmetrical foil section. The V section flap has the effect of making the foil respond very quickly to minor wind variations so that when in the free rotation mode the MastFoil feathers itself quickly and precisely into the wind. The new flap design has been named the V-Flap (TM), and a patent is pending.
A further benefit of the V-Flap configuration is that the center of pressure in the foil remains relatively constant. This permits the MastFoil axis of rotation to be located closer to the center of pressure, which considerably reduces the trimming (sheet) loads on the foil. By reducing the trim loads, a simpler device can be used to rotate the MastFoil, making the process of adjusting the foil much quicker.
Other changes to the original MastFoil design include an increase in mast stiffness and a reduction in the foil weight. These changes, while less visible, are also important contributors to the success and refinement of the whole MastFoil rig.
Operating the new MastFoil is really easy. The foils trim with little effort and can quickly be set in either free rotation (as you would when tied to the dock) or trim mode. The V-Flap has 3 positions: right, left and center. Typically when sailing the V-Flap is deployed to the windward side of the foil. During a tack it is switched over to the opposite side. This takes all of about two seconds and very little effort. If short tacking the V-Flap can just be left in the neutral center position.
The MastFoils are trimmed similarly to a sail in the sense that it is sheeted in until the leeward tell tales break, and then is eased off a bit. The main difference of course is that the rigid foil does not shake or otherwise complain when it is luffing, or pointed too close to the wind. When in doubt about how to trim, the best thing to do is just let the foil go. It will rotate to its neutral position into the wind, then sheet it in 15 to 20 degrees.
Overall the MastFoil rig is efficient and powerful. Upwind speed and tacking angles look to be equal to a conventional rig, although it is always hard to tell for sure without a comparable boat alongside for comparison. The helm is well balanced and steering is always easy. Tacking and gybing are simpler than ever.
One thing that stands out to me about the MastFoil rig is the way the boat tacks. Even the best sailing cats tend to hesitate when coming through a tack. As a conventionally rigged cat loses speed coming through the eye of the wind, the leech of the mainsail wants to weather cock the boat back into the wind thus slowing, or in some cases preventing, completion of the tack. Once through the tack the boat is often nearly stopped and in the process of getting going again the mainsail tends to push the boat sideways more than ahead - slowing the acceleration out of the tack. In contrast, the MastFoil rig flips right through the tack, losing less speed in the process, and accelerates very quickly on the other side.
Gybing the MastFoil is also extremely low stress. Both jibs have booms but these booms are short and lightweight compared to a typical mainsail boom. In addition, the jib area up high is small and concentrated near the luff in contrast to a normal full roach mainsail where there is lots of mainsail area up high and well aft of the luff. When the massive large roached mainsail gets moving fast in a poorly controlled gybe it can do damage when it comes to an abrupt stop. Instead of gybing over with a crash and a bang the jibs of the MastFoil are very docile and can be gybed hard with little risk.
It's interesting to see what the boat can do with the sails put away and drive coming only from the foils. In light winds beam reaching, boat speed under MastFoils alone is about 30% of the true wind velocity. While that is not very exciting sailing it is pretty good considering the small area of the foils. What is particularly interesting and fun to do is to retrim the foils to a "reverse" setting and watch the boat come to a complete halt and start to sail backwards! I know it sounds strange but I suspect that that feature will come in very handy in many situations. Simply putting on the "air-brakes" might be the first and simplest reef in some conditions, slowing the boat and reducing the apparent wind. Used in opposition to some prop thrust, one or both MastFoils trimmed to drive toward the stern quarter should make it easy to work off a dock when pinned against it by the wind. The list of unconventional maneuvers will surely expand as time goes by. It takes time to learn any new boat and A47 MastFoil, being the New New Thing, will take more time than usual to discover all the tricks that can be done.
There have been many inquiries about the performance of the flapped under water hull fins. Unfortunately I still don't have any solid answers about the performance gain or lack thereof. Trying to measure a 2 or 3 degree difference in the boat's course made good is challenging under any circumstances and even more so without a comparison boat of similar performance or else very steady sailing conditions and well calibrated instruments. Sailing upwind, my gut feeling was that the fin flaps w ere helping but I was hard pressed to see it on the chart plotter. It's sort of like measuring the performance of a boat with a dagger board all the way down or half way down. You see it when racing, you can't see it otherwise. We will continue to evaluate this feature.
While I am certain that we will tweak this and that for many years to come (as is done with any design if you are paying attention) the A47 MastFoil design is currently fully functional and stable. All the A47's under contract now will be rigged with MastFoils, and they will be constructed similarly to what you see in the photos and video posted here.
My thanks and deepest appreciation to the gang at Alwoplast for hanging with me through the difficult and sometimes trying development stage. Turning an entirely new rig concept into reality takes lots of time, hard work and money. While it all seems so simple after it is done, the path here included a few dead ends and wrong turns. All of which were confronted and resolved with the good natured enthusiasm inherent in people who love their work.
March 22, 2013
MastFoil™, Christopher R. White
V-Flap™, Christopher R. White
Full Speed Ahead
Design innovation continues with the launch of the first Atlantic 47 MastFoil ™ (patent pending)
In late October the first of a series of MastFoil equipped A47 cats hit the water for initial testing at the Alwoplast boatyard in Valdivia, Chile. Results were excellent, with the MastFoil rig demonstrating its power and excellent ease of handling.
• From dock to sailing trim in seconds.
• Reef or furl all sail quickly and easily in any wind direction.
• Fast "hands off" self tacking.
• Effortless and safe gybing in strong winds.
• Sail handling just does not get any easier.
The A47 is well balanced under all points of sail, handles crisply and comes about very fast. The steering system has a great feel with plenty of rudder feedback. It is a sailor's boat - providing performance for the experienced go-fast sailor and docile handling for the short handed cruiser.The spacious aft deck is a great place for lounging and dining. The awning, not shown, provides shelter from sun and rain.
The MastFoil rig is aerodynamically very clean, meaning there is very little drag. This is readily apparent sailing upwind, where the rig is extremely quiet. A conventional rig makes a fair bit of noise in apparent wind speeds over 20 knots, but the MastFoil hardly makes a sound. Less aerodynamic drag equals better performance.
Upwind tacking angles look very good on the GPS chart plots and more definitive data will be forthcoming. One pleasant surprise was how effectively the MastFoil rig sails to windward in 15 kts true wind WITHOUT SAILS! Measured course made good to the true wind direction was 65 degrees! Pretty impressive for a sailboat without any sails flying.
Close reaching in 18 kts true wind speed under MastFoils alone generated 7.5 kts boat speed. The helm was balanced well and the boat fully controllable.
Of course the intent is to use soft sails for the majority of power in light to moderate winds and unrolling the sails pumps up the performance to the typical Atlantic Cat standards. But still it is a unique feeling to be sailing at “conventional boat” speeds under nothing but the two relatively small and easy to manage MastFoils.
While beauty is in the eye of the beholder, everyone who's seen the A47 in person agrees that she is one good looking cat. And, there are many new features to the A47 design in addition to the rig.Note: photo shows the interior still under construction, without seat cushions etc.
• The new enlarged pilothouse interior is stunning, with great views all around.
• Oversize opening windows to the aft deck provide ample ventilation.
• The raised galley puts the cook at eye level with the large pilothouse windows - providing a fantastic view and lots of working light, while maintaining a dedicated galley workspace.
• The inside steering station allows hand steering in squalls and bad weather, while the large nav area to port permits the navigator to see forward while working -
• The spacious aft deck incorporates a walk through to the transom, making boarding from the dinghy easier than ever.
After initial testing, Hull #1 is back in the shop undergoing installation of owner specified electronics and other equipment as well as various improvements resulting from our trial sailing. Tuning and tweaking a completely new design does take some time. There were a number of things to experiment with and sailing the full size rig provided many insights on ways to make the boat even simpler to operate than she is already.
Several Atlantic 47's are currently building at Alwoplast. Sales have been strong, and for good reason.
There is nothing else like the Atlantic 47 MastFoil, anywhere at any price.MastFoil™, patent pending, Christopher R White
September 2012 Update
Progress on A47MF #1 is going very well, the interior structure is complete and final painting and joiner work is well underway.
The main structure of A47 #2 is complete and the interior is being installed. A few weeks ago the A47s under construction were being moved around in the shop. While hull #1 was in the travelift the Alwoplast crew took the opportunity to splash the boat and see what she looks like in the water. It's certainly handy to have a waterfront boat shop and your own lift! She looked great, even though floating very high without the rig and machinery. One of the Atlantic cat owners summed it up well when he said,
"It's the best looking catamaran I've ever seen. A combo of bad ass and elegance!"
With rig and a paint job I do think she will be a stunner.
At the same time, the first large MastFoil was moved out of the shop and erected in front of the Alwoplast shed in order to check the bearings and the flap control. Everything worked well and the foil rotates freely. The rigged MastFoil was standing for a couple days but eventually got in the way of boatyard operations so it was taken down. Next time it stands it will be on the deck of the A47.
Sails, winches, furlers and deck hardware as well as the final rigging parts are all in transit to Chile for boat #1. The current plan has a launch mid October with sea trials commencing about a week after launch.
Obviously, we're all very excited to sail the real thing after so much hard work, and it's a busy time pulling the multitude of loose ends together to meet the launch schedule. Also, quite a few customers and prospective customers are making arrangements to travel to Chile sail the MastFoil so it will be a busy time once we have a working demo.
One area of particular concern has been the behavior of the foil in very high winds. To investigate this further, we mounted a test section of the A47 MastFoil on a trailer and pulled it down the highway at 70 mph. The foil behaved very well with no vibration or oscillations. When it was disturbed by a gust from a truck coming the opposite way, the foil shook momentarily then immediately stabilized. I don't foresee problems feathering the foil in storm conditions. The ability to feather the foil with any wind angle is a key component to the inherent safety of the MastFoil design, as is the ability to use the foils as effective and easy to handle storm sails.
If I had not had the opportunity to build and sail the 23' MastFoil rigged cat last year I would be slightly terrified at the prospect of showing anyone the first full size cruising MastFoil. However, between what I learned from the prototype, a year spent sorting out design details for the A47MastFoil and the excellent feedback and testing of component parts by Alwoplast during its construction I think we have a very good chance of avoiding most of the teething pains. But as they say, time will reveal all.
The next update is likely to come after launch. With any luck there will be all good news to report.
MastFoil™, Patent Pending, Christopher R. White
May 2012 Update
There have been numerous requests for an update on construction progress of the first A47. To be truthful, Alwoplast is charging along and I have been struggling to keep ahead of them with the design work.
After designing multihulls for almost 40 years you'd think by now I would have some idea how much time it takes to work through all the design details for a new boat. Well, all I know is it takes nearly forever! In addition to all the normal design drawings the MastFoil requires considerable thought to work out the structural details and construction methods as well as inventing new parts to accommodate the unique function of the mast and foil. While it's a lot of work, it's also a great deal of fun for me as it is all completely new stuff that has to be created. It gives me a chance to exercise my inventor/engineer gene.
Little by little the MastFoil rig details are being fleshed out, drawn in detail and sent to Alwoplast for their input before we finalize the construction. We made a decision to build the MastFoil rig "in house" rather than try to contract it out to a spar builder. There were several reasons for this, one being that much of the rig construction more closely resembled boat construction than typical mast construction. Another was that we would have complete control over the details. And it's the details that will make or break (literally) a successful boat.
The mast is a carbon fiber tube and the first one has recently been constructed. The tube needs to undergo structural testing when it is fully cured to verify the strength calculations and then we will proceed with the second mast tube. Meanwhile the MastFoil flap has been constructed and the main foil mold is ready.
Design of the mast to foil bearings has been worked out in detail and sent to Alwoplast. While the loads in the bearings are low and generally not difficult to deal with there is the need for all of the bearings to be immune from corrosion. And the main bearing at the base of the mast needs to be both inspectable and field replaceable. Several alternatives were looked at in detail before settling on a bearing surface of Teflon. While not the lowest possible friction, overall this seems to be the most durable, corrosion free, easily serviceable material.
The hull and deck structure is well advanced. The first pair of hulls were joined to the under wing and major bulkheads bonded in place in late April. The wing deck and pilothouse is complete and awaiting bonding to the hulls. The flapped hull fins are constructed and were bonded to the hulls before the hulls were turned upright (much easier that way).
Turning over the Deck, May 2012
The A47, wherever possible, is using composite spars. This includes the forward crosstube and the associated fore and aft compression beam. Over the years I have designed quite a few varieties of crosstubes using aluminum mast sections, common aluminum tube, carbon mast sections and custom composite sections. In addition there have been a variety of different attachment methods used to join the crosstube to the hulls as well a variety of different types of spreader (and spreader-less) designs, headstay bridle materials and tensioners. The goal is always to minimize weight, maximize strength and endurance all at a reasonable cost.
Fatigue endurance is really critical since the entire headstay load gets resolved into the headstay bridle and magnified 3 fold due to the shallow angle. Everything up forward is bathed in salt spray while it undergoes cyclical loading- the worst possible combination. A failure in the crosstube, spreader, bridle or its attachment will lead to dismasting so it is imperative that the design be good. We finally settled on a relatively simple elliptical section composite crosstube with a single carbon/epoxy spreader.
The main hang up was how to make a light and durable headstay bridle that will be visually as well as aerodynamically clean.
Many custom cats use a carbon fiber strap for the bridle. This is lightweight, resists fatigue well and can be relatively inexpensive to construct. The problem with this solution is that the carbon strap needs to be epoxy bonded to the ends of the crosstube. And this done in a way that can't possibly pull loose, which means an extensive bonding area. But the bridle is exposed to damage from anchors and chain as well as collision with anything- fixed or floating. So the need to repair or replace the bridle is not out of the question. If replacement involves the massive rebuilding of the ends of the crosstube then the ability to replace it becomes an issue and the costs skyrocket. Another issue is that the carbon strap can't be tensioned because both ends are fixed to the crosstube. So that concept, while initially attractive, was rejected.
Designed in 1987, the Superior 54 cat utilized a composite crosstube with a Nitronic 50 rod bridle. The bridle ends were lead through a tubular receptacle laminated into the end of the crosstube and tensioned with a nut on the end of the rod. A very simple system and it has proven to be reliable for more than 20 years. However if it were to fail the likely place would be at the threaded end. This is because Nitronic 50 like many high strength metals is susceptible to stress corrosion cracking a process further aggravated by salt water and cyclical fatigue- exactly the conditions on a cruising sailboat.
Bronze has a very long history of use in marine structures. Primarily composed of copper, there are dozens of different bronze alloys with a broad range of properties. Some of the bronze alloys have remarkable strength, and superior resistance to corrosion, far surpassing stainless steel,. In particular the nickle aluminum bronze alloys are exceptional in this regard and this alloy is what was chosen for the rod bridle. Not only does it offer superior reliability and longevity but it is easy to replace if need be.
A new design offers countless opportunities for improvements throughout the boat. While weight reduction is always high on the list of priorities it shares importance with durability and ease of maintenance. Having the lightest/fastest possible boat does you no good if it is constantly broken or needs a mobile pit crew to keep it running. Sadly this seems to be the current state of affairs in the world of mega-yachts where the ratio of sailing time to shop repair time is pitiful.
The A47 MastFoil is, by nature, designed to provide low stress sailing by eliminating sail and rigging stresses, sail handling difficulties and the associated mental stress that causes. Why not take that concept a step further and strive to build the most reliable, lowest maintenance structure too? Doing that, obviously, is the only real choice.
Now that the holidays are behind us, everyone (including me) is back into the swing of things working hard to create the first Atlantic47™ at Alwoplast Marine, Chile.
Construction of tooling is the first step in hull construction. It is important that the hull mould be precise and fair. It is a process that takes time and does not benefit from being rushed. The female mould is made over a male "plug" which has identical shape to the final hull. It was nice to see the final hull shape in the finished plug. The A47 hull shape is similar to her Atlantic sisters, although overall somewhat narrower than the A48 which has almost the same waterline length.
Every yacht has her own center of gravity which has to be carefully calculated at the start of the design phase. The A47's is a bit further forward than her close Atlantic sisters (A46/A48) and more like the CG position of the A57. This will give her a very nice motion going upwind in rough conditions.
The design of the sail plan and deck hardware layout is now complete. I love it! The A47/MF deck is so clean and un-cluttered. The number of control lines in the cockpit is decreased by 2/3's compared to the conventionally rigged Atlantic Cats. Also, most of the highly loaded sheets, vangs and halyards disappear in the MastFoil rig. So not only is it simpler and less cluttered, but the effort required to manually control this rig is reduced by a huge margin.
Then of course with MastFoil we have the ability to quickly reef and furl all sail from inside the pilothouse as well as outside. How could it be any easier? If anyone has an idea to do that please let me know.
The interior plan is also well advanced. Here dimensions get so critical for comfortable living and operation, that the final position of most items inside the boat can only be located after the final hull and deck lines are drawn. While the original interior concept remains the same, many changes have been made as parts were jiggled this way and that to make the interior work better.
Something new in the A47 are the opening aft windows in the pilothouse. While we've been using opening windows here for a long time, having larger openings would be an advantage. The problem is to maximize the open area of the window without having the open window obstruct either the pilothouse or the aft deck. The solution is what we see every day in our cars; make the windows slide vertically. A button controls the up and down, and the windows are concealed in the retracted position. It will be pretty slick in operation and really help cool the boat in the tropics.
One area of the A47 interior that presents some options is the port hull aft cabin. This space is fairly large and can be configured differently depending on the owner's wishes. So far we have developed two different double bunk layouts (one with an en-suite head), a cabin with two single bunks and another layout with a large office/working space. Undoubtedly customers will have requests for further variations.
The MastFoil rig presents a whole new set of design requirements and I am well along the way to having the multitude of details worked out. Building the prototype mastfoil in my barn last summer was essential to get my head wrapped around the unique structure of the mast and foil and I am very glad to have had the chance to do that.
The mast inside the foil will be carbon fiber and produced by Alwoplast. The mast mould is being fabricated now. One of the great benefits of having the yacht builder fabricate the mast and all its parts is that we have complete control and can avoid the problems that we have had with spars contracted from even the most well known and expensive mast builders. The mast itself is incredibly simple - it is a long tapered tube. There are ZERO holes in it (masts typically fail at holes). There is a simple carbon composite masthead fitting and another simple composite receptacle mounted on the deck at the mast step.
The foil that slides over the mast is somewhat more complicated to construct. But because it is divorced from the mast compression loads the foil can be very lightweight. The airfoil will be a foam cored glass/carbon fiber laminate, hollow, with a number of low friction bushings along its length. Due to the low loads in the foil these bushings should wear very slowly and last a great many years. But when the time comes the foil can be easily removed from the mast and the bushings replaced.
Alwoplast Marine, Valdivia Chile
The design of the control mechanism for foil rotation is well advanced and will be simple to operate. This control allows the foil to rotate freely, 360 degrees around the mast as will be necessary when tied to a dock or navigating a storm. It also allows the foil to be trimmed to any position and locked in place, as will be necessary when sailing.
The A47 will use a new steering system. It is the lowest friction, simplest, lightest and most straight forward steering system that I have seen used on any catamaran, aside from transom tillers linked by a crossbar.
Steering system failures are mostly caused by component failures. The chain is only as strong as the weakest link. I have seen steering linkage on some expensive high performance cats that use 4 different types of linkage between wheel and rudder. So many joints and parts to fail! And they do fail. I just heard of another one last week on a 50' cat (not designed by me) owned by a friend. One small universal joint popped and the whole system became inoperative. My approach has always been to keep the parts count as low as possible and this has proven to increase reliability.
Basically, the A47 steering system is like the original catamaran steering where two tillers are linked by a crossbar. The problem here is that we want to be able to steer from midships - not sitting on the transom. The solution is to split the crossbar in the middle, align them in a V formation and rejoin the ends on a bell crank under the miship cockpit. The bell-crank is connected to the steering wheel via rack and pinion steering and voile'- it's done. Two ball joints and a long tubular push rod is all there is between wheel and rudder. As far as reliability goes I can't imagine a better way to build it. Rudder "feel" should be superb.
One last A47 innovation to discuss is the flapped hull fin. This was first mentioned months ago when the A47 was introduced with the conventional rig. I received quite a bit of email, for the most part skeptical, about the benefit of the flapped fin compared to a daggerboard. While I am perfectly willing to accept that a daggerboard would be slightly more efficient sailing upwind I am not at all convinced that the overall performance of the flapped fin will be inferior to a retractable board. This is particularly true when you consider the weight reduction and low vulnerability of the fin to damage compared to a daggerboard. But we shall see. Many of the questions about the flapped fin had to do with the way it would be controlled. There are certainly many ways to do that and I wrestled with the details of all the basic types I could think of until deciding the best way to adjust the flap is via an electric actuator which is attached to the flap shaft under the floorboards. The actuator is similar to the tilt control on an outboard motor, but it is located inside the hull, thus protecting it from salt water. There is a rocker switch and angle indicator at the helm for each fin which allows them to be operated independently. It will take some experimentation to find the best flap settings for upwind, downwind and reaching but I am confident that they will prove to be an asset to the boat.
There are many people eagerly awaiting the first sail of the A47 MastFoil, and count me at the front of the line! Progress is steady, that day is coming.