Atlantic 47 MastFoil™ Update


January, 2012

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.


Deck Mould

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.

Chris White