An update on our Flattens; Performance for Furling Sails

Conscious that it has been (a long) 2 years since Simon Fry and Dan Primrose formed Primrose Fry Technologies (PFT), they thought they should show some of the images and videos from all their extremely exciting (patent pending) work, and why they think they now have a product that could change the Performance of Furling Sails. All this work has ultimately led to a J-111 in the USA, called "Spaceman Spiff" winning her class at Quantum Key West Race week earlier this year, with a full set of Flattens in their Light-Medium Jib. The feedback from the trimmers and sail makers on and off the boat was nothing but extremely positive and the Flattens had allowed them to trim the sail in ways that were not possible with existing furling battens systems. Here are some of the images from that week, from North Sails library.






J-111 "Spaceman Spiff" with NS L-M Jib with full set of Flattens



J-111 "Spaceman Spiff" with NS L-M Jib with full set of Flattens



 

close up of Lower Flatten on J-111 "Spaceman Spiff"




Furled jib on J-111 "Spaceman Spiff" with full set of Flattens

  

So, back the beginning.... Simon and Dan concentrated most of their development on a J-111 jib kindly lent to them by Kirsty and David Apthorp, from J-Dream in the UK. This was a 3.5 jib, for heavier conditions, but was invaluable for them to try out various configurations of Flattens that they developed as they went along. Due to the nature of the Flatten pockets, Simon was able to simply add them to the existing sail, allowing Kirsty and David to sail with their furling or non-furling battens. PFT chose this size of boat (national level, club racing) as they felt that this was the largest, potential market where a performance, furling batten could be used, and the spec of the final batten was chosen to suit the latest thinking as far as sail shape goes for this type of yacht. Once they had proven the concept worked in this area, they could carry on developing the Flattens for other size of boats, as well as other sails (i.e. in-mast furling and sails flown on a cable, the Super Yacht Market and perhaps most importantly, the cruising sail market)

Whilst a lot of the development they have done will have to remain under wraps for a little longer, here are some words and images that will hopefully give the sailing community something to think about when weighing up the options for furling batten systems for their yachts.

When Simon and Dan started this project, they were pretty sure that the furling ability of the product would be good, but were not 100% sure about the sailing performance. However, these doubts were very quickly dismissed when images of the J111 sail were compared to the original design files, and showed to be "almost spot on". This was a major milestone for the business and gave Simon, Dan and Oscar Strugstad, who had by then joined them as Chairman of Primrose Fry Technologies Ltd the confidence to move ahead with project. Whilst they got excited about the sailing performance potential, onlookers were also extremely complimentary about the furled sails, which were as good, if not better than a sail with no battens due to the unique nature of the Flatten where it actually holds the furl tight. This means that approx. 100 off 1m Flattens could be shipped in a 60x60x30cm box.






2 off 1000mm Furled Flattens

So here are some images that we can show, that will hopefully show why PFT's confidence level is so high. Most of the testing that has been done has been in lighter winds, which as anyone who has used a furling batten knows, is the hardest conditions to get them to work as they should (i.e. produce a tight furl whilst still giving the correct profile for the flying sail). Testing has of course been done in all conditions up to near gale force and were all very successful; "the Flattens were faultless and very good value" to quote the owner of the boat that was racing, shorthanded, offshore. In these extremes of conditions, the simple fact that the Flattens are "stable" in both sailing and furled forms, makes them unique and will give the end user the advantage they are looking for.

This sequence of images were taken in early 2012. They clearly show the sail shape, both furled and unfurled. One point that will always be made by sailors (who by nature, are always thinking about the overall aerodynamics) is that the luff-90 pockets (which Simon and Dan have spent approximately 60% of their time developing, and have made significant advances on the current pocket configuration). There is no denying that they are not going to be as aerodynamically efficient as a moulded-in pocket, for example, and Simon was concerned about this very early on in the programme. However, after some basic calculations, CFD and some aero studies on the water, the additional drag from 4 pockets on a J-111 sized sail is almost insignificant. This was reinforced when we analysed the airflow over the actual sail when they went sailing with strategically placed tell-tales placed on the high and low pressure surfaces, with respect to local boundary layer thickness.





J-111 Code3.5 Jib Upwind with Full set of Flattens in 9kn TWS





J-111 Code 3.5jib Upwind with Full set of Flattens in 9kn TWS








J-111 Code 3.5 jib Upwind with Full set of Flattens in 9kn TWS






J-111 Code 3.5 Jib Furled with Full set of Flattens



Here are two video clips, again from the J-111, sailing and furling with a full set of Flattens in about 9 knots TWS.





As mentioned, Dan & Simon have also been developing the Flattens for In Mast furling and sails flown on a cable (i.e. code zeros etc.). This testing is still on-going whilst they concentrate on the final spec for the baseline Jib Flattens but below are two more videos showing some of that work.

The first shows some early work done with Seldon Masts in the UK who are keen to find a viable batten system that will complement their existing In-Mast furling systems. Although this particular video shows the tests done on a "boat show" sized rig, the results are scalable up to full size. And as with the jibs, the actual furl inside the mast is as good, if not better, than with no battens as the sail is held by the furled Flattens.

We have also tested the Flattens on a light-medium jib set on a cable on a 50ft yacht (i.e. no foil or luff-groove) and a J111 Jib flown on a J109 (with Foil), both in 18-20 knots TWS. The end results was that the test teams felt that the performance of the Flattens (both sailing and furling) was better than they had seen with other batten systems. A particularly noticeable in this short film is just how "resilient" the Flattens are, even during some aggressive flogging, and that when you have a batten with the correct stiffness, as shown here, the sail shape is much more powerful as its sheeted on.

 

So, as we move into 2014, Simon, Dan and Oscar are at the point where they have "real" boats sailing with Flattens in the jibs, and are all performing really well. Here are a few (very honest) words from a J109 owner, using the Flattens on his AP3 Jib (which has been left furled on the head stay for nearly 4 weeks in total with the Flattens still fitted, in temperatures down to -5 deg C)

"....We had some prototype furling battens in our headsail as the original ones failed after the Fastnet and we were having to use regular battens. With a furling headsail one can either go for vertical battens - which are not as good as horizontal ones - or horizontal battens than can collapse when the sails furled in. Or of course, regular battens meaning you drop the headsail when downwind...."

"...The original furling battens that came with our AP3 sail are made up of two pieces of plastic, not unlike two halves of a curved venetian blind vane, facing each other inside a fabric envelope. They popped rigid when laid flat, but flattened as the sail was wound in...."

"...Anyway - that style clearly has issues with longevity - as the original battens had broken we think with compression damage probably caused as they are inserted into pockets from mid sail. Being closed off at the aft end means the battens got no where to go as the sails wound in, and hence get scrunched up. These new prototypes after fitted into bigger pockets but are fed in from the leach. The battens themselves look like a largish C plastic section, which also flattens when furled one way and pop back to shape when the sail is pulled open. They are held in with elastic at the pocket opening, and that allows them to move slightly out the pocket when the sails furled. I presume that should help avoid any compression damage. The batten pockets are a bit bulky on the sail, so one could wonder about aerodynamics etc., but hey, the sail shape looked super with them in. We believe they are stiffer than the original battens, certainly give the sail more depth when it was needed, and we certainly did not lack for pace during this race...."

"....Pleased to report that upwind and down, it felt like we had better boat speed than JIBE this week. Maybe it was the new battens, which certainly seemed to give the headsail more depth, or maybe it was simply a cleaner bum. Maybe a better kite. Maybe luck!..."

"...Yes, the battens looked good and again, we felt we had legs upwind when sailing alongside other J's..."

They are continually looking at the finer details (i.e. half furled sails, as below, and Flattens for smaller and larger yachts)




J111 Jib with Full set of Flattens, sailing with 30% reef

J111 Jib with Full Set of Flattens, showing possible semi-Furled sail

and working toward to end goal of being able to put them on any yacht that needs that extra edge as far as adding Performance to Furling Sails.