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Saturday, July 19, 2014

Paving the Way

Lots to report as we continue to test over the winter... 
We are working on the next-generation Paradox A Class Cat design for the 2015 season, resolving the details for all new tooling to be created in-house at a new facility. 
Now that our new expanded production facility is operational we can tackle such jobs with confidence. This gives us more control than before when we relied on contractors for certain aspects of production.

The path we are taking is, as always, very empirical. Every idea is assessed for potential merit, tested objectively, evaluated, then either discarded or developed for the next round of testing.

The focus is on perfecting a foil package that will be a significant improvement on current designs. ‘Improvement’ in this case is strictly defined as the ability to generate better performance around the racetrack in most conditions. So ease of handling, maneuverability and acceleration play a role as well as outright straight-line speed.

We began this phase of R&D by prototyping a series of ‘acute L’ (AKA 'L/V') foils. These all shared a common vertical strut but had incrementally different horizontal chord, span, tip-up angle, and section characteristics. For testing they were inserted from below into simple straight (parallel-sided) cases. These cases are installed in one of our test platform (the orange boat nicknamed Glamorous Glennis) in the exact same position as the production ‘comma’ foils we used at the NZ Worlds.

Following are some thoughts on the testing process and the state of play in the Class:

Rudders
Two candidate revised rudder designs were tested. More on the selection of rudder design in future posts. For those of you who missed the previous related post, the 2014 version of the cassettes is pictured below. 
You will notice that the rake adjustment system has been simplified and construction beefed up to maximise stiffness.

Robust cassette assembly machined from billet. Available now.
Rod end/spherical bearings have been deleted and rake adjustment can now be easily done on the water
Continuing Foil R&D
Imposing the constraint of a straight vertical strut simplifies progress by reducing the number of variables. It also reduces production cost, allows us to use the full horizontal span permitted by the rule and makes fitting of the structural foil case very simple.
Relatively quickly we came to some definite conclusions regarding ideal tip-up angle, shape, and area for reliable stable foiling using the leeward foil only. Needless to say this configuration is extremely promising with upwind foiling and foiling jibes being a given. The key is the ability to use all the beam of the boat to generate righting moment. A marked difference can definitely be felt when the windward foil is out of the water and no longer pushing the windward hull up.


As an aside, the market has proved very hungry for this type of foil. Many customers want to retrofit their boat with the simplest, most cost effective package to just get out on the water and enjoy foiling.
Since racing in the A Class was always integral to our design brief, we have also devised a way to legally fit the final selected L/V foil in compliance with Rule 8. Perfecting this aspect of the concept will be the next step and hopefully the result will be relatively elegant. I say relatively because any solution other than inserting from below will be more complex than strictly necessary. But our challenge is to minimise the rule-mandated unnecessary complexity.


No Stone Unturned
Part of the test series is a radical concept that could potentially achieve two goals simultaneously: Firstly it could be inserted from above through a very modest slot/case with no complex cassettes. Secondly it could displace the horizontal lifting surface forward, increasing separation from the rudders, without affecting helm balance. 
A side-benefit is that the full horizontal span could be used without needing to put the vertical extremely outboard. 
Stability would still come from a tip-up angle (leeway coupling) exactly as for an L/V foil. 
This concept does involve a wetted area penalty (in the form of the area of the horizontal tube). 
It poses some structural challenges (flex in the tube and twist in the vertical foil) and it has a higher induced drag because it has more free tips exposed to the flow. 
Preliminary calculations showed that it had enough potential to warrant building a prototype for testing. We will know soon how it does in the real world…



In Parting
That sums up our status along the fascinating journey of performance development. 
Now to explain the title of this post: Observing competition in Europe we have been happy to note that the approach we took for the production V2 Paradox is now finding acceptance by other manufacturers.
Our 'bent' foils (as opposed to curved) that exit the hull vertically then transition quickly to a span with pronounced dihedral, have been emulated and refined to different extents (functionally the working portion of the foils in this concept is not dissimilar to that used successfully by Hydroptere).
Interestingly some newer designs place the ‘elbow’ further down so that the hulls effectively sit higher when the foils are working in equilibrium. It looks more spectacular and arguably gives a bit more wave clearance, but the penalty is extra foil area - a compromise with respect to performance in displacement mode. This can be alleviated by raising the windward foil such that the lower bend passes above the hull floor when sailing upwind and in light airs. Getting the foil to locate properly when partially retracted requires engineered bearings rather than a simple slot. Our bearing technology remains unsurpassed. The effectiveness of our self-aligning bearing design is such that our ‘bent’ foils ‘autotack’.

Our V2 production foils pictured at the NZ Worlds.
This concept of transitioning from a vertical exit to a Hydroptere style dihedral setup was a first in the A Class and has now adopted by others.
The upper bend in our design allowed the windward foil to adjust automatically to optimum dihedral when sailing upwind.
It is certainly great to see a move away from unstable J foils toward more stable (less unstable) arrangements. The guys at the Europeans are to be congratulated for some great performances with well set up ‘four point’ arrangements. It is also great to see validated our findings that loaded surface-piercing foils require careful treatment of camber and entry angle to delay ventilation. Mischa Heemskirk using sections designed by Gonzalo Redondo of D3 seems to have nailed that aspect of foil setup.
Interestingly the foils and beams on other designs have moved forward to closely match the positions seen on our production V2 boats. 

We were happy with the performance of our equipment at the NZ Worlds. But the next steps are already in testing. So that is where we are concentrating our energy now. 

There is yet another avenue we are exploring that has shown great potential in terms of safe, easy, reliable, fast foiling. More news on this and on our new testing centre in the coming weeks... 

Soon we will have to decide which way to go for the production boat. It may be that the market will continue to demand ‘unadulterated’ equipment in parallel with a competitive rule-legal version. So we will continue to offer both options.

The flattery of imitation is a great confidence booster, but pushing forward into the unknown is an even greater thrill.

3 comments:

  1. As you probably know, many top sailors are using the Exploder T rudder foil on every kind of competitive platform. I continue to believe the L foil is a better solution because of inherently lower drag, easier storage and lower manufacturing costs. The rudder head you manufacture is a beautiful and elegant piece of equipment, but is unfortunately out of my budget. It would be great if you could manufacture and sell an L rudder that fits conventional swinging rudder heads. No one else appears to be addressing this market potential. What do you think?

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  2. 'Inherently lower drag' for an L rudder is only true as long as the required area allows you to have a good aspect ratio within the allowed span.
    This was the case for our 'skimming' foil-assisted solution.
    For full foiling we need more elevator area.
    We can only push the rudder outboard until it is around 100mm from max beam. This is because going any further outboard we would run out of transom width and place the cassette in the free water flow next to the hull (instead of hiding it behind the transom).
    So thanks to Rule 8 we have only 300mm of span for an L. To get the area we need our chord would have to be considerable.
    So it makes sense to extend the elevator outboard as well as inboard. That way we have a 400mm span and for a given area the chord can be shorter. Plus the structural loads become more manageable.
    On balance the trade of intersection drag and induced drag comes out in favour of the T for full foiling.
    My hunch is that in future as efficiency improves and foils get smaller we may be able to go back to an L. But at the moment with the still far from ideal J foils most commonly in use, we recommend the T rudders as a retrofit to other designs. Ls still work best with C foils and with our own comma foils (the inspiration for the Z foils currently being developed by other manufacturers).
    Regarding cassettes, people have bought our rudder blades and fitted them to existing kick-up boxes.
    All you need to is create a flat area around the head of the rudder by bogging out the section around where the cassette will bear on the blade.
    In my opinion the advantages of a sliding cassette are too significant to ignore. They range from precision in setting the AoA of the elevators to the ability to vary rudder depth easily. All without changing blade balance.
    I think kick-up rudders are surviving right now only because nobody is foiling properly. Once flight becomes more stable and reliable, then the shortcomings of any systems that allows slop or variation in the elevator AoA will become too apparent to ignore.

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  3. Thankyou for your thoughtful reply. I didn't know you are currently advocating t-foils for full foiling. I am still not convinced the T is superior. I guess time will tell. I do agree the structural issues are simplified with the T foil, however the t-foils are subjected to much less vertical load then the dagger foils.

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