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Friday, July 25, 2014

Think with a Twist

In response to an avalanche of questions about how our experimental foils with the lifting surface mounted at the forward end of a 'fuselage' tube can be extracted from above... Here are some illustrations:


First the foil is raked top-forward so the tube sits vertically through-hull slot.
Then the foil is rotated about the long axis of the now vertical tube so the main foil strut points inboard.
Finally the lifting surface is extracted through the slot.

This concept requires that the minimum clear length of tube is equal to or greater than the local freeboard of the hull.
Obviously if a boat were designed with this in mind from the outset and a shorter longitudinal displacement of the lifting surface were required, then the local freeboard could be reduced accordingly. In fact it would only need to be stepped down inboard of the slot.

The legal lifting foil is around 450mm in span (a bit more than the 400mm max legal horizontal distance because it has a tip-up angle). So the slot can be at a minimum around 380mm long. The width of the slot is equal to the diametre of the tube which on our prototype is 35mm.

More testing is needed, but initial indications are that stability is good, performance at foiling speeds is promising but the drag penalty at low speeds is significant.


Finally, and also in the spirit of sharing our development journey, an answer about the way we intend to extract from above an L/V foil with an acute included angle:
The smallest possible cassette would be one with a length equal to the span of the horizontal foil and a width equal to the chord of the foil. The foil would be rotated 90 degrees about a vertical axis once the cassette is raised.

The search continues, but so far the Class has seen only solutions that are either inventive but unnecessarily complex (cassettes, hinged foils, leeboards etc.) or limited in terms of performance (J and 'comma' or 'chevron' foils).

The latter are perceived by many to be an acceptable compromise and have in some cases turned opinion back toward keeping the Rule unchanged.
However the unexplored potential of 'true' foiling (as opposed to sometimes foiling on compromised appendages) remains vast. Exploring it is fascinating. Doing so within a now anachronistic rule makes it more challenging. But challenging quests can have surprisingly positive outcomes. So let us press on...

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.