Bravo

Congratulations to Sergio Vela, who placed third at the European Spring Championship, using retrofitted Paradox 2014 steering system. Full results here.

Image source: Circolo Vela Arco

Farewell 2014

Some images looking back on a year of regrouping, transition and growth:

Production L rudders, proven at the A Class Catamaran Worlds 

Mould for experimental T rudder elevator with junction bulb.

 Part of extensive R&D work on appendages

Rudder gudgeon assembly with 'between races' rake adjustment

Experimental gudgeons with 'on the fly' rake adjustment
via tiller extension twist-grip

Billet rudder cassette. Our concept of 'dagger' rudders with offset axis has been widely adopted

First A Class 'V' foil concept. 'Inspiration' for current Z foils

Retrofit foil case kit with rotating bearings

Moth bow swivel fitting developed with Scott Babbage. Production version available here: http://www.sailingbits.com/class-specific/moth-bow-mechanism/

Moth bellcrank developed with Scott Babbage. 
Production version available here: http://www.sailingbits.com/class-specific/moth/moth-adjustable-bellcrank/

Bolts with streamlined heads. Used on UAVs and various sailboat classes

Experimental Finn mast chocks for NB Sailsports

18' Skiff rig spanners for Allmarine. Available here:
http://www.allmarine.com.au/shop/boat-specific-products/18-foot-skiffs/all-marine-rig-spanner/

Tasar fittings for NB Sailsports.
Available here: http://www.nbsailsports.com.au/store/product-info.php?pid1365.html

Fairleads

Trophies for A Class Catamaran Nationals

Inevitable

Here is an extended mix showing some early runs with experimental control system foil configurations.
Though there is still vast untapped potential, these sequences give a flavour of what is surely to come.
Everyone who tried it commented, through a persistent grin, that it is easy and feels secure.

As often repeated on this site, the goal is performance, not foiling at all costs.
Passive systems such as L/V foils give some measure of heave stability at the cost of some additional lift-induced drag. If properly designed they are competitive and manageable. The key is to design the system to work with the hull so that the highly foil assisted mode remains fast. In the right conditions and with the right technique the skipper can then push beyond a 99% lift share and transition to full foiling.
So far this has only been proven to pay downwind in flat water when fully powered up. But undoubtedly the profitable flight envelope will steadily grow, expanding to lighter winds and upwind.
By all accounts engaging this mode is hard work and requires judgement to give net gains in VMG. But since gains are definitely available, it is a challenge to be relished.
V, comma, and now Z foils have improved performance, added a challenge and made the A Class safer to push hard, without taking away from the delicious responsiveness of this lightweight boat.

The difference between a passive system and a control system is that the latter is simply relentless. The boat will remain foilborne essentially until it stops, allowing for the skipper to look around, sit in, change gears and ride out lulls... All while the ride height is directly reacting to changing inputs.
So enjoy this first glimpse into just what is possible under this great class rule!

Make no mistake: there is a concrete measurable difference between current passive systems and truly stable foiling. As long as speed gains are out there, people will experiment and discover ways of realising them. Whether this is made easy and safe or expensive and dangerous is determined by how the rule is administered.

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.

Another Result

Using Paradox rudder blades retrofitted to his customised DNA platform, Mischa Heemskerk dominated the first Dutch event of the 2014 season at Muiderzand with 5 bullets out of six races.

Skilfully balancing in good foiling trim,
the instant expertly captured in a nice still image.
Remaining in this trim requires very active control.
Image copyright Jasper van Staveren

Report here: http://www.a-cat.org/?q=node/389
Full results here: http://www.roerkoning.nl/2014/klev_apr14.html

This win further supports our findings regarding the effectiveness of the concept, shape, section and construction of our rudders.
Various skippers confirm that they offer better 'damping'  than any others on the market with consistently less drag and the ability to remain effective for longer (higher heave values) without losing grip.

However it is worth noting that the combination of even the best rudders with J foils (where both foils are used at the same time), while undoubtedly faster than non-foiling configurations, is a very compromised solution. And one that we are hoping will be greatly improved upon very soon thanks to the development and testing work we are carrying out now.

Using two foils halves the effective beam. In reality the leeward foil contributes somewhat more than half the lift,
but you can see that the windward one is always trying to raise the windward hull.
Leeway coupling has the effect of unloading the windward foil with increasing ride height,
adding a further element of non-linearity.
Since most lift comes from the bottom of the foil, there is no inherent heave stability.
This video gives a graphic illustration of the difficulty involved in sustaining flight on J foils: https://www.youtube.com/watch?feature=youtu.be&v=-Ittw41D-Hk&app=desktop#t=50s

The ultimate solution will undoubtedly be a foil where total lift varies inversely with ride height.
So far these exist in three 'flavours':
- L/V type concept with that relies on heave/leeway coupling;
- Control system using surface sensors and flaps;
- Pair of Z foils that work together as a V.
Ideally all the lift should be generated on the leeward side, thus utilising the full beam of the boat to generate maximum righting moment, giving maximum sail carrying power.

We urge anyone contemplating an upgrade to contact us before committing to J foils as these may soon be proven outdated.

Mythbusting

Some thoughts on our recent testing with heave-stable 'acute L' foils (L/V for short).
This experiment had one aim: To prove that a simple cheap upgrade is possible to convert existing A Class catamarans to stable foiling without major structural modifications.

The story so far

We knew from previous testing that L/V foils give stable foiling. Our conclusion was that the crossover speed was relatively high so the overall advantage of this configuration for racing would be marginal.
The complexity of 'tacking' the L/V foils tipped the scales in favour of adopting our 'comma' foils for production and racing. These proved competitive giving skimming flight with neutral stability when required and minimising drag when in foil-assisted mode.

After the Worlds we revisited the crossover numbers armed with new knowledge about kinetics and the tactical options made accessible by foiling. It is now beyond doubt that foiling will pay.
L/V foils maximise righting moment, are inherently stable and can be made to work within the rule.

While it is tempting to wonder whether there is some lateral breakthrough design somewhere within the 'four point' design space, all the evidence right now points to the fact that 'three point' foiling offers the best performance with consistent stability (and hence safety).

An objective application of existing A Class rules allows simple, cheap conversion. More tortured interpretations may require workarounds such as hinged foils or large cassettes.

Stretching Rule 8 to serve the interests of the 'no foiling' constituency adds no value but instead imposes complexity and compromises efficiency. It creates costs that bring no benefit.

A growing majority of Class members is asking whether a simple retrofit foiling solution would be feasible.
Any lingering doubts revolve around ease of handling and, especially, the difficulties of converting existing boats that may otherwise become obsolete.

Modifications

The foils in these videos are old Marstrom C boards with new horizontal legs bonded on.
The horizontal legs are a proprietary shape. Critical features such as the area, tip-up angle, twist and angle of incidence were determined in light of the work carried out over the course of our Paradox development programme. However the Marstrom verticals were not modified.

For some runs the foils were installed in the original cases of a Melvin A3.
For other tests they were mounted in the existing foil cases of a Paradox test platform. In the latter boat the rotating bearings at the hull and deck were replaced with simple plastic blocks.

In both instances the foils are held down by a rope led to a deck cleat. They are retracted using pre-tensioned bungee that pulls them up when the down-line is released.

Rudders are standard Paradox with some transom reinforcement added to the older boat.

Longitudinal placement of the foils on the Paradox is further forward than usual because that happened to be the arrangement on this particular boat.
Previous testing has already shown that, within limits, keeping the foils further aft gives a maneuverability advantage without adversely affecting foiling stability. At any rate, installing a simple foil case further forward is cheaper than putting in a cassette.

Findings

In short the transition is surprisingly gradual with drag falling away as the hulls rise.
Once 'unstuck', the boat rises more rapidly until the heave control features of the L/V foils come into play.
At this point the normal instincts of a cat sailor remain applicable. However there are a few interesting differences:

The most important lesson is to do less rather than more.

Pulling away aggressively in response to building wind strength can force a reduction in ride height, especially if it is done after the boat begins to heel in response to the gust. The foils automatically go to work to restore level flight but the momentary reduction in ride height does sap energy.

Once the coupling between steering and heel is noted (if heeled to leeward, steering into the wind will make the bow come up. Pulling away will make it go down), then one quickly learns to anticipate. The usual response of letting the windward hull rise then bearing away is somewhat modified:

As pressure increases, the best technique seems to be to ease the sheet a tiny amount, let the boat heel to windward ever so slightly, then pull away as normal. This results in addictive, exhilarating acceleration in total safety. Unlike a displacement cat where forward buoyancy gradually runs out, the foils provide more lift as pressure from the rig increases. The feeling is one of total immunity to nosediving (so far!).

It is easy enough to become accustomed to just trusting the foils and keeping steering inputs to a minimum. Obviously the boat will spin on a dime when foiling so the key is to be subtle with the tiller.

Heeling to windward a tiny bit helps to increase ride height when bearing away. This really boosts VMG downwind. Interestingly the same technique works upwind because luffing up to depower helps lower the bow and settle the ride height. But more on upwind foiling later.

For reasons I do not yet fully understand, Keeping the sail more open works better than strapping the sheet on. Letting the traveler down slightly (say to the hiking strap) and allowing a few degrees of twist causes the boat to fly higher. Closing the leech seems to lock the foils up so the boat settles closer to the water. More investigation is needed here because as speeds rise and the apparent wind goes forward, sheeting in will become necessary.

My best theory at this stage is that increasing sideforce causes the equilibrium ride height to decrease. This is based on the coupling between leeway and lift built into the L/V foil geometry.
Another factor may be that, since drag when foiling is so much smaller, it is not necessary to load up the boat with maximum sail CL. Instead the goal is to have the greatest drive force component exploiting fore-and-aft righting moment rather than resistance to heel...

Sailing downwind with both foils down could lower the crossover speed significantly.
Having both sides down effectively gives a pair of V foils. The reduction in foil area due to the inboard tips breaching the surface becomes the dominant heave-control mechanism instead of leeway-coupling. This is an advantage because stable foiling becomes possible at small sideforce values. It is important to note that this arrangement is draggy at higher speeds and definitely unstable as soon as sideforce becomes significant.

Raising the windward foil and relying on leeway-coupling effectively doubles righting moment whilst halving foil area. This is good when sail power is 'excessive' and speeds are very high.
In lighter winds the leeward foil would have to be bigger (if used alone) for the same takeoff speed. More importantly you would have to sail much higher to generate enough sideforce to fly a hull while trapezing.

In other words you would have to generate enough sideforce to lift the windward hull and enough speed to takeoff on one foil only. This is achievable at a much lower windspeed upwind than it is downwind. Having both foils down instead allows a very early takeoff while sailing deeper because righting moment is effectively halved and foil lift is doubled.

I suspect that top level sailors will gradually be able to bring down the critical windspeed for 'downwind windward foil raising'. But for now this option allows mere mortals to foil safely in as little as 6 knots TWS.

Conclusion

We have now proven objectively that it is feasible to convert an existing A Cat platform to stable foiling with minimum fuss and expense. The boat remains practical and exploitable but it offers a whole new level of performance.

On the emotional side, the feeling of foiling is just fantastic. I am sure that hundreds of Moth sailors already knew this. But it must also be said that foiling on an 18' cat while on the wire, and with no mechanical control systems is special in a wholly unique way.

It really is simple to learn and no outstanding athletic ability is required. I have no doubt that this will be the future. Many top level sailors agree. The only question for the Class is this: Will we be permitted to do it in a way that is simple and cheap or will we have to use complex and expensive workarounds?

After the thrill of the 'magic carpet ride', touching down feels like sailing through honey. It becomes frustratingly restrictive. This really must be tried to be understood. Hopefully many A Cat sailors are about to do just that.

A World(s) of Learning - Part 2

One more post on appendages. Then we can look at other areas of development such as aerodynamic tailoring and control systems/ergonomics.

Glenn Ashby balancing nicely on J foils and Paradox rudders.
Photo by Rhenny Fermor of www.sailingshots.com.au

Steering system

The new kinetic techniques used to promote early flight, combined with much higher top speeds, really put our cassette and gudgeon fittings to the test.

When foiling high, immersed rudder area  is much smaller but, since speeds are higher, the equilibrium sideforce generated by the rudder is the same. Dynamic forces are bigger.
Because these forces are exerted at a greater distance from the hull (further down), the moments on the cassette assembly, gudgeons and transom are considerably greater than previously measured.

When retrofitted to the transoms of existing boats, some reinforcement may be required to create a stiff connection between gudgeons and hull. This can be done internally or externally.
Applying extra carbon reinforcement internally is ideal. But simply bonding on some carbon plate to the outer skin of the transom is an easy and quick solution.
Care must be taken that any external bonded-on reinforcement remains within the hull overall length limit. If this is exceeded then some material must be sanded off the bows.
Some filling of the core may be needed in way of the gudgeon fastening bolts if the area around the new bolt positions is not already 'cored out' with carbon or filler.

External transom 'C-plate' reinforcement. Plus stiffening added to sideplates.

Initial observations were that our cassettes were too flexible when subjected to the higher loads. They were not in danger of failing but their flexibility impinged on the 'crispness' of the feel/feedback through the tiller extension when flying fast.
It should be noted that these cassettes evolved through our in-house testing on Paradox platforms fitted with our more stable foil setups. The inherent stability of our foiling geometries did not require the aggressive inputs needed to correct unstable configurations. Therefore we progressively reduced the gauge of the sideplates connecting the top and bottom machined 'stocks' that hold the rudders and swivel pins. The earlier versions (round holes) had thicker sideplates than the later (triangular holes) design.

Since the flex was in the sideplates only (the machined stocks are robust and fit the rudders snugly) it was easy to reinforce them by adding carbon plate or box section to the sides of the cassettes.

Latest cassettes developed on stable Paradox platform had very thin gauge sideplates.

These were flexing on other boats when steering aggressively to stay 'on top of' unstable foils.

The production cassettes have been revised to incorporate stiffening ribs in the sideplates.
Aluminium remains the better material choice for production when weight and cost are considered together.
Aside from stiffness, strength seemed adequate. None had broken after the equivalent of three seasons on our various prototypes.
The more surprising failure we had at the Worlds was shearing of the rod ends (off-the-shelf spherical bearings) connecting the gudgeons to the cassettes. We had been warned early on by experienced Moth sailors about the possibility of fatigue failure in these components when they are loaded cyclically in bending over long periods of time. Therefore we inspected them often and monitored the hours each unit had sailed so that if and when one failed, we could know the expected fatigue life.
It seemed the parts (8mm SS) were conservatively over specified.
Even so we replaced them before the regatta.

Brittle failure of 8mm SS rod end fitting.

In our application the fittings are loaded almost exclusively in sheer, with bending moment minimised: They are not used to adjust the steering geometry so they are always wound all the way into the gudgeons.
The rod ends that broke (one in practice and one during a race) exhibited brittle failure with no sign of fatigue.
The instantaneous load simply exceeded the strength of the part.
We have since sourced a higher-spec equivalent rod end made with a forged/rolled process using a stronger steel.
These were used for the remainder of the series and held up well.

Looking at failures of rudder fittings on other designs (and there were a few), especially on boats where conventional gudgeons were adapted to take some vertical lift, it is obvious that the engineering has to take into account much greater moments. The transoms and fittings must now be engineered accordingly.

As always the learning curve is absorbing and the weakest link is constantly exposed as it is chased around the system. Fascinating times!

Applied

Here is the updated design to emerge from the experience.
More details later but, as you can see, the spherical bearings have been replaced in favour of machined sliders. Existing systems can be updated with higher spec rod ends or swapped for the new system as mounting hole spacings and rudder housings are compatible.

Update

With the A Cat Europeans and Australian Nationals coming up, it is a very exciting time in the class. Paradox will not be at these events as we are well into finalising the production design that, as you will see very soon, is a totally new boat with most key concepts re-visited.

Looking back at the brief, we had to make some honest assessments about the goals that had been achieved and the price we were paying in terms of performance and complexity of use.
With the same goals in mind, we revised our approach focusing on minimum drag and low-demand 'set and forget' systems.

Over the past few months we tested different concepts, using different ideas compared to the initial forward mounted S foils and max-span L rudders.
Our assessment is that the S foil solution involves too many compromises in this application.
Better all-round geometries exist that allow stable, easily managed foil assisted and full foilborne sailing where the skipper can push hard with confidence.

The hull shape has changed slightly to suit, the beams are tweaked and many engineering details are revised.

Indulging my obsession for elegant, beautiful detailing and top quality finish, even more fittings are custom and the overall package is even more refined.

At the same time the production process is being streamlined further to make the cost even more competitive.

Carbonicboats will have a presence at the A Cat nationals as a race day sponsor, supporting the class. It was a tough decision to sit out this regatta but ultimately it was a matter of resource management and rationalising priorities.

Given the lessons learned during the summer, it made sense to spend the winter getting the production boat sorted to offer the best possible product to our customers.

The coming summer will be upon us soon enough and it will bring a full calendar of racing that we thoroughly look forward to.

We want to be there with well prepared weapons and hope our fellow sailors will believe in us enough to put in more orders soon.

Our red 'periodic table' logo is there as we prepare

to get back into the fray very soon...

A Different Look

Some quick snaps of the last shell just out of the mould.
We are building a series of 10 Katana Marbleheads using a special hybrid cloth.
The red bits are Kevlar.
No change in structural properties, just a different and unique look.
We will keep the boats in stock so grab yours today!

Versatility

This week we started production of tooling for an improved rudder design for Paradox.
Design work from here on in is entirely in-house.

Considerable drag reductions should be possible through increasing the efficiency of the ‘L’ surface. 

This is achieved by improving the aspect ratio of the horizontal foil. 
Increasing the aspect ratio dramatically reduces induced drag. The new aspect ratio is in the realm of competition sailplane wings. 

Careful structural optimisation has allowed us to exploit this solution with no cost or weight penalties.

Mk1 rudder shown yellow, new version in red

At the same time we have confirmed that the actual force the winglets have to generate is considerably less than initially predicted. We will test progressively smaller winglets to validate the new calculations. 

When you add together the increased efficiency and the smaller force required, the size of the winglets reduces dramatically (close to 50%), giving a significant drag reduction.

Mk1 rudder shown yellow, new version in red

The new rudders are conceived to be versatile in two ways:

1) The winglets have an untapered portion near the tip so they can be trimmed off at any length and still maintain an efficient planform shape. 

Cutting them off 180mm from the root gives equivalent area to the “+” winglets being offered by other manufacturers (typically a pair with 100mm span each, giving 200mm total span). 

However the L solution is free of the interference drag created by the intersection of three separate foils. 
Any intermediate area can be chosen to suit the preferences of the user.

2) The top of the rudder is tapered such that the whole blade can be reversed. This gives the option of eliminating the winglets all together in light conditions while having them 'on standby' ready to deploy if the weather changes.

The compensation has also been refined (increased and redistributed vertically) to give a lighter feel on the tiller.

The new rudder will come standard with every Paradox.

The versatility of the new rudders allows us to confidently offer them for sale separately to customers who want to retrofit them to existing boats, with or without our cassette and gudgeon system.

More Machining

Another nice piece of CNC milling for production tooling...

Digital Age

The first batch of our new Swing Rig Blocks. They come in three different 'flavours' to accommodate different main boom angles for different clew heights between suits.

As our regular followers know, we are always passionate about sharing lessons learned in development and explaining evolving methodologies.

For Katana we engineered and prototyped moulds for making integrated main and jib booms over a short length of 14mm ID carbon tube. The booms were then cut out of foam sandwich such that the core was in the vertical plane. The skins captured the piece of tube which effectively replaced, and created a bulge in, the core around the intersection with the mast. The 14mm ID tube that formed part of the boom/yard moulding would then be bonded to the outside of the mast tube.

Even with well thought out moulds this would have been a relatively labour-intensive approach. The result had good structural efficiency in the boom section but required considerable reinforcement around the junction area, offsetting most of the gains. Windage was marginally higher but the deck sealing effect could be maximised as the booms could be cut to exactly follow the foot droop permitted in the rule.

So we revisited an old solution that seems to have been abandoned due to an irrational preference for the latest material over an objective analysis of suitability for the application.
The difference today is that CNC milling allows exact replicability without expensive fixtures.
Most importantly, the penalty for adding complexity is considerably less than for manual processes (including laminating carbon fibre).

After several iterations, our late stage prototypes use aluminium in the high stress junction area where it is desirable to react the forces on the boom and yard over the shortest possible vertical distance to keep the mainsail tack close to the deck.
Carbon tube is used for the boom and yard as this provides an excellent compromise between stiffness, windage, ease of assembly, and cost.
Being machine laminated, tube has good consistency and, being round, it allows efficient attachments and adjustment systems.

Previous similar blocks by other manufacturers did not incorporate angled main boom connections so the boom was usually either made from bent aluminium (heavy and flexible) or required an elbow somewhere along its length (structurally inefficient).
With the correct angle machined in, efficient straight booms (cylindrical or tapered) can be used.

FEA allowed us to take as much weight as possible out of the part and hard anodising ensures good resistance against corrosion. Different colours are also possible.

Stay tuned to see the parts at work on our Katana test boats.

The New Black

Katana Marblehead specimens just out of the moulds. More to follow shortly...

In the Metal

Katana appendage tooling machined directly as female moulds from solid metal...
The fin incorporates additional drought so it will be suitable for larger boats such as 10 Raters.
It can also be adapted for classes with restricted drought such as the IOM.
The lower Reynolds Numbers characteristic of IOM class boats makes it advantageous to use the top part of the fin mould, keeping the trunking design common.

Initial coarse passes shown. The machine will then return with progressively finer steps down to less than 0.1mm. The only final hand finishing required is a very light sand and polish.

For such small, shallow, rigid moulds that can be made directly as female tools, the investment in more expensive and slower to machine materials is warranted. 

The step of laminating a female mould from a pattern is eliminated and the final tooling will be capable of withstanding high mechanical pressures and elevated temperatures to produce very compact laminates.

Bulb mould also shown at coarse stage (below). The plate that will form the fin cavity is visible on the left. Pouring hole for the lead and vent holes fore-and-aft are visible on the right.

These shots also courtesy Alex Kryger, Aptec Composites.

Katana Tooling Takes Shape

From virtual to reality.
The magic is being worked by Aptec Composites.
Images courtesy Alex Kryger.

Hull plug/pattern (above) and deck plug (below) machined ready for surface finishing.

Notice the bonding flanges for mast tubes and centreboard case, as well as all deck features, integrated in the tooling to ensure accuracy and repeatability.
The mould flanges and locating features to close the hull and deck mould together are also machined at this stage.

There is an interesting tradeoff between material cost and the expense of surface finishing.
In the case of larger simpler shapes we found it more economical to use an easy to machine stable but comparatively low cost material and go through the process of sealing and hand finishing to get the required surface finish.
Smaller and more detailed tooling will be machined from metal or plastic, requiring only a final polish after fine machining.
Where the parts must be made at high temperature, plastic plugs will be used to make female moulds in the same material as the eventual parts.