A Blur

Finishing and assembly phases on the first A Cat platform.
Validating important choices both technical and logistical.
As explained in the brief, each choice has several components and must strike a balance between performance, reliability, durability, cost and being repeatable in a scaleable production context.
Building information into the tooling is vital to keeping production hours within economically sustainable limits.
The supply chain is relatively complex and identifying the best suppliers, methods of transportation and lead times has been a very interesting challenge.
We are looking forward to reporting on the first on-the-water tests.

Beamed Up

First A Cat prototype platform is now in one piece.
Stay tuned for more...

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.

Paired Up

First set of A Cat prototype hulls structurally complete. More detailed info about construction choices will follow soon.

Rule Driven

I prepared this diagram for the last installment of the series on foils to be published in Australian Sailing + Yachting Magazine. It illustrates a great example of how rule spaces drive solutions that may differ to address the same problem.

This a seminal time in the development of dynamically stable foiling systems.
Since the limits of foil assisted sailing are now regularly being reached, their inherent limitation (inability for lift to exceed displacement) must be overcome to unlock greater performance.

Given that constant radius ‘C’ foils on multihulls cannot be stable in ride height because their dihedral angle increases with altitude, the race is on to invent a multihull foil configuration that is stable, fits inside conventional beam dimensions, and works without adding complexity.

One solution will be unveiled on our new A Class currently in the final stages ofconstruction. Another much discussed solution has been tested recently and spectacularly on the first ETNZ AC72.

Background

Returning to the initial point about the effects of rule peculiarities, the AC72 rule seeks to restrict the major speed producing factors to keep racing close.
Length, beam, displacement and sail area (wing height, girths and sail corner points) are controlled so that the key ratios are precisely similar between boats.

By restricting beam and displacement, righting moment is fixed, equalising the loads that determine the sizing of stays, fittings and sail handling gear.

When formulating the rule, one concern was the possible use of the windward foil to generate downward lift to augment righting moment. 
It was deemed desirable to discourage an arms race in the pursuit of additional righting moment. However no satisfactory wording could be agreed that would have the desired effect without requiring physical measurements of actual foil force. 
The argument was that, with variations in pitch and heel, scrutineers could never be certain that a foil did not, at some time, generate some downward lift. 
My thoughts at the time turned to past experiences such as the ‘Hula’ of TNZ and the double rod rigging loophole in the 2003 AC cycle (in both cases proving that two elements did not touch when in use opened a proverbial can of worms). 
I therefore voted (in my capacity as a Challenger representative at the time), for mandating that the windward board be raised during straight line sailing. 
This in turn required definitions for circumstances such as tacking and jibing, but such provisions would be reflected in the racing rules, and seemed relatively simple to enforce on the water.

Closed Door

An unintended consequence of this rule is that, since the windward foil is not in the water, it cannot be set to increase sideforce. This counter intuitive arrangement is used by 'tripod' foilers such as the Hydroptere: by setting the windward foil with ‘toe-in’ such that it pulls up and to leeward, sideforce is increased. This forces the leeward board to produce a greater hydrodynamic reaction force compared to what it would when just working against sail force.
Since vertical lift is a component of foil force and is therefore tied to sideforce by dihedral angle, if sideforce is below a critical value, foil force cannot exceed boat mass without adding sideforce artificially.
If vertical lift cannot be made to exceed the value given by the component of sideforce determined by dihedral angle, a single angled or curved foil cannot support the mass of the boat except at very high speed and sideforce values.

Forces on Hydroptere tripod configuration when sideforce is small - so vertical component is less than displacement

And at high speed/sail force/sideforce. Both possibilities are precluded in the AC72 Rule

Constraint

So any foiling solution for an AC72 must rely on surfaces at or near the leeward hull. 
The windward rudder can contribute but stability should remain positive when it clears the water at moderate heel angles.

Solution

The ETNZ solution appears at first glance to use an ‘L’ foil with the vertical part pulling sideways and the horizontal part lifting upward. This is indeed the case in upwind mode where boatspeed is still in the foil assisted range and speed control is relatively easy, so stability in ride height is not an issue.

However the tight inflected bend in the top part of the foils makes them cant inward when partially retracted. 
Partial retraction is desirable for downwind sailing because speeds are higher and sideforce is a smaller component of total sail force so less lateral foil area is required to limit leeway.

The key is that, as the foils ‘kick in’, the horizontal portion of the L rotates such that the tip (inboard) is higher than the root (outboard). 
As ride height increases and vertical foil area diminishes due to the top portion clearing the surface, initially leeway increases. 
This reduces the AoA on the kicked up L tip, reducing lift and allowing ride height to settle. 

Elegant and effective if specialised. 

The stable regime is narrow but can be tweaked by adjusting foil rake and dihedral. 
Rake is controlled by displacing the top bearing forward / aft, and dihedral changes with retraction thanks to the inflected top portion.

Pitch attitude is again provided by rudder T foil control surfaces.

More to Come

Look out in future for sophisticated interpretations of the rule that permits only a single axis of rotation as teams explore adjustability to extend the stable regime.

And Repeat

More details from the A Cat build

Boat 1 Hull 1

The first of the black stuff in the A Cat hull moulds...

Parts

Machined fittings for the A Class cat in anodised aluminium, stainless steel, plastic and bronze.
Contact us for more info or for your custom CNC machining requirements.
Carbonicboats can take you from an idea or sketch, through 3d modelling, to finished components in any quantity...

Another Rubicon

Chris Woods, John Fisher, and Roger Paul, have been building the latest incarnation of our Rubicon 10 Rater under license.
They have added their own touches in deck layout and fit-out, and the project is moving along nicely.
Production of our Marblehead Katana in house is underway.
Our IOM is next on the list as, for the time being, it is only available from licensed builders in Europe who are struggling to keep up with demand.

Jigsaw

Blogging about the new A Cat should resume soon after a pause enforced by transport times.
Getting everything in one place across this big country is a great logistical challenge...
A Class Cat mould making has now started in earnest. Rolls of the black stuff visible too.

Another Teaser

More Angles

Some more views of the A Cat shapes in far away Mareeba...

Glossed

The process and resin we are using for our Katana Marblehead are optimised to obtain the best ratio of resin to reinforcement fibres.
In practice this means minimising the amount of resin that cures around the fibres which are themselves a fixed quantity determined by the weight and number of layers of carbon fabric put into the moulds.

The hull and deck skins are vacuum bagged to draw out entrapped air and any resin that is not closely in contact with the fibres.
The upside is a stiffer laminate because the matrix is effectively more tightly packed with reinforcement.

It also means that the fibres appear extremely close to the surface of the finished material simply because there is no surplus thickness of transparent resin to give the visual effect of 'wetness'.
This is what modern composite parts look like. It is a sort of satin finish with perhaps a utiliterian or militaristic 'stealth' quality to the surface finish.
It is interesting that the actual surface is smooth and glossy, replicating the mould surface which in this case is CNC milled then polished to a high gloss and waxed. However the gloss has no 'depth' because the fibres are densely packed microns below the outer surface.

For those who prefer the 'old fashioned' glossy look showing off the fibres encased in an amber like transparent glossy surface, we offer the no cost option of a tough polyurithane varnish which is applied by specialists at YachtMod.
The aesthetic coating is kept as thin as possible thus minimising the associated weight penalty.

As always, the choice is up to the individual. Some prefer one look and some the other. Some want to save every last gram and others are willing to sacrifice a tiny sliver of weight for the sake of beauty. It must be said that the difference in performance is too small to measure so either option should be competitive.

The varnished option offers the possibility to wet sand the boat periodically which is considered good practice by most skippers. Cutting the surface back with 1200 or 2000 grit paper can get rid of any scratches that may accumulate with use and decontaminates the surface from any dirt or oil.
If done correctly it leaves a low sheen (yet another look) that allows water to form a thin coating over the surface without beading.
There is an argument that this characteristic prevents air bubbles from sticking to the surface and acting as trip-turbulators thus possibly delaying the transition from laminar to turbulent flow until somewhere further aft.

However if conditions are sufficiently rough to cause enough pitching to introduce air onto surfaces below the waterline, then the oncoming flow will be turbulent anyway.
Specific tests on this aspect of boundary layer behaviour are few and in my opinion inconclusive.
As long as the surface is smooth and free of contaminants such as road film or dust, drag will be close enough to the practical minimum.

Volume distribution, foil shape, rig positioning, weight distribution, stability and sail trim have effects greater by orders of magnitude.
In a tight class sailing skill will be the key.
The design that best complements the class rule and can be sailed fast with greatest ease will give the sailor the winning edge.

Transit Time

No new interesting images this week since parts are on the road and other projects tick along in that phase where a lot of work takes place but the visible differences are small...

For now, here is a video of the Aptec CNC machine at work on the A Cat rudder plugs.

Thanks to all our regular followers for the great feedback so far. Stay tuned and keep them coming.