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.

Tamahagane

Another symbolic milestone: the last batch of Katana Marblehead hulls from the existing tooling is here.
The old moulds have been 'retired' and work will begin soon on updated tooling.
Deliveries are expected to start again in mid 2015.
Get in touch for more details...

While You Are At It...

Katana M in orange Durepox

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!

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.

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.

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.

Piercing Insights - Part 3

We saw in Part 1 and Part 2 that generalised statements about the handling qualities of ‘wavepiercing’ bows miss the point that bow profile is a reflection of sectional volume distribution, which is a much more useful indicator of design priorities.

Multihull bow sections have recently tended to carry volume lower down rather than above the water ‘in reserve’. Maximum buoyancy is available at smaller bow-down trim angles.
These shapes are inherently slab-sided so tend to come together in upright stem profiles.
Such sections, combined with peaked foredecks designed to shed water easily, characterise modern bow profiles, though there is still considerable variation in the details.
Generally it can be said that such shapes behave more lineally: Gone is the sudden ‘tripping’ effect generated by a wide flat deck suddenly becoming submerged.

So far we have concentrated on downwind bow burying conditions. However the choice of bow shape must also take into account more common cases.

Image source

Straight Line Sailing

As we saw in our look at the A Cat state of the art, multihull volume distribution must consider the doubling in displacement of the leeward hull as the windward one leaves the water. As flying a hull has become more common, limiting immersion or ‘sink’ of the leeward hull has become more important. Another reason for more U shaped sections.
In this respect, the decision must take into account the relative importance of wetted area and cross sectional area, values that can to some extent be traded.

As average speeds have increased, prismatic coefficients have grown, making the ends fuller.
This has led to very interesting findings about the sharpness of forward waterline endings. The concept of a fine bow ‘cutting’ the water has been replaced by more sophisticated ideas that have more in common with aerofoil leading edge theories. Fuller bows have evolved into more bulbous elliptical entries that are less sensitive to changes in the angle of the oncoming flow.

Image source

Pitching

Dynamic periodic motion is a complex subject but the simplified rule of thumb is that the damping effect of fuller extremities is greater than their contribution to pitching.
This is the one context where ‘wavepiercing’ is an apt description. Meaning the upper part of the bow does not contribute to pitching moment as there is no upward component to the hydrostatic pressure. On the contrary, there is a small cancellation with the lower part of the bow. Interestingly, stern flare helps with pitch damping as the dynamics there are slightly different.

Conclusion

Modern bows come in a variety of profiles reflecting different design choices in section shape.
Rather than bundling all these types into one sweeping category and then drawing generalised conclusions, much understanding can be gained by looking a bit more carefully at the underlying section shape.
This should enable us to make a good educated assessment of the priorities driving the design choices in each individual case.

Piercing Insights - Part 2

As we've seen in previous posts, conventional hulls resist bow down trimming forces by immersing more volume forward.
This shifts the centre of buoyancy forward.
If the centre of gravity remains stationary or moves aft, the resulting separation gives a bow up righting moment.

Tornado style ‘conventional’ raked bow profiles indicate flared hull sections.
Meaning the sections get wider moving up, resulting in more volume at the top of the bow.
Such additional volume in the upper part of the hull is what we mean by ‘reserve buoyancy’.

Compare the two IOR maxi bows in the foreground with 
the modern VO70 bows in the background. The hollow profile of the red bow (Steinlager II) reflects progressively widening flare in the topsides. In some cases the bow rake is made less extreme by ‘cheating’ the natural intersections of the two hull halves with a variable radius between the two surfaces. Image source 

Downwind

Conventional bows seek to marry a fine waterline entry with extra volume that only becomes immersed when needed. 

Inherent in this mechanism is a need for significant bow down trim in order for the reserve buoyancy to take effect. 

On a conventional multihull this is not a problem: As the bow is pressed down, the boat will keep sailing horizontally along the surface as the bow immerses. The additional volume going into the water at the front will shift the CB forward and a new equilibrium will be reached. A few degrees of bow down trim has no adverse effect.

Boat trims bow-down and reserve buoyancy gets to work. Image source

The limiting factors in this case are bow freeboard and additional hull drag due to the progressively blunter entry of the trimmed immersed shape. 

Freeboard limits the absolute amount of reserve buoyancy available. Hence the use of 'ski jumps'.  

Additional drag limits acceleration which in turn affects apparent wind (accelerating downwind reduces pressure in the rig, relieving bow down trimming moment).

Multihull evolution has seen reserve buoyancy move down, progressively closer to the normal water level. Meaning sections have developed from being ‘V’ shaped to more ‘U’ shaped. It is no coincidence that this trend occurred at the same time as the advent of angled/curved foils.

Imagine a conventional Tornado style hull with angled or curved foils. 
When reaching at speed the foils would be providing significant vertical force helping to keep the bow up and reducing effective displacement. 

Now imagine this hypothetical boat encountering a gust: The rig would power up and press the bow down. Since the reserve buoyancy is some distance above the water, bow down trim would initially increase to bring the reserve buoyancy into play. 

But at the same time the bow down trim would reduce the angle of attack of the foils, possibly even bringing it below neutral. 

The boat would not tend to follow the water surface. Instead it would want to follow the chord line of the foils. This would create a feedback loop where bow down trim would increase bow down trimming force…

Having reserve buoyancy low down in the bow sections makes it immediately available. This is desirable when pitch attitude is critical such as on foil assisted boats.

When things get out of shape, the wide flat deck of a conventional hull abruptly increases drag at the very point where reserve buoyancy runs out. 

A carefully shaped ‘upside down’ bow brings the water flow back together cleanly above it, giving the boat a better chance of accelerating and shedding water to allow the bow to pop back up. 

Image source

But this is not the exclusive preserve of radical inverted bows. 
More moderate shapes such as the Boyer MkIV A Cat still benefit from this effect. 

This brings us back to the premise that 'wavepiercing bow' is too generic a term to be indicative of behaviour or performance.
The vertical location of the maximum section width is the feature that tells you the most about the design priorities of a particular boat. 

The bow profile is an indication of this vertical volume distribution.

In the final Part 3 we will look at the more subtle considerations of straight line sailing and wave induced pitching. 

The New Black

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

Piercing Insights - Part 1

We are receiving many questions about the pros and cons of so-called wavepiercing bows.
There seems to be much debate among sailors, partly fueled by unsubstantiated claims from manufacturers.

As our regular followers and clients know, at Carbonicboats we do not make dogmatic proclamations about what our products will do.
Instead we explain the reasoning that leads us to each design choice.
We aim to demystify the principles at work, acknowledging that in most cases there are tradeoffs involved.
Sharing the process is a way to communicate our passion for the art of design.

So let’s look at modern bow shapes.
Unsurprisingly, the ‘piercing vs conventional’ debate is founded on a false dichotomy.
The obvious visual character of a bow profile is in fact almost incidental.
It is driven by something more subtle: The distribution of volume in the cross sections.

Each cross section shape naturally comes together to give a characteristic bow profile.
To understand how this works, look at the following illustrations.
The port and starboard hull halves are shown in red and green respectively, and the transverse section lines are in yellow.
By extending each hull half past the centreline, you can clearly see that the way the two sides intersect defines the centerline profile of the bow.

So now when you look at a bow profile you will be able to read the section shape.
It follows that wavepiercing bows are not just conventional bows 'chopped off' with the excess freeboard removed.
Instead they are simply a consequence of a particular section volume distribution.
It doesn’t make sense to say that they are inherently more or less susceptible to burying as is being claimed by certain parties.
The question instead becomes: ‘what are the pros and cons of different section shapes?’
That will be the subject of Part 2

Production Line

Some images of Katana Marblehead tooling coming together nicely...

Busy Times

Progress continues on RM tooling preparation in the workshop.
In the office the A Cat design is approaching completion.
R10R and IOM developments are in the pipeline and consultancy work continues on aerospace components.

Wax On... Wax Off

Progress on RM tooling: Plugs/patterns have been delivered, now preparations begin for taking female moulds.

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.