Volvo Inshore Foiler--Technical Design Information

[sigurd]

I don't think there are any efficient and fast boats that use a spinaker. Boats that sail up to several times the windspeed always sail into the apparent wind, and a spinaker requires wind from aft to work, due to its huge camber. Fast dingys and cats use a flatter sail called a genaker (or asymetric spinaker), and even more efficient boats, such as foilers, might barely be able to use a code zero (which has camber in between a genaker and genoa).

The extra foil is just there to lower the takeoff windspeed or you could say decrease the wetted area at cruise speed. It is shallower than the others so that it can rise above the surface at speed. They can not retract it without blocking mast rotation (unless they have some mechanism not shown in the render). The position they have put it is the only place they already had 'bury' for it, ie. the main aka with its dolphin striker.

What was it you wondered about the hulls? They look normal to me. I think the volume in this case is just a byproduct of the length, desired freeboard, a fuller Cp than was usual 40 years ago and a minimum drag hull width.

 

[TANSL]

Thank you very much, @sigurd, for your explanations. I think that, in addition to marveling at these beautiful things, the interesting thing is to try to find out for what and why these things are the way they are. The photo with the render can also be found on Facebook but this forum is much more than that.
Regarding the spinaker or genaker, I suppose the explanation is that the apparent wind is never the stern wind. But to get the position of the figure, it is necessary that the ship, somehow, get to increase its speed a lot with an apparent wind that, at least initially, comes from the stern. (excuse my inappropriate sailors terms).

Hulls seem to me very bulky but, of course, it is only an appreciation. Perhaps the mechanisms that carry inside define its dimensions.
The central foil, I still can not find an explanation that convinces me. It should be placed at a point where it would facilitate the balance of the set and not place it under the mast because there is no other space. In any case, the balance of the support boat in 4 points is always more problematic than with three points because between two non consecutive points there it is created an undesirable pivot axis. One could wonder and explain why you can not increase the surface, or create a more efficient profile, in the side foils to get the takeoff with softer wind.
On the other hand, it seems that it is a single-seater (there is only one seat and or one point where a moderately safe crew member can go). Can a single man handle this artifact?

 

[Doug Lord]

Vote for this project here: FW AWARDS 2017 Vote http://www.foilingweek.com/pages/season-2017/foiling-week-awards-2017/fw-awards-2017-vote/

 

[David Cooper]

It's shorter than the other foils because it's only needed for early flight - if there's enough wind to fly high, there's enough wind to fly with it retracted, and it's also possible that there's always enough wind to fly with it retracted as soon as the hulls are clear of the water. (This neatly gets round the problem Fire Arrow has where it can't reduce the amount of foil in the water once it's up - it has early flight, but its higher speeds are held back by extra drag until its ability to generate downforce reverses the disadvantage.) Unfortunately, T foils aren't great upwind unless they're canted, so a boat that doesn't cant them is just asking to be beaten by a better design.

 

[sigurd]

And how would you retract it underway? Not saying it can't be done, but I don't think they intend to. Dropping it for every tack maybe? Or do they have a rotating daggercase that I haven't noticed?

 

[Doug Lord]

Info from Doug Schickler from a thread of mine on SA :
Part 1--
So, the first thing to understand about the project as you see it, is that it was a concept that was developed for a very specific type of event. Inshore, short course, 99-100% foiling fleet racing. ST does not for a moment think that this kind of craft is there to erase all other forms of sailing. Those who say that if this is the future of sailing, why sail? Well, sail what you like. I like small skiffs / dinghies and large cats. I am infatuated with minis. Davide loves the moth. Davide and I have not done as much foiling as maybe half of the readers of this forum, but that does not negate what we bring to the table as designers and engineers very much in the thick of foiling design work e.g. dna G4, Luna Rossa, Team France and many other projects in between.

Does anyone dispute that the development from AC45, GC32, AC72, AC50 and others that the current layout, with crew crossing the boat and a foil layout that, when things go very wrong, too often ends in a nosedive, does not provide a platform where VIP sailors and/or non-sailors can be safety foiled around the race course by a professional team? That is the goal of the design, at its heart. If not going from side to side, Frank Cammas does not nearly lose his leg falling overboard. If not positioned in the hull cockpit, Team Softbank Japan sailors do not get narrowly saved by the shroud of their boat in a pre-start. Foiling racing with just 2 boats is a fair bit more dangerous than most sailors have experienced. Just as racing an ultimate tri trans ocean is more dangerous than foiling an A class.

The canopy was a very difficult choice for me personally. We debated a lot about the problem of blocking out the environment. But, it is the decision we made for this boat. I had discussed the same with Paul Larsen at the little cup in Falmouth. It was a close call for SR2 IIRC. You may hate it and think it is ridiculous. It is a reality on this boat for reasons of safety of the crew and the VIP. Not just for crashes, but also for ease of communication between the crew, and the guest. Additionally there is windage to consider, which is a huge portion of the total drag at these speeds.

The sail trim position has been criticized in other forums (fora?) and I have been perhaps too cavalier in answering the comments. Yes it is a rotating mast, yes the main twist will be crucial in the sail trim of the boat. But there is a really substantial difference in this craft that essentially only a handful of boats have utilized. The co-pilot, the second person in the cockpit, has a primary job of controlling flight height and RM, through the use of differential lift of the port and starboard main foil flaps. All of the boats foiling RM is developed through hydrodynamics, and it has to ultimately be capped by monitoring rig tension. We had a simulator made to test this craft, just as they have done in the Cup teams. The outcome is that RM will be directly adjusted before most sail trim changes are made. Foils will be actively trimmed even more frequently than sails, because weight is not moving and its more responsive than changing the sails.

Looking at it another way, on e.g. a moth or an A-class, your position on the boat is crucial for the stability and limited in range. You cannot move more outboard (or aft or fwd) than you are able to do with rack or trapeze. You put your weight there for stability, not to get the best view of the sail trim. You go to max stability when you can because it is fast. To stay there you trim a lot. On this foiler, the crew needs to be forward. Putting them in the hulls was rejected for safety and weight reasons. Again, they are positioned not for sail trim, but because the force balance dictates where they need to be. So, they have to adapt to the sail trim view they have. In a high tech boat such as this, expect there to be electronic means of seeing/feeling/sensing the sail trim many times a second.

I will go ahead and post this much, expecting some replies. I hope a few positives and not only what can happen here on Anarchy. Future topics to elaborate on are the decision to use flapped T foils, the canard configuration including forward rudder (which I am pleased to see Steve shares) and the decision not to use a wing (or a boom). (edit - don't expect much comment on the packing in a container or non beach launching the boat, please read the tender doc before you throw stones)

In the mean time, if you think this project merits your vote for innovation, please link through to the foiling week and do just that. FW AWARDS 2017 Vote http://www.foilingweek.com/pages/season-2017/foiling-week-awards-2017/fw-awards-2017-vote/
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Part 2-


I wanted to continue on my earlier post, and will speak to points made by Steve, GBR, etc at another time.

The decision to use flapped T foils is based on a couple of factors. The project brief asked for the ability to have a lake version, capable of sailing and possibly even foiling in pretty light winds. At the same time, it had to be used far up the wind range too. So, different sets of foils with different area were more or less imposed. At the same time, there is a reliability and build budget aspect that cannot be ignored. Trust me, I know that it seems ridiculous to complain about budget when the idea is to build a 40 foot racer for 700k, with the benefits of the economy of scale. That said, it can take up to 3 months of work to build a daggerboard for the AC50. Based on experience of the G4, a forty footer, could we really commit 100k Euro to a pair of foils, have two sets, prepare to build a few spares for the fleet AND still have a budget for the systems, spars, sails etc? In addition, positioning foils that would weigh up to 70 or 75 kg in an accurate quick raking system to get the kind of reaction times necessary is expensive. Raising and lowering foils as in the AC really takes up a ton of energy apart from the rake and yaw. Hydraulics and control systems require a budget and juice. The accumulator needs to be topped up to have ample pressure and flow of oil.

The answer is to unload the maneuvering system, so that it requires the minimum amount of energy for the maximum benefit. Lessen the build cost of the foils, and chose a means to swap out parts or entire foils that is simple and robust. Letterbox insertion of struts, that remain lowered, with the possibility given a couple of screws to swap lift foils. Flaps are chosen specifically because the weight of the boat is carried by the fixed strut, flow across the leading edge remains attached despite changes in lift force, and the energy required to articulate the flap is a lot less than raking rams.

The canard configuration serves a couple of purposes. It requires the crew to be forward. So the sail and the crew no longer have to be in the same position longitudinally. That may be more of a happy outcome, and extra benefit, than a goal, but it is there nonetheless. The first reason was the direct action of the changes in pitch. If you want to create upward angle to the main foil you use the canard foil to lift the bow, not push down the stern and wait for the lift force of the main foil in front to lift the bow. This is a fundamentally more direct way to alter pitch and of course comes from aircraft design, it cannot be denied. The canard layout has another meaning too. The main lift foils carry the majority of the mass. As speed increases and the need for RM goes up, the leeward foil lifts more and more, while the windward pulls down. They will therefore be much more loaded in terms of pressure distribution as well. If the main foil ventilates or cavitates due to this pressure field, flow is lost and lift is lost. The weight of the boat is aft of the remaining lifting foil at the bow, so the stern drops. The current AC45/50 layout does the opposite, and if downforce is used for stability (which it is on the windward rudder) it become even more critical. Loss of the flow and lift of the leeward L foil leads to a nose dive. As does ventilation of the windward rudder stabilizer which up to then was adding RM, if it does not lead to capsize first. So the canard layout is seen to have a more acceptable crash mode.
==============================

Part 3-
last installment of design considerations. Above I was describing the choice of a canard configuration.

This led of course to discussions of using the forward rudder. In this situation, there is a bit of break from aircraft technology. Even most canard type airplanes have tail rudders. But not all. The B2 bomber is a notable exception. It has no forward rudder either, for that matter. Stealth dictated that it have none and steer with other means (thrust/drag). We discussed internally the risks and benefits of a forward rudder. It was the SailRocket 2 that was the most convincing case for a forward rudder, although it is not a foiler but a skimmer. It did however prove that course holding at high speeds could be done effectively with a forward rudder, even in the absence of fly-by-wire. By that I mean an electronic means to control dynamic instability using a control system that can monitor the need for very small and frequent corrections while at the same time executing user chosen maneuvers. We really wanted to stay with a high performing 3 point layout of foils, just for drag reasons. And we wanted to have the rudder/elevator setup right at the helm position, where the skipper or pilot is making the maneuvers, in part for feedback and in part for cost containment. For these reasons we opted for a forward rudder and only one on CL. The straight line VPP and dynamic simulation performed have not given a good reason to change that. A nice bonus from our point of view is that when things are going their worst, and the bow is heading down toward the water, the helms ability to alter course is getting better not worse. And it should be the same amount of rudder available in cases of heel angle given the foil type.

I will be honest with you all, we do think there may be some steep operational learning curve steps when this boat is built. The bear away from a standstill in the starting arena is a move that I have thought a long time about. Could the boat trip? Maybe but doubtful, still more drag aft of the CG and CE. How easily will it transition from 0.2 knots with 100% stability based on beam to 20 knots a few moments later with 100% stability based on differential forces up and down? We have a feature at the bow of each hull, a spring loaded and over compensated foil on the inboard side. The spring keeps this foil at its horizontal lower limit for windage reasons. But the axis of rotation is well aft of the foil center of effort, so that a nose down entry into the water can create a good angle of attack, maybe 15-20 degrees from horizontal. At even moderate speed, and when more so when accelerating, this should produce a strong bow up moment. This lessens the need for really huge hull volumes, which in turn add windage. What hull volume we do have in the hulls is more forward (where the weight is) so it floats normally at the dock. The hydrostatic effect of the larger bows is a nice consequence to add to the foil lift for ... imperfect maneuvers.

Lastly, the deck sweeper. For economic, container deployment, reefing, and just plain familiarity reasons we opted for a soft sail on a rotating rig. It is well proven, and the use of such a rig has not stopped the GC32 from foiling well. We wanted to get away from a headsail, and felt we could except for very low winds. So far, that seems to be viable in the VPP, in no small part because of using a deck sweeping main. Really and truly deck sweeping. We have no reason to pass from side to side, so it became clear that no boom should be used. This has been utilized on the most recent A-class worlds (and very likely is something that has been tried repeatedly in the history of the class). Instead we developed a two ram system led to an arced track that allows the trimmer to control foot and leach pretty much independently from each other and from the LE-TE angle (not boom angle you see). Add to this a cunningham and a zipper reefs (as seen in mini headsails) and the sail profile and plan will be adaptable. More drag than wing, yes, but more pragmatic and light weight. We can take a lot of lessons out of very high performance wheeled and ice borne sailing craft when it comes to rig and sail setup. The only caveat is that we need to get up on the foils in order to change our drag situation. Therefore we kept a larger furling headsail, only to be fit when conditions are 9 knots or less, so as not to have it dragging when we have 10 plus.

OK, I think that covers most of the design points for the VOR foiler project, if you have questions I will be checking back.

 

[Doug Lord]

It's shorter than the other foils because it's only needed for early flight - if there's enough wind to fly high, there's enough wind to fly with it retracted, and it's also possible that there's always enough wind to fly with it retracted as soon as the hulls are clear of the water. (This neatly gets round the problem Fire Arrow has where it can't reduce the amount of foil in the water once it's up - it has early flight, but its higher speeds are held back by extra drag until its ability to generate downforce reverses the disadvantage.) Unfortunately, T foils aren't great upwind unless they're canted, so a boat that doesn't cant them is just asking to be beaten by a better design.

==============================
I don't think its a problem. Among its many duties the main foil also works with the rudder T-foil to augment pitch stability
and it's pitch control ability stays intact through the whole range of wand movement/flight altitude* including lift or downforce.
And don't forget: as soon as the boat begins to fly the mainfoil begins to unload reducing induced drag.
*main hull flight altitude results in a preset angle of heel for the whole boat.

 

[OzFred]

…if it is retractable, why it is much shorter than the other foils…

It's not retractable. If it was, then when retracted it would interfere with the bottom of the sail and possibly boom when tacking or gybing, leading to an instant capsize.

It's an optional extra foil intended to help get foiling in marginal conditions and lift clear of the water once foiling. I think it's one of those things that seems good as a concept, but in practice will not be useful.

Optional Central T foil: Operates as a light wind booster. The central foil raises out of the water when boat speed is high enough

 

[OzFred]

It's shorter than the other foils because it's only needed for early flight - if there's enough wind to fly high, there's enough wind to fly with it retracted…

You mean removed, since the boat can't be tacked or gybed with the foil raised.

…(This neatly gets round the problem Fire Arrow has where it can't reduce the amount of foil in the water once it's up - it has early flight, but its higher speeds are held back by extra drag until its ability to generate downforce reverses the disadvantage.)

There is also additional drag from the countering additional lift from the leeward foil (so wearing double the drag penalty). This theory has never been confirmed by detailed calculations or simulations, or in practice. If conditions require the extra foil to get foiling, it won't be needed for downforce to increase righting moment.

In a boat that also has an always–down windward foil, the central foil doesn't need to produce downforce at all. That job can be done very much more efficiently by the windward foil.

 

[OzFred]

Why?

Automobiles have very sophisticated steering systems, with mechanical linkages, gearing to dampen feedback and (lately) power assistance to ensure they are stable, robust and easy to operate. Their range of operation is also much restricted when compared to a rudder e.g. the steering wheel may have 3.5 turns lock–to–lock, moving the wheels through roughly ±45°. Rudder steering systems are crude in comparison.

A vehicle steering system similar to a rudder is that of a typical back yard billy cart. In it's simplest form, the front wheels are fixed to a beam that rotates around a central axis. In most designs, the driver has their feet on the steering axle, using the strength of their legs to provide stability. There's usually a rope too, but that's more just to hang on (and drag the cart back up the hill…).

Try going fast down a hill and steer with just the rope and no feet on the steering axle. You will find it very difficult and unstable, so wear a crash helmet and body armour.

 

[Doug Lord]

You mean removed, since the boat can't be tacked or gybed with the foil raised.



There is also additional drag from the countering additional lift from the leeward foil (so wearing double the drag penalty). This theory has never been confirmed by detailed calculations or simulations, or in practice. If conditions require the extra foil to get foiling, it won't be needed for downforce to increase righting moment.

In a boat that also has an always–down windward foil, the central foil doesn't need to produce downforce at all. That job can be done very much more efficiently by the windward foil.

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Wrong. The center foil downforce has been proven in month and a half testing where it prevented capsize or pitchpole* on the second day of testing in overpowered conditions. Detailed calculations were done to find the area of the main foil,flap area and potential downforce-and modify it during testing--- as was done with every foil and every aspect of the boat including the major bottom modification before sailing tests even began. Fire Arrow has a substantially oversquare beam which enhances the effectiveness of downforce from the main foil. Using the windward ama for downforce on Fire Arrow is completely impractical. The main foil works well and automatically produces downforce as needed. Also, the fact is that the net effect of downforce is a gain due to the increased RM-well proven.(see post 31 on the next page)
Center foil downforce is also possible on Maserati(where I know it was used-manually controlled) and Gitana 17 and, possibly, Banque Pop.
* correction: downforce did not prevent a pitchpole but lift from the center foil did more than once.
And Gabart wishes he had it on Macif:
Found by Dolfiman in the Macif round the world thread-----
In François Gabart 10 nov. message :
""You have to find the balance to be able to stay in support on the central hull, but it's not so easy when you go fast. I cannot stay on the central hull all the time and I'm still not comfortable sleeping like that. It's starting to come, it will take training again. But my sleep is damaged, despite fatigue. I still managed to take a few naps."

Is it not in this case that a foil on central daggerboard, when adjusted to provide a small downforce, which can add passive safety when the singlehander is sleeping ? In case of gust of wind with a move to more heel, the inflow incidence on this foil increase instantly and can provide an extra RM which adds to the one due to the weight. And moreover in steady state condition, this foil RM component is in squared speed boat, can increase in parallel with heeling moment in squared apparent wind speed. I am right ?

 

[TANSL]

The main foil works well and automatically produces downforce as needed.

On several occasions you have indicated that in the Fire Arrow "The main foil works well and automatically produces .....". Is this a feature that only your Fire Arrow has?. How is this automatism achieved?. Does it simply mean that it occurs when the foil is under the water?

 

[Doug Lord]

On several occasions you have indicated that in the Fire Arrow "The main foil works well and automatically produces .....". Is this a feature that only your Fire Arrow has?. How is this automatism achieved?. Does it simply mean that it occurs when the foil is under the water?

====================
I wrote this yesterday for you-seems like you must not have read it. Ask questions if there is something you don't understand. Fire Arrow(and WOLF) are the only boats using a wand surface sensor for automatic control of the mainfoil flap on a trimaran. However, the other three boats using this basic system may or may not have some electronic means of controlling the mainfoil lift.
From the Test Model thread yesterday:
Downforce may be hard to understand for some because what isn't shown in the sketches is the LIFT of the main hull due to wind pressure on the rig*. As the boat begins to fly the mainfoil is unloaded due to this pressure. Just before downforce begins the mainfoil is at zero lift. Lift on the main foil is automatically controlled by a wand surface sensor. As the wind pressure increases the boat heels a bit causing the wand to reduce the down-flap angle until the flap reduces the foil lift to zero. Downforce is caused when the wand raises the flap above the no lift point. At the no lift point, the mainhull is entirely supported by the wind pressure on the rig. As wind pressure on the rig increases further the wand causes the flap to rise which generates downforce.
*The mainfoil can lift the main hull BEFORE there is enough wind pressure to do so.

 

[TANSL]

I'm sorry Doug but I'm not reading all the threads that are on similar topics that are mixing types of hulls, types of foils, with totally different opinions and with explanations, to my mind, unclear, with little technical support. Recently I try to learn about foils and, truthfully, it is not easy for me to understand what, in some ccases, is not well explained.
Thank you, again, for your answers to my stupid and repetitive questions.

 

[OzFred]

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Wrong. The center foil downforce has been proven in month and a half testing…

Your exaggeration is to the point of absurdity. Your testing diary published here reveals 4 sessions totalling 1 hour and 50 minutes of sailing, with a maximum of 15 seconds of continuous foiling and "[p]robably a minute + for the whole day".

…where it prevented capsize or pitchpole on the second day of testing in overpowered conditions.

And you established that how, particularly since conditions were marginal for foiling? You don't have measurements or even calculations of overturning moment or downforce on particular points of sail in various conditions and heal angles. Nor do you have equivalent testing without the main foil to determine capsize or pitchpole conditions empirically.

BTW, as far as I know that's the first time you've ever claimed the central foil prevents pitch poling. Another claim with zero evidence.

Found by Dolfiman in the Macif round the world thread-----
In François Gabart 10 nov. message :
""You have to find the balance to be able to stay in support on the central hull, but it's not so easy when you go fast. I cannot stay on the central hull all the time and I'm still not comfortable sleeping like that. It's starting to come, it will take training again. But my sleep is damaged, despite fatigue. I still managed to take a few naps."

Is it not in this case that a foil on central daggerboard, when adjusted to provide a small downforce, which can add passive safety when the singlehander is sleeping ? In case of gust of wind with a move to more heel, the inflow incidence on this foil increase instantly and can provide an extra RM which adds to the one due to the weight. And moreover in steady state condition, this foil RM component is in squared speed boat, can increase in parallel with heeling moment in squared apparent wind speed. I am right ?

Gabart is theorising that setting the main foil for downforce while he's sleeping may be a safety feature. That is completely different to using a central foil with downforce to increase RM and VMG. That is the theory that is yet to be proven.

Please also note that I am not saying "you are wrong" about the RM, only that you have no proof in regard to your theory.

A feature of that proof would be comparison with and without the foil generating downforce and with other methods of generating adjustable righting moment, such as using water ballast or canting the rig, along with an analysis of the conditions where it's beneficial, when it isn't and the limits in terms of structural integrity and safety.

I take my hat off to Gabart and the Macif team, and to Gitana and others that put large amounts of their money, time and effort to test their theories. They make it clear when they are theorising, when they are talking from experience and where they see the limits.