Tornado-Cat

Boats and foils comparison

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9 minutes ago, Basiliscus said:

Foil thickness is a major driver of the cavitation speed.  Going faster requires thinner foils.  I haven't tried to calculate how much volume is required to achieve the necessary weight of foil to meet the c.g. requirement of the rule.  But it's quite possible the mass could drive the thickness to get the necessary volume, and this could limit the cavitation speed.  A bulb would allow the foils to be thinner and less subject to cavitation.

Yes that's a good point! ENTZ foils look like they carry more surface area. So maybe they need to, to get them thin enough. Based on the mass required??

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Just now, uflux said:

Yes I agree! ENTZ foils look like they carry more surface area. So maybe they need to, to get them thin enough. Based on the mass required??

That and there will be more demand on controlling the ‘flight surfaces’ with a thinner foil...

 

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@uflux How unbiased are you?

Being an out and out ETNZ fan I would love to believe what you say.

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Crude pictures but they give you the idea. So the fairings on the ugly one could hide hinges  like these. 

E6065377-2820-473A-AFA4-69298ADAA1B0.jpeg

CD75F6FE-D8C5-4612-94DC-9B367E47F62E.jpeg

6CE0958D-923B-40AC-9B39-9672BD1756BD.jpeg

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1 minute ago, Kiwing said:

@uflux How unbiased are you?

Being an out and out ETNZ fan I would love to believe what you say.

Oh, I am definitely an ETNZ supporter. But want that boat to have the best design solutions whatever they are! 

It does help that they have the best foil designer currently...

Anyway this cup won't be won with foils. This cup will largely be about sail solutions. Who can manipulate the sail shape the most efficiently.

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6 minutes ago, amc said:

Crude pictures but they give you the idea. So the fairings on the ugly one could hide hinges  like these. 

E6065377-2820-473A-AFA4-69298ADAA1B0.jpeg

CD75F6FE-D8C5-4612-94DC-9B367E47F62E.jpeg

6CE0958D-923B-40AC-9B39-9672BD1756BD.jpeg

Yep that would do it !

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4 minutes ago, uflux said:

............

Anyway this cup won't be won with foils. This cup will largely be about sail solutions. Who can manipulate the sail shape the most efficiently.

Wow you are the first person who has come out and said that,  Thanks I agree.  That is why I started Twin skin but not of facts to talk about except the "no boom" LR and we can only speculate.

See you over in Twin skin, perhaps, now it is starting to hot up and we might see some close ups of sail shapes? Look down from a drone???

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20 minutes ago, amc said:

Crude pictures but they give you the idea. So the fairings on the ugly one could hide hinges  like these. 

E6065377-2820-473A-AFA4-69298ADAA1B0.jpeg

CD75F6FE-D8C5-4612-94DC-9B367E47F62E.jpeg

6CE0958D-923B-40AC-9B39-9672BD1756BD.jpeg

I think it could comply with 15.4 if considered as "cross section".

As for you previous demonstration, I don't know if it could comply within the limit of 15.9 if considered a "connection span".

15.4 At any cross-section, the only permitted movement of a foil flap relative to a foil wing is a rotation about
an axis that remains approximately stationary with respect to the foil wing at that cross-section. This axis
must be designed to be stationary
, but is permitted to have some movement resulting from:
(a) play in a mechanical bearing; or
(b) a flexure or soft hinge, such as a thin flexible material joining the foil flap to the foil wing.
15.5 Through a foil flap’s range of rotation angles and twists, a foil flap cross-section shall not significantly
deform except as permitted in Rules 15.4, 15.8 and 15.9, or as a result of external forces.
15.6 Both foil flaps of a foil shall have the same range of angular rotation and twist. With both foil flaps of a
foil centred in their ranges of motion, each foil flap shall be symmetric with respect to the other about
the foil wing symmetry plane, with a build tolerance of 3.0 mm.
15.7 At any cross-section and all rotation angles, when projected on to the foil wing projection plane, the length
of a foil flap must not be greater than 50% of the chord length. Hinges or other parts of a component which
occur at occasional cross-sections for connection purposes can be excluded from the projected lengths.
15.8 A foil flap may contact a foil wing, and in the absence of external forces, and at any cross-section and
rotation angle, either may cause deformation in the other in a single zone covering not more than 20% of
the local chord length. Outside this zone, neither shall cause deformation in the other.
15.9 Connections between sections of a foil flap are exempt from Rules 13.9, 15.4 and 15.5, providing such
connections span a combined total of no more than 10% of the span of a foil wing, where the span is
measured along the rondure.

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sails / foils / hulls

im not sure having the best in any one section will win the series

im also not sure anyone yet has a market on all 3

 

 

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oops

and the on water teams

 

weather is an unknown but will be a chaos factor

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5 minutes ago, phill_nz said:

oops

and the on water teams

 

weather is an unknown but will be a chaos factor

I don’t think they’re allowed them any more. Publicly available sources only. 

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4 hours ago, phill_nz said:

sails / foils / hulls

im not sure having the best in any one section will win the series

im also not sure anyone yet has a market on all 3

Isn't it why most of us are here, to be the (very objective) judges?

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4 hours ago, Tornado-Cat said:

deformation in the other.
15.9 Connections between sections of a foil flap are exempt from Rules 13.9, 15.4 and 15.5, providing such
connections span a combined total of no more than 10% of the span of a foil wing, where the span is
measured along the rondure.

Seems to me they are talking about connections in the direction of span, or lengthwise from tip to root here, no?

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2 hours ago, barfy said:

Seems to me they are talking about connections in the direction of span, or lengthwise from tip to root here, no?

I think so. So the length of the hinges. 

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A new class and nobody find efficient examples to follow. Result, four completly different projects.
This is what I love about intellectual isolation. It generates vairability, and produce much more fun to me.
Globalization instead looks deadly boring.
Let's impose totally ignorant designers in the Deed of Gift
 

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9 minutes ago, ollallero said:

A new class and nobody find efficient examples to follow. Result, four completly different projects.
This is what I love about intellectual isolation.

Couldn't agree more - variation was sadly lacking in Bermuda with too many one-design elements and the Oracle poodles. 

Whilst the amount of variation this time around might make the racing more one-sided, it makes the build-up *much* more interesting.

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Regarding the bulbs on foils, everything else being equal, I imagine they would potentially be stronger at the join than foils without the bulbs?

Is there some special dispensation to teams who experience foil breakages/failures or would there be significant merit in having the strongest possible foil construction?

Also, it appears to me that the water/foil interaction must be insanely complex at the time when the foils are being immersed and lowered or raised and that a bulb must, at the least simplify the flow, and at best encourage quicker attachment, in a dynamic situation perhaps?

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13 hours ago, Basiliscus said:

Foil thickness is a major driver of the cavitation speed.  Going faster requires thinner foils.  I haven't tried to calculate how much volume is required to achieve the necessary weight of foil to meet the c.g. requirement of the rule.  But it's quite possible the mass could drive the thickness to get the necessary volume, and this could limit the cavitation speed.  A bulb would allow the foils to be thinner and less subject to cavitation.

This is what I have been thinking.  Also, who says that the NZ foils have the required mass?  Didn't some of the test boats that use "winged foils" that didn't have all of the ballast at first?  Maybe the Kiwi's are the ones on the training wheels?

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15 hours ago, uflux said:

Sweet.. thanks for confirming my point

 

14 hours ago, Basiliscus said:

Foil thickness is a major driver of the cavitation speed.  Going faster requires thinner foils.  I haven't tried to calculate how much volume is required to achieve the necessary weight of foil to meet the c.g. requirement of the rule.  But it's quite possible the mass could drive the thickness to get the necessary volume, and this could limit the cavitation speed.  A bulb would allow the foils to be thinner and less subject to cavitation.

As a baseline, if the wing, flap, fairing was all steel - at 7850 kg/m^3, 0.124 m^3 volume is required per side. 

Very roughly:

0.50 m avg chord, 0.11 thickness, Eppler 817 for example

image.png.336886ab56dcae80e3fcdf82e870815f.png

Max span 4 m (rule)

Volume = 0.07317 m^3 in the foil wing

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7 hours ago, ollallero said:


This is what I love about intellectual isolation. It generates vairability, and produce much more fun to me.
Globalization instead looks deadly boring.

 

That is exactly what the original intent of the Hundred Guinea Cup was about - design isolation: I bet ours are faster than yours.

Long may it continue. 

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5 hours ago, buckdouger said:

 

As a baseline, if the wing, flap, fairing was all steel - at 7850 kg/m^3, 0.124 m^3 volume is required per side. 

Very roughly:

0.50 m avg chord, 0.11 thickness, Eppler 817 for example

image.png.336886ab56dcae80e3fcdf82e870815f.png

Max span 4 m (rule)

Volume = 0.07317 m^3 in the foil wing

So, are you saying that the foil wings don't have enough volume to provide the needed weight?

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6 hours ago, buckdouger said:

 

As a baseline, if the wing, flap, fairing was all steel - at 7850 kg/m^3, 0.124 m^3 volume is required per side. 

Very roughly:

0.50 m avg chord, 0.11 thickness, Eppler 817 for example

image.png.336886ab56dcae80e3fcdf82e870815f.png

Max span 4 m (rule)

Volume = 0.07317 m^3 in the foil wing

Why use steel, tungsten is nearly two and a half times heavier? Other boats have.

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1 minute ago, Sidecar said:

Why use steel, tungsten is nearly two and a half times heavier?

There is also room in the base of the foil arm itself

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21 hours ago, Basiliscus said:

Foil thickness is a major driver of the cavitation speed.  Going faster requires thinner foils.  I haven't tried to calculate how much volume is required to achieve the necessary weight of foil to meet the c.g. requirement of the rule.  But it's quite possible the mass could drive the thickness to get the necessary volume, and this could limit the cavitation speed.  A bulb would allow the foils to be thinner and less subject to cavitation.

Would a bulb at the T root also help to prevent cavitation spreading from one part of the foil to another?

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1 hour ago, Sidecar said:

Would a bulb at the T root also help to prevent cavitation spreading from one part of the foil to another?

Not in the manner you are thinking.  Cavitation is due to the water at a given location boiling.  It's not like ventilation, which is air that makes its way into separated flow on the foil..  Cavitation is all about the local pressure compared to the vapor pressure of water, so it's not going to spread unless the adjacent areas also have pressure below vapor pressure.  

A bulb at the root can help prevent cavitation by countering some of the interference between the strut and the foil.  The most important thing is you don't want everything to get fat at the same place.  You can think of the velocities around the strut being superimposed on the velocities around the foil at the junction.  This causes the pressure to be lower at the junction than away from the junction.  One way to help avoid this problem is to add a body that has a dumbbell shaped pressure distribution.  You put high velocity on the body where the foil/strut has low velocity, and you put low velocity on the body where the foil/strut has high velocity.  That way the body partially cancels out the foil/strut velocities and the net interference is not so great.  A good example is the fairing that OTUSA used on their AC72 rudders:

Haulout_228.thumb.jpg.609fea1062712487a17cba28ed5c2796.jpg

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@Basiliscus Thanks. My lazy mistake, I meant ventilation.

And the real point of my question was if there was any other benefit in root bulbs except for increasing ballast....

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24 minutes ago, Sidecar said:

And the real point of my question was if there was any other benefit in root bulbs except for increasing ballast....

Possibly to house the mechanical linkages that may control horizontal foil flaps - allowing thinner lower drag foils and yet have enough mechanical control through the use of sophisticated gearboxes and differentials to have each foil that hangs of the intersection bulb to be controlled independently.

This will allow lift to be controlled from both at transition (that is takeoff....)where maximum lift is required from both horizontals on the foil arm but then trimmed to be from the most outside foil (most leeward foil) and also allowing the inside to be trimmed to near neutral - thereby maximising RM leverage and yet minimising global drag.

Speculative on my behalf, but highly probable given where Rudder differential got to in the AC catamarans. (They will chase every avenue of possible development given that flight control and drag reduction will be paramount, and much of this class is prescriptive OD or tightly controlled box rules.)

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On 10/2/2019 at 10:33 PM, Herfy said:

Let me throw out another idea about the torpedo or bulb foils in use by AM and LR.  When these boats are foiling, the foils will be just below the surface of the water.  The torpedo/bulb could give some bulbous bow effect or be similar to a swath hull.  As such, it may reduce the drag of the foil arm in the water.  I suspect that the foil arm may not be long enough to get the same wave cancelation effect, but at the speeds these boats will be going it may be a factor.  Add that to the versatility of "foil modifications" with the 80/20 rule, improved control of the RM (weight in one spot) and some possible super cavitation effects.   And to think, I haven't been drinking...

Nobody has responded to my brain fart that I laid earlier in this thread.  Can the bulbous bow or swath hull come into the picture?

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The torpedo bulbs were originally intended to reduce foil to foil interference especially as the speeds approach cavitation, just below 50 kts. As Basilicus points out there is some fine tweaking to be done with the fillets of those foil bulb/torpedo interfaces but now in these boats the bulb becomes a good place to place ballast. So the bulbs are serving double duty here, first if stalling the cavitation between the junction between the arm and the lifting foils and in addition as a good place to utilize the needed volume for the ballast requirements. A real win/win situation.

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27 minutes ago, Rasputin22 said:

The torpedo bulbs were originally intended to reduce foil to foil interference especially as the speeds approach cavitation, just below 50 kts. As Basilicus points out there is some fine tweaking to be done with the fillets of those foil bulb/torpedo interfaces but now in these boats the bulb becomes a good place to place ballast. So the bulbs are serving double duty here, first if stalling the cavitation between the junction between the arm and the lifting foils and in addition as a good place to utilize the needed volume for the ballast requirements. A real win/win situation.

I don't see where you get the foil to foil interference idea from? The foil wings are swept so any span wise flow is from the root to the tip of each foil, so no interference there. The Challengers bulbs don't appear to be using the Area rule profile (as per the rudder example) in their bulb designs...or at least from any angle I have seen....So yeah sorry.. not buying the cavitation argument currently.

Screen_Shot_2019-10-08_at_4_30.15_PM.png

Screen Shot 2019-10-08 at 4.34.41 PM.png

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11 hours ago, uflux said:

I don't see where you get the foil to foil interference idea from? The foil wings are swept so any span wise flow is from the root to the tip of each foil, so no interference there. The Challengers bulbs don't appear to be using the Area rule profile (as per the rudder example) in their bulb designs...or at least from any angle I have seen....So yeah sorry.. not buying the cavitation argument currently.

 

 

Not sure if this helps, but it is the combined effects in the 'elbow' of the two adjacent spans of material. Both the vertical and horizontal members locally increase the flow velocity by occupying volume, and in the corner, there is the least amount of space for the flow to pass, so it has to accelerate the highest. The local pressure dips down, and cavitates if unaddressed. The superposition notion is the combination of pressure drops from the two outboard sections to drop even lower in the middle section. 

image.thumb.png.d110aba88ac045d1a95b7309b4cf51b0.png

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24 minutes ago, buckdouger said:

Not sure if this helps, but it is the combined effects in the 'elbow' of the two adjacent spans of material. Both the vertical and horizontal members locally increase the flow velocity by occupying volume, and in the corner, there is the least amount of space for the flow to pass, so it has to accelerate the highest. The local pressure dips down, and cavitates if unaddressed. The superposition notion is the combination of pressure drops from the two outboard sections to drop even lower in the middle section. 

image.thumb.png.d110aba88ac045d1a95b7309b4cf51b0.png

Nice description.  So the two low pressure zones overlap and create an area of extreme low pressure that can lead to cavitation.

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On 10/7/2019 at 6:01 PM, buckdouger said:

 

As a baseline, if the wing, flap, fairing was all steel - at 7850 kg/m^3, 0.124 m^3 volume is required per side. 

Very roughly:

0.50 m avg chord, 0.11 thickness, Eppler 817 for example

image.png.336886ab56dcae80e3fcdf82e870815f.png

Max span 4 m (rule)

Volume = 0.07317 m^3 in the foil wing

....... Unless the foil design is for super cavitation.......

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1 minute ago, dachopper said:

....... Unless the foil design is for super cavitation.......

Not sure I follow; the above numbers are simply a calculation of volume for required ballast using steel as an example. The above is simply a baseline, the comments about using tungsten and putting ballast in the connection to the foil arm are all valid directions, along with the bulb strategy.

 

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13 hours ago, uflux said:

I don't see where you get the foil to foil interference idea from? The foil wings are swept so any span wise flow is from the root to the tip of each foil, so no interference there. The Challengers bulbs don't appear to be using the Area rule profile (as per the rudder example) in their bulb designs...or at least from any angle I have seen....So yeah sorry.. not buying the cavitation argument currently.

Screen_Shot_2019-10-08_at_4_30.15_PM.png

Screen Shot 2019-10-08 at 4.34.41 PM.png

I'm not trying to sell anything here uflux, just stating something that seems to gone over your head. Spanwise flow is not a factor in my statement and you are talking about stalling as supported my your diagram which is not the same as cavitation at the junction of the foils.

    Area rule is so 1950's, get caught up with the times. 

     Buckdouger knows what I'm referring to and his diagram is perfect to illustrate. Thanks Buck.

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1 hour ago, Rasputin22 said:

I'm not trying to sell anything here uflux, just stating something that seems to gone over your head. Spanwise flow is not a factor in my statement and you are talking about stalling as supported my your diagram which is not the same as cavitation at the junction of the foils.

    Area rule is so 1950's, get caught up with the times. 

     Buckdouger knows what I'm referring to and his diagram is perfect to illustrate. Thanks Buck.

Ah...no my point still certainly stands. Buck is talking about the flow around vertical and horizontal members combined causing localised cavitation. My point above explains that there is no foil to foil interference  of flow...my explanation is not simply concerning the flow around stall conditions. There is always a sideways component to the flow over a swept wing (do you really need another diagram??) Combined with the the design choice of using anhedral angles to the foils. So now even less possibility of foil flow interference.

 As for the area rule. I am simply pointing out the the method used by oracle to reduce localised cavitation conditions has not been used on the challengers designs. So even with a bulb they could still find that cavitation occurs. Yes you are correct that this was a popular solution in the 1950s. It is interesting that ETNZ solution involves pushing the foils  forward of the arm and integrating some pretty complex shapes to mitigate  cavitation issues as the flow moves around this junction. A much more “modern” approach to the problem than what the challengers are doing ...In my humble opinion.

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Real interesting interview posted in the U.K. thread by Stingray.  
 

https://mailchi.mp/tipandshaft/tip-shaft-45-nholroyd-everybody-is-watching-everybody-how-the-organisers-of-the-vende-globe-expanded-the-list-of-registered-skippers?e=e564adae35

Holroyd discusses the boats.  He has a lot to say, here are a few tidbits.
 

About NZ: 

their boat as one which has to some extent disregarded any floating races

About AM: 

American Magic is probably closest to us in terms of a boat which will perform well in the floating condition. It is a nice boat, very well executed and they are on the water early and learning. It is a good programme.
 

About LR:

Luna Rossa is quite an extreme boat, their foils are very, very small. There is learning for us to take from them.
 

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Interesting. Just goes to show how a little knowledge can be a very dangerous thing.

Nick says just about the opposite to the collective 'conclusions' drawn in SAAC about Flipper's hull design rationale.

I love this place.

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8 minutes ago, Sailbydate said:

Interesting. Just goes to show how a little knowledge can be a very dangerous thing.

Nick says just about the opposite to the collective 'conclusions' drawn in SAAC about Flipper's hull design rationale.

I love this place.

Yeah, but he would say that. 

I’m gonna continue to crowd source my knowledge. ;-)

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2 hours ago, Sailbydate said:

Interesting. Just goes to show how a little knowledge can be a very dangerous thing.

Nick says just about the opposite to the collective 'conclusions' drawn in SAAC about Flipper's hull design rationale.

I love this place.

I thought of the same thing.  Our SA common knowledge seems to be just the opposite of the "insider" assessment on which boats plan to spend time on the water and which don't.

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2 hours ago, Sailbydate said:

Interesting. Just goes to show how a little knowledge can be a very dangerous thing.

Nick says just about the opposite to the collective 'conclusions' drawn in SAAC about Flipper's hull design rationale.

I love this place.

I thought the conclusion was the bustle allowed earlier liftoff and minimal interference from touches, doesn't that pretty much align with no floating races?

Anyhow after we have seen ETNZ up and foiling with her code zero on a total drifter of a day, they are probably right about there being very few floating races.

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Holroyd’s observations about foil sizes runs counter to some of the spec here too, we need to get better at that!

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10 minutes ago, Boybland said:

I thought the conclusion was the bustle allowed earlier liftoff and minimal interference from touches, doesn't that pretty much align with no floating races?

Anyhow after we have seen ETNZ up and foiling with her code zero on a total drifter of a day, they are probably right about there being very few floating races.

There won't be any floating races. We had this circular discussion with the cats. 

 

1 minute ago, Stingray~ said:

Holroyd’s observations about foil sizes runs counter to some of the spec here too, we need to get better at that!

Ha, ha. He's been paid well for doing this shit for 23 years or so, Stinger. Go for it, mate.

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1 minute ago, Sailbydate said:

Ha, ha. He's been paid well for doing this shit for 23 years or so, Stinger. Go for it, mate.

Hard to do from an iPhone...

Surely some among us can start getting fancy with taking pretty-accurate main and rudder lengths, areas, maybe wing shapes too? Where are the fine yellow lines?? 

Fun subject, wish I had time to try it on a laptop. 

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4 hours ago, Sailbydate said:

Interesting. Just goes to show how a little knowledge can be a very dangerous thing.

Nick says just about the opposite to the collective 'conclusions' drawn in SAAC about Flipper's hull design rationale.

I love this place.

Interesting but I don't read it that way:

  • I don't remember that the "collective conclusions" here was that Flipper would perform well in floating conditions, but I may have missed something. I always thought that flat hulls accelerates faster on flat water (but not with waves)
  • I remember saying that Manta had small foils. Nick Holroyd: " Our smallest foil is about as small as anyone in the fleet, down there with Luna Rossa in that sense and our bigger foil would be roughly midfleet – compared with Team New Zealand in terms of area."
  • I think that was said here, often to be insulted by the usual trolls. Nick Holroyd: " It is very hard to go past the Team New Zealand boat for two reasons. There are few bits of information to which we are not privy to, like the wind limits might be etc., and two, we had five months from class rule to launching boat 1, they undoubtedly had this concept in their simulator a lot longer than that, I was taking to them in October the year before so they probably had six months more. 

Anyway, thanks for the post ! :)

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Always interesting to read Jack Griffin. Sometimes we post here parts of his letter, sometimes he finds some inspiration here.

Good to see he is a reader and appreciated contributor.

http://cupexperience.activehosted.com/index.php?action=social&chash=ac1dd209cbcc5e5d1c6e28598e8cbbe8.334&s=636c42aac183d7dd32cc0c066da9013e

 

 

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34 minutes ago, Tornado-Cat said:

Always interesting to read Jack Griffin. Sometimes we post here parts of his letter, sometimes he finds some inspiration here.

Hi Jean-pierre, so Torn-rat is not your real name?

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So jack isn't buying the Italian Guys bulb theory of more design iterations? Hmmm, a professional jealousy thing?

(Link to newsletter above)

"All three teams with test boats added bulbs at the T-joint between the foil arm and the foil wings. Only ETNZ did not use bulbs. The bulbs almost certainly are intended to reduce cavitation. Apparently the teams' simulators don't agree with each other. Now they will all find out if the water agrees with their simulations."

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And 

"American Magic - the first team to foil an AC75, thanks to the experience with their test boat.    Photo: Amory Ross"

(Jack's letter link above)

Not sure yet how much was gained from the test boat. Certainly engineering timeframes around boat launch had more to do with 5? Days difference to be first to foil. Rumors are etnz is tacking and gybing nicely. AM hasn't given us much to go on. Jury still out.

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10 hours ago, barfy said:

And 

"American Magic - the first team to foil an AC75, thanks to the experience with their test boat.    Photo: Amory Ross"

(Jack's letter link above)

Not sure yet how much was gained from the test boat. Certainly engineering timeframes around boat launch had more to do with 5? Days difference to be first to foil. Rumors are etnz is tacking and gybing nicely. AM hasn't given us much to go on. Jury still out.

Give it a break....  You have to admit that AM learned enough from their mule for them to put up the sails and foil 90 minutes after getting the hull wet for the first time.  It is OK if other teams may be slightly better than your home team in a few things for now, you don't have to make excuses.  They are all learning a lot about these boats and that is the fun part for us to watch.

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On 10/8/2019 at 6:16 PM, buckdouger said:

Not sure I follow; the above numbers are simply a calculation of volume for required ballast using steel as an example. The above is simply a baseline, the comments about using tungsten and putting ballast in the connection to the foil arm are all valid directions, along with the bulb strategy.

 

I mean thickness and chord would be a lot different

 

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Just a question, why not put the foils the furthest front as possible to ensure more stability of the boat ?

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24 minutes ago, popo said:

Just a question, why not put the foils the furthest front as possible to ensure more stability of the boat ?

Because the rules say you can't?

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3 hours ago, Herfy said:

Give it a break....  You have to admit that AM learned enough from their mule for them to put up the sails and foil 90 minutes after getting the hull wet for the first time.  It is OK if other teams may be slightly better than your home team in a few things for now, you don't have to make excuses.  They are all learning a lot about these boats and that is the fun part for us to watch.

Not making any excuses, and I'm having fun watching. I'm just saying that for JG to cite the test boat as cause and effect as to why AM foiled slightly earlier than a team that didn't have a test boat is supposition. If that were true why aren't Ben and LR next up on foils?

Just calling out baseless supposition, feel free to ping me the next time I make a statement of fact based on ...not much.

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3 hours ago, popo said:

Just a question, why not put the foils the furthest front as possible to ensure more stability of the boat ?

Taking into account the tremendous lateral forces on the sails (heeling moment), it's very important to have the righting moment generated by the foils being somewhere close to the center of effort of the sails - if the foils were up front it'd probably induce a massive turning moment every time they swapped foil, and the yachts would be yawing back and forth wildly during maneuvers.

The function of the foils is to provide both lift out of the water as well as a righting moment to counteract heel. It isn't accidental where they've decided the foils should be placed on the boats.

Furthermore, the bow has the biggest range of vertical movement during pitching, so even if it were permitted, having the foils up front would make it much harder to control the angle of attack of the foils and be unlikely to provide optimum stability anyway.

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Interesting vid on tank testing foil

Notice how the cavitation shy's away from the bulb.

 

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3 hours ago, See Level said:

Interesting vid on tank testing foil

Notice how the cavitation shy's away from the bulb.

 

In the comments, someone says they think the water flow reaches 18m/s which would be about 35 knots.

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5 hours ago, Tornado-Cat said:

Flipper foil, seen from the side it looks like we see big flaps, seen from the front it could be a curve.

There was a closeup pic from under it at the launch.

About half of the apparent flap is a flexible cover, my guess the actual flap is about 30%, about half of it covered by the flexible cover.

 

From what I've seen of them & my understanding of the theory there is a night & day gap in the quality of the foils between TNZ & the rest.

Including the 'TNZ style' foils on sub-scales.

 

The TNZ foils are frigging exquisitely detailed, they're getting similar distribution of the pressure curve at the intersection but without a huge frontal cross-section/non-lifting wetted area penalty that the bullets bring.

 

The only question I have is TNZ has large planform area, it might be a wash on total wetted area though given all the area in bullets & fairings the others have.

It may be simply light wind vs higher wind designs but it may be a different philosophy in foil size vs hullshape stability.

 

We've seen TNZ apparently being able to rely on the foils to produce sufficient righting moment to be able to get away with their very tender, lower wetted surface hull design & pop out onto the foils at apparently very low wind while we've seen AM looking really sticky in the light with its flat hull.

The flip side of that may be that while the 'small foil' teams need to rely on hull stability for initial acceleration, once up & foiling they could have smaller wetted area -> less drag -> higher top speeds.

But again that depends on the total wetted area/frontal area including the bulbs etc and I'm not sure the 'small foil' designs actually do win on that.

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11 hours ago, KoW said:

Taking into account the tremendous lateral forces on the sails (heeling moment), it's very important to have the righting moment generated by the foils being somewhere close to the center of effort of the sails - if the foils were up front it'd probably induce a massive turning moment every time they swapped foil, and the yachts would be yawing back and forth wildly during maneuvers.

The function of the foils is to provide both lift out of the water as well as a righting moment to counteract heel. It isn't accidental where they've decided the foils should be placed on the boats. 

Furthermore, the bow has the biggest range of vertical movement during pitching, so even if it were permitted, having the foils up front would make it much harder to control the angle of attack of the foils and be unlikely to provide optimum stability anyway.

 

good point

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4 minutes ago, Ricky Craven said:

Basiliscus AKA Paul Bieker????  ... saved OTUSA in '13 by whipping up a couple torpedoes on the fly

Bieker did whip us those 'need them yesterday' bullets for Oracle but he had been using them for some time. Take a look at this wild rudder he did. image.jpeg.5f0a2cef87e325cd483f49e54974034d.jpeg

 Basilicus is a foil guru who goes back even further and it shouldn't be too hard to figure who he is if you know the history of foil development. Not the same person anyway.

Look! Bullets!

image.thumb.png.e753bc08899dc1b3f504194969464ddd.png

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11 hours ago, hoom said:

There was a closeup pic from under it at the launch.

About half of the apparent flap is a flexible cover, my guess the actual flap is about 30%, about half of it covered by the flexible cover.

From what I've seen of them & my understanding of the theory there is a night & day gap in the quality of the foils between TNZ & the rest.

Including the 'TNZ style' foils on sub-scales.

The TNZ foils are frigging exquisitely detailed, they're getting similar distribution of the pressure curve at the intersection but without a huge frontal cross-section/non-lifting wetted area penalty that the bullets bring.

The only question I have is TNZ has large planform area, it might be a wash on total wetted area though given all the area in bullets & fairings the others have.

It may be simply light wind vs higher wind designs but it may be a different philosophy in foil size vs hullshape stability.

We've seen TNZ apparently being able to rely on the foils to produce sufficient righting moment to be able to get away with their very tender, lower wetted surface hull design & pop out onto the foils at apparently very low wind while we've seen AM looking really sticky in the light with its flat hull.

The flip side of that may be that while the 'small foil' teams need to rely on hull stability for initial acceleration, once up & foiling they could have smaller wetted area -> less drag -> higher top speeds.

But again that depends on the total wetted area/frontal area including the bulbs etc and I'm not sure the 'small foil' designs actually do win on that.

I don't know much about cavitation but if I understand Basiliscus correctly and if what I observed is right, Flipper has foils with a wide beam, probably for light wind, and a thin section + sophiticated design  in order to keep the same pressure on different parts of the foil at high speed, thus preventing cavitation. However this thin section may be good at high speed but not the most stable one whatever the speed. The Starfighter plane had also a very thin profile wing, amazing performances, but was crashing regularly.

Another option is the one adapted by Orca which also prevents cavitation, is more draggy but also more stable. If I understand correctly.

Manta seems between, small foils, thin section, less complicated than Flipper but with small torpedos, looking like a B52.

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3 hours ago, Rasputin22 said:

...Look! Bullets!

image.thumb.png.e753bc08899dc1b3f504194969464ddd.png

That's a good illustration of the higher velocity in the junctions due to interference effects.  The more acute the junction, the stronger the interference.

 

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From Tip and Shaft as posted in another thread:

"Out of the four pairs that have so far been launched, there are two distinct families: one without a bulb, Team New Zealand, and the other three with, which leads Dimitri Despierres to say, “The Kiwis have gone for a very radical option without a bulb and with foils with large surfaces. That means they have put the weight in the wings and they must have believed that they needed a greater surface area to be able to take off. The others have bulbs and foils with smaller surfaces, so we can see a clear trend." For Vincent Lauriot-Prévost, who pointed out that the bulb on Ineos is smaller than on Luna Rossa and American Magic, "It’s always down to the same problem: power against drag. The smaller the bulb, the less the drag, but that may mean less righting moment too." 

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2 hours ago, Tornado-Cat said:

From Tip and Shaft as posted in another thread:

"Out of the four pairs that have so far been launched, there are two distinct families: one without a bulb, Team New Zealand, and the other three with, which leads Dimitri Despierres to say, “The Kiwis have gone for a very radical option without a bulb and with foils with large surfaces. That means they have put the weight in the wings and they must have believed that they needed a greater surface area to be able to take off. The others have bulbs and foils with smaller surfaces, so we can see a clear trend." For Vincent Lauriot-Prévost, who pointed out that the bulb on Ineos is smaller than on Luna Rossa and American Magic, "It’s always down to the same problem: power against drag. The smaller the bulb, the less the drag, but that may mean less righting moment too." 

Not seeing the righting moment difference given the required mass is the same for all teams. 

Another quote in the article from Nick Holroyd seemed to confirm @basilisus' comment that LRs outboard pods were housing actuators. 

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4 hours ago, buckdouger said:

Not seeing the righting moment difference given the required mass is the same for all teams. 

Another quote in the article from Nick Holroyd seemed to confirm @basilisus' comment that LRs outboard pods were housing actuators. 

Yes tix for that.I wasn't gonna call that one,but how does less drag/smaller bulb = less RM ??

And it's strange to call the kiwi wings radical, when they are the same general form as all the testboats sported? 

Anyway

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4 hours ago, barfy said:

Yes tix for that.I wasn't gonna call that one,but how does less drag/smaller bulb = less RM ??

And it's strange to call the kiwi wings radical, when they are the same general form as all the testboats sported? 

Anyway

Think of Fin Keels vs. Bulb Keels.

What they are saying is that ETNZ is Fin Keeled 

Others are Bulb Keeled 

Which in the traditional sense has a overall lower COG - now consider that the lower the COG the longer the effective lever arm = More RM

Therefore - No Bulb is less RM than heavily Bulbed arm - remember that all arms are the same length - so then need to weigh up RM against global drag......

These are the compromises in play......

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On 10/8/2019 at 7:37 AM, Sidecar said:

Why use steel, tungsten is nearly two and a half times heavier? Other boats have.

Rule 6.3 says "Materials shall have a maximum density of 11,400 kg/m3". Tungsten has a density of 19,250 kg/m3 so way too dense. It might be part of an alloy though.

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31 minutes ago, Boink said:

Think of Fin Keels vs. Bulb Keels.

What they are saying is that ETNZ is Fin Keeled 

Others are Bulb Keeled 

Which in the traditional sense has a overall lower COG - now consider that the lower the COG the longer the effective lever arm = More RM

Therefore - No Bulb is less RM than heavily Bulbed arm - remember that all arms are the same length - so then need to weigh up RM against global drag......

These are the compromises in play......

Yes, but if as seems to be the opinion of most, all the weight is in the foil on ETNZ then the COG is as low as it can be, if anything lower than the bullet/foil combination, so RM is greater.

 The "penalty" is increased wetted surface area, but that could well be offset by greater lift?

Buggered if I know which is the best solution, but there's definately two schools of thought going on here, it'll be interesting to see how it pans out.

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22 minutes ago, Woolfy said:

Yes, but if as seems to be the opinion of most, all the weight is in the foil on ETNZ then the COG is as low as it can be, if anything lower than the bullet/foil combination, so RM is greater.

 The "penalty" is increased wetted surface area, but that could well be offset by greater lift?

Buggered if I know which is the best solution, but there's definately two schools of thought going on here, it'll be interesting to see how it pans out.

OK. and yes fair point, but we are approaching this from positions of different assumptions.

And yes I do know what assumptions lead to.....

You, I believe, feel that all Ballast (whether that be Lead, Tungsten or Unobtainium) is all outboard of the end of the foil arm structure, in either Foil wings (ETNZ) or Foil and Bulb packages (all other teams).

On one hand we need to consider whether the Ballast Torpedoes fulfill a dual role - which allow small, thin and therefore low drag foils to be utilised, whilst overcoming the not inconsiderable issue of flap control to be achieved through housing of split differentials, gearboxes and actuating rods which can be buried in that  Ballast torpedo.

or 

Go with Larger planform and thicker sectioned foil wings that can be actuated with out the need for an equivalent torpedo to house the volume of ballast required.

But.

There is also the possibility that the voids of the foil arms and the team added fairings could also house ballast packages - which whilst not as far outboard as Torpedoes, may globally be a superior package if the Drag reductions are greater by not running Torpedoes, and forfeiting a tiny reduction in RM by housing the ballast closer to the centreline.

The hunt to reduce Drag may be calculated and seen as a more profitable route - than accepting that you must have maximum RM regardless of all other considerations.

The Hingeless upper surface of the ETNZ wings hints that not only is this a technically superior construction but would give a globally lower drag outcome.

Only hydrodynamisists would know where the cross over between thin and small with bulb, outperforms larger and and thicker, with clean root terminals, in terms of lift vs drag.

Have they moded for early takeoff? - evidence so far from light wind observations supports this, but could hardly claim to be conclusive.

Will this place a glass ceiling on ETNZ's outright speed potential? Probably - but if their modelling suggests Cup races in windspeeds lower enough to not reach cavitation speeds anyway;  then this becomes moot and an Oracle style of developing speed performance potential that can never be realised is a fruitless design cycle.

We are so early in the testing phase that everything written here is with enormous speculation, but I have consistently said that since during the last cycle - that foiling performance is often driven as much by drag reduction measures as it is by chasing power creating ones......

All we do know really, is that there is so much we do not know or see. ;)

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2 hours ago, Boink said:

Only hydrodynamisists would know where the cross over between thin and small with bulb, outperforms larger and and thicker, with clean root terminals, in terms of lift vs drag.

I don't think (if you talk about it) Flippers foil is considered thick, I would say large and thin vs bulb + smaller foil.

The span helps early take off and the thin profile allows speed.

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The amount of lift is a delicate balance.  The more lift from the foils than the quicker the takeoff, but it also has more surface area and more drag.  Another point that many are ignoring is that the "quick take-off" foil may produce too much lift at higher speed and they will have to be adjusted to reduce lift which adds even more drag.  They will need to "bleed off" some of the lift to keep the boat at the right height when foiling, so that means changing the flaps which will increase drag. 

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1 hour ago, Herfy said:

The amount of lift is a delicate balance.  The more lift from the foils than the quicker the takeoff, but it also has more surface area and more drag.  Another point that many are ignoring is that the "quick take-off" foil may produce too much lift at higher speed and they will have to be adjusted to reduce lift which adds even more drag.  They will need to "bleed off" some of the lift to keep the boat at the right height when foiling, so that means changing the flaps which will increase drag. 

I think that foils with a bulb allow shorter and a thicker profile as those we have seen with those using it.

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6 hours ago, Boink said:

one hand we need to consider whether the Ballast Torpedoes fulfill a dual role - which allow small, thin and therefore low drag foils to be utilised, whilst overcoming the not inconsiderable issue of flap control to be achieved through housing of split differentials, gearboxes and actuating rods which can be buried in that  Ballast torpedo.

or 

Go with Larger planform and thicker sectioned foil wings that can be actuated with out the need for an equivalent torpedo to house the volume of ballast required.

But.

There is also the possibility that the voids of the foil arms and the team added fairings could also house ballast packages - which whilst not as far outboard as Torpedoes, may globally be a superior package if the Drag reductions are greater by not running Torpedoes, and forfeiting a tiny reduction in RM by housing the ballast closer to the centreline.

This is interesting, I was under the assumption ballast was to be in the wing area, when I read your post and the rule again I see that the arm fairing could be ballasted. I'm not sure how self righting could be achieved if some team say, ballasts the top third of the arm fairing. 

Maybe the entire bulb ballast thing is a red herring, and it's just a cavitation reducing radius as mentioned by bascilus. This would make sense with test boat teams pushing for More Speed on the second iteration. And etnz doing their own thing, as they do. Early take off is obvious, low speed angles. Worked last time.

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What does the Rule say about limits to the max weight and limits to where the COG is - of the entire foil including arms and wings?

I thought is was pretty restrictive?

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1 hour ago, Stingray~ said:

What does the Rule say about limits to the max weight and limits to where the COG is - of the entire foil including arms and wings?

I thought is was pretty restrictive?

AC 75 class rule

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623Aze8.jpg

 

Original rule was a bigger radius, might have changed again in the non-public versions of the rule.

MucM4Dp.jpg

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Thanks, so this is the key? 

Maybe it got lowered from 3500 to 3375 after the arms got heavier but the need is still there to get the weight (whatever that limit is) as far outboard as possible.

2A09C6AC-F852-4CA4-A57C-BA41E9008739.thumb.jpeg.a500b79b73e5dedaff46dfb0fe39e150.jpeg

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