Which rudder?

[Paul Kotzebue]

Originally Posted by MikeJohns

There is no superior knowledge where you can sit down solve a system of pde’s and out pops the perfect foil and planform. In the real world there’s observation, tank testing and CFD and then there’s always a current trend.

I agree.

[jehardiman]

Originally Posted by Ad Hoc

"...What do you think should be best choice for a fast sailboat?.."

In addition to what has been said above...whatever works for you!..and define 'fast'.

I've designed some very very basic 'spade' type rudders on boats which would be considered "fast" by sailing the fraternity, ie flat plates. So long as the rudder provides the yaw/moment required, without being overly draggy, the final shape is almost irrelevant.

This statement is so full of win.

I concur about flat plate rudders for some "high speed" sailing vessels. Increasing speed is all about controlling as much power as possible while maintaing drag to a minimum at the speed you are currently going. For over powered vessels, fully cavitating rudders are a viable option and for those, area and location is all that matters

Given the ISAF Executive Committee decision to include kiteboards in the sail speed records, that opens the door to all sorts of high speed sailing "yachts". If someone with a depressor constrained semi-rigid wing pod sailer isn't doing 80 knts after 10 years, they just aren't trying hard enough.

[MikeJohns]

Originally Posted by Paul B

...........
This guy Johns is always spouting off about things like "frustrated helmsmen with stalled rudders", but he is always too cowardly to name the boats/designers ....... It is a ploy he and his ilk use all too often.

Paul B
I can never work out why you are so scared of the engineers/NA's here, you have made similar delinquent remarks to many of the professionals that contribute to this forum.
The same people would be happy to engage you in sensible dialogue if you tried being civil .

As for cowardly behaviour perhaps you could provide your own details. Your full name would be a start

[Paul B]

So many strange ideas, I wold guess you have never participated in high end sailboat racing and don't have the basic understanding of the princliples. First you said this:

Originally Posted by jehardiman

It must be remembered that rudders are not keels nor wings

By this quote it seems you don't know what is going on under a modern fin keel/spade rudder monohull when going upwind.

Originally Posted by jehardiman

Well, as a king once said "Honi soit a qui mal y pense", and my statement is not an insinuation on anyone’s character though if you wish to make a shoe out of it and place it on your foot while stating that it fits....so be it.

If you make the statement you should at least have the stones to own it.

Originally Posted by jehardiman

A quick survey of bleeding edge "high speed" sailing will show that designs are not standardized and that over the course of an ocean race 10-30% of the racers (depending on hull type) will suffer some form of failure

Another laughable statement by you. Of course you can cherry pick disasters like the '79 Fastnet the like. But your assertion is not true, and you should be better at statistics than this.

Originally Posted by jehardiman

The person who makes the final decision is rarely the hydrodymancist and rarely is the final decision based solely on engineering performance. More often the customer who makes the decision is presented differing and often conflicting criteria. Ok, all designers raise their hand if the customer has told you "I want it done this way" and you did it even though there was a better way.

At the top of the heap (America's Cup, TP52, etc) the designers don't have any "customer" making the decisions. The design team does. In fact, some top design offices routinely turn down work from owners who have their own "ideas". It isn't worth the time, effort, and the firm's reputation to deal with these people.

Originally Posted by jehardiman

Fashion sells. Nobody wants to be too far from the crowd so they (customers and designers) all bunch up around a design that may not be the best but is currently winning.

The designs bunch up because they ARE the best at the time. Please list all the "fashions" that have been winners, but were not correct for the time/rule.

Originally Posted by jehardiman

Often a good helmsman who had a good race sets a design trend when people believe that it was a piece of hardware that beat them, not that they themselves were out performed.

Please give examples of this. I know many designers who look at something that wins by "fluke", and they sure don't follow that line.

Originally Posted by jehardiman

Australia II's winged keel was not hydrodynamicly more efficient than Liberty's but the manipulation of the chain girth measurement gave it a sail area advantage.

There was more to the AII keel than the chain girth advantage. While it is true it was probably less than a percent or so advantage, even the smallest advantage is something that is not left on the table.

I hope you realize the days of AII were still the dark ages of modern design and the process is not remotely the same today.

Originally Posted by jehardiman

Same thing with IOR bustles; they didn't make the boats go faster.

The bumping of the IOR boats at measurement points did make the boats faster in relation to their rating. That was the game, and it took a great amount of skill to balance the bumping attributes vs deficiencies.

Originally Posted by jehardiman

Same as the shark fin keels of a decade ago...the humpback flipper fins of today… or elliptical planforms. No real performance advantage, just look “better”.

Tell us what reputable design firm has used a "shark fin keel" in the last 10 years..or 20..or 25? What reputable firm uses the "humpback flipper fin?

If you don't think elliptical (not actually elliptical planform) keels were not a performance advantage in the days of IOR you clearly have no clue.

[Paul B]

Originally Posted by MikeJohns

Paul B
I can never work out why you are so scared of the engineers/NA's here, you have made similar delinquent remarks to many of the professionals that contribute to this forum.

This is hilarious, considering I am the VP of Engineering at my firm.

What I object to is someone with no practical experience in solving the problem pontificating about their abilities. Hell, you know so little about composite construction you couldn't come up with any way to transfer loads of a fin keel in a composite hull except to "add steel".

Last year I was interviewing for an open req. I was given one resume of a friend of a co-worker. He was a good engineer with years of experience in his field. However, I would not have interviewed him, except for the personal request.

He came in and during our chat I gave him a part and asked him how he would make it. The answer he gave was appropriate for the materials and processes he used in his previous positions, but it was totally useless for the materials and processes we use.

If it came down to my decision to ask about performance sailing I would trust great engineers/NAs like John Reichel, Marcelino Botin, or Rolf Vrolijk before I would think about asking someone who welds plate onto workboats.

I would never ask anything from someone who obviously looks the other way when presented with data that doesn't follow his pre-conceived, archaic ideas. This is the person you have proven to be.

[booster]

Jehardiman and Paul B!

Good comments there Jehardiman and Paul B. Regarding strength of composite structures, like rudders, some general purpose finite element codes (FE-codes) can handle it. The latest version of ABAQUS incorporates several fracture models for composite structures. As always the results are strongly influenced by the material parameters. These are not always easy to find. The same is true for the loads. Here CFD=Computational Fluid Dynamics can help. Who doesn't remember John Bertrand's come-back in the America's Cup. That fracture (and ultimately sinking) probably could have been avoided if some FE-calculations had been performed. One can analyze different load-cases such as accidental, when using the winch at the wrong side of the boat (introducing torsion). The same is true for the other America's Cup yacht which also got v-shaped (altough the load-case probably was different). ANSYS is another FE-code that as been used to solve these kind of problems. I believe the German team used it in their latest America's Cup campaign.

Regards,
Booster

SIMULIA develops the Abaqus suite of general-purpose nonlinear finite element analysis (FEA) programs for mechanical, structural, civil, biomedical, ...
www.simulia.com/


Welcome to ANSYS, Inc. - computer-aided engineering technology and engineering design analysis software products and services.
www.ansys.com/

[MikeJohns]

Originally Posted by Paul B

This is hilarious, considering I am the VP of Engineering at my firm.

If you actually read what I posted, it's not funny at all, that’s rather sad, maybe that’s why you are so frustrated. You respond so emotionally to every technical discussion and you are the master of the tactics of which you so vehemently accuse others.

Originally Posted by Paul B

What I object to is someone with no practical experience in solving the problem pontificating about their abilities. Hell, you know so little about composite construction you couldn't come up with any way to transfer loads of a fin keel in a composite hull except to "add steel".

Would you care to put a link to this creativity? Perhaps you’d like to consider who exactly is outside of their field. Just who is ‘pontificating’ Paul?

Post technical facts, quotes from previous posts and lets discuss them technically. Not this emotional leap to the grand racers viewpoint that you are so keen on.

Originally Posted by Paul B

He came in and during our chat I gave him a part and asked him how he would make it. The answer he gave was appropriate for the materials and processes he used in his previous positions, but it was totally useless for the materials and processes we use.

And that qualifies you for what Presumably from your previous statements you are not an engineer ?

Originally Posted by Paul B

If it came down to my decision to ask about performance sailing I would trust great engineers/NAs like John Reichel, Marcelino Botin, or Rolf Vrolijk before I would think about asking someone who welds plate onto workboats.

You know I’m not a welder anymore than you are. As for this ‘trust’ you would trust them to produce an optimal performance foil for the racing you would engage in, that’s not quite the issue we touched on a raw nerve of yours here is it.

Originally Posted by Paul B

I would never ask anything from someone who obviously looks the other way when presented with data that doesn't follow his pre-conceived, archaic ideas. This is the person you have proven to be.

What data? You have never offered any that I can recall. In fact you contribute nothing in that regard but prejudiced opinion. I keep asking you to post facts and data ….please .

To suggest that others do this to you is a joke. Your substitute for data tends to be vitriolic diatribe. Like here in this thread.


This thread should be about discussing rudders, discuss the strengths and weaknesses, the hydrodynamics of the foil shape and plan-form, the structural reliability, materials and likely modes of failure.

Here’s something I’d like you to consider :

A few high profile racing boats have sunk recently because their large diameter CF rudder shafts have snapped at the max BM inside the vessel, are all the designers rushing to retro-fit a partial bulkhead or enclosure to remedy this? Should a broken rudder shaft sink a boat quickly? What’s really wrong with adding the extra 10kg to prevent this happening in an offshore vessel? Will this ever happen without regulation when winning and robust conservative design are such uneasy bed partners?

[MikeJohns]

Originally Posted by booster

......... Regarding strength of composite structures, like rudders, some general purpose finite element codes (FE-codes) can handle it. The latest version of ABAQUS incorporates several fracture models for composite structures. As always the results are strongly influenced by the material parameters. These are not always easy to find. The same is true for the loads........

How to account for matrix aging, micro crack propogation and the service limits for such structures is less predictable.

There's also a few gremlins lurking in composite layups that can bite when highly stressed, even under lab conditions with ideal layup and best practice there is often quite a large scatter from test coupons.

[Ad Hoc]

"...even under lab conditions with ideal layup and best practice there is often quite a large scatter from test coupons..

Exactly and not to mention that FEA is also significantly affected by the mesh size and the element choice too. So when using FEA, especially with composites, a database of "reality fudge factors" is required to be taken into account; the more coupon tests the better. Simply because what is shown on the 'design' drawing, is very rarely achieved when actually made by the laminator, in terms of 'as designed strength'.

[Paul B]

Originally Posted by MikeJohns

This thread should be about discussing rudders, discuss the strengths and weaknesses, the hydrodynamics of the foil shape and plan-form, the structural reliability, materials and likely modes of failure.

Er, no.

This is the topic of the discussion:

Originally Posted by Fidippide

Hi everybody, I studied 6 naca profile with xfoil: 0008, 0010, 0012, 0014, 0016, 0018 at various Re (from 100000 at 1000000). What do you think should be best choice for a fast sailboat? Thanks.

Your psychological issues prevent you from seeing that not every discussion is about your crusade to save us all from ourselves.

After reading the things you write it is no wonder you don't have a full order book.

[booster]

Hi!
Well, the discussion starts to resemble that canting-keel issue:

Originally Posted by Paul B

Er, no.

This is the topic of the discussion:




Your psychological issues prevent you from seeing that not every discussion is about your crusade to save us all from ourselves.

After reading the things you write it is no wonder you don't have a full order book.

On my 2.4mr (4 knots max speed) I have a NACA manyzeros12. I tested a manyzeros15 and the boat got easier to hanldle in gusts, but the general feeling was negative. The plane-profile is elliptic, which is not so sensitive to stall-out. On the other hand, it introduce vertical flow. I tested a square plane-profile that stall-out more easily, but the vertical flow is minimized. By placing the rudder out-balanced, I got the same good non-stall-out feel as on the elliptic plane-profile. I seems that the out-balanced rudder place the rudder in relatively more non-turbulent flow behind the keel. Perhaps it compensates for the stall-out sensetivity.
Regards,
Booster

[booster]

MikeJohns and Ad Hoc!
Yes, matrix aging is difficult to take into account. Mesh-density dependence is avoided by adaptive meshing or the old-fashioned patch-test. Several fracture models are mesh-density in-sensitive, like the Hillerborg fracture model which is mesh-density independent. The softening region of the stress-deformation relationship must be taken into account, not the stess-strain relationship. The coupled fracture modes can roughly be taken into account by old fashioned expressions similar to combined tension-, buckling- and shear. More sophisticated methods exist as well.
Regards,
Booster

[Ad Hoc]

Booster
you need to be careful. All 'decent' FE codes must pass the patch test, at the very least you can do this yourself to ascertain the limits of the elements. But the mesh density I'm referring to, is not how the element 'works', I'm referring to how the whole model is working to produce a realistic result. Having a mesh density from 1 to say 5, 50, 100, and then up to 1000 elements in a corner region, for example, doesn't mean with increasing density from 1 through to 1000 the accuracy will improve the result, quite the contrary in fact!. The model doesn't know intuitively that it is working correctly. It needs real world input to validate the model and the mesh and boundary conditions.

Many papers have established that a mesh density of around 1/2t (t=thickness of 'material') provides acceptable results when doing detailed analysis for hot-spot stress, for example.

[booster]

Ad Hoc et al!

Yes, absence of radii in the CAD makes use hot-spot stresses even more important. Sometimes one finds engineer rookies using the p-method on very coarse meshes. A lot of red in the results! However, Ad Hoc, I presume you were talking about the h-method. Some regulations like DNV specify methods for this. Often the traditional tangent method, using the path towards the singularity, can be used. Maximum principal stresses are plotted vs. the path. The traditional 20% criteria can be used. As always the extrapolation of the results from the integration points to the nodes can be confusing. Here, the new C3D10I-element of ABAQUS is an important improvement. The analysis of carbon-fiber rudders is important. How doesn’t remember the rudder failure of the Tony Castro design Justine. If some FE-calculations had been performed the failure could have been avoided. Justine was happy to get a new rudder from a bigger boat having the same rudder-stock diameter. The managed to win before a Ron Holland design (Vento perhaps was her name), impressive. The event started a trend towards rudders with bigger area. In some sense
keel area was transferred to the rudder. Especially the French designers were adopting this.

Regards,
Booster

[Ad Hoc]

booster

"..If some FE-calculations had been performed the failure could have been avoided..." I'm not overly familiar with the history of this vessel. However, i would not make such a bold statement, as this implies a total reliance upon computer software to problem solve rather than a good solid education and training.

My calculator, which i might add is 30 years old, works a treat, has more computing power in it than Apollo 13 had. It wasn't technology per se that got men to the moon...!!!

Slight digression and off topic, sorry.