Principles of Yacht Design, Fourth Edition

David, I did not write clearly enough what my irritation was.
I still think that the Delft tank test data, that is now available online, is a great gift to the world and it was right that PYD used this database. But now M. Orych designed the YD 41. He comes from a totally different world (see here http://www.flowtech.se/company). He uses shipflow for preliminary design work and variants testing. He is a software developer who worked all his life at the university. If you study the website you will see, that they do not mention the necessary back up with a towing tank and regression analysis is also not mentioned on these pages. They propose to use the "modern" way. Can he switch sides and get into the shoes of a designer who does not have access to CFD?
I do not have the book, but it would be interesting to see how they combine these two worlds in a way that there is a consistent design philosophy.
Since only prosperous yacht builders can afford the multi-core hardware and the high annual costs of CFD-software these "two worlds" might even exist in the real world. CFD for the racing yachts and Delft regression for the affordable cruiser. But there is hope. If you look at Leo's Flotilla, there might be a bridge now between the two, at least for thin ships. My aim is still to find an affordable optimization process for the cruising sailor with a limited budget. The RANS simulations that I had access to created more questions than answers.
Uli

 

As far as I know 12215-9 is still incomplete, and is a work in progress (although it is used in its current form).

So your exchange, from the point of view of a neutral third party, was a non-NA trying to tell a group of highly experienced NAs how to do their job, yes?
Not surprised your input wasn't terribly welcome!

I'll bet Dolto didn't actually write: "I'm not interested in experimental or scientific results".

The Delft data also came to us from academics who spent all their time at university.

I don't know where you get the idea that this book is for yacht builders.
It's intended audience is yacht designers (i.e. a sub-group of naval architects), and any professional yacht designer (below a certain age, at least) is going to have CFD software available to him.

 

The audience is broader than a sub-group of naval architects who design yachts. If it was limited to that small group it would not have sold sufficient numbers to be in a fourth edition. From the Third Edition front cover fly-leaf: "PRINCIPLES OF YACHT DESIGN is the ultimate resource on the subject for practicing designers, naval architecture students, discerning boat owners and the boatbuilding industry as a whole." The introduction to the Third Edition makes clear that the book is intended for "professional, as well as amateur designers" and says "we believe the book could be of interest to yachtsmen in general".

What does a designer's age have to do with what software is available to them?

 

The fly leaf is marketing.

I'm sure they'd be happy to sell a copy to everyone on earth, but that doesn't stop the target market of a book on yacht design being yacht designers.

This is not a manual written for backyard builders, so complaints about discussing CFD are unwarranted.

I just didn't want to make a blanket statement about ALL designers. There may be some older ones who started long before CFD software, and still don't bother having anything to do with it.

 

It is a final published rule. But this is the first edition, and rules always evolve.

90° load case is not the hardest one. Grounding is more challenging. But then up to what speed a keel can hit ground undamaged is absolutely not a technical/scientific issue. It has more to see with general public seamanship or consumer expectations.

I expected that professional yacht designers are a technical level well above "PRINCIPLES of yacht design".
Professional yacht designers who design for homebuilders, or small yards (not racing) do not use any CFD software. CFD cost is over the design budget of their customers.
It is way more productive for these customers to spend design hours on how to reduce building cost (save man hours, or expensive tooling) than to win 0.01 knot on mathematical weather conditions.

 

I've made no comment on the technical levels of yacht designers, nor of professional yacht designers.

I suppose there must be yacht designers somewhere who don't own copies, but I'd guess they're rare beasts.

The extent to which CFD is used is also not something I commented on.

They have access to it: if not immediately then they certainly have hardware that can run it, and can afford the software (it isn't ridiculously expensive these days), and are capable of using it.


When you read a book written by an expert in CFD that includes discussion of CFD, but you don't like/use/understand CFD, you have to at least consider the possibility that you aren't the target demographic for that book.

 

I bought the second edition some years ago and figure I am typical of the audience for such a book -an engineer interested in the field for personal use -not likely professional. Even years ago I found the methods did not take advantage of what computers could do so easily. I understand that there are international standards that would be slow and deliberate, but I would expect that academia would run ahead and use the new tools to show where standards stood relative to theory. In the process they would lay the foundation for new standards using CAD, FEA, and CFD. I still recommend the book but would expect current professionals to have moved on to computational methods. By the way, I mention these in order of difficulty. CAD I expect from any 4 yr degree, FEA takes a masters to completely understand, and CFD takes a PHD to work effectively. I am not saying that's what it takes to generate answers, rather that's what it takes to generate trustworthy answers.

The book is still a good read but maybe someone should write one about yacht design with CAD. Tossing CFD into this text would be completely out of place though it would be nice to have some CFD graphics to explain design behavior. I also think the delft series has some years of use left for performance interpolation -use CFD only for extrapolation.

 

I think you'll be hard pressed to find many professional yacht designers who don't own a copy of this book.

Presumably as a professional engineer you own books on principles of engineering, and some physics reference books - you don't think the primary target audience for those is non-engineers who want to dabble in engineering do you?

Standards don't concern themselves with the method by which the goal is reached - i.e. using computers or not. And this book only has them tacked on - as its title suggests, it isn't primarily about the tools used.
The principles used aren't affected by the tools: they apply to everyone, including academia.

As has already been pointed out in this thread, CFD analysis of a design is very expensive, so none but the most expensive vessels (very large, or racing) use it to a significant degree.

What absolute rubbish.
CAD you can expect from a 2nd year student.
CFD from a 3rd tear student.
FEA from a 4th year student.
PhD students aren't taught anything more about CFD, they simply rack up many hours using it (if their thesis requires it).

The principles used would be identical. The book would sit alongside this one, not replace it. New methods don't replace old principles - they only replace old methods.

 

David, this link might interest you:
At least one design office (Marc Lombard) has replaced the Delft database by a database generated with CFD.
http://www.innovsail.com/wp-content/uploads/2013/03/3-Huetz_hydrodynamics_paper_revised-3.pdf
Most likely they will use the two regressions in parallel for quite some time to gain experience. We can do that too, because the numerical values of the new regression coefficients are in the publication!

 

Thanks for the link. Creating a good regression model using CFD based on the hull types of current interest could be a good investment for a design office anticipating multiple designs of the same general type. The Delft series is not universally applicable; application outside of the range of hull types tested is at the user's risk.

 

Yes, and it's already quite old. The older it gets the further it moves from modern hull shapes.

 

Can you suggest another book suitable to teach basic yacht design. Skenes?

I agree with DCockey's last comment

Richard Woods

 

I do not consider myself 'old' yacht designer, but we do not use CFD in office. And yes, we use Delft series and similar methods.

We outsourced CFD few times and the results were not satisfactory, for power catamarans in particular. Maybe it works for displacement boats, but for high speed craft the results are still dubious and need to be verified with use of tank tests, systematic series or full scale data. There was an excellent paper at Chesapeake Symposium 2012 by R.Datla comparing CFD with tank tests for planing boats; even the trends of lines are different!

I would say that naval architecture and yacht design (yacht designers do not only design sailboats!) in particular is the art of playing with margins. The designer does not need to know the resistance exactly (anyway it can only be verified with some accuracy), but he needs to guarantee the speed by using with proper power margins. Take the pessimistic predictions, apply expected overweight factor, look at sea trails conditions specified in TR and add margins for wave, engine de-rating factors - and here we are with speed/power figures. For this purpose, systematic series are sufficient, and the complete results of full-scale trials of similar vessels are essential. Yes, CFD can be used to study details of shape, but I would not rely on only CDF for power/speed prediction, for high speed craft and yachts.

Moreover, I would not consider knowledge of CFD or other software as essential entry ticket to design world. Design is much more complicated than just 'software usage'.

 

Delft is updating :
http://www.boatdesign.net/forums/hy...eries-resistance-equations-variety-39154.html

Latest evolution of systematic series would be in :
http://www.orc.org/rules/ORC VPP Documentation 2013.pdf , page58 and later. Based only on 2 parameters dynamic Length‐Volume ratio (LVR), and Beam to Canoe‐body‐draft ratio (BTR).

 

You mean adding more (newer) hull shapes to their data? I don't think so, and I didn't see anything in your links that suggested they were...