Cat design, estimating bare shell weight

No need for an apology, to me at least, I'm not at all offended, just trying to offer a counterview. It is an interesting idea to present a parametric tool in a web interface that will allow major variables to be played with by the user.

I think the key issue that people are seeing is that with your tool, when one variable is changed, the others will change based on the pre-programmed algorithms, whereas most people perceive design to be about varying the algorithms, not just the variables, something that is VERY difficult to program, hence the price of NA software.

Nevertheless, whilst most NA's, even the small craft sector, already have such a tool for their own use, putting one up onto the web for prospective customers to fiddle with is an interesting exercise, albeit of questionable economic viability. I wouldn't worry about putting NA's out of a job. If such a tool encourages more people to try custom boat ownership, the NA's will benefit in the long run, as this tool will not design the boat, just give some indication of the shape.

 

If you are standing on the floor (the sea presumably?) you will sense greater accelerations when the heavy cube falls than when the light one falls. But if you are on or in the cube (the boat presumably?) the reverse applies.

 

The idea is absurd. Boat design is no different to designing an aircraft, unless of course you simply want something that floats.

If you came to me asking for a new private jet design, and I showed you something that sounded like what you were after, and then you said " that's exactly what I'm looking for, however I'd just like to move the wings forward 2 meters, make the tail half the size, and put all the heavy stuff up the back... The plane would never fly... Same applies here, naval design requires understanding structural requirements, weights and locations, volume distributions, and much more. You can't simply change "things" around and expect the designer to make it work once your done...

 

I agree! this short article says more

http://sailingcatamarans.com/index.php/faqs/15-general-questions/80-rocket-science

You can build a house extension without the building heeling over, or put a church steeple in any corner, or add extra windows where you like

Even on a static house boat you cannot do any of those things.

Richard Woods

 

This is getting out of topic and I'm going to stop my posts (hopefully) with this one as I'm not fond of a pointless debate.

Richard, Groper and all, first of all, I'm talking about a design concept, not a specific person writing the software (like me) it can be you, or any experienced NA or a team, you are assuming I am taking the role of an NA, write some kiddie playing software and call it boat design. In my view, you are losing a lot of details on the way before saying it is impossible and it is rocket science.

If you are saying that an NA puts a web model for display and a client can adjust a simple parameter like the standing height inside a limited cabin area with no other major implications on the design, just a 10 cm raise of a cabin roof for example, and call it rocket science, I beg to differ, but fortunately we are all entitled to our own opinions. If you tell me a customer could choose to uniformly add 10% displacement to a hull that was already engineered to be able to take that extra and call it rocket science impossible, again, I beg to differ. The aircraft design parallel is not accurate, I'm talking about changes that are accounted for in a certain range in a predetermined and engineered model, where a customer has the freedom to make certain adjustments. If you tell me that you engineer a model for a 14m tall mast and a customer wants less sail area and a shorter mast and call that change impossible in a predetermined model, again I beg to differ.

I'm not here to change your opinions on design or what is possible, nor am I trying to revolutionize the small boat design segment. For the moment I am involved in a passionate study of what can be possible and how I can best serve my boating interests with the skills that I have. Telling me that a 5% change in the CoG cannot be accounted for with provisions to relocate cargo and dynamic weights on the boat (a short distance), is impossible and it is rocket science is something I cannot accept.

The ultimate truth is that most designs allow, require and need adjustments and trimming, moving weights around to float atrim, rudders adjusted and rig adjusted for the ultimate concert. Many times those adjustments are never done. The truth is that there is never a real optimum reached , because of all the conditions the boat needs to sail in, work in and adapted to owners requirements. I am talking about certain changes in a pre-designed parametric model a customer can make in an easy to use environment, changes in limited ranges that are pre accounted for and you call this impossible. I am pretty sure, over the design process the NA already analysed the model with all those ranges and again, you call it impossible. This is your wall you hit, not mine. I am happy to discuss other things, but this is a pointless debate now.

Florin

 

As others here have said, there is plenty of computer modelling (CAD) software available that could allow you to adjust the displacement of a completed boat design by changing just a few of the input values, or if you really want to, just one input value. This can be achieved without needing to do anything that would normally be described as 'computer programming'.

For the benefit of the uninitiated, this is called parametric modelling and examples of software that include such capability would include Inventor, Solidworks, Siemens NX, Catia, there are others. In recent years I have mostly used the first two of these and have found that it is quite possible to design a boat, estimate the weight and CoG, then if the the submerged volume (i.e. the displacement) is not right adjust an input variable or two to change the hull shape to achieve the correct match of weight to displacement. Mind you, it is not always an instant process. Consider a rather basic situation where you have specified in your parametric model that there will be a certain width of walkway down the middle of a hull cabin. Also you have specified that alongside that walkway there will be a certain size of cooking stove, leaving little space to spare in the width of the hull. Then you change a number or two to reduce the displacement and that results in some reduction in overall beam. The chances are that the software will not know what to do about that stove and will draw it sticking out of the side of the hull. The next thing that happens is that it gets in a complete muddle trying to draw the brackets that mount the stove and the bulkheads that surround it. You could typically spend an hour or two (at least!) sorting out this kind of mess, but its still on the whole quicker than not using parametric modelling and certainly quicker than manual drafting where a change in hull beam would probably mean starting with a fresh sheet of paper.

Florin said that he is using Rhino. I have not used that software but I understand that it does not have quite the same kind of parametric capability that one would find in the software I list above, hence Florin may have to do some kind of 'programming' to add that capability to his model.

 

John,
Rhino has its entire geometric engine exposed to scripting (programming). I write Rhino plugins for myself (and others). The possibilities are endless. There is instant visual and hydrostatics feedback loop for any minute change in Grasshooper (Rhino plugin). You can link any input to a web interface with .Net and Rhino.Python. Regarding the stove or other constraints, it is all about how much code you write, in this case, the stove size would be a hard constraint and you could account for it throwing a warning and saying that parameter "x" cannot be higher or lower than this value, you could even determine optimum values for certain parameters within certain constraints with free and easy to use numerical solvers.

I will be releasing a hull design software (Rhino plugin) probably after I get back from my volunteering months. It's basically the code I used to generate my hulls maybe someone else might want to play around with it.

 

isvflorin, I think it's great you're developing plugins for Rhino. I'm also a software developer, mainly for AutoCAD, and I love this job.
If what you want to do is something on the naval architecture area, note that the construction of a model is the part, in my opinion, less interesting of all naval architect calculations should be performed. It is the easiest part of the whole process leading to design a boat. While it is true that it takes some special skills to build a model. But for your plugins are interesting for a naval architect, you need to have much knowledge and solve many topics that are not resolved by a parametric model.
Your plugins may calculate, I'm sure, hydrostatic values, but have you thought about how to calculate the cross curves of stability ?. What about stability criteria?. Have you thought, for example, how can you calculate the stability after damage?. What about tanks definition and calibration?. How to calculate heel due to wind?, and so on...
I know you can say that your program is used to build the model and the rest should be done with other software, but that's not an interesting solution. That, fortunately, it exists and, I think, it works well enough. So you should explain well the properties that differentiate your plugins from other existing and why yours are more interesting.
Not to be pessimistic but explain what, in my opinion, the current situation.
Cheers.

 

TANSL,
I don't want to write anything for anyone else than myself now. And I might release what I write for myself for who ever wants to play with it at some point. Stability, heel and alot of other physics can be simulated in Rhino with physics engines like Kangaroo (free). As you know software development is very laborious if it wants to address the "mass". I don't want to write Naval design replacement software in any case, but collections of small plugins to help people with various tasks.

However what I believe it is interesting for me is not a do all NA software for any shapes and any possibilities. Instead, an integrated parametric model with all (or some) calculations necessary over a range of inputs. I believe it would be lovely if NA's would offer this to their clients. Imagine it like a kit home. You don't have to write CAD software for it, just develop a model with options on top of a CAD package.

And anyway, in any case, I would not venture to write big do it all software for NA's alone, as you said, I don't have all the knowledge for it. However, with the knowledge of an NA, a package addressing various tasks could be written. You know - working in TEAMS. It seems to me a lot of people are so used to working alone on design (Naval, architecture, whatever) and forget about what could be possible if more skills would be used together. If you read the comments above, people say it is impossible for ME to do whatever it is I'm doing or wanting to do. It is like they already rule out team work.

The massive advantage of writing Rhino plugins, is that you have an already highly advanced geometric engine and you can write on top of that, less coding maintenance to do, endless possibilities with other 3rd parties, scripting environment, available numerical solvers, physics engines, all already made. Much easier to tend the code, debug, rebuild, choose your flavour of language, VB, NET Python, C# and outstanding support from the Rhino developers.

Imagine the coding work needed to maintain, make changes and write new stuff for a stand alone Naval design software. Pretty big task.

This should be now in the software section, got off topic.

 

isvflorin,
as I said before, I totally respect your work and, as I do perfectly know it, I know the merit and value in what you want to do.
It's great to have the time and the resources to do something just for yourself.
I insist that, I think, what you want already exists. If you want to do, great, you'll have a good time and get great satisfaction checking how you manage to do what you had proposed. But in my opinion, not get more than personal satisfaction, nothing useful to others. If this does not matter, the better for you.
On the other hand, if you knew the field of naval architecture in all its amplitude would understand that a single model, parametric, fits-all type of boat is not possible.
I do not think a fairly important boat, say over 12 m, can be designed by one person. It would be possible for someone with more knowledge than normally we have, and with much more time available than any designer has.
I repeat again that make the model hull is a fraction of what a designer has to do to design a boat.
So, enjoy your work and good luck with your project. I hope and sincerely wish that in the end you can show us something new.
Cheers

 

I noted this in the thread I made on the subject here. The Shionning G force seems to have bows like this. Nice boat but I am not a fan of the bows.

http://www.boatdesign.net/forums/multihulls/reverse-bows-cruising-cats-pros-cons-46412.html



Good luck with your build!