Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Software
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read Most Recent Posts Gallery Images Search

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-23-2012, 04:43 PM
TealTiger TealTiger is offline
Junior Member
 
Join Date: Sep 2009
Rep: 10 Posts: 23
Location: Toronto
Structural Analysis Software!?

What software if any is used to do a structural analysis on a boat? I know it will have to be checked (at least) by an NA but I'd like to do as much as possible myself first. This is for a typical 38' ocean cruising cat using conventional materials, but in an unconventional mix/way.
Reply With Quote


  #2  
Old 03-23-2012, 04:49 PM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,968
Location: SE Michigan
Who will model and mesh the boat in a manner suitable for structural analysis using the software?

Where will the loads come from? This is a non-trivial question.

Who will interpret the results?
__________________
David Cockey
Reply With Quote
  #3  
Old 03-23-2012, 05:46 PM
TealTiger TealTiger is offline
Junior Member
 
Join Date: Sep 2009
Rep: 10 Posts: 23
Location: Toronto
Hi David,

Thanks for the questions. I'm not up on this stuff yet, so I may not be using the best terminology. I'm not sure if I need the detail that your question seems to indicate to me. I certainly don't need FEA. I want to take a fairly conventional cat (like a lighter simpler Lagoon 380) and find out if my material choices and spec's are aprox. strong enough. If so, I can pay more to get it thoroughly to get it done. So before I throw a lot of money at doing a through job of what might be a waste, I'd like to do everything I can to minimize the job of finding out if I'm on the right track. I'm interested in hearing any advice the people here might have to say. Thanks.
Reply With Quote
  #4  
Old 03-23-2012, 07:12 PM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,215
Location: Japan
Quote:
Originally Posted by TealTiger View Post
I want to take a fairly conventional cat (like a lighter simpler Lagoon 380) and find out if my material choices and spec's are aprox. strong enough...
Save yourself money and:

1) download any of the Classification society rules that are now available for free, such as here: DNV HSLC & SNC 2012 Rules

and

2) Buy a good book on composite design.

No need for fancy FEA....unless you like looking at pretty coloured pictures?

1) Will tell you if it is strong enough, since if Class accept the layup, then it is a good baseline minimum.
2) A good book on composites shall highlight areas that Class does not, and also pointers for practical things to consider.

If these are beyond you to begin with, then best seek a NA that deals with composite design. Good luck
Reply With Quote
  #5  
Old 03-23-2012, 10:45 PM
Alik's Avatar
Alik Alik is offline
Senior Member
 
Join Date: Jul 2003
Rep: 1192 Posts: 2,306
Location: Thailand
2AdHoc
I would not use DNV HSLC for 38' cruising cat, as thickness of bottom sandwich skin would be excessive.

Use ISO12215-5 is much better option; here on forum it was free calculator for these rules.
Reply With Quote
  #6  
Old 03-23-2012, 10:48 PM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,215
Location: Japan
Quote:
Originally Posted by Alik View Post
I would not use DNV HSLC for 38' cruising cat, as thickness of bottom sandwich skin would be excessive.
Interesting.

I designed a 15m cat to the DNV rules a few years ago...all came out ok. As I expected really. So, either the DNV rules are excess, as you say, or ISO is deficient. Either way...take your pick
Reply With Quote
  #7  
Old 03-23-2012, 11:16 PM
Alik's Avatar
Alik Alik is offline
Senior Member
 
Join Date: Jul 2003
Rep: 1192 Posts: 2,306
Location: Thailand
They have min glass weight requirement for skins. Those are a bit excessive, for sailboat of 38'.
Reply With Quote
  #8  
Old 03-23-2012, 11:23 PM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,215
Location: Japan
Quote:
Originally Posted by Alik View Post
They have min glass weight requirement for skins. Those are a bit excessive, for sailboat of 38'.
Depends upon your definition of ..."excessive"
Reply With Quote
  #9  
Old 03-24-2012, 02:22 AM
Petros Petros is offline
Senior Member
 
Join Date: Oct 2007
Rep: 1437 Posts: 2,295
Location: Arlington, WA-USA
The vast majority of boats are built without a structural analysis, but rather using rules and design tables for hull thickness/frame size/spacing, etc. from one of the class rules. These are design rules based on long experience and observations on what works. Too much is impractical to design for, so these formulaic designs based on size of boat and usage is more practical.

Burrow through those rules listed above to get an idea on how much structure you need.
Reply With Quote
  #10  
Old 03-24-2012, 02:31 AM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,215
Location: Japan
Quote:
Originally Posted by Petros View Post
These are design rules based on long experience and observations on what works.
That is not strictly correct. Rules, such as DNV or LR etc, whilst in the beginning (eons ago) were based upon "historical" evidence, today, there is a significant amount of R&D that is done to validate, justify and modify rules. It is no longer a hit and miss affair. There is sound engineering behind them.
Reply With Quote
  #11  
Old 03-24-2012, 03:34 AM
daiquiri's Avatar
daiquiri daiquiri is offline
Engineering and Design
 
Join Date: May 2004
Rep: 3126 Posts: 4,203
Location: Italy (Garda Lake) and Croatia (Istria)
Quote:
Originally Posted by Alik View Post
They have min glass weight requirement for skins. Those are a bit excessive, for sailboat of 38'.
Alik, I don't have statistics to demonstrate it, but I believe that the probability of grounding gets higher as boats gets smaller, primarily because of crew experience factor and tendency to sail closer to the coast. Large yachts are more likely to have a more experienced payed skipper and crew aboard, which (at least in theory) should diminish this probabilty.
Well, it's also true that, from time to time, even on ships around 300 meters of LOA it happens to find a Schettino in command, but that's a bit out of this topic...

So, I believe that for small boats it is more sound to stay on the "excessive" (to be defined, as Ad hoc noted) side of scantlings, unless you are designing a pure racer.

Cheers
Reply With Quote
  #12  
Old 03-24-2012, 03:42 AM
daiquiri's Avatar
daiquiri daiquiri is offline
Engineering and Design
 
Join Date: May 2004
Rep: 3126 Posts: 4,203
Location: Italy (Garda Lake) and Croatia (Istria)
As for the OP's question, I use Strand7 software for the FEA (http://www.strand7.com), which allows me to perform linear and non-linear, frequency and modal, buckling, transient, inertial and thermal analysis, all in static or in time-domain analysis. But on the other hand I am an engineer trained in this kind of analysis. If you are not, then I'd advice you to follow DCockey's and Ad Hoc's advices and stick to the classification societies' and ISO scantling rules. Errors can cost very much in this job.
Reply With Quote
  #13  
Old 03-24-2012, 04:13 AM
Ad Hoc Ad Hoc is offline
Naval Architect
 
Join Date: Oct 2008
Rep: 2285 Posts: 4,215
Location: Japan
Quote:
Originally Posted by daiquiri View Post
I use Strand7 software for the FEA (http://www.strand7.com),...


I first used Strand in 1991, hated it...was terrible. Full of bugs, non-intuitive, poor graphics interface. Although I'm sure it is somewhat better today 20 years later

I use Cosmos/M, which is now sadly all wrap up in Solidworks as a CAD package, no longer stand alone. (http://www.solidworks.com/sw/product...on-sofware.htm). But i still use my older stand alone package, does everything I need it to do...
Reply With Quote
  #14  
Old 03-24-2012, 04:28 AM
DCockey DCockey is offline
Senior Member
 
Join Date: Oct 2009
Rep: 1399 Posts: 2,968
Location: SE Michigan
From the original post: "This is for a typical 38' ocean cruising cat using conventional materials, but in an unconventional mix/way."

What knowledge is needed to use classification society and ISO scantling rules with materials used in an unconventional mix/way ?
__________________
David Cockey
Reply With Quote


  #15  
Old 03-24-2012, 04:31 AM
daiquiri's Avatar
daiquiri daiquiri is offline
Engineering and Design
 
Join Date: May 2004
Rep: 3126 Posts: 4,203
Location: Italy (Garda Lake) and Croatia (Istria)
Quote:
Originally Posted by Ad Hoc View Post
I first used Strand in 1991, hated it...was terrible. Full of bugs, non-intuitive, poor graphics interface. Although I'm sure it is somewhat better today 20 years later
You were lucky to have a graphical interface at all, back in 1991! I had to write my own software for nearly every task, back in those good old days.

I'm pretty happy with Strand. It works well and is one of the most reliable software I have. It never ever crashed, hanged or similar stuff which happens from time to time to nearly every other program on my computer. Evidently, the software house has managed to considerably improve the quality of Strand over the decades.

An off-topic rant:
The AutoCAD used to crash every now and then just until 5-6 years ago. The newer versions crash very rarely, but at the cost of high frequency of automatic backup save instances. I have noticed that some commands which on older versions used to cause a software crash, now don't cause a crash but a backup save before the command executon. Guess that folks at Autodesk weren't too much confident that they have managed to resolve the problem, so they said "hey, we better save the drawing before we run this command". Or perhaps it is a concealed way of recovering from a command-module crash which has happened after the command button was pressed.
It can be pretty annoying when I have to work on a server-based drawing, because of the time-lag in the access to the file. You hit a command button and then have to wait few seconds because AutoCAD want's to save the drawing first, so it slows down the work. Can that be considered a good software-programming practice? Yet the AutoCAD is an industry standard, so one would expect the excellence in every regard...

Ok, ok, I'm over now.
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Laminate design and analysis software Parkerconv Software 3 04-04-2011 12:53 PM
Motion analysis software catsketcher Software 5 04-22-2010 08:36 AM
structural analysis of frp yacths amateur mariner Software 6 02-02-2010 10:10 AM
Marine Structural Analysis Software Casper Software 7 11-27-2008 09:35 AM
Analysis software concrete canoe Boat Design 2 02-01-2005 08:50 PM


All times are GMT -4. The time now is 07:28 AM.


Powered by: vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2014 Boat Design Net