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 Boat Design Forums How to illustrate scantling

#1
09-03-2012, 09:07 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
How to illustrate scantling

Dear all, am a student and I was asked to illustrate whether the scantlings of a vessel are suitable for her after the proposed modifications have been undertaken for the vessel.
The vessel is a dry cargo coastal vessel of about 31.85M LOA. The scantling details are as follows:
Bottom and side shell plating is 9.5mm,
centre keelson, 280m*9.5mm intercostal web with 152mm *12.5mm continous face flat, A side keelson is fitted to port and starboard 1,295mm from the centre line with a 280mm * 9.5mm intercoastal web and a 102mm * 12.5mm continous face flat, Frame spacing is 533.4mm with 280mm * 89mm angle floors at every frame, web is 15.5mm thick and flange 9mm thick; side frames are 101mm * 76mm * 9.5mm toe welded angle apart from frames 21, 29 and 37, in the hold, which are 280mm * 9.5mm web with 102mm * 12.5mm face flat
Deck plating is 9.5mm and hatch coaming 12.5mm.

Any help will be much appreciated.

Regards
Mike
#2
09-03-2012, 07:05 PM
 Ad Hoc Naval Architect Join Date: Oct 2008 Rep: 2188 Posts: 3,733 Location: Japan
Mike

You have to do 2 things.

1) Calculate the maximum bending moment the hull shall experience. Either from a wave (via class rules or otherwise) and/or from loading of the cargo holds.
2) Calculate the hull section modulus before and after.

Once you have done #1 and #2, you can calculate the stress in the hull under both loading conditions before modification...and then after. You then have your answer.

Good luck.
#3
09-04-2012, 05:01 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
Many thanks Hoc, i was very surprise that this is the way to solve d question, maybe i was thinking it doesn't have any word relating to scantling. i shall act as you said; though i didnt have the lenght after loading, can i use loadline lenght for the lenght after loading?

Regards
Mike.
#4
09-04-2012, 06:58 PM
 Ad Hoc Naval Architect Join Date: Oct 2008 Rep: 2188 Posts: 3,733 Location: Japan
Quote:

If you state your assumptions, for your calculations, such as LL Length, that's fine.

But I'm still confused by your question?
#5
09-05-2012, 10:10 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
Dear Hoc, i am having some problem in drawing out the scantling to be use for the calculation. I get some formulars in a texbook for finding moments on a hull girders. the table goes like this:
Item, ship Beam x thickness of plate, Lever, Lever x beam x thickness. Since i can only knw the no of lever applicable to each plate from the drawing, this is were my problem comes from.

Pls any help on how to draw this out.

Regards
Mike
#6
09-05-2012, 07:04 PM
 Ad Hoc Naval Architect Join Date: Oct 2008 Rep: 2188 Posts: 3,733 Location: Japan
You need to sketch up the hull like shown:

Hull girder modulus.PDF

Arrange each part of the hull,. I have shown just 4 sides, as a simple box, but it could be many. You also have to include deep long.t girders too.

Itemise them and then calculate the area of each. Then from an assumed axis, which is the lowest part of the structure, find the level (distance) from that axis to the centre of the structural section (by area, either calculate or guesstimate it). Then you multiply each area by its lever and again. The sum of the 'ah' over the sum of areas,'a', gives you the location of the neutral axis.

You then work out the k^2, for each member, that is to say its own inertia. Then sum up the ah^2 and add it to the ak^2, to get the inertia about the assumed axis.

Then you move the axis to the neutral axis, by the ah^2, where a = area of the section in the second column and 'h' is the distance you previous calculated as Y(na)

That's it.
#7
09-06-2012, 03:15 PM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
Many thanks Hoc. i wil do it the way you said and i will get back to you.

Regards
Mike
#8
09-11-2012, 04:11 AM
 Ad Hoc Naval Architect Join Date: Oct 2008 Rep: 2188 Posts: 3,733 Location: Japan
Any luck Mike?
#9
09-11-2012, 04:53 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
Yes! i have done some calculation with those formulars u gave me. Am about to post it to you yest. nite wen my system gt problm.

Am on mobile web now; so as soon as i rectify the PC i wil post it to you.

Many thanks for the assistance.

Mike.
#10
09-11-2012, 06:21 AM
 TANSL Senior Member Join Date: Sep 2011 Rep: 119 Posts: 476 Location: Spain
Adeleye, if you have an outline of the midship section, with longitudinal, plates and profiles, and their scantlings, I could give you the physical properties of the same in a few minutes and show you how to do it, with great precision, in AutoCAD.
#11
09-11-2012, 07:00 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
ok Tanzl. the profile drawing are not clear. but they gave me some scantling details which can be use. I have post the scantling details on the top of the page. I wil upload the drawings and the calculations which i have solved earlier.

Many thanks
Mike
#12
09-11-2012, 10:42 AM
 Adeyele Junior Member Join Date: Jun 2012 Rep: 10 Posts: 46 Location: Lagos
The vessel's profile drawings

Dear Tansl, please kindly check the drawings that i posted below for the vessel. though the mid-ship section drawing was not given to like i said. the tutor gave me only the scantling details because the drawing were not clear. what i need from you guys is d drawing prior to the calculation. As i said, i will post the work i have done so far later today when i rectify my system.

regards
Mike
Attached Thumbnails

#13
09-11-2012, 12:12 PM
 TANSL Senior Member Join Date: Sep 2011 Rep: 119 Posts: 476 Location: Spain
I got what you can see in the attached file. The Main Section, I'm sure, is incomplete so, if you give me more information, I can make the exact calculation
Attached Files
#14
09-11-2012, 04:35 PM
 Nick.K Senior Member Join Date: May 2011 Rep: 60 Posts: 124 Location: Ireland
Hello Mike
Looks like we are doing the same course. I'm also doing this exercise. five hours so far today on it.
(I'm dissapointed with this module, insufficient information in the course work and lack of professionalism in the exercises set... the first issue was ridiculous...do sea trials on an imaginary ship and take photos!! Second issue not possible because of missing information, third and current issue? I imagine you feel the same frustration?)
Nick.
#15
09-11-2012, 05:47 PM
 DCockey Engineer Join Date: Oct 2009 Rep: 1337 Posts: 2,371 Location: SE Michigan
What is the course?
__________________
David Cockey