# Bulkhead design

Discussion in 'Boat Design' started by saeedfa, Jul 15, 2020.

1. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

hello
i want to design a watertight bulkhead, so according to DNVGL the require thickness for plate and stiffener section modulus are calculated. there are one vertical center girder and two horizontal girder on the bulkhead.
the question is, in calculation of vertical girder, the span of girder must be from keel to deck or the spacing between two horizontal girder?
i consider the span of two horizontal girder from bulkhead side to vertical girder.

2. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

thank for your answer
in the first stage of design i dont want to use any horizontal or vertical girder, but the vertical stiffener become so large, so i use 2 horizontal girder to decrease them. but because of large width of bulkhead, the span of horizontal girder is too much, so i decided to use a vertical girder for decrease it.
now i dont know in the calculation of vertical girder span, i must consider the span of vertical girder from keel to deck or from keel to horizontal girders

3. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

thank you TANSL
are you familiar to DNVGL rule for HSLC?
i have a post about ICE class vessel, please put a comment if you can help me
is there any reference for unsupported length of web frames according to DNVGL? i see a post about unsupported length of girder according to ABS, and they say if there is a knuckle in hull that angle more less than 150 degree, so that is a support point for girder. is there a reference like this in DNVGL?

4. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

Decrease the pitch of the verticals stiffeners.

5. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

Ad HOC if your mean for Pitch of vertical stiffeners is the spacing between them, i consider it about 200 mm, so i think it is very small.

6. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

Well, if the WTB is only 0.3m wide...it is not an issue. If the WTB is 10.0m wide, it is an issue.
Without seeing the WTB, and its dimensions, there is little else to offer.

A picture tells a thousand words...

7. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

the bulkhead width is about 5.4 m and the bulkhead height is about 1.8 m

8. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

Thanks for the picture.

Well... I dint see anything wrong with what is shown.
The only way you can reduce the number of verticals, is as you attempted. But it is bit of a fools errand since the depth of the WTB is not much at all.

A horizontal member must support the verticals, if you wish to reduce the number of them... thus, the horizontal member will be over sized.

Whichever way you go...shall depend upon whether you think 200mm spacing is sufficient or not.

9. Joined: Aug 2013
Posts: 21
Likes: 1, Points: 3, Legacy Rep: 10
Location: iran

### saeedfaJunior Member

I have question about pressure on bulkhead vertical girder:
in the calculation of section modulus for bulkhead vertical girder, we must use pressure on bottom of vertical girder or pressure on mid span of girder ?

10. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

That's up to you and how much redundancy you feel you need. Assuming worse case is usually best procedure.
But.. in general, you if want, you can assume the location of the pressure to be at 1/3rd from the base, since the pressure from max at bottom to zero at the top.

11. Joined: Sep 2011
Posts: 6,519
Likes: 391, Points: 93, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

Not correct

12. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

As noted on your other thread Saeedfa, you need to understand structural terms.
As it appears other posters whom make invisible posts, for some unknown reasons, also do not understand basic structural terms.

When the head of a WTB is 0, the pressure is zero.

Pressure = rho.g.h.

Rho = density of fluid
g = 9.81 m/s2
h = depth from top of member vertical down.

When h = 0, Pressure = 0.

Simple.

13. Joined: Sep 2011
Posts: 6,519
Likes: 391, Points: 93, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

When calculating watertight bulkheads, a load height is taken that is above the top of the bulkhead, a height that the regulations give, varying its value according to the type of watertight bulkhead. Therefore, at the top of the bulkhead, the design pressure is greater than zero (h>0, Pressure>0)

Simple.

14. Joined: Oct 2008
Posts: 6,840
Likes: 795, Points: 113, Legacy Rep: 2488
Location: Japan

### Ad HocNaval Architect

Oh... look.. the post is still there.. how strange!... must be a trick with the eye.

And where in structural theory does it refer to rules... hmm....it doesn't. Thus, who is talking about regulations?
That's the problem with posters only debate referring to rules rules and rules, rather than understanding structural theory, it takes more than a cut n paste of rule.

But hey, wait 5mins, i'm sure the post will magically disappear like the others .... and then the thread shall return to normality again.

15. Joined: Sep 2011
Posts: 6,519
Likes: 391, Points: 93, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

Yes, the post is still here and the next one will also remain in this thread (and perhaps others) :
I am not impressed by your money, position or title. I am impressed by how you treat others.
It´s nice to Be Important, But More important to Be Nice¡

Aaah, sorry, i forgot :

Simple.

Last edited: Jul 17, 2020
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.