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RE: [PSUBS-MAILIST] Steel Pipe Hull
Alec,
Are the heads on a K boat the same thickness as the hull or are they
thicker? In order for an ellipsoidal head to act as a head and a
stiffener, it must be thicker then the hull. Adding a generous bevel
around the inside of the head so that the head thickness gradually
transitions to the hull thickness is an important detail in this
location also. Does Kittredge specify a bevel (assuming the thickness
transitions)?
Adam
-----Original Message-----
From: Smyth, Alec [mailto:owner-personal_submersibles@psubs.org] On
Behalf Of Smyth, Alec
Sent: Monday, January 29, 2007 9:08 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Steel Pipe Hull
I agree with your figures. But it's interesting to note that the K boats
have stiffeners right on the ends of the cylindrical sections. I guess
Kittredge went for the extra insurance since the transition is such a
critical area.
Alec
_____
From: owner-personal_submersibles@psubs.org on behalf of Adam Lawrence
Sent: Mon 1/29/2007 8:55 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Steel Pipe Hull
May I chime in?
The ABS calculations work for hulls that do not have ring stiffeners and
are geared toward finding the most efficient combination of all the
variables. In the case of no ring stiffeners, (along with the case of
having ring stiffeners), the heads on either end of the hull (or pipe)
act like stiffeners. There is a picture of this on page 78 in the ABS
rules. The center to center spacing becomes the distance between the
heads at a distance of 0.4 times the inside head height. For example, ¼
thick heads that are 10 inches in diameter have an inside head height of
3.88 inches with a 1.5 inch flange. The center of the head stiffener is
located 3.052 inches from the face of the head (0.4*3.88) +1.5. If the
center to center spacing of the stiffeners is 60 inches, the actual hull
(pipe) length will be around 54 inches. The abs rules cover three
failure modes, one of which says that a long un-stiffened cylinder is a
bad idea, unless it ok to be thick and heavy.
Adam
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Monday, January 29, 2007 12:39 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Steel Pipe Hull
Hi Doug,
I think we need Cliff Redus to comment.
I checked your spreadsheet and compared it to mine, and the difference
was the center to center spacing of stiffeners. I left mine at the
default value of 10 inches and you had changed yours to the length of
the pipe (I assume) which is 60 inches. The output doesn't make sense
to me either since I assumed a .0001 stiffener and web was essentially
equal to not having a stiffener. The center to center spacing of
stiffeners shouldn't be a factor in that case. I'm guessing there are
some assumptions built into the formula's behind the spreadsheet geared
towards a reasonably sized hull and it may not be applicable to
pre-manufactured small diameter pipes without stiffeners.
Hopefully Cliff will see this message and take a look himself.
Jon
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of
djackson99@aol.com
Sent: Monday, January 29, 2007 12:12 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Steel Pipe Hull
Jon
Your right about the stiffeners, but there must be other problems. Now
I get 8 psi :) What are you using for "Center to center spacing of
stiffeners"? When I change it the outcome changes, and that does not
make any sense. Your calculation can not be right either; 57 psi for a
1/4" think 10 inch pipe? No Way! I get 57 psi out of a garden hose and
I've used 10" steel pipes for temporary colverts and had concrete trucks
drive over them. There is just no way they would not perform to
anything less than 1500 feet.
You can download my sheet from here:
http://www.submarineboat.com/sub/BOB2_Hull_Calculation.xls to have a
look if needed.
I really do appreciate this exercise I hope the outcome is a simpler and
more full proof approach.
--Doug J
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