[PSUBS-MAILIST] Terminating a conical transition

Sun May 4 10:17:55 EDT 2014

Joe,
When I mounted the tanks back on Gamma, I changed the mounting location to give a greater angle also I did what Vance is saying on a small scale.    I then poured a gallon of paint in  each tank and rolled the sub slowly to ensure there was complete paint coverage.  If I was operating in salt water I would mount some nipples to the tanks with plugs.  After a dive in salt water, remove the plug and you have access to spray fresh water inside and rinse the salt water out. A large panel is a good idea also because you
can open it up after each dive and let it dry out.   
If I had a K350, I would not copy the Nekton tanks exactly.  I would change the shape so they have more volume at the top reducing the rolling effect. Also I would consider making them from SS. Also SS heads solves the problems entirely. Start watching ebay for ss heads.  I once saw a ss tank exactly the same as a 500gal propane tank for 1,500 dollars on ebay.
Hank
--------------------------------------------
On Sun, 5/4/14, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Terminating a conical transition
 To: personal_submersibles at psubs.org
 Received: Sunday, May 4, 2014, 8:32 AM

 Joe,

 Consider using an elliptical head back there, for
 starters. You aren't building for much depth here, so
 the K-350 size will be fine (.375" ish). The ellipses
 are cheaper, do the same job, and give you a touch more
 inside room. Then I would have a cone rolled
 with a short flange on the major diameter, maybe a couple of
 inches, to match the hull OD.

 The Nekton cone-to-dome caused a
 pinch point that was always a hassle to clean and paint, and
 ultimately left some pitting in the pressure hull that had
 to be weld-repaired. A short cylinder on the sheet metal
 would give you a little more room under there to sandblast
 and paint during assembly and later for overhauls. I would
 say for maintenance a couple of flush-mount, gasketed panels
 in the tank would serve you well. Don't make them too
 ornery to remove or you won't do it as often as you will
 wish you had.

 I'm wondering now about my own
 boat and using tanks like that. Is there anyone in the group
 who can plug and chug a metacentric height on Nekton tanks
 installed on a K-350? Assembly would be so simple that way.
 And it would tow better, which is always a good thing. The
 Nektons roll a bit, but are reasonably stable. A K with the
 pods should have plenty of weight down low. Hmm. Would it
 work? I'm thinking yes. Anybody else have an opinion on
 that?

 Vance

 -----Original
 Message-----

 From: Joe Perkel via Personal_Submersibles
 <personal_submersibles at psubs.org>

 To: personal_submersibles
 <personal_submersibles at psubs.org>

 Sent: Sun, May 4, 2014 12:28 am

 Subject: Re: [PSUBS-MAILIST] Terminating a conical
 transition

 Vance,

 Rethinking that aft assembly to make it all soft tanks aft
 of a hemi head ala Nekton.

 If I go weld-on to the head ala Nekton, how best to attach
 to the head to allow for periodic access and maintenance?

 Joe

 Sent from Yahoo Mail for iPad 

                                 From:

                             via Personal_Submersibles <personal_submersibles at psubs.org>;

                                 To:

                              <personal_submersibles at psubs.org>;

                                 Subject:

                             Re: [PSUBS-MAILIST] Terminating
 a conical transition                            

                                 Sent:

                             Sat, May 3, 2014 2:03:36 PM     

                                         Joe,

 It
 seems like an expensive and complex assembly for what you
 get. Why not close the aft segment in a simpler way and fair
 the stern to the shape you prefer? A hemisphere with an
 extended shaft housing to put the prop where you want it,
 for instance.

 Vance

 -----Original
 Message-----

 From: Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org>

 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>

 Sent: Sat, May 3, 2014 8:17 am

 Subject: Re: [PSUBS-MAILIST] Terminating a conical
 transition

 Sean,

 Yes,
 a bolted flange with O ring.

 I've
 attached an image of what's on my mind. This hull is
 36" OD, cylinder length is 120". Anything bigger
 in diameter, simply gets way to big and bulky for
 handling.

 I'm
 thinking at this size, I must bolt at least two hull
 sections together for outfitting and maintenance, and the
 cones can be un-stiffened or perhaps only at the
 joints.

 Joe

   On Friday, May
 2, 2014 9:50 PM, Sean T. Stevenson via Personal_Submersibles
 <personal_submersibles at psubs.org>
 wrote:

 Each cone section in that case is considered
 alone, so if you were using stiffeners, you would need a
 heavy stiffener at every joint. Depending on the size, it
 may be simpler to use unstiffened geometry for such an
 assembly.

 The rules do not address bolting pressure
 hull sections together, but I don't see why you
 couldn't, provided you meet the requirements in terms of
 the stress analysis under the maximum combined loading
 conditions, which are prescribed in the ABS rules. Might
 require some FEA to be sure. You're thinking an O-ring
 groove seal? Or other arrangement?  I think an ASME
 code compliant flange would be a good place to start, but I
 would make sure that the cross-sectional area of each half
 of the flange considered individually met the requirements
 of a heavy stiffener per ABS, at a minimum material location
 (bolt hole). I would also be inclined to use SuperBolts for
 the connection. 

 http://www.nord-lock.com/superbolt/multi-jackbolt-tensioners/

 Sean

 On May 2, 2014 6:03:21
 PM MDT, Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:
 Sean,

 Would the heavy stiffener rule apply equally to several cone
 segments stepping down at different angles?

 Also, do ASME pipe flange specifications translate equally
 to bolted pressure hull sections? Have I missed a section
 somewhere on bolted cylindrical sections?

 Very helpful Sean thank you!

 Joe

 Sent from Yahoo Mail for iPad 

                                 From:

                             Sean T. Stevenson via
 Personal_Submersibles <personal_submersibles at psubs.org>;     

                                 To:

                             Personal Submersibles General
 Discussion <personal_submersibles at psubs.org>;     

                                 Subject:

                             Re: [PSUBS-MAILIST] Terminating
 a conical transition                            

                                 Sent:

                             Fri, May 2, 2014 11:45:11 PM    

 2:1 semi-elliptical heads are usually
 fabricated with some length of straight flange (tangential
 cylindrical section) beyond the axis of the ellipse.
 Hemispherical heads may or may not have a straight flange
 section, but in either case are permissible to use adjacent
 to conical sections, provided all other requirements are
 met. For stiffened cones, you must have stiffeners meeting
 the "heavy stiffener" criteria at both ends, as
 close as practicable to the cone-to-cylinder and
 cone-to-head transitions. For unstiffened cones, the length
 L_c used in overall buckling calculations must be the total
 length between the next heavy stiffener to either side of
 the entire compartment length, or between the 40% of head
 depth points if otherwise unbounded.  Cone to head
 welds are done in the same manner as cone to cylinder welds,
 and if your
  head is supplied w!
  ith a
 flange, it is the same
  thing.

 Sean

 On May 2, 2014 2:48:52
 PM MDT, Joe Perkel via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

 I have
 spotted the ABS diagrams and specifications for
 re-enforcement and butt welds at conical to cylinder
 transitions. I am somewhat unclear however as to terminating
 at the head.

 For
 example, the diagrams in the 2014 ABS underwater vehicles
 and hyperbaric chamber publication shows conical transitions
 either bordered by a cylinder at either end, or simply open
 at the small end???

  I want to terminate the small end of a conical transition
 directly to a small diameter hemi-head without another
 straight section, but I am unclear as to whether or not
 that is acceptable
  in practice.

 Joe

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