Re: [PSUBS-MAILIST] Fiberglass Hull

Dan,

I've enjoyed seeing your custom fiberglass work on Persistence. I've been looking into different ways of producing mold plugs and was interested in how you made yours. I think I've seen most of the pictures of your sub available on the internet. How ever there is only one pic I've seen of one of the mold plugs you made up and I would love to see any other pictures of you forming the plugs if they are to be had. From what I know now if I were to try to make those plugs I would render section drawings with outside measurements from my CAD work onto transparency's and then use a overhead projector to enlarge them to the proper size. Once they are projected onto a sheet of plywood or thick MDF which is vertical up against a wall, I could trace the outline of the drawing onto the plywood then cut it out. These plywood sections are then attached to a strong back and then covered with inch wide by 1/4" thick strips of pine or cedar with a bead and cove milled into the tangent edges like used on a stripper canoe or kayak.

www.actionfish.com

Then I can sand and bondo to my hearts content, then primer, gel coat, mold release wax, and apply PVA mold release agent twice. Is there an easier way to make plugs or is this basically what I need to do? I've also seen plugs CNC machined out of high density foam, but that can be cost prohibitive for larger applications.

With regards to composite pressure hulls made out of fiberglass, kevlar, carbon fiber, etc., when using a high quality epoxy resin or other resin they do have some compressive strength. Look at the Bionic Dolphin which has a carbon fiber outer hull and a kevlar inner hull with syntactic foam sandwiched in between. For the lay up he is using vinylester resin which is not as strong as epoxy resin and he's not going that deep with the craft for a number of reasons not really having to do with the main composite hull collapsing. However Doc is putting an extreme amount of hydrodynamic external stress on the hull when jumping and crashing into the waters surface. Of course the syntactic foam is taking a certain amount of this stress off the outer and inter hull.

http://www.redrockstore.com/resin.htm

http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0605963

Regards

Brent

" The difference between genius and madness is a fine line called success."

From:  " Dan. H." <jumachine@comcast.net>
Reply-To:  personal_submersibles@psubs.org
To:  <personal_submersibles@psubs.org>
Subject:  Re: [PSUBS-MAILIST] Fiberglass Hull
Date:  Sun, 28 Jan 2007 14:58:05 -0500
>But where is the real advantage of the design?   You still need to
>have a rather elaborate framework of steel.
>
>If it's the outward appearance your trying to customize, you can do
>that with fiberglass fairings.
>
>Remember, a sub has to replace it's weight in water so the weight
>savings with fiberglass will have to be offset with lead or steel or
>something making your sub as heavy as an all steel design.
>
>All I see is, your trading some of the smell of welding for the
>smell of fiberglass resin.  And also trading a long proven material
>for one not quite as proven in the sub world.
>
>Dan H.
>
>----- Original Message ----- From: "Mark Roberts - Harbortronics"
><Mark@Harbortronics.com>
>To: <personal_submersibles@psubs.org>
>Sent: Saturday, January 27, 2007 9:59 PM
>Subject: Re: [PSUBS-MAILIST] Fiberglass Hull
>
>
>>I was just thinking something long those lines too, as I arrived
>>home tonite....  of course the framework will have to be sized to
>>hold all of the stresses, but it could be done.  The construction
>>process could be simplified quite nicely, and retro-fits would be
>>so much easier.
>>
>>----- Original Message ----- From: "Charles Perkins"
>><chuck@memetech.com>
>>To: <personal_submersibles@psubs.org>
>>Sent: Saturday, January 27, 2007 12:19 PM
>>Subject: Re: [PSUBS-MAILIST] Fiberglass Hull
>>
>>
>>>
>>>On Jan 27, 2007, at 10:37 AM, Mark Roberts - Harbortronics wrote:
>>>
>>>>One guy per the link points out a very important thing with
>>>>regards  to fibers....  they can be very strong in tension, but
>>>>have  effectively no compressive strength. To my mind, that's a
>>>>show  stopper right there.
>>>>
>>>
>>>
>>>A show changer, true... but not necessarily a show stopper. All
>>>one  has to do is put the casing of the pressure vessel under
>>>tension,  rather than compression.
>>>
>>>How?
>>>
>>>As a thought experiment, imagine a soccer ball. Let's replace the
>>>seams with steal beams, and the skin with fiberglass... but allow
>>>the fiberglass to bow inwards. The fiberglass under tension will
>>>transmit the compressive force to the steel framework which can
>>>resist it  under compression and bending forces.
>>>
>>>One could make a cylinder similarly... take a hexagonal lattice,
>>>roll  it up, etc.
>>>
>>>Chuck
>>>
>>>
>>>
>>>
>>>>
>>>>----- Original Message -----
>>>>From: Brent Hartwig
>>>>To: personal_submersibles@psubs.org
>>>>Sent: Saturday, January 27, 2007 4:34 AM
>>>>Subject: RE: [PSUBS-MAILIST] Fiberglass Hull
>>>>
>>>>Doug,
>>>>
>>>>I'm not qualified to answere your questions about fiberglass
>>>>composite sub hulls under external pressure, but here is a
>>>>interesting thred about just that sort of thing. Here is the link
>>>>  and a small quote from the discussion that has the most meat in
>>>>it.
>>>>
>>>>http://www.eng-tips.com/viewthread.cfm?qid=174497&page=1
>>>>
>>>>"Spend some time looking through ASME III (Unfired Pressure
>>>>Vessels) for vessels under external pressure.  And keep in mind
>>>>that if you intend to operate at 100 ft (~45 psi) that you'll
>>>>want  a hefty margin against any kind of pressure boundary
>>>>buckling  failure.  Think in terms of emergency recovery time
>>>>from a depth  overshoot if you experience horizontal control
>>>>plane malfunction  while descending at some speed and down angle
>>>>when nearly at your  maximum operating depth.
>>>>
>>>>I may be able to find a more specific ASME reference for you, but
>>>>  for a number of reasons I don't think I can provide any hints
>>>>as  regards a design collapse depth, so you're on your own there.
>>>>
>>>>
>>>>Norm
>>>>arto (Mechanical)
>>>>12 Jan 07 9:46
>>>>also look under ASME PVHO (Human occupancy)  & Sec. X {fiber
>>>>reinforced plastic) pressure vessel codes"
>>>>
>>>>end quote
>>>>
>>>>In the past I saw a web site for a deep diving live aboard
>>>>submarine project called the Neptune. They were working on a
>>>>design  for a carbon fiber pressure hull that they claimed could
>>>>be used  down to 6000 meters. The web site
>>>>waswww.neptunesubmarines.com but  it's a dead link now. I was put
>>>>onto this site originally by a web  site for the Perendev
>>>>magnetic motor. At one time I thought it  might be a great motor
>>>>for subs in general but there is some  serious greed problems
>>>>with the owner of the company. Neptune  Submarines were wanting
>>>>to put the Perendev magnetic motor in there  live aboard
>>>>submarine to replace a nuclear type power source. Maybe  someone
>>>>here knows what happened to this Neptune Submarines group  out of
>>>>Switzerland? Here is a pic of there submarine design.
>>>>
>>>>http://img224.imageshack.us/img224/7608/24243158bk0.jpg
>>>>
>>>>Regards
>>>>
>>>>Brent
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>From: djackson99@aol.com
>>>>Reply-To: personal_submersibles@psubs.org
>>>>To: personal_submersibles@psubs.org
>>>>Subject: [PSUBS-MAILIST] Fiberglass Hull
>>>>Date: Fri, 26 Jan 2007 00:35:40 -0500
>>>>
>>>>I know  it's an old  topic but I have mostly ignored the previous
>>>>  post regarding fiberglass because I never thought I was going
>>>>to  give it a second thought.  ...wrong again.
>>>>
>>>>1) Did anyone ever come up with a way to calculate even a
>>>>ball-park working depth given all, or at lease some of the
>>>>variables for fiberglass construction?  If so can you point me in
>>>>that direction?
>>>>
>>>>2) I know that the externally loaded working psi for a non-
>>>>reinforced cylinder is lower than  it's internal working psi.
>>>>That  makes even more scene to me when thinking about the
>>>>alignment and  tensile strength of glass or carbon fibers
>>>>compared to their  compression strength. However it seems that
>>>>there would be a ratio  that could be used to estimate the
>>>>reduction in loading ability.   Would that be true?  For example
>>>>if pipe section is rated for  1000psi, could it's external load
>>>>psi rating be stated as x% lower,  say 20% lower, based on the
>>>>type of material?
>>>>
>>>>Thanks --Doug J
>>>>
>>>>
>>>>
>>>>
>>>>Check out the new AOL. Most comprehensive set of free safety and
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