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Brent,
The plug can be mocked up in many ways. I'm
not familiar with 3D CAD but I imagine working it out on a computer and
then making wafers of the plug and cutting them out of something would be about
the easiest. If not CAD I know you can do the same with technical
descriptive drafting. (Old School) But that's time consuming and you can't
get a 3D feel on flat paper. Once you have wafers, of maybe half inch thick
something, you could fill in or grind off the excess to form the smooth 3D
shape. I kind of did that but didn't use anything so technical. I waited
until I had my hull built to design my fiberglass so I could see it all in real
life.
With my hull already built, I
cut two shapes out of one inch Styrofoam, one for the X axis and one for
the Y, taped them to the hull and walked around it reshaping until I
was satisfied. Once I had the approximate size worked out I checked the
volume my MBT would have and tweaked the shape some. Following this
approximate shape I cut a stack of one inch thick Styrofoam pieces and glued
them together with construction adhesive. My sheets of Styrofoam were
stacked flat on the horizontal against the finished hull. Form there it
was a matter of sanding off the sharp edges that were sticking out farther then
the surface I wanted and then filling in the rest.
Actually I sanded the Styrofoam a bit smaller then
what the finished plug would be so I was sure to cover it all with
plaster.
Once my Styrofoam was to shape, I applied plaster
of Paris to all the larger sunken cracks and crevices. Plaster of Paris
doesn't shrink when it cures and cured to it's full depth fast. That was
then sanded to shape or a bit below.
After that I started with spackling compound.
Spackling compound sands easier then plaster of Paris so it's best if you remove
any plaster that you think will be to high before applying the spackling
compound. Also spackling compound cures slower and shrinks some.
It's better to apply it thinner and more times then to thick and have it not
cure to depth. With the spackling compound, it's a matter of applying even
coats until the entire plug is coated with it. Apply enough so you can sand it to the finished shape.
Once you start block sending on it you'll find
dips. You can apply a bit more to them and resand. It's a
simple matter of applying spackling compound and sanding over and over until
your happy with it. It's done exactly like a body man would does body work
on a car, only the spackling sands much easier then body putty. Keep
feeling with your hands and eyeing it up until all your curves are smooth with
no roller coaster looking surfaces. If you think your getting
out of shape, make some cardboard templates of one side and fit it to the
opposite side to see if your curves match. Remember, you can't
see both sides at the same time anyway so if it looks good to you as your
studding it, it should look great to the casual observer late on. Be sure
you have no Styrofoam showing through because the fiberglass resin will eat it
away.
Once your happy with the plaster plug, give it
several coats of wax to fill the finer sanding scratches and then mold release
if you want to. If I remember correctly, I had a tough time applying the
mold release to the waxed surface. Even if your mold stuck on the plug in
some spots, you could just destroy the plug to get it all out.
You still have a second chance to repair small
defects by working on the inside of your mold but it's tough working on the
concave inside rather them on the convex outside of the plug, so
get it as close as you can. Also, for durability, all repairs to your
mold should be done with auto body filler.
When your satisfied with the mold, wax it and
apply mold release, then the jell coat and lay up the glass. Even on the
finished part it's not that difficult to repair spots with fiberglass resin body
putty. You'll be painting the entire sub anyway. By now your body
man skills should be pretty good!
I have a friend in the body shop business. He
never did fiberglass plug and mold stuff but he was a great help in teaching me
how to work on achieving the surface I wanted by feeling the imperfections
and work them out.
There you have the long story. I hope it
helps. The best teacher maybe trial and error. Take it slow and
be observant as you go.
I'll look around to see if I have any more
pictures.
Dan H.
----- Original Message -----
Sent: Sunday, January 28, 2007 5:13
PM
Subject: 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.
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://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
>>>>security tools, free access to millions of high-quality
videos
>>>>from across the web, free AOL Mail and
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>>>>
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