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Hi & thanks Alec & Greg,
I've vacillated between fiberglass & steel for
nearly 2 years now & have a few good books
on the subject. It's very complex unlike steel,
that's why when I get the polystyrene full
scale model as close
as possible to what I want, I'm going to draw up the
design &
book in some time with a composites engineer. I've
had a brief talk with a design engineer who's
worked on Americas cup yachts. His firm
has a large program that can analyze for pressure
& design a lay up plan also. Maybe I'll have to draw in big safety margins. I'm
prepared
to abandon the idea of composites if it's looking
too costly or not viable in other ways.
& no I'm not going fiberglass to make it
lighter. It's going to end up heavier as I have to go
thicker than with metal. Bottom line also is it
will be tested unmanned to twice the operating depth.
I'm trying to make this really small wich has been
my design ambition from day 1. This involves an
ergonomically designed hull that transitions from
spheres to cones to cylinders & involves varying
thicknesses of material, wich would be really
difficult to achieve with metal.
Regards Alan
----- Original Message -----
Sent: Thursday, June 03, 2010 5:56
AM
Subject: RE: [PSUBS-MAILIST] Fiberglass
hulls
Alan,
I really hate to throw
cold water on someone's dream boat, but please reconsider this path.
There is room for lots of innovation yet in sub design, but there are a few
fundamentals that one really cannot escape with any confidence. What
worries me is not so much the calculated strength of the hull, but the degree
of confidence in that number. Use of non-standard geometries or materials
introduces uncertainty in both calculations and fabrication. Consider just the
fabrication aspect. In a conventional cylinder, if the roundness is off by
just a tiny percentage the depth rating falls off out of all proportion to the
fabrication variance. Greg recently mentioned something very
similar having to do with acrylic windows that were not correctly
annealed -- their performance went from many hundreds of feet to 50
feet. Composites can be strong, for sure, but my understanding is that
their strength varies tremendously with the skill of the person using them.
There have been composite hulls, such as those made by Hawkes, but they were
not hand laid.
Composites are
wonderful for things that want to fly through the air or float on the surface,
but a sub is the only type of vehicle I can think of where weight is actually
an advantage. You'll still have plenty of opportunity to use them on
non-structural components like fairings and soft tanks. But if you make a
light pressure hull, you'll end up with lots of lead on board to make it
sink.
Thanks,
Alec
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Hi, Frank , Glenn & Vance.
My sub will be about 25" in diameter in a semi spherical shape around my
upper body
& transitions down to about 14" around my legs. The
hulls about 6 ft long with external battery
pods out the back. So it's not much more than a kayak. My program
shows that the shell
only needs to be .5" thick at the most on the 25" dimension to get a
crush depth of over 1000ft.
Some reinforcement will need to be 2" thick. I only need to go to 250 ft
to match my dome.
So for my design in epoxy & fiberglass ( not wound carbon fiber) it
doesn't seem too prohibitively expensive.
I agree it would be stupid to use it for a big sub, but how many kayaks
are made out of steel?
Alan
----- Original Message -----
Sent: Wednesday, June 02, 2010 4:50
AM
Subject: Re: [PSUBS-MAILIST] Fiberglass
hulls
I like some of the benefits of a fiberglass hull like no rust and the
ability to make complex shapes. As for the cost though, It's not cheap. The
fiberglass fairings and dive planes I made cost almost a thousand
dollars just in material. They are a minimum of 3/8 inch thick with some
small areas up to 1-1/2 inch. If a guy was to be making a 5 inch thick
pressure hull from fiberglass, I can't imagine what the cost will be. ( LOTS
$$$ )
Now I know there are places to get FRP materials cheaper than where I
went but the cost savings isn't all that much. It's not only the resin and
cloth. There's all kinds of stuff needed. It's the little things that add
up. Brushes, buckets, acetone, tools, tape, glue, paints, mold materials,
dyes, mold release, sand paper, rasps, and that list just goes on and on.
And another note.....Fiberglass dust will EAT an electric motor like a
grinder, sander, saw, or whatever tool you've got. Keep the dust out of the
motor with masking tape and be careful not to overheat the tool.
Frank
D.
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