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Hi, Frank - there may be a way out of
this.
Depending how important the planing aspect of your
sub is, it may be possible to use some galvanised or Al2 sheet to construct a
"bra" or sled for your sub. Fairly inexpensive but you'd have to
figure a way to operate your attachment point(s) from inside the
sub.
You'd be able to generate the lift
from variable tanks in the sled, added length, and proper planing hull
configuration. In essence, you're putting your sub onto a sled that
will be towed. Your sub, while moving, wouldn't even be in
the water. The stern doesn't even have to have a transom on it, similar to
some racing sailboats. You don't even need static lift in the stern.
Once you're dead in the water, the stern would simply sink once the tanks were
emptied.
A seaway would prevent challenges, as
usual.
Rick
----- Original Message -----
Sent: Sunday, October 25, 2009 12:36
PM
Subject: RE: [PSUBS-MAILIST] Git
Kraken
Frank,
Pulling out a handy book
(The Nature of Boats by Dave Gerr) for rough order naval architecture
calculations quickly supports my contention that you have a displacement hull
that will not plane (your model would not necessarily show you this due to
scaling issues and Reynolds number issues). Despite your efforts that
you have made in streamlining the forward portion of your hull, you still have
a displacement hull. Your displacement to length ratio is 400 which is
classified as very heavy. Your forward quarter-beam buttock angle is
greater than 7 degrees (classifying you as having a displacement hull).
You have a soft bilge that does not contribute to lift necessary for
planing. Based upon the shape of your hull at its maximum width, I would
lay money on it that it has a prismatic coefficient around 0.51 to 0.56 which
would make it a displacement hull. A planing hull needs to be very
square for at least the after ½ with little deadrise (a flat bottom with
little if no V). I attend a seminar this summer as part of a school
activity and this same author gave a presentation on what was wrong with 3
different planing hulls, and most of the above issues were discussed.
Doesn?t matter how many horse power you throw at this hull, it will not
plane. Wish I could tell you different but basic physics are against you
and there isn?t any easy solution to turn it into a planing hull due to your
displacement/draft.
R/Jay
From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
ShellyDalg@aol.com
Sent: Sunday, October 25, 2009 4:06
PM
To: personal_submersibles@psubs.org
Subject: Re:
[PSUBS-MAILIST] Git Kraken
In a
message dated 10/25/2009 12:13:55 P.M. Pacific Daylight Time, jonw@psubs.org
writes:
of
instability and I suspect those will ultimately prove effective. I'm
looking forward to seeing your sub as well since it is a design I am
considering.
Hi
Jon. Ya, don't jump in yet. I'm hoping to create some converts to the saucer
shape. Take a ride in mine before you commit to steel.
Your
extensive experience makes me listen very closely to your thoughts and
suggestions.
The
idea of getting your face "up close" is what subbing is all about. The dive I
made in the Aquarius was a blast and really brought home the whole "in your
face" aspect of windows.
My
own design has some limitations with visibility. I made a trade off between
having a big dome up front and being able to tow at high speed. Although there
aren't any blind spots, I have to look through different windows to see it
all.
I can
visualize your short/stubby hull with a big dome up front and if the hull
diameter is large enough, I bet it will feel very much like my saucer shape. I
considered replacing my 20 inch window with a larger one and maybe on the next
one I'll go that way.
The planing
(sp?) aspect of my sub isn't something I've talked about much, so let me
explain it here.
As
I've said, I wanted my sub to tow quickly and safely for long travels
offshore. To accomplish this the front end is pointed like a boat, and the
front ballast tank has several dimensional forms similar to a ski boat
hull.
The
main window is 24 inch OD.
That
makes a huge obstruction to towing so to counteract that, I have an acrylic
sheet 1 inch thick that attaches to the bottom of the ballast tank/tube steel
frame in the front. The area between this plexi and the window is free
flooding but will allow the front to plane across the surface. This
configuration was tested with my models in the lap pool and it seemed to work
well. I hope the 1 inch is thick enough.
I'm
also hoping that bubbles won't cause me grief when I submerge.
As I
was telling Vance, the front ballast tank does restrict my vision through the
front window. It's like a tunnel in some respects. The 1 inch plexi cover is
basically a triangle from the tip of the nose down to the bottom of the round
window. It adds impact protection for any debris that may be encountered while
towing and sheds water to the sides as the boat is towed. It's attached
to the front structural steel so any impacts are absorbed by the frame without
impacting the ballast tank.
The
front ballast tank is sharply pointed, and has "flutes" along the sides to
channel the water along the sides. The area where the front fairing meets the
ballast tank has a "flare out" rib to deflect water out and down as it
travels through the water, and the fairing has another "flare" along the side
to act as another flute to shed water out and down. It also acts as a bumper
when docked or maneuvering near objects.
It probably
sounds complicated but I think you'll get a better understanding of my
thoughts when you see it.
I'll
try to get some more pics up so the flow design is more
apparent.
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