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.