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Hi, Joe . . .
If I am understanding what I have learned so
far "floodable interior space" is the total displacement of the air volume that
you are trying to submerge.
I've never heard that particular term before. It
seems contradictory. Rather than complicate things by establishing
nomenclature [just for the moment] I'll refer to the interior dry volume
(cabin) as the bubble I have to force underwater.
A dry cockpit volume of 4 x 4 x 4 will yield 64 cubic ft.
or 4100 lb. of buoyancy. Weight includes two occupants at 150 lb.
ea. Also include the seats, instruments, dash panels, batteries,
controls, a good book [Busby - at least 35 lb.], a packed lunch with thermos and
a sleeping bag and misc. other items. Obviously, if you have 4100 lb. of
keel ballast in the form of, say, lead, you're going to the bottom fast.
Let's put less lead in the amount of all that cargo we mentioned above.
Lead + cargo = cockpit bubble. That's
it.
All other materials, say, ply hull,
fibreglass/resin, motors, deck fittings, anchor/chain/rope, skeg, etc. that will
be fully immersed will have an amount of buoyancy depending on their particular
specific gravit
This is the difference between dry weight
and what would be required to submerge to neutral buoyancy. Quite frankly, I am
having trouble determining how to look at it, whether soft water ballast is
"increasing" weight or "decreasing" displacement or perhaps both?
"Soft tanks" are upside down glasses that you fill with
air at the surface to lift the boat higher out of the water. Open at the
bottom like a glass. Very little inherent pressure internally. No
reason to have much pressure. They still have to be sturdy.
That figure above is roughly the 30% ratio
to interior volume for a seagoing boat as Carsten had pointed out. He had also
pointed out that high volume soft ballast ratios are not unheard of as in this
example so I am still playing with the idea.
Take a look at your own boat. Everything other than
your dry cockpit/cabin will be wet. Those areas will be flooded
100%. No mystery. Your hull is for streamlining and lifting your
boat out of the water while surface running.
Where the confusion may be arising is in the hard
tank[s]. At the surface, having lots of hull space to force air into will
lift your boat up high. Those are the soft tanks.
The hard tank [as in "hard-walled" to resist water
pressure] is used to fine-tune your neutral buoyancy. It is NOT open at
the bottom - it's sealed against pressure. Ideally, if this sealed box is
full of air, the sub will not dive - it's too light. Your cockpit canopy
will be awash. If this box is filled 100% with seawater, your boat will be
too heavy - it will sink.
During normal use, if the usual occupants' weight is
known, the weight of Busby's book is known, your cell phone, note pad, video
camera, box lunch and pina colada thermos are all known weights, THEN you can
remove lead to the point where your hard tank will be filled about half way to
achieve neutral buoyancy.
Until then, using these known weights, your canopy will
forever more be doomed to be awash until that hard tank is filled half way with
sea water.
So why is it hard? To keep Boyle's Law out of your
hair. An open [soft] tank will accomplish the same thing as a hard tank -
for the first few feet of depth. Once the air starts to compress, you'll
face every diver's dilemma - keeping neutral buoyancy.
A hard tank will isolate the ocean pressure from the
contents and the air in this hard tanks will not contract.
A company called Dacor designed a hard tank scuba pack
[back in the eighties, I believe] to get around Boyle. It wasn't a
success. Apparently the pack wasn't strong enough to last through to
full scuba depths and you had to release pressure mid-dive. Not easy
to control. Now, if you build one out of Al2. There's
thought.
If you want to maintain some degree of scale
in a replica you run into these volume and length problems. What have you worked
out for your Typhoon replica "Magical Child?"
Hardy-har. Finally someone else with the same
dilemma!!! These subs were designed around using the entire interior as
dry volume.
Your particular affliction - and mine - is to maintain the
same degree of "look" or authenticity as the original. It wouldn't look
cool if the lines weren't right. You, I suspect, have an artsy streak
running through you. I'd be willing to bet you'd never be happy with
anything but an Italian motorcycle [damn the
electrics]. http://www.motoguzzi-us.com/bikes/v11lemans/index.html
Soo-weet.
[origin of the name Magical Child: http://www.thewellspring.com/cat/adult_books/magical_child.html ]
For Magical Child, I've had to compromise between authenticity [the cool factor]
and the length of my workshop. I truncated Magical Child until I could
squeeze it into my 18 foot shop. A 15 X 2.5 ft. [NOT the original Typhoon
L/B ratio] hull allows tandem seating [not my first choice] and a 6:1
ratio. Not bad. It'll flow smoothly on the surface, offer a large
deck area for movement, lounging, etc., will be fairly kind in a seaway [no
thanks to its bows], will be hydrodynamic underwater, and will keep the props in
the water during heavy seas.
It'll also be aesthetically pleasing.
Dans words keep ringing in my ears though
and I believe it was you who suggested a "proof of concept" boat. I am seriously
looking at downsizing even further to a two man craft or smaller.
I'd like to share the u/w world with my
kids, hence the two seater. Think "kayak" around a cockpit. See
this link. http://www.psubs.org/pic/wet.html#sleepingbeauty
It's a wet boat - pic contributed by someone back in the '90's.
;-)
Put a canopy on it, compensate the cabin and Bob's your
uncle. Proof-of-concept still has to be fun. I have not the
resources to do this solely as an intellectual exercise (hmmm . . . that
didn't come out right). It HAS to be fun as soon as the thing hits
the water.
The S-boats at 219' by 20.6' could be scaled
to roughly 1/10 and come to about 22' x 3'. A single cylinder
diesel/electric would be damn cute!
A different L/B ratio would simply make a fatter
boat. Decent lines could still be
maintained. I enjoy inserting a jpg of a sub drawing into Word, then using
the image markers to expand or contract the image as I see fit. Hold a
ruler up to the screen or use Word's built in rulers and you can get INSTANT
visual results with ratio changes.
Do it with both the elevation and plan views. It's a
scream. BTW, if the technique appeals to you, mess with the sectional
views, too. Print out a copy of the proportions you like, white-out the
yucky parts, draw in your own canopy design, scan it back in to the puter, then
play with THAT jpg in Word.
A word on modeling: I've bought several well proportioned
human figures so I could work with them during the modeling
sessions.
http://www.psubs.org/pic/typhoon.html
This link shows one of my human figures. Obviously, the gentleman in the
picture is not in proportion to the hull he's sitting in. It was for
roughing out. I've since bought three more Typhoon hulls of different
scales to play with as well as several other human figurines/dolls.
The Magical Child model I'll be building will
be thirty inches long because the figure I've chosen is twelve inches
tall. His arms, legs and torso all bend at the right place and
are anatomically well proportioned (my smart-ass 13 year old daughter,
looking over my shoulder, wants to know if he has a penis) Same boat
building techniques as the final build: glass-over-ply.
Warm regards,
Rick
Vancouver
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