Sean,
You are correct, the "lock out" terminology is for a 1 atm design. I borrowed "wet trunk" from you as a description for what I might have used. If you look at my design http://www.frappr.com/?a=myfrappr&id=269116
There is approx 28" of vertical space in the foot well forward of the pilot's seat. A watertight oval hatch in that forward bulkhead would allow the space to be flooded, and with a little "acrobatics" you could shimmy yourself into the forward space then out a side hatch, if one was so inclined.
The problem for me is that space needs to be baffled to control the free surface area of my design when surfaced, so unless I build a big boy, I ruled it out.
I thought of the "escape trunk" idea for the main hatch but, the inverted coaming would eat up my interior space. Same problem of scale.
"Interesting photos of that sportsub - maybe I'm looking at the wrong pictures,
but I don't exactly understand the under tail entry."
Their ambient designs are hovering "diving bells" with the main cabin being a MBT along with two smaller ones, the opening faces aft and requires just a bit of acrobatics to get in and out. Wet in...wet out, but a damn clever design for warm waters.
Joe
From: "Sean T. Stevenson" <cast55@telus.net>
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Dif. Between Ambient & 1ATM
Date: Wed, 15 Feb 2006 08:19:18 -0800
>First off, Joe, I think you might be confusing terminology, or maybe I'm just
>getting confused - a lock is not necessary in an "ambient" design, since the
>interior of the sub is already at ambient pressure. Is that what you meant, or
>is it a 1ATM design which requires blowing the lockout down to depth?
>
>Dealing with the exit of an occupant is easier in designs with larger internal
>volumes, since the proportional volume change is so much less. In my design, a
>diver exiting the lockout chamber will cause the water level in the exit trunk
>(between double hatches) to rise a bit. With a single diver, this is not a
>problem as the level restores itself (more or less) when he returns. With more
>divers exiting, the water level may rise so much that it overflows the trunk
>into the lockout compartment bilge - not a problem, but not something I want as
>as SOP. In this case, pressure is increased in the chamber to compensate for
>the lost personnel volume, pushing the water level down. The water level iself
>is not measured, but rather, the pressure of the compartment is automatically
>maintained at the pressure of the sea at a level just above the bottom of the
>exit trunk. (Just above, so that the system does not continuously pump gas out
>the bottom of the trunk). When the divers return, their volume pushes the level
>right to the bottom of the exit trunk, so once the lower hatch is closed there
>is only a little bit of water remaining that needs to be pumped out. That takes
>care of volume change. The weight loss is compensated for automatically by
>pumping seawater into the auxiliary ballast tank(s).
>
>With a small sub, this is not so easy to do since the effect of the change is so
>great. As you mentioned, you need to compensate for weight by either being
>negative (only safe if bottomed), or by adding ballast as the diver exits. You
>also need to compensate for volume, if the design of the boat doesn't lend
>itself to easily accomodating the water level rise. One simple way of
>accomplishing both tasks is with a varable volume "soft" tank within the
>interior, to which you can admit seawater when a diver exits - simultaneously
>compensating for volume and weight. This tank would then be pumped out when the
>diver returns. This might be getting complicated for a small psub, though.
>
>Interesting photos of that sportsub - maybe I'm looking at the wrong pictures,
>but I don't exactly understand the under tail entry.
>
>-Sean
>
>
>Quoting Joseph Perkel <joeperkel@hotmail.com>:
>
> > I have been thinking about this problem for my (ambient)design and came up
> > with the "wet trunk" idea as well but, ruled it out because of the buoyancy
> > problems you mention and access.
> > I found that to egress, you would have to be bottomed, well "negatively"
> > flooded and stable to accommodate the loss of the occupant'(s).
> > Where to put access was problematic for me as well so I ruled it out. But I
> > have to tell you, Sportsub has this problem licked nicely with their
> > particular ambient design. http://www.ivccorp.com/
> >
> > Joe
>
>
>
>
>
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