Dean,
You may not have a problem with your MBT valves
located low. The problem comes in when they are located above the
waterline. Depending on the depth of the bubble in the MBT, it may contain
maybe one PSI of actual air pressure when inflated. If the valve is high
above the water line, the air pressure has to be high enough to blow any
remaining water in the line up and out of the vent, on top of the valve.
On a K-350 it's often not enough so you have to open the hatch and lean
out to blow in the vent tube to clear the line of water. It works,
but sure doesn't look professional. I bet if a sharp looking lady was
piloting it would really drew attention.
After dealing with this problem, I installed a T
and a short piece of tubing that blows a jet of air into the line from the MBT
side by giving my fill valve a fast blast. That clears the lines, but it's
extra stuff to fix a problem. Better to not have the problem in the
first place.
The most unstable time in the sub is when your in
that transition stage of "not on top" and "not submerged." When a tank,
whether it's fore and aft or side mounted, is partially above the water line,
the sub is stable. When tanks are below water they add lift but tend to be
unstable. The air bubble in a tank moves around (water sloshing) and acts
on the sub with different amounts of leverage depending how far from the center
the lift actually is. That is, if the sub pitches nose down the bubble in
the aft tank runs back farther it has more of a lifting effect on the aft
part of the sub making it pitch even lower in the front. Side tanks
add another dimension to the problem. Install baffles if it's long. If
their small so are the problems with them but if they are large and totally
below the water line, you'll have to be careful with them. Any tank if unstable
when it's partly full of water and totally submerged. You just
have to work with it.
On the whole, the K-350 is a very stable sub.
It's almost impossible to role it over. When surfaced I can stand on the
side of the conning tower rim and it won't role to take on water. When
diving there is little effect on role when one side thruster is thrusting up and
the other is thrusting down. When a passenger moves from behind the
pilot to the forward looking viewport the pitch changes by about 10
degrees.
My total weight added to dive my sub is, me at 160
pounds and about 400 pounds of lead weights. My hull is of the two person
design and pretty much to the plans as far as hull weight. My side
thrusters are probably each twenty pounds heavier then the original. If
your using Minkota thrusters you'll save a bunch of weight. The
K-thrusters as are heavy buggers.
I don't have the exact total weight in my head or
here with me now, but it's a few pounds over 4000.
And I do agree about the plans. They contain
97% of what you need, but from a professional drafting point, they leave 20 %
more to be desired. Did you get to the T bracket that isn't there
yet? The important part is the hull, and it's pretty clear. You
may have to guess at some other small stuff but the important stuff is covered,
except that dam T-bracket. Mine is now a heavy triangle bracket of my own
design. I know it's heavy enough.
Happy Building, Dan H.
----- Original Message -----
Sent: Friday, March 14, 2008 10:44
AM
Subject: Re: [PSUBS-MAILIST] k-350
Modifications
Dan I want to thank you for your post. Your
experience is of great value to me, and I am sure others. Of concern at
the moment is the problem of air lock on the MBTs, I had not thought of
that.
I have mounted my MBT valves on the sides of the pressure hull,
so they will actually be under the water line on the surface. The
plumbing is 1/2" sched 80 black pipe. Do you think I wll have a problem
with this?
I am planning, and will very soon extend the rear MBT at
least 12" deeper. I am also adding saddle tanks to make up for my
additional weight. Do you foresee and problems with this?
Also I would
like to know how much lead you ended up with. And how much your total
weight is.
Being an old Draftsman I am a little disappointed in the
plans. I find them to be a little confusing and not complete.
Dean
Ackman
-----Original Message----- From: Dan. H.
<jumachine@comcast.net> To: personal_submersibles@psubs.org Sent:
Fri, 14 Mar 2008 8:33 am Subject: Re: [PSUBS-MAILIST] k-350
Modifications
Hi Scott,
Congratulations, in about a month. Building a sub
is a great project. Plan to spend some time doing it. If you get
frustrated, put it aside, but don't forget to get back to it. To many
get started and not finished. Think long term and you'll have a
sub.
I built a two man K-350 "Persistence." There
are plans for a short one person version and the two person version. The
two person version has a hull tube that is six feet long and then another foot
for each end cap making the pressure hull eight feet long in total.
If your building the two person version, I would move
the battery pods aft six inches to a foot. Study the plans to see what
else this will effect but as it is, most of my internal weights are located
far aft to trim to level. You could also lengthen the battery pods by one
battery. If I take a second person with me, they usually prefer to lay
on the deck under my seat. This puts their nose right up to the forward
viewport, which is a great view, but it makes the sub nose heavy.
Enclosing the MBT's is a good idea. Mine are
enclosed far more then the original and they work great. Just be careful
not to enclose to much so if one tank got filled with
air accidentally, you aren't totally nose up or down. If that
happens you may not be able to blow the lower tank. A few holes
drilled at the end should work.
The K sub plans don't give a clear idea of the size of
the MBT's. I gauged mine by the size of the frame that supports
them. Now I think my forward tank could be a bit bigger.
Another thing I'd change is, put your MBT vent valves
right on top of the tanks and run linkage to the conning tower or where ever.
Don't put those two valves in the conning tower then run lines to them.
They take to long to vent and sometimes they get air locked when water is
caught in the line.
Depending on how and where you plan to launch your sub
you may want to consider saddle tanks also. Launching from the trailer I
have it takes five feet of water to launch my sub. If I had saddle tanks
that could get the sub up a but higher, it would be easier launching
from shallow boat launches. As it is, there are many boat launches I
can't use. My sub's water line is right at the lowest part of the weld
that transitions the conning tower to the hull.
No need to lower the conning tower. When the sub
is surfaced, you can't lay it over enough to take on water if you try.
It's pretty stable but you sure don't want to be lower to the water and take
in a wave. Don't change that.
Maybe a bigger front viewport would be nice, but your
getting into a big structural change there.
Just my thought.
Good luck, Dan H.
----- Original Message -----
Sent: Thursday, March 13, 2008 1:57
PM
Subject: [PSUBS-MAILIST] k-350
Modifications
I am going to start my k-350 here in about a month. We are
pretty close to being prepped for the project. I would like to ask everyone
for suggestions from previous experience about what modifications to the
k-350 you all would have done if you could have gone back and done it again
to improve the use and cost of production. I am pretty sure I am going to
make the con tower a little bit shorter to reduce the above water weight
while surfaced and to make the sub a little more stable. I have heard making
an enclosed ballast is better to reduce settling. I have also heard rumors
about using trawling motors instead of thrusters.
Suggestions? Thanks, Scott Waters
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