Re: [PSUBS-MAILIST] Weighing

["Gary R. Boucher" <protek@shreve.net>]

Carsten,

     Did you say you were supplying the Barbeque?  I would almost fly to 
your country to witness a SWB!

     I have a couple of thoughts on weighing your sub.  I once thought of 
devising a lever with a ball bearing pivot point.  It could be constructed 
from a long piece of channel iron.  When one end is pulled down the other 
raises.  In other words lots of mechanical advantage.  The short end would 
be under some structural lift point.  The longer end is where extra weight 
could be added.  If you had several of these placed at strategic locations 
left, right, forward, and aft of your boat and enough weights were added to 
the levers to lift the sub slightly, the sub could be weighed to locate the 
longitudinal, and lateral CMs.  The calculations are easy if you have the X 
and Y locations for each scale with the weight indicated on each.  You 
don't even have to have them in any particular locations.  You just have to 
know the X and Y coordinates of each.  Just lift the hull so that all 
weights are handled by the scales and the numbers will come out.

     What kind of weight are we talking about.  I know its huge!


G Boucher



At 11:34 AM 8/4/2002, you wrote:
>Nice.. you have to work more acurate than
>with the bathroom scale experiment sample :-)
>
>For the reason than the most parts of a subs hull like the cylinder, the
>frame
>and the endcaps, stern conus, front dome etc. have there CM and CB in
>the middle
>line of the cylinder - I prefer to calculate the vertical CM. Its quick
>done
>- just some 14 days on Cssx.. Smaller items on board have not a so great
>influence
>on it.
>
>I am not so affraid about the vertial CM to CB because this can be
>calculate
>in a very early project stage. Will not move much during building.
>
>The longitudinal CM to CB is a much bigger deal
>because of the long lever any mass at the ends of the boats have.
>
>The stern of torpedo shapped long Sgt.Peppers for example is almost free
>flooding,
>no bouancy/lift there. I calculate the stern engine weight with 7 kg (14
>pounds) but the real things was more in the 14 kg (28 pounds) area. Put
>all the lead in the bow area.. was boat was
>still to heavy on the stern.. remove the plastic bow thruster pipes and
>made
>some from steel. Works better but for the reason that the bow is much
>closer to CB than the
>stern didn't reach zero.. Final solution was to remove stern battery
>No.4
>Lost 25 % of endurance - just because the main stern engine was a little
>to heavy..
>
>Back to the bathroom scale - just told your neighbours  that you want to
>make a
>SWB : a Submarine-Weighing-Barbecue - and they have to come with there
>scales..
>use 3-4 with a longer angle iron should fix the 2 inch problem to a 6-8
>inch..
>
>How can I make the angel iron experiments on a 57 ts boat - without to
>cut the boat
>in two - or lower/sunk the iron into the street ? :-)
>
>For the other guys.. note that the CB on surface station can be
>different form the CB
>on diving station.
>
>Sample 1
>Imagine a sub with a big pressuretight tower in the bow area.
>Imagine that this boat is perfect in trim horizontal underwater (CB on
>top of CM at zero degree)
>- if this boat surfaced the CB moved aft and the boat stick the nose
>deeper into the
>water than the stern - create a trim to the nose on surface station.
>
>Sample 2
>The same boat - but in perfect horizontal trim on the surface. If the
>boat dive the tower creates
>bouancy forward of CM and the nose raised.
>For this reason boats with a pressuretight big tower forward of CM
>should be in a trim stage
>of laying some degrees to the stern on the surface.
>
>Carsten
>
>Gary R. Boucher schrieb:
> >
> >      Sometimes we in the States refer to Trigonometry as "Trig."  As to
> > finding the vertical CM, imagine that position directly above the fulcrum
> > when the sub is level and balanced.  Call this vertical distance to the CM
> > location (Ycm).  If you allow the sub to pivot forward just a few degrees
> > this CM moves forward, actually rotating around the fulcrum pivot with
> > constant radius Ycm.  This distance is what we are looking for.  The CM of
> > the boat is always a Ycm away from the fulcrum.  Now when the sub has
> > rotated slightly (just a few degrees) the CM would project downward on a
> > true horizontal plane slightly in front of the fulcrum.  Call this forward
> > horizontal projection (H).  Call the bow down angle of the sub 
> (Ang).  Thus:
> >
> > Cos Ang = H / Ycm
> >
> > or
> >
> > Ycm = H / Cos Ang
> >
> > Now a forward torque equal to W (weight of the sub) times H (moment arm we
> > just defined) is generated holding the bow down firmly.
> >
> > To lift the bow we go to the stern and add weights until the point where it
> > just barely "Begins" to move toward level from its bow down angle Ang.  The
> > weights are placed on a vertical line attached to the stern where that
> > line's distance to the fulcrum in a true horizontal direction is (D).  The
> > amount of weight added lets call (WA).
> >
> > Just as the bow starts to rise from its resting position the WA x D has
> > created a torque equal, but opposite, to the W x H shown above.  Therefore:
> >
> > W x H = WA x D
> >
> > or
> >
> > H = ( WA x D ) / W
> >
> > and finally
> >
> > Ycm = [ (WA x D ) / W ]  / Cos Ang
> >
> > Now you don't want to measure the angle (Ang).  It should be calculated
> > from drop of the bow and distance from the fulcrum.  It requires great
> > accuracy and a protractor is not sufficient.  The angle may be only a few
> > degrees.
> >
> > This technique allowed me to find the CM in the vertical plane.  My sub
> > behaved exactly as predicted.
> >
> > Gary Boucher
> >
> > >Gary I did not understand what you excact did.
> > >Can you explain the little "trig" to
> > >meassure and calculate the vertical CM ?
> > >
> > >best regards Carsten