Re: [Paddlewise] FW: Pro's and Con's of the

I just posted essentially what you said as one speculation and on checking
for new mail read this. I think you are right and this is the most likely of
my alternative speculations.
-----Original Message-----
From: Chuck Holst <CHUCK_at_multitech.com>
To: 'Paddlewise' <paddlewise_at_lists.intelenet.net>
Date: Wednesday, June 02, 1999 4:08 PM
Subject: [Paddlewise] FW: Pro's and Con's of the


>
>You guys are mostly way over my head, but it just occurred to me
>that the initial displacement of water around a sub happens when
>it submerges. Once it is submerged and the sub starts to move
>forward, the water in front of it has to go somewhere. Does it move
>upward to create a bulge or wave on the surface of the ocean? No,
>it moves around the sub and behind it into the space the sub is
>vacating! Nature abhors a vacuum, you know. ;-)
>
>Chuck Holst
>
> -----Original Message-----
>From: Dave Kruger [mailto:dkruger_at_pacifier.com]
>Sent: Wednesday, June 02, 1999 5:58 AM
>To: Matt Broze; PaddleWise
>Subject: Re: [Paddlewise] Pro's and Con's of the
>
>
>Matt Broze wrote:
>
>> Nick responded:
>> >Submarines do have wave drag, it is just very small. Submarines have
the
>> >advantage that they can displace water in every direction. So, they
don't
>> >have to displace as much water to acheive the same motion.
>>
>> This doesn't seem to make sense. Liquids like water are virtually
>> incomressable, which is why they do not make good shock absorbers but
work
>> well in the brake lines of your car. Water flowing under a sub can not
be
>> squeezed between it and the bottom so something must go up. Either the
sub
>> and all the water directly above it or all the water the sub is
displacing.
>> I don't really know if this reaches the surface in the form of a wake
and if
>> so where.  [big snip]
>
>I read Nick's statement: "they don't have to displace as much water to
achieve
>the same motion..." as meaning "they don't have to displace as much water
*per
>unit of surface area of contact with the water* ..., " but now that I've
typed
>that, I'm not so sure.  Maybe *Nick* will tell us what he meant!  <g>
>
>I suspect that submarine "wave-making" has substantially different
>characteristics than "wave making" by a surface ship, inasmuch as the
surface
>ship's wave-making is mostly (?) at the surface of the water.  In
contrast, a
>submarine is neutrally buoyant, so the restoring forces are almost
entirely
>due to the visco-elastic properties of water, and I do not see that there
must
>be a rise in the water surface *fully equal to* the sub's volume as it
passes
>through a water mass.  Rather, displacement of the surrounding water is
>(mainly) normal to the sub's surface, and would propagate to the sides,
>bottom, and top of the sub. (Agreed the component which goes down can't
>compress the water there -- so some fraction of the sub's displaced
volume has
>to go up!)
>
>'Bout that component of a surface ship's "wave making" which may not be
very
>evident (in deep water) as a change in vertical position of the surface:
you
>must be acquainted with the "surge" off a ship's bow which reaches an
observer
>ahead of the "main" wake.  I don't think I have ever detected that surge
when
>floating in deep water near a ship passing by, but see it every time when
the
>ship passes shallow water as a slow "suck" followed by a huge "surge."
You
>know what I'm talking about, Matt?  I think that "surge" wave is a
different
>kind of water wave than the "bow wave" we see as massive vertical
displacement
>of the surface of the water.
>
>Could be just a very low amplitude, very LONG wave-length surface wave,
now
>that I think about it, I guess.
>
>Or, am I all wet?
>
> --
>Dave Kruger
>Astoria, OR
>
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