RE: [PSUBS-MAILIST] New comer w/ROV Question

["Karl S. Luttrell" <SDECO@prodigy.net>]

Interesting ROV application!

My company just spent some time deploying samplers in concrete blocks in the
Detroit River and after a month's incubation, retrieving two sample modules
from each block.  Working in river current makes for interesting diving
indeed.  Using DGPS on deployment and precision drop marking on the DGPS
point prior to retrieval, we have been within about ten feet or less of the
objective.  Can't compare to the days of Loran and compass bearings from a
boat being pushed by wind and current, followed by bottom clinging diver
search.  Too easy on the newbies on the dive crew.

Have also used sonar in body recoveries in Michigan lakes.  Snowmobilers
through the ice don't always ride the machine to the bottom.  One in
particular ran across the rotten ice, shedding his helment, liquor bottle
and gloves before finding another spot of open water.  Two days of
traditional diver search from plywood rafts and john boats through the bad
ice had easily located the machine, but not the almost lucky driver.  Ice
was steadily improving as temperatures and wind chill bottomed out.

We took a Simrad sector scanning head, processor and VGA display and
generator out to look around for a reasonable target.  We suspended the head
about 18 inches off the bottom and placed a passive reflector about 30 yards
away for reference.  Ice was getting stronger, but about five or six fire
axe blows made a reasonable hole.  FD in survival suits with rescue toss
bags stood around to assist, if necessary.

We imaged and measured a few likely targets, got the bearing and range, and
opened a new hole and dropped the pasive reflector to see how close we were
to the target.  After a few attempts, we were able to see the body and hook
it up to the ice. FD cut a larger hole and completed the recovery.

In a river current, we would use a weighted tripod for the sonar head
support.  If head can be kept stable and there are not many air bubbles in
water, reasonable images should be obtained.  Locating and classifying
targets should keep the diver search to the most efficient level.  TV
cameras could also be used deployed on tripod with stabilizing vane or other
reasonable platform before commiting divers. Options include housed rotate,
tilt, zoom cameras, low light cameras, etc.  The better the scene is imaged,
classified, etc., the more efficient and safer the divers will be.

ROVs work in a river much like a diver.  They need to duck the brunt of the
current by either gettin down quickly and hugging the bottom or following
the bottom out from shore.  If the ROV is to be boat deployed, optimizing
the anchor set using multiple anchors to allow repositioning by adjusting
anchor lines is important.  Working off the stern, the method of clump
weighting the umbilical to the ROV through a snatch block and lowering the
clump wieght first will help get the ROV down quickly and provide a position
reference.  While hugging the bottom, the ROV can pull umbilical through the
snatch block and work downstream and, if it has enough power, upstream as
well.  The clump weight also takes most of the load of the current on the
umbilical alowing the ROV to work better in the lower current bottom
boundary layer.

Deep Ocean Engineering, www.deepocean.com has made some hydrodynamic models
designed to be deployed by helicopter for mine countermeasure and other
military applications.  We represent Deep Ocean and Kongsberg Simrad in the
Great Lakes. If you need information, tech specs, etc. email me directly.

Regards,

SciDiver

SDECO@prodigy.net


-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Captain Nemo
Sent: Wednesday, July 18, 2001 2:11 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] New comer w/ROV Question


----- Original Message -----
From: "Jonathan Grant" <scuba4fun97321@yahoo.com>
To: <personal_submersibles@psubs.org>
Sent: Thursday, July 19, 2001 12:14 AM
Subject: [PSUBS-MAILIST] New comer w/ROV Question


> I am working on a ROV for my first project.

Hi Jonathan,
I'm mostly into subs, but there is some ROV interest at here, so you'll
probably get the answers you need.  If not...
I haven't visited the site lately, but I remember a place called ROVTECH
that had a lot of info and parts for people into this sort of submersible.
Try:

www.rovtech.com



I have
> been doing some victim recovery diving in the pacific
> north west.

My ol' splashin' grounds.  Whereabouts?

 The fresh water recovery can be tricky due
> to the 12 to 18 knot currents in some of the rivers I
> have been dealing with.As a diver being 10 lbs over
> weighted and carrying a 35 lb lead anchor it is still
> difficult to fight the currents. I would also like to
> use this for deep ocean use.

I'm thinkin' 18 knots in a river?  With a ROV?  Hmmmmm.   Ocean sounds
better to me.

>    I am working on a submarine shaped (approx 8" X
> 30") ROV. I believe with the bow planes, and making
> the sail so I can adjust (pitch side to side) for
> control at the front of the sub. Combining this with
> the rudder control on the aft end, I will be able to
> control the ROV using the currents to my advantage.

Wait a minute, yer confusing me here.  Let's establish some terms: Pitch is,
say, moving the nose up and down; yaw is moving the nose right and left, and
roll is rotating the hull; OK?  Now, I see you pitching the nose up and down
with your bow planes; and yawing the boat left and right with the aft
rudder; but what are you doing with that adjustable sail: making her roll?
Sounds like you're after three axis control.  Hmmm.  R/C model subs do
sometimes have a tendency to roll in response to tendencies generated by the
sail when they are yawed vigorously.  You probably could roll her with a
maneuverable sail at a high enough speed or in a good current flow.  Then
again, you might get by without it.  Keeping her bottom heavy and controling
two axis (pitch and yaw) might be enough.  You might want to think about
vectored thrust for maneuvering, too.


> A strong motor to push against the currents.
> Transparent nose cone for camera, sonar,...
>   If anyone has any suggestions they would be greatly
> appreciated.

Well, you're going to need some thrust to overcome 18 knots with enough left
over to go driving around.  With the size of the hull you've mentioned,
you're limited for space.  Are you thinking internal battery pack or power
supply umbillical cord?  Maybe batteries inside, motors out?

Camera?  That shouldn't be a problem; all types and sizes around these days.
Think they used to have some at ROVTECH; if not, I know you'll find one
somewhere.

Sonar?  Again, the size of the hull is going to be a factor.  Are you
thinking about the towed array from one of those high-dollar sidescan jobs
like they drag from boats?
>
> Also can anyone share the formula for pressure at
> depth of sea water?

Same like they told you in class when you quallified for your C-card: one
additional atmosphere for every 33 feet of depth.  (When this comes up, we
usually get a lot of people with different ideas of what one atmosphere is:
some ballpark it at 15 PSI; others say 14.8, 14.75, etc.  Divide 1500 by 33
and multiply by, say 14.8 and you'll get the pressure of about 672.73 PSI.
Or if all you want is an easy, rough estimate you can do in your head, just
divide depth in half minus 10 percent of the result: that'll get you pretty
close.)

 For example, how many pounds per
> square inch would be applied at 1500 of sea water.

See above.  About 673 PSI uncompensated pressure, in excess of that 14.8#
surface pressure you had inside the hull when you capped it shut at sea
level.


> What is the best material to use, aluminum (1 piece
> machined) or welded steal?

I like steel, but I think in your application, aluminum has advantages.  You
don't have a very big hull, so you want enough strength with minimal weight,
so you'll be able to put all your goodies inside and still float the boat;
and if you machine the cylinder out of a single piece, you won't have a seam
to worry about; and even better, you can get it really, really round; and
that's pretty important in, as Phil says, "keeping it from turning into a
Halibut".  I'd go with aluminum.

How thick should this
> material be to resist the 1500 fsw?

Need a little more information about the type of material, the shape of the
hull, etc.  Don't have the specs in front of me, but someone here probably
will.  Let us know more about the shape of the thing, and what kind of
material you decide on.

> The transparent nose cone acrilic or polycarbonate?

I've used both; I'd go with acrylic.

> And how thick?

I don't have the specs for that either; but how about a hemisphere?  I'm
just guessing, but one measuring  8" by 4", made out of acrylic, and
properly mounted, wouldn't need walls any more than , say,  3/4 inch thick
to do the job.  Maybe less.  Anybody wanna do the math on this?

> I hope this is not below anyone to help on something
> so small but as I said I'm just getting started

Nope!
>
> Thank so much
> Jonathan

Yup!

Pat