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Prawns are trapped on the Pacific coast at between 500
and 1500ft depth. In this the depth is 1000ft where
water pressure is approx 450psi.
We have to assume two traps raised one at a time.
The trap is dropped along with a cylinder contraption
that is just below negative bouyancy. The cylinder
is
sealed at one end. Inside attached to the sealed end is a
gas bag containing a spring, also attached to the sealed
end. At the other end of the spring and gas bag is a disc
that is water tight and will slide along the length on the
cylinder. The other end of the cylinder has a cap with a
valve that will open one way at 400psi.
At full depth the cylinder valve opens and water enters
the cylinder at 400+psi compressing the spring/gas bag.
The disc has spring-loaded fingers that when full
compression of the spring/bag is reached fit into holes in
the side of the cylinder fixing the disc and spring/bag in
place.
At surface, the cylinder cap and valve are fixed to a
fitting that opens the valve. A second device pushes the
disc fingers back into the cylinder allowing the cap to
slide freely. Once released the water in the cylinder is
forced through the valve by the spring and gas bag
pushing on the disc. This water turns a flywheel or a
turbine or dynamo that runs a winch that raises the trap.
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Annotation:
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self-raising crab traps sound great. this avoids the problem
of lost crab traps after the rope to the buoy breaks (due to
weather and/or rival crabbers). |
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So storing water pressure energy from desired depth that can be utilized at surface? |
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Would the energy in the cylinder be enough to hall the drag of a full prawn trap and a, yet to be determined, cylinder volume containig 400+ psi of seawater up on to the deck? |
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No, because there are inevitable losses through friction and the non-adiabatic compression of the gas. |
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There are two intertwined ideas; the self-recovering trap, and the recovery of lost potential energy. The second is dubious; since the trap is only just negatively buoyant, the energy to recover it is mostly going to be drag as it is raised. The faster it's pulled up, the more energy is consumed. |
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Self-recovery involves engineering a change of buoyancy. The simplest scheme is probably the best - a container of rocks, sufficient to give the pot negative buoyancy, held closed by a catch with a water-soluble element. Tha makes it very failsafe. Best would be three containers; when one releases, the pot gains slight positive buoyancy, two gives it lots. The chances of all three mechanisms failing is proportionately small. |
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Put a lightweight mast with a passive radar reflector on the top to make the floating pot easy to spot. |
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Simplicity is indeed best. |
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A general rule of thumb is that any mechanism more
sophisticated than a brick will fail at sea. |
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So still a good idea then, but needs a totally different implementation to use the brick to get the pot up with that little extra jump from surface to deck. |
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So, not "self-rising porn trap"? |
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Only you* would think of that, [xen]. |
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* and of course various members of [MB]'s family. |
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*sigh* This constant besmirching of our family names saddens
us. Can I remind you that Vinnie is still on holiday from
prison? |
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// This constant besmirching of our family names saddens us. // |
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Then you should get your family to stop doing it. |
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An alternative to the self-raising prawn trap would be the
self-raising prawn. Simply create a bicarbonate-based snack
that is irresistable to prawns, and shovel it over the side of
the boat. It sinks, the prawns eat it, and their digestive
juices cause it to bubble up. After a couple of hours, you just
have to skim the prawns off the surface of the water. |
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"Another pint of fizzy prawns, landlord, and put a good head on it ! " |
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A general rule of thumb is that any mechanism more sophisticated than a brick will fail at sea.
— MaxwellBuchanan, Jan 04 2020 |
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This device sounds so reliable it brings to mind the tragic death of Audrey Mestre. |
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I fell into the trap but shouldn't this have autoboner's warning. |
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// this avoids the problem of lost crab traps after the rope
to the buoy breaks // |
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No, because it's specified to use a winch and the rope to pull
itself to the surface. |
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// So, not "self-rising porn trap"? // |
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