If I simply make something heavier than the amount of water, it displaces will it sink to the bottom regardless of the depth? When I am deep sea fishing I have to adjust the weight according to the depth. i assume it is because of the weight of the string and the amount of resistance to currents pushing against the string. ( I am thinking of the recent submarine disaster)
I just looked it up and monofilament fishing line is 12% heavier than salt water.
In principle, both the water and the thing you’re sinking will both change volume as the pressure increases, which (depending on what changes more) could result in either an increase or decrease of buoyancy.
In practice, though, both water and most things one might use as a weight will change volume only by a very, very small amount, so this probably isn’t what you’re looking at.
It might be the weight of the fishing line. Can you give us some numbers, here? What’s the thickness of the line? How much weight, for what depths?
When you say “deep sea fishing”, do you mean trolling behind a moving boat?
Because if so, the varying weight is all about overcoming the boat’s motion which will tend to make the line trail horizontally on/near the surface behind the boat.
if the boat is stationary, any amount of weight (density greater than water) is enough to get the line to drop nearly vertically. More weight just makes the bottom of the line fall faster. Given how very light monofilament is, it make take hours for 500 feet of light mono to descend into a straight line down beneath a stationary boat.
I do know that the line is 12% heavier than salt water. It does appear that the current plays a major role as it pushes on the line but I am not sure. For example if I am fishing at 800 ft I need about 2# weight. I probably should have thought a little more before I posted. Now I am thinking it is just the surface area of the string over coming the weight because of the current. .
What are you fishing for at that depth?
For example, when they went down in the Trieste, for 20 minutes in the 1960’s, they had a float chamber that was filled with gasoline, which is lighter than water, but is incompressible, so it wouldn’t crush at depth, and would remain lighter than water at the bottom of the deepest part of the ocean.
Same deal with ballast, if it’s heavier than water, and doesn’t change volume/density, it will stay heavier than water at depth, because water doesn’t change volume or density appreciably even down to the bottom. Very different than air that changes density like crazy.
Several species of Rockfish. I have caught halibut at that depth.
I think it would be that. A little bit of motion in the water could lift a lot of line along it’s 800 foot length. I’m not all that surprised you need a 2 pound weight. It’s more than I’ve seen used, but I haven’t ever fished for anything that deep. I don’t even like getting far enough from land that the water gets 800 ft. deep.
Quite right that air changes density radically. But water isn’t quite as simple as “incompressible”.
Ref the recent Titan submersible accident, the water at ~12,000 feet down is ~5% denser than that at the surface. Due to the horrendous pressure of the tremendous weight of water above. For the OP fishing a mere 800 feet down the difference is indeed minimal. If the OP wanted to fish at 12,000 feet he might need 2 lbs + 1.5oz of weight to achieve the same effect as his 2# gives at 800 ft.
Whether that’s “appreciable” or not kinda depends on the mission at hand. For real-world fishing, almost certainly not. As you suggest.
For planning a successful descent to extreme depth, it may well be.