Posts by Guest
-
-
. . . (It was an aluminum frame too - thought I should mention that. Figured that'd make a diff as it transmits heat easier to inside the handle.)
Yes, good point. Forming handle grips around an aluminum frame is a little harder for me than when I use a Delrin frame, for exactly that reason. The aluminum conducts heat, so the inside of the grip gets squishy, and the final shaping is a little more difficult because the grip wants to move around on the frame. Once cooled, it's fine. It just takes a little more patience.
-
I know from past experience that I need 8-10 level tablespoons full to do a handle. But it is no big deal to pinch off any extra, or stick more on if you find that your original guess was off. If you are trying to keep a uniform color, then I would err on the side of mixing a little too much, and removing any excess.
-
I haven't had any trouble with the Shapelock on my hot aluminum boat in the summer. But I guess a hot car in the sun might be asking too much.
It's very easy to color. I use a small tube of dye that I got at West Marine. It's the stuff they sell for coloring gelcoat, and cleans up with water. Wood Guy had some stuff that we used for Core's handle a while back that did NOT clean up with water! Both worked fine, though the oil based stuff will probably hold brighter colors longer.
The Shapelock comes in the form of little pellets. If you want to color it, it works best to do so BEFORE you form the pellets into a larger shape. Measure out how much you want, and dump the pellets into water at about 150°. The white pellets will slowly turn clear as they heat up, and they will stick together into a spongy looking mass. When the whole thing is clear, take it out and shake off excess water. Apply a several little BB sized blobs of dye, and knead it until the color is evenly dispersed. If it starts to cool and stiffen, just drop it back in the hot water for a minute to reheat it.
It does take a fair bit of kneading to get uniform color. But once the dye is thoroughly mixed in, it will not leach out even if it is the water based variety.
To get a multi colored look, start with a base piece, and wrap thin, colored, shapelock strings around it. As you knead and mold it into shape, the strings will squish and deform into a more random pattern.
-
Does it float?
It sinks, but just barely.
How "tough" is it?
Let's clarify "tough". Shapelock is not as hard as ABS or some of the plastics typically used for molded handles and muzzles. It can be scratched and gouged by sharp rocks, barnacles, etc. But it is "tough" in the more technical sense of being able to absorb energy by bending without breaking. I would say that it is similar to UHMW plastic in that respect. Bending a thin strip back and forth does not appear to fatigue it.
What other uses for spearing could shapelock be used?
I kept meaning to make a thin, form fitting knife sheath out if it, but then LunkerBuster posted that other stuff he uses. I also find it handy in the shop. If I am trying to hold an odd shaped round part in my vise, for example, I will sometimes mold shapelock around it to make a square block that I can easily grip without damaging the part.
-
Hau - The mechanism case is 1" tall.
-
I don't think so. The problem occurs when the spring pulls the trigger forward, past the point where the trigger sits when the mech is cocked.
I think I will just put a small pin through the mech like the picture below. That should keep the trigger from moving forward too far. I am curious to know if this is a problem on un-modified Reef mechs, though. It looks like it would be.
-
I ran into a minor problem while installing my line release. The release lever operates fine as long as the trigger is pulled back and stays back until the release lever swings. But if for some reason the line were to not release quickly, and the trigger moved back slightly forward of its original position (which the spring causes it to do) then the interior point of the release will get hooked on the spring, or the little nub where the spring is attached. In this case, the release lever will not rotate.
I think that this scenario is unlikely to happen in the real world, but it still bugs me. I plan to limit the trigger swing so that it can't rotate forward beyond the cocked position.
Does this happen with an "un-modified" Reef mech?
-
What post? <img src= " height="23" srcset="https://spearfishing.world/forum/images/smilies/emojione/1f606@2x.png 2x">
-
I'm reaching here. But maybe if you were diving in a rocky, but relatively shallow area with a substantial current or surge. If you had to let go of it, a sinking gun would get dragged along the bottom and beaten up or maybe snagged. If it floated this would not be a problem and the gun could be quickly retrieved by an alert boat driver?
I'll admit it sounds like a pretty specialized situation that is probably rare.
Or maybe if you were diving over a relatively deep wreck that extended a good bit off the bottom. If you had to drop a sinking gun, it might get snagged in the wreck deeper than you could dive? Although I guess that could be mitigated with a floatline of the right length?
I don't know, just thinking out loud.
-
The Buoyant Force of the similar objects is the same. Buoyant Force is based solely on VOLUME DISPLACED.
The ability of an object to sink or float is based on the objects weight and if it is greater than the Buoyant Force.I agree 100% with this part, so let's see if we can figure out where we got off track. This is the point where you lost me a little:
Yes but the factor is more deciding on whether it sinks or floats is based on the density of the material used.
My point was that the density has nothing to do with the buoyant force. Buoyant force is based only on displacement (as you said above), and not on the properties of the material. The net Buoyancy, however, is the sum of the upward acting buoyant force, and the downward acting force due to gravity (weight).
I thought that you meant the density of the tube. Maybe you were refering to the "total density" of the entire barrel? This being a composite of the aluminum barrel and the air inside? If that is the case, then your definition of density does come into play because it (along with volume) determines the weight, which is one of the two forces which determine the net buoyancy.
Help me understand which part we do not agree on.
-
Archimedes 1 st principle states " A body immersed in a fluid experiences a vertical buoyant force equal to the weight of the fluid it displaces.".
You are absolutely right in this respect. I think that we are hung up on semantics. Maybe the definitions that I learned and use are slightly different. You are talking about a buoyant force. Just one force due to the volume of water displaced.
But Buoyancy is the total sum of ALL vertical static forces acting on the object. A concrete block sitting on the seabed experiences a "buoyant force" due to the water that it displaces, but the "buoyancy" is still negative because of the weight.
So why is the Buoyancy in both cases not the same. .
The buoyant force due to displaced water is the same in both bottles in your example. But he buoyancy is different because the weight of the bottle filled with water is greater.
When you minus the mass of the body times gravity you are calculating the immersed weight of the body.
This IS the buoyancy of the object.
-
Help me Seaweed! I don't know how else to say it.
If I take a sealed barrel, and stick it in a full bucket of water, a certain amount of water will overflow the bucket. That is the displacement of the barrel, wich includes the volume of the metal in the pipe, plus the volume of the air contained therein.
If I take a second barrel, with a hole in the side, and submerge it in a full bucket of water. I promise you that LESS water will overflow the bucket. Because some of the water which would have overflowed, has leaked through the hole and into the interior of the barrel, displacing the air (which we assume leaks out as the water leaks in). The volume of water that overflows the bucket is equal only to the volume of the metal used to construct the pipe.
The displacement of the sealed barrel is greater. Consequently, its buoyancy is greate (ignoring the weight of the air and plugs).
I'm going to bed.
-
The volume of metal in the tube is the same in both cases. But the total volume of the system (and therefore the volume of water displaced) is different. When submerged, the tube without the hole will displace more water than the tube with a hole. In the case of the tube with the hole, some of the water that would have been displaced flows through the hole goes inside the tube.
-
Ok, let's see which parts we can agree on.
We have two identical spearguns, consisting of aluminum tube barrels (ignoring all the other parts like handles, shafts, etc.). Barrel "A" is plugged, but has a hole in it, so it floods with water when submerged. Barrel "B" is identical to Barrel "A", but has no hole.
I submerge barrel "A" in a bucket of water, so that I can measure the volume of water it displaces. Water fills the barrel through the hole, so the barrel only displaces a volume of water equal to the volume of the metal which forms the tube. Essentially Pi/4 * (OD^2 - ID^2) * length.
If I submerge barrel "B" in a similar bucket, it will displace more water. It will displace a volume of water equal to your equation, or as I stated it, the volume of the metal, plus the volume of the trapped air. The displaced volume in this case is Pi/4 * OD^2 * length
Barrel "B" is therefore more buoyant because it displaces more water when forced under water in the bucket. If I don't force it down, it may even float if it's weight is not sufficient to overcome its buoyancy.
-
They do have different volumes. An unsealed tube floods when submerged. So it only displaces a volume of water equal to the volume of the metal in the tube.
But a sealed tube displaces more water. Air is trapped inside the tube (between the plugs). So the displaced volume is equal to the volume of the metal (as above) PLUS the volume of the trapped air inside the tube.
Which part is wrong?
-
They do have different volumes. An unsealed tube floods when submerged. So it only displaces a volume of water equal to the volume of the metal in the tube.
But a sealed tube displaces more water. Air is trapped inside the tube (between the plugs). So the displaced volume is equal to the volume of the metal (as above) PLUS the volume of the trapped air inside the tube.
-
Yes but the factor is more deciding on whether it sinks or floats is based on the density of the material used.
Negative. Ships are built from steel and even concrete, and they float. As a ship sits lower and lower in the water, the hull displaces more and more water. When the volume of water displaced by the hull is equal to the weight of the ship, then things are at equilibrium.
Aluminum is heavier than water. An aluminum ingot will obviously sink because its weight is greater than the weight of the volume of water it displaces. But if I take a hollow aluminum tube and seal it to make a speargun, then the COMBINED composite weight (aluminum + air) can be less than the weight of the displaced water, and the tube will float..
-
Buoyant force though has nothing to do with whether the object sinks or floats though, well not really.
Buoyant force has everything to do with it. If the buoyant force (which you correctly defined) is greater than the object's weight, then the object floats. If the buoyant force is less than the weight, then the object sinks.
-
Hau - That's because his wetsuit compresses with depth. The tiny air bubbles that form the insulation compress and lose buoyancy at depth, so the diver is heavier. The bubbles expand at the surface, so the diver is more buoyant.
But I think there's another factor that affects buoyancy. That is to say if the object is just barely buoyant at the surface, if you take it down to certain depth, even if it doesn't compress it may no longer be buoyant at that depth. I'm not sure about this..
If we want to be thorough, then we can add that anything which changes the density of the surrounding water changes the buoyancy of an object suspended in that water, giving us the obvious differences between net buoyancy in a freshwater pool vs. the ocean. The density of seawater changes with salinity and temperature, so there could be changes as you pass a thermocline, for example, or if you are diving near a river where there might be a layer of fresher water on top. But I think these changes in density would be pretty small in typical open water diving.
