fish- designed for speed
- Thread starter jdupre'
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Great question Joey, and one I have also pondered previously. Stood on a walkway once and had a dolphin swim underneath me as it were. The speed was phenomenal and yet the effort seemed so small. Anyways after lots of pondering I came to the conclusion, fish know something we don't... dolphins too.
Saw a documentary once 'bout a japanese sceintist building a mechanical fish, hopefully harpoon proof, with efficient propulsion for use on/in water being his goal. He could just about replicate the swimming action of a fish, but said he would never be able to make it as fast or efficient by just relying on that mechanical action.
Saw a documentary once 'bout a japanese sceintist building a mechanical fish, hopefully harpoon proof, with efficient propulsion for use on/in water being his goal. He could just about replicate the swimming action of a fish, but said he would never be able to make it as fast or efficient by just relying on that mechanical action.
Hitch hiking on both Joey and John, a fishes body - along with that of sharks, whales, dolphins, et al - flex smoothly. They also are not hard shelled, but the skin itself flexes and flows along with pressure ripples. I think this may have something to do with the coefficient of friction along their bodies.
I don't know if any of you have watched a boat going threw the water , it has a bow wave , to some degree. That wave is the water being pushed by the boat and offers resistance to the forward motion of that boat.
Not the wave from the bow that comes back in a "V" shape along the boat. The wave out in front of the bow as it pushes the water in front of it. The water actually rises to a degree depending on the size of the boat.
Then water from the sides is drawn in under the boat to compensate for the water being pushed out in front of it , to replace it. When you are out paddling , watch the river bank when a large boat comes by , the water along the bank will recede as the boat passes and then rise back up followed by the boats wake. If he slows down as he passes you.
Large fish will do the same thing when in shallow water , there is a wave or a rise in the water in front of them. It's a slight rise but one that marks where the fish is and helps a person when Bow Fishing to locate the fish.
If you could remove that resistance or just reduce it then speed would pick up , a boat up on plane ( skipping over the surface of the water does not have that problem) The lower speeds , it is there.
The problem beside resistance is the displacement of water caused by the boat , you do displace water in any craft , some more then others. Displacement would cause resistance or friction and hinder the forward movement. Remember you are trying to move ( Plow) threw a (for better words ) a semi solid item and not over the top of it.
Don't believe me , try walking in water up to you hips and then on dry ground , see which has less resistance to your movement. :roll:
Holding on to that thought ... That might be why a thin , sharp knife will slice some cheese or meat a lot easier then a wide blade that is dull.
Could this be why racing hulls are long , sharp and very narrow , over the canoes duller and wider body ? Or for you fishermen , a bone fish over a manatee. I know no comparison one is sleek and fast the other has a geezer speed but they are in the same locations. :roll:
Chuck.
Not the wave from the bow that comes back in a "V" shape along the boat. The wave out in front of the bow as it pushes the water in front of it. The water actually rises to a degree depending on the size of the boat.
Then water from the sides is drawn in under the boat to compensate for the water being pushed out in front of it , to replace it. When you are out paddling , watch the river bank when a large boat comes by , the water along the bank will recede as the boat passes and then rise back up followed by the boats wake. If he slows down as he passes you.
Large fish will do the same thing when in shallow water , there is a wave or a rise in the water in front of them. It's a slight rise but one that marks where the fish is and helps a person when Bow Fishing to locate the fish.
If you could remove that resistance or just reduce it then speed would pick up , a boat up on plane ( skipping over the surface of the water does not have that problem) The lower speeds , it is there.
The problem beside resistance is the displacement of water caused by the boat , you do displace water in any craft , some more then others. Displacement would cause resistance or friction and hinder the forward movement. Remember you are trying to move ( Plow) threw a (for better words ) a semi solid item and not over the top of it.
Don't believe me , try walking in water up to you hips and then on dry ground , see which has less resistance to your movement. :roll:
Holding on to that thought ... That might be why a thin , sharp knife will slice some cheese or meat a lot easier then a wide blade that is dull.
Could this be why racing hulls are long , sharp and very narrow , over the canoes duller and wider body ? Or for you fishermen , a bone fish over a manatee. I know no comparison one is sleek and fast the other has a geezer speed but they are in the same locations. :roll:
Chuck.
The other night I was sat fishing, I said fishing, not catching. The water was very flat but with a probly 5+ mile an hour tidal current from say left to right of me.
From the opposite direction, (my right), to the current a boat would pass doing say fifteen MPH. This was almost a third of a mile away across the water. Sure enough a few minutes later about twenty waves similar in height to the one which left the bow of the boat came ashore beside me. At 45 degrees these waves had travelled about half a mile to reach shore. Twenty waves, say eight + inches high travelling half a mile would have to equal literally hundreds of tons of water moving against a quite strong current! All this water set in motion by fifteen or so foot tinnie (thats an aluminium boat) With about a 20hp motor.
While paddling on flat water stop, turn your head around and look at the paddle prints fifty or so metres behind you. They are still working as mini whirlpools, long after you took your paddle from the water.
The dolphin mentioned in my previous post left no apparent wave formation on the surface... It would appear we expend the five or so hundred percent Joey mentioned of our effort moving water rather than moving water craft.
My next build will be a kayak/hovercraft that I will be able to paddle at about forty knotts against a strong headwind.
From the opposite direction, (my right), to the current a boat would pass doing say fifteen MPH. This was almost a third of a mile away across the water. Sure enough a few minutes later about twenty waves similar in height to the one which left the bow of the boat came ashore beside me. At 45 degrees these waves had travelled about half a mile to reach shore. Twenty waves, say eight + inches high travelling half a mile would have to equal literally hundreds of tons of water moving against a quite strong current! All this water set in motion by fifteen or so foot tinnie (thats an aluminium boat) With about a 20hp motor.
While paddling on flat water stop, turn your head around and look at the paddle prints fifty or so metres behind you. They are still working as mini whirlpools, long after you took your paddle from the water.
The dolphin mentioned in my previous post left no apparent wave formation on the surface... It would appear we expend the five or so hundred percent Joey mentioned of our effort moving water rather than moving water craft.
My next build will be a kayak/hovercraft that I will be able to paddle at about forty knotts against a strong headwind.
That's a good observation, Jon. One thing we haven't touched on is the boundary layer of water next to an object moving through the water. It's a layer of water that is carried along with the object at the same speed. Less water is pulled along as the distance from the object increases. That water could amount to several hundred pounds that must be moved along.
A while back there was a thread about a hydrofoil kayak that went 20 mph or so. I would guess the greatly decreased wetted surface of the hydrofoil substantially decreased the amount of water pulled along.
Maybe the fish's secret is how he sheds that boundary layer. My hunch is that the fish kind of "wiggles around" the grasp of that boundary layer using tail and body movements with the aid of a slippery slime layer. :?:
Joey
A while back there was a thread about a hydrofoil kayak that went 20 mph or so. I would guess the greatly decreased wetted surface of the hydrofoil substantially decreased the amount of water pulled along.
Maybe the fish's secret is how he sheds that boundary layer. My hunch is that the fish kind of "wiggles around" the grasp of that boundary layer using tail and body movements with the aid of a slippery slime layer. :?:
Joey
John, those waves are foolers. The energy moves out laterally while waves move up and down. As the energy passes, it first raises the water, then lowers it. It's a sine curve. (I guess the bow wake on the other side of the boat is a cosine curve?)
I know I was being over simplistic with my waves thing. But they are evidence of wasted effort.
Individual water droplets will move around in a body of water virtually unimpeded by friction. When you stir your coffee millions of droplets individually act as one entity.
Given that and Joey's boundary layer of water thing. I would make a bet that the density of water is almost identical to the density of a fish. Am thinking the dynamic set up between the fluid nature of ... How do I say fish movement...and water itself will IMO lead to the explanation of why fish are faster than... :roll: turtles. Without being all metaphysical on you'se all I reckon, The fish are as one with the water.
Wow! I just re read that and either I got clever or I made an ass outta myself
again
Jack, would that be one of them seven deadly sines?
Individual water droplets will move around in a body of water virtually unimpeded by friction. When you stir your coffee millions of droplets individually act as one entity.
Given that and Joey's boundary layer of water thing. I would make a bet that the density of water is almost identical to the density of a fish. Am thinking the dynamic set up between the fluid nature of ... How do I say fish movement...and water itself will IMO lead to the explanation of why fish are faster than... :roll: turtles. Without being all metaphysical on you'se all I reckon, The fish are as one with the water.
Wow! I just re read that and either I got clever or I made an ass outta myself
again
Jack, would that be one of them seven deadly sines?
john the pom said:Without being all metaphysical on you'se all I reckon, The fish are as one with the water.
Wow! I just re read that and either I got clever or I made an ass outta myself
again
Jack, would that be one of them seven deadly sines?
Luke Skywalker, use the FORCE!!!!!!!
John, I gave up worrying about sines and sin a long time ago. Two reasons. First off, if sin were defined by a Master Creator instead of by people, it would be the same across all cultures and all times - it isn't.john the pom said:
Most importantly, though, people would say "It hurt like sin!" I found out that sin feels pretty good.
I never looked back.
I think that John may (inadvertently) be on to something there with the comparative density of fish and water. I also think that the flexibility of their skin in part of it.
Joey is talking about laminar flow of a fluid next to a moving object. Immediately next to the skin of an object that is moving through a fluid (a liquid or a gas), will be a layer of molecules of that fluid. They seem to adhere to the object, and move along with it.
Actually they flow. New ones are added at leading edges, and old ones fall off of trailing edges.
Joey is talking about laminar flow of a fluid next to a moving object. Immediately next to the skin of an object that is moving through a fluid (a liquid or a gas), will be a layer of molecules of that fluid. They seem to adhere to the object, and move along with it.
Actually they flow. New ones are added at leading edges, and old ones fall off of trailing edges.