Bollard Pull in Pounds

This needs a little more thought, my first idea was to take the formula for wind load and change the density from air to water, but the viscosity of water is probably higher and the fact that it is in the confinement of the tube. This will not give you a good estimate of the ball moving though open water, the water in the tube must accelerate passing the ball and this screws up the pressure.

Any help... its just a "round-about" method to calculate.

It can be as much as 20 pounds or so off base either way and I'll be good to go.

I've got some research gear ( Mamou Trawl) working up in the Beaufort Sea. The biologists are encountering Lion Mane Jelly fish. These critters are screwing up the spread, catenary and speed of the gear. I want to make a point that just a single 10" sphere at 2 knots can cause "X" amount of Bollard Pull on the the tow warp.

Thank you for any thoughts on this......

I'd say about 60lbs....

OK...that is a number we can start with.

Thank you.

Thank you for the information.

I am not able to make any in-the -field tests right now. My question is just to get an average so I can explain that although these jellyfish are free floating, near bouyant, they DO present a force of restriction when water is moved against them.

The beach ball and tube of water scenario is just my idea of the simplest way to explain the fact that weight is NOT such an issue to underwater gear, as is pressure from objects interacting with the normal flow of water down and through a net system.

A smooth beach ball is in fact not the same size or shape as a Lion Mane jellyfish...but it gives a mental picture.

I need to make a case today or tonight as the research team has only intermittent cell phone signals. Its just a " put out the flame before it becomes a fire" issue that i deal with constantly. They may already have guessed that gear that opens 8 Meters with a couple of dozen 'dickie' fish.....is NOT going to perform the same with a couple of dozen 10-18" dia. jelly fish with 5-7 meter trailing tentacles.

In fact, just a 30 gallon trash can liner ( plastic bag type) if it hits just right in the cod end ( rear end that holds the fish) will produce an incredible amount of drag on the gear.

Before their next sampling trip, I'll get them an Ejector Frame to mount inside the cod end, that will shoot about 80% of the big jelly's right out the top of the net and still keep 80% of their research catch. I just wanted to calm any fears they had right now as to why the gear is NOT deploying to its full operating size.

Thank you for the information.

418x0.021=9psi However, there would be a shape factor that would reduce this, perhaps by 25%. Check me, from these two sites.

Pressure in Pa

Conversion table

If I read this correct, the ball is in a cylinder, as the ball and cylinder move through the water the ball is acting as a restrictive device compressing the water against the sides of the tube creating an added drag ...this would be different than just pulling a globe through the water....

Yes, that's what I said in my first post but that is fluid dynamics and I know nothing of them. If my calculation in my second post is correct, it needs modification to account for the Bernouli effect of the restricting pipe on the pressure.

correct.

I just wanted an analogy for them to visulaize, even it were an exagerated factor.

I'm just doing damage control so they have a litle understanding as to the dynamics of what happens when you collect objects that do not weigh much, but are indeed large enough to cause bollard pull to increase.

Thank you again.

Are you saying that biologists can't get their heads around the idea that a net clogged with jellyfish is going to increase the drag even though they weigh next to nothing?

...I just wanted to be ahead of any questions later on. They asked about gear dimensions for three days BEFORE telling me they were in jelly fish.

I once had a team of biologists drag a net upside down for a full week before calling me to ask about mud being plugged up in their FLOATS!

[ HUGE eastern USA engineering school] graduate argued that fish netting cut on a specific taper would NOT yield an increase in total length. His computer said it was equal. My experience said different. I had to make a small scale model and photograph it for him before he agreed to let me make the necessary changes in his design.

I had a [even larger Southwest university ] professor and his crew of biologists install one of my Bycatch Reduction netting devices to remove unwanted bycatch( little fishes) in a commercial shrimp trawl. They installed the dang thing BACKWARDS....even though I marked the FRONT with green and BACK with red. They video taped the whole thing underwater (NOT functioning) and distributed the video across the entire Gulf of Mexico and Southeast USA. It cost me business. * They printed a tiny retraction in an insignificant news paper months later* Too litte ...too late.

The stories can go on and on .

Its why I just wanted to have some information before hand. I sincerely feel this crew now understands. They seem very sharp and alert. The information however may come in useful the NEXT time around.

Thank you for the comment.

They asked me the question several times about the parameters of the gear, It was only on the third day they mentioned the jelly fish.

I just wanted a make sure they understood that even though there were only a FEW of these in their small net, the fact that each of these would produce enough DRAG to close the net to some extent and slow the speed down.

A net CLOGGED with jellyfish would not be an issue as it is easy to see and distinguish....its when a few enter each sampling effort that I was concerned about.

I was not making an assumption that Biologists are not smart enough to see this. I was just making sure they understood WHAT they were seeing was enough to cause a 10-15 or even 25% reduction in the gear deploymnet.

* when thse jellyfish are picked up and dumped in the boat, they look like harmless little dish rags...nothing as large and obtrusive as when they are fully inflated and in the water.

* I once had to make a scale model of a net to demonstate to full Professor at a huge Eastern USA university (that is world known for engineering).....that his calculations were way off on a net system he was trying to design. He argued for days that his calculations were correct. I had to make a scale model to show him that his 3% error would carry exponentially across the net and yield a 1.75 Meter difference on a net that could NOT have more than 5cm diffrence either way.

Heck, everything looks good on paper....its why I use AutoCAD ha ha !

Take care. Monsoon season is just around your corner.

Can't help you on the calculations, but.

There is a local park with a crown green bowling area surrounded by a fence made of 2" pipe framing wire mesh panels. The river that runs close by floods now and then. In summer the fence can be totally submerged, ie in flowing water a meter deep. the water drains away, no problem. In an autumn flood the pipes are bent to about 30 degrees from the horizontal.The difference is the leaves in the water push against the fence.

There is a similar example where a 30ft high fence to protect a house from golf balls can stand up to gales, but can't stand up to gales with leaves in.

Try a different browser to upload. I can't get on here at all in IE, but no problem in Firefox

Cnc Jim

Understood. Its why storm surge causes sooo much damage as it is leaving the coast...its dragging tons of debris with it....not just plain water.

Ask the Biologists if they would rather jump with a parachute made of an empty fish net or that same net but then lined on the inside with several of Granny's nickers.

* I am having soooo much trouble uploading ANY kind of drawing. Even when I try BOLD , the screen on CR$ freezes up. *

As CNCJIM suggested, if you're not using Firefox browser then do so. I had issues with 2 other browsers then had a go with Firefox and the "how to" instructions and the advice of posters now make sense.

I'll try it. I just got this new computer made for my AutoCAD and its got OUTLOOK 2010 and windows 7. Everything looks new. I am still trying to get my configurations looking right on that.

Thanks for the information.

Approximately 38lbs force.

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Stu.

Thank you again for the calculation.

What you need here I think is the drag force.

Fd = ½*ρ*ν²*Cd*A

where ρ is the density of the fluid, ν is the velocity, Cd is the drag coefficient for the shape, and A is the area (cross section) of the object.

Cd for a sphere is about 0.45.

Using the sphere and flow in the original post I calculate that the drag force should be 8.8 Newtons or about 2 pounds force.

ν² is the significant thing here, increasing the velocity will have a lot of effect on the result.

The weight of the ball is not relevant unless you want to calculate terminal velocity when it is dropping.

Search 'drag force' for more details.

Cheers,

Dave

Thank you again.