Bollard Pull on THIS

If this is a pool, I'll pick the 10kgf square. (And then later, I may decide to buy some other square(s).

It would depend upon whether the fluid doing 3m/s is either air or Lyle's Golden Syrup.

It is freshwater, not syrup or my wife's gumbo.

So what's the problem (rhetorical question - NNTR)? An estimate can be made from the wetted surfaces and their shapes, and the empirical correlations in Perry, "The Chemical Engineer's Handbook", any edition.

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The device is a grid that keeps large floating pieces of debris from going into a net system. I know already what the net system will produce at 1, 1.5 and 2 knots. I just want to know about how much extra tension the frame will add.

As for the Chemical Engineer's Handbook. . . . , I would not even know how to fill in those variables. Its why I ask folks here.

However, if someone would send me a formula with an explanation as to what goes where, I would try it myself.

I guesstimate ~ 16 kgs....(You may have visited the well 2 often)...

....(You may have visited the well 2 often)

Not sure of what this means ol' buddy, but thank you for the estimate. 16kg would work out fine for the bridle and hp on this gear.

Thank you.

We were here or hereabouts a few weeks back, and it generated a lot of contributions. Maybe that's what SolarEagle was referring to! If you want to work it out, as your #7, the earlier exchange pretty much covered it. We settled on a shape factor 0.5, but it might be 0.7, as passingtongreen used.

On the current query, if it's at 45° it's the projected area of the side bars that counts, = 1/√2 x, but that doesn't apply to the horizontal members.

But will it be at 45°? I estimate apparent weight in water ~ 12 kg, so the tie lines will take an angle determined by the weight and the drag (which also changes the angle of the frame), if I understand your set-up right. Much like the earlier query.

I just need to guestimate if these guys can get away with a large outboard or a do they need a diesel inboard rig. At under a 500 kg total net and all, an outboard will do.

After that, I will recommend them waiting until a larger boat is available. the net will pull at 180 to 225 kg. as used with a load cell years back.

* On the side note, do folks here think I am introducing too many of these problems? I am not looking to be abusive with anything. This is our busy season and things like this show up every day or two. Most I can handle, the really difficult stuff I can take a guess at...the 'new' devices are scary when it comes to these physical stress problems ! All help from CR4 is always appreciated. However, I do not want to create any friction here....I always get more then I give here.... that is a fact. I am NOT an engineer or even a good mathematician. I do not participate in answering other posts because I am sooo far out side my skill set.

No problem, you raise interesting questions and nobody who doesn't want to need get involved in the discussion. And as Wal said you join in and give clarification when asked, whereas often in that situation the OP is never heard of again!

But having said that, your #7 says "However, if someone would send me a formula with an explanation as to what goes where, I would try it myself."

I'd have thought that was covered in the dangling ball question. Force = velocity pressure x projected area x shape factor. Velocity pressure = 0.5*ρ*V². You have to get the units right. If you want more explanation feel free.

Thank you. I would still be lost as I would not know where or what a 'shape factor' would be or how to find it. My guess is I will leave the serious calculations to those that deal with these formulas every day.

Thank you again.

Pressure approx. = ½ x (density of material) x (current speed)² x (shape factor)

0.5x992x3²x0.7= 3125N/m². = 319kg/m².

Area = 7x2x0.025 = 0.35 ).35x319=112kg.

OK. That is a huge difference from the other answer.

This would affect the use of the present engine hp .

I will use this as a worse case scenario and plan for requiring the hp be upgraded as well.

Thank you for taking the time also.

I'm sure you are aware that as you collect and accumulate debris on this the load for the motor/ engine will be higher!

If you want to test this, the force is based on the total length of the 25mm rod. You could pull a single rod of, say, one meter long, that would reduce the pull to one fourteenth, measurable on one of those spring scales for luggage, especially if you used it in the line on one side only, that would reduce it to one twenty eighth.

That is a simple enough test.

Thank you.

Is there any reason not to simply build this grid and check it out directly?

Just to CMA, I'll now double up/down on a 20 kgf square, but nowhere near 112.

I agree that an empirical test would answer this but it would be good to have some idea first.

Just thinking about it now. If you dropped this frame into a 3m deep pool and tried to pull it up through the water at 3 m/s then you and your mates would be struggling.

I'm guessing >200kgf.

Suck it and see netmaker. Drop it into your stream and hang on.

The device will be mounted ahead of the actual net system and it will be at a 45 degree angle. The debris in question will be ice chunks and some large pieces of log. they will be deflected up and over. Should a large chunk wedge itself inside the.50 meter bars, the gear will be stopped and hauled back and cleared.

* the frame shown is mis-drawn.... the actual rig will have the bars running Up and Down.*

I will be no where around this equipment. in fact, I will never even meet up with the clients. I wanted a general idea of bollard pull before I authorized the building of the frame at the machine shop. In many cases on the gear I build, I will never have the opportunity to make scale models. As for testing, I will not have the time nor the funding to hire a boat and crew to run any such trials. In about 95% of all the gear I build, I have to try and hit the bulls eye the first shot, sight unseen,,, no practice runs.

Thank you all.

Make a call and hope for the best. Yeh....

Had to do that many times and not bitten yet or ever I hope.

The rig has to be able to survive being total blocked with your ice and log and beaver carcass debris.

It needs to be able to survive the worse case and that's what you should design for. It needs to be able to be stopped and hauled back and cleared without breaking or permanent deformation.

Someone else suggested doing your load calcs based on a flat board of those dimensions.

That advise should be considered if not heeded. Maybe 50% area would be realistic (most of the time).

Don't know. i think the answer will be a big number.