Stable Torpedo Weights

Make it like a fish, the front from 1 or 3 and the rear from 4....

Dunno, my experience with arrows would suggest have 3 at the back at 120 degrees. But arrows spin, due to feathers being curved and having one smooth side and one rough side, presuambly adding a rotaing joint at either end is an unwanted complexity.

Might be worth looking at shapes of arrow fletchings.
Del

The cable tension alone should keep them mostly straight.

Straight pipe no fins. The tension on the line will keep it stable. The fins will make it unstable. In most net arrangements tension direction on the line is not parallel with the pull of the boat. Which would cause the weight with fins to shake. Commercial fishing equipment can get beat up pretty good. Fins would have to be durable.

Not sure I would leave the pipe open at least on the leaning end would have the same effect. Maybe why you get the wobble now. Bullet nose would work better.

They make swivels to reduce line twist. Maybe make the weight a swivel.

What ever happen to using chain?

I would think just a single, heavy fin attached at the center, to hang down, would be a stable design.

Or, how about just a piece of heavy chain attached to the center? It would hang down in the water and since it would be both heavy and 'flexible', it would not react much to any below-surface currents. you could fit a loose sleeve over it to keep it from getting snagged.

IMO it all depends on what you want these torpedo weights to do.

At the mentioned speed, your net creates some drag, that pulls the lines. Is the purpose "weight", than these need to be heavy in a way that they overcome the drag tension and bring your net lower in the water. In this case you'll best off with a spool type - like a torpedo is made and most hulls of submarines.

If you want to have the speed to lower your nets, fins are required, but can also easily damage your nets when pulling them in.

With this scenario, I suggest to make one fin that has to be pointed to the bottom and also needs a T upside down below and scooping it downwards.

For this reason I would try with 2 pipes, in a way that the outer pipe can turn around the inner one: your ropes or cables will otherwise direct where the fin will end up, and that needs to be at the bottom. The T fin can be a piece of T channel (profile) that is weld upside down under an angle. (some sailboats have a keel like this)

And don't make it too light. Point the front and back to make less turbulence in the water.

The inner pipe needs to have a stop to keep everything in place and this will be the one to attach your lines to.

Of course, this is my simple explanation. Maybe the "Stable Torpedo Weights" need to help you solve other problems, like spreading the net open e.g.

For the Bahamas it is simple: fishing with nets is forbidden.

However, I am a North Sea guy where nets are used to fish for about everything.

Thank you. I have several designs of pelagic trawls with Icelandic doors that would fix the problem easily....IF we were selling to commercial fishermen.

These are scientists that are looking for critters measured in microns and 10ths of a mm. A big catch is less than a 1/4 lb

No Gloria Rope trawls or Polyice midwater doors needed here.. . . ha ha.

I'm not understanding. Are you trolling?

I'm thinking that if you're looking for tiny critters, maybe your net is too big.

Going that deep, I'd consider using a fairly substantial torpedo weight, with half a dozen small nets placed equidistantly around the center; perhaps just slightly behind the weight. Maybe attached to the weight itself, or slightly separated by a rigid bar running to each one.

Kind of like a spoked bicyle rim, with a weight in the center, no actual rim, only 6-8 spokes, bent backwards, and small nets about the size of nylon stockings attached to the end of each spoke.

Or...looking at your picture; just make the circular part at the front of the net, into the weight itself, with the bottom being heavier than the top.

There can be no variation in design of the 60" circular hoop. The customer wants this model.

The hoop is heavy and can be made heavier.

I just have a feeling that a Stabilizer weighing in at 30-50 lbs could make the unit dive quicker and maintain an even depth for the 10 or 15 minutes required for the sample protocol.

These guys just don't kick a net over and drag it around. they have protocol on time, depths and speed.

Thank you anyway for the suggestion.

Oh. I'd just kick it over the side and crack a beer.

Regular torpedos have gone fairly straight for a long time..

.

Maybe just borrow these old designs.

http://www.hnsa.org/doc/jolie/part2.htm

Maybe under the shroud, a free spinning prop would help stabilize the ride. I'm not sure.

All jokes aside, putting a four fin gizmo on the "torpedo" may just be the trick!

This Torpedo is meant to act as a stabilizer for a net gear we have used in a smaller version 1 Meter dia.

The present gear has a canard that dives the net....but at increased speeds of over 4 knots and depths below 2000' the net is thought to be oscillating back and forth, up and down as the canard can not control the net by itself .

We may need to increase the size of the Canard, but I would like to try a stabilizer first.

In net design, water pressure always supersedes weight....a 100kg chunk of chain would dive it and maybe hold it steady, but would create an issue when the rig is used in 200 feet of water.

I have the net working like it should in the 1 meter size, but now that we are expanding it to 1.75M dia.

Then torpedo is just a stabilizer to help keep the Circular net behind it, remain stable.

I also believe that the 3000' of cable in front of the rig may have an influence.... I do not have a budget to hire a ROV to take a look-see.. ha ha!

So, think stabilizer.

comments welcomed.

Get the scientists to put a battery operated camera and lights in the net. That will tell you how the system is behaving.

If the scientists knew how to do all that, Netmaker wouldn't have any work.

....That may actually happen at some point.

The canard is located at the bottom of the frame....not such a good drawing.....

Hi Netmaker,

Have a look at some of the images for paravanes. While some are fishing lures, others are designed to do what you intend to do. Maybe there IS a mini otter-trawl solution to your stability issue.

https://www.google.ca/search?q=paravane+fishing&tbm=isch&tbo=u&source=univ&sa=X&ei=2SLiUeD-BcG0iQKmpIBQ&ved=0CDMQsAQ&biw=1024&bih=466

You know, you got me thinking. The paravanes or downriggers hold a trawler steady in rough seas when they have there outriggers down and are trawling.

If I took the idea of the paravane, a 3 fin device with a torpedo body, I bet we could slant those side fins and dive this rig at a steady pace.

thank you for the good idea.

Hi Netmaker

There is always this..... Could make one to suit your requirements.

Brgds

I remember you had been working on these.

I will speak with the customers and see if they are interested in trying one.

It would have to be big enough to deal with a 60" x 32' long net , that creates about 1400 lbs. of bollard pull at 3 knots.

It also has to be able to function in a range of 50 fathoms to 500 fathoms or slightly deeper.

You always did have some really interesting gear.

I'll be in touch of I get a bite.

Yes.... and still working on it! The forces and depths are no problem for the ATS.

I am sure you getting some flow-induced vibration or oscillation on the warp which is creating an instability. I remember there used to be a company, Dirigo or something like that, which made trawl warp vibration meters for the shrimpers in your area. Something like this might give you a better understanding of what is happening.

Just a thought ..... what if you towed your pipe thing behind the net instead of in front of it?

Maurice,

Someone else suggested dragging it behind like a dead weight on a beach seine in heavy current to keep the sack from inverting. It might work.

I am with you on this warp vibration...... Once they peel out 2000' or so of wire they noticed something happening to the wire.....at 4000' they suspected a oscillating type movement.

I would want a smooth ride with the net as that deep down there is no light and fish, even small ones, feel vibration in the dark and get the heck out of the way.

I would use a piece of steel pipe, open at both ends. Drill a single hole at one end of the pipe through the tubing wall an inch down from the cut, and do the same ON the OPPOSITE SIDE of the pipe so they line up diagonally through the length and width. Attach eye-bolts to these holes and attach the cables. The pipe will line itself up with the direction of flow and it's nose will want to go down. It will be like flying a circular box kite upside down.

I actually have this already BUT ... I went through the entire pipe with the bolts and shackled onto the bolts INSIDE the pipe.

Your concept is simple and makes sense. By making the pulling points off-set, the pipe would catch water and dive also.

Like this?

Right on the money my friend! That's it, and it will "fly" like a kite, a very stable one.

I meant the top illustration!

If your holes are big enough, you can just run the shackles right through them and eliminate the eye bolts.

In increasing the diameter of the opening was the surface area of the trailing net taken into account? 100 mesh has a open of .006 inch which is about 30% open area of the net. You list even smaller at 1/10 mm. If you are moving faster then the water can pass through then it will cause the net to be unstable.

Ozz,

The design of this net has taken into account the IPW ( Internal Pressure Wave) which causes the effect you are describing.

The Coefficients in the various nettings ( netting to rope and netting to netting) are within the parameters of what we have been building and using in gears for decades.

12mm raschel x 210/12 ply x denier x 2 stitch cross over allows for a Coefficient that yields a 45% opening. The smaller netting is even lighter in denier and the shape of the weave and crossover is different ( to allow more water flow too).

The Cod end has a special square mesh( warp and weft) weave polymer material that simply blows water through like there was a giant hole there.

There are some additional mesh designs NOT SHOWN in the picture, that blow out the IPW at three different locations in the net system.

At or near the surface this net can and does run at 6-8 knots with no trouble. No worries ol' buddy...the water passes through alright

The hundreds of pounds of weight and drag on the 2K-4K of 5/8" steel towline as well as ocean cross currents seem to be causing some wobble.

Thank you for the comments.

Use a camera to tell you what is happening.

Very much like to use a camera. But I am not going on these trips nor does the customer want to spend funds to do so. * Industry secret* Its why we have business like this... I have to practice Forensic net design on a monthly basis..... someone asks us to design something outside-the-box ( or tweak an existing gear) like this Chas Net and then we have to hunt around for how to make it better and correct any issues. We do not have the luxury of seeing a lot of the gear we buid, in use. The hunt always involves a minimal amount of clues, sort of like building a production piece in the dark. This is just one aspect of our little business....heck sometimes we even find an answer! ha ha ha!

Industrial Secret No.2 : Its why I come here to CR4.. . . but don't tell my competitors.

Thanks to everyone.

Would there be any reason not to attach a drag to it? I am thinking a small teardrop shape with 4 to six fins in the six to eight inch range about 5 meters behind the net. Of course the rig may not be able to handle the extra drag at that point. It would give less disturbance on the intake side for sampling purposes.

just a thought.

Do you mean in the FRONT of the net where the torpedo goes or at the rear or behind the net itself?

Behind the net..... last thing being towed

I was thinking behind the net with nothing in front. trying to stabilize the rig from the rear using drag and slight directional stabilization. Don't know if it is possible since I don't know the actual specs for the sampling. My thinking is to remove any interference/ sound/ vibration from the front of the net that could spook your intended victims and let the size of the rig provide some of the stabilization with minimal correction/ interference.

the drogue/drag could be made to spin or rotate slightly to help with maintaining an even pull on your rig and it might help stabilize any wobbles in the process. In any case, stabilizing something that far down and that far behind is always a bit of a challenge when using a rig that is completely passive.

Hell what do I know, I'm trying to get an antique Dole Pineapple canner to use modern poptops without popping them as soon as it seams them. LOL been through a few cans today.......

This whole concept reminded me of my kite days and the box kite, whether round or square, was very stable even on long lines. With the net acting as a "tail" the weight can just be flown with the hookups done like a box kite with a tail.

I bought a box kite from someone who dealt in surplus once that I still have. It's a metal frame kite with two attachment points, one at the very top, and one partway down the first panel. It was an antenna kite for a life raft! The thing flies like nobodies business in strong wind with the attachment at the top. I've flown it on over 1000ft of line and can lift a 1lb camera with it. Stability is what this thing is all about.

Do the same thing in water with a piece of pipe and you should be golden. At the right speed it should try to fly under the boat as close as it can get with the drag on the line and the net. Low and slow I would think would be the way.