Placement of a Canard

It seems to me the dive plane would have to be near the bottom, or possibly even extended below the bottom to insure that the control surface is submerged upon deployment, but the probability of snagging seaweed or debris on the plane would seem to present a problem....but as long as the guide lines are inclusive of the plane, I guess that's as good as it gets.....so I would suggest that the plane be in the middle or below....

This is a Neuston Trawl with Nytex or P-Tex micron netting.

They either stay right at the surface or attach a bodacious Tom Weight right past that Yellow swivel to sink the rig.

The job I am working on requires NO Tom weight and the rig has to dive on its own AND work at the surface on its own.

I also can not have the "bat wings" of a Manta trawl either...too expensive for the customer and too clumsy from a small boat.

http://www.bing.com/images/search?q=manta+trawl&qpvt=manta+trawl&FORM=IGRE#view=detail&id=286B95FEDB08AEB7DFAC5DBEF6388D16359583D8&selectedIndex=4

I looked up pelagic and I still don't know what is going on in that sentence.

You probably are in a constant conflict between adding strength and reducing weight. Center would seem to eliminate a moment arm. Being off center would seem to require additional strength to eliminate/reduce breakage.

pe·lag·ic

[puh-laj-ik] Show IPA adjective 1. of or pertaining to the open seas or oceans. 2. living or growing at or near the surface of the ocean, far from land, as certain organisms.

Zoned out man...

http://macmillanmh.com/science/2008/student/na/scienceinmotion/Common/SIM.html?Module=../Grade6/Chapter4-ZonesOfOceanLife/

6th grade science? I might have been out sick that day.

I did watch a movie about that forth zone down from the top. Mary Elizabeth Mastrantonio and Ed Harris were good in it.

If you passed the test at the end, we can give you a makeup credit....

Bridle configuration will take care of that.

Probably no more than 500 lbs. bollard pull under the worse conditions.

How is the net rigged for duty? 2 lines midway, 4,1 at all corners? Is the canard fixed or adjustable, or steerable?

4 lines, one to each corner.

Canard would be fixed ( and removable) at the TOP and at the BOTTOM. ( 38 degree angle up or down)

Or, if I decide to go back to the original plan, dead in the middle.

Can you just lengthen the lower two lines?

Yes, but at a certain speed the net will rise anyway.....only a heavy Tom Weight or Torpedo with fins can drag it back down.

Seems to me that if you want it to run on the surface the canard should be mounted at the top of the rig. When it breaks the surface, lift stops.

To sink it, you may want the canard on the bottom, tuning the angle to the speed of trawl.

Does that mean that one net will "go both ways" depending if the canard is on top, or bottom? Maybe.

Well if you're going to do that then why do you need a dive plane at all, just make the upper and lower frame angled....

That's fine for diving, but for lift, you only want one, at the surface.

Seems to me you could adjust the lines pulling the top a little longer and change the angle of attack to flat.....so that adjusting the harness would then rig the net for top or below surface use...

You have a good point. This could solve both problems with a simple adjustment.

Sorta like flying a kite.

Your fish in your drawing are going to look more like THIS!

Even though it might work out, I'd like to keep the frame looking like the other gears, squared up and rectangular.

MY bad, I misunderstood your drawing. You are not changing the frame.

* too much crawfish on Good Friday*

Thank you all for the input.

A magic ball or Tom Weight as it is called, will settle the issue of sinking to a point . However, once you begin to speed up and the net fills with water, the IPW ( Internal Pressure Wave) will cause the rig to come to the surface almost every time.

In this case, with this customer, no weights are desired. He has seen our larger framed nets work and wanted a smaller version. Its just I have never done this with something so lightweight and thought about moving those canards for added 'rudder' power.

Working from the middle of the frame does work, however, I am curious about IF moving them would increase the rudder power on something that will be so lightweight.

* I am breaking my own rule about "Don't fix if it ain't broke!" ha ha !

What about a modified manta where the the wings have a cable going from the wingtips to the corners of the frame so you can deploy them after the net is over the side? just thinking out loud...

I'd put it in the middle, or perhaps TWO in the middle even if one doesn't generate enough downforce to keep it submerged at speed. you need to keep them spaced away from stuff or each other or the net or frame will interact with them and affect the lift generated.

Hey Ol' buddy...haven't heard from you in long while. Good to see you are still on the planet and the aliens ain't hijacked you!

You are thinking like a Bi-Plane....two canards, dead center, but with enough space in-between so as NOT to negate one another?

These frames are small, real small compared to what we have done before. I am trying to get away from that Manta frame with the wings....all it can do is surface fish. These guys want to get under the surface a little ways BUT would like a simple rig.

Thank you for the suggestion.

yes exactly what I'm thinking. BECAUSE the frames are small, one canard may not generate enough downforce to keep the net down. but the problem then becomes do you have enough open area to catch anything without fouling the canards with everything? consider putting a "tent" shaped rectangular wire screen with openings big enough for your intended catch to try to keep your canards from getting fouled, sort of like a TED for seaweed... you could even mount a third canard in the middle of the "tent" and use it to generate leverage to alter the angle of attack, like diving planes fore and aft on a sub.

again I don't want to tell you your business, youve been making nets longer than some of us have been outta diapers, but I assume you are going to make it neutrally bouyant so you only have to worry about dynamic lift, not trying to fight the weight of the frames too right?

If I didn't want suggestions, I would not come on here. Fire away. Only a really stupid man thinks he knows everything!

The other guys mentioned putting the canards Top and Bottom. I am going to try both center and top and bottom, BUT I will try it with a Duplex set up like you suggested. These rigs are small enough to be inexpensive to test out.

The Tom Weight is an entity I am trying to lose, BUT if I need to, it is easily adapted into this design.

There will be 4 Amsteel bridle lines. They should be able to avoid any detritus in the water to speak off....*maybe some micro plastic flotsam and jetsam* as this will be in the open Pacific gyre*.

I can install a reversible Sno-Cone net inside the main net to catch junk that wanders in. I have a net right now in Alaska that is 72" diameter x 4mm mesh..... and has a 50mm HDPE Sno-Cone for the detritus and such.

I am trying to keep from having rigid bridle configurations as I need ( customer needs) the rig easily shipped, air freighted and stored. Rigid bracing can get bent.

The bottom pipe frame will have a 5/16" chain pinned inside and the sides and Top will be drilled so they hold no air pockets.

This Duplex thing has me interested....maybe I'll call the net a Sopwith Camel Trawl.

Thank everyone. I feel I have a handle on this small rig now. I will let you all know how it goes.

er, stupid question but what is the purpose of the chain in the frame? ballast? keep the pipe from collapsing? I don't get it. when we were working on ROV's we avoided any sealed volumes of air if at all possible so you didn't have crush issues and used syntactic foam to make it neutrally bouyant. for places where we couldn't avoind sealed volumes (like electronics enclosures), we filled them with incompressible (and non-conductive) hydraulic oil and then used a rubber diaphragm to equalize pressure.

* Canards on Tom weight and frame are opposite...my error *

Simple ballast when they chunk it overboard. They drop these things from 20' skiffs and 150 hp outboards to 250' vessels with twin 60" screws and 1500 hp. Wheel wash and Bow wake create havoc with small rigs like this.

** Our larger ones, with skid plates that weigh in between 300 and 900 lbs. , have no issues with rocking or flipping at the surface....get down 9,000 feet and hit a cross current and sea mount at the same time and that is another story.!**

These gears also move a little faster than an ROV and have no where near the sophisticated stability your ROV has, so the when they do speed up, the extra weight helps with the 'rocking'.

You are going from Star Trek to Fred and Barney Flintstone. ha ha!

ok, just simple dead weight to act as a keel. makes sense.

I feel comfortable having this frame made up with slots to handle Duplex Top, Bottom and Center. The idea makes a lot of sense.

Sopwith Camel is too clumsy of a name..... I think maybe a Spad Trawl?? ha ha!

Thank you all again. Lunch over, gonna' be a long afternoon and night...........

Just another thought. . . . . would a curved canard work better than a flat one?

say, something with a very slight radius....????

As it gives more surface area, yes, it would be able to generate more downforce for a given length. It would also stiffen the canard as well.

...then its off to the machine shop.

Thank you.

wait, do you mean curved like a venitian blind (or a wing crosssection) or curved like an arch? both would stiffen the canard but only the arch would increase length.