MAGING SHALLOW WATER REEFS, ETC.

[deepsix47]

An inherent risk of Magging shallow water, especially reefs, is snagging and losing the fish. Not only does this get very expensive, it also can cost a great deal of time in locating and recovering the unit. I was just wondering if anyone had come up with a solution for this issue. The most common thoughts such as tubes, surf boards, etc. have all been tried and are sadly lacking in their effency as they either do not work in heavy sea conditions, at varying speeds or do not want to tow true behind the boat.

I had an idea when we were working the 1715 fleet and Aquanut and I were able to mag any water that we could run the boat in at any speed (I'm not going to share it here yet as we kept it pretty quite and I haven't talked to him yet) but will if he agrees.

Anyway, who else has solved this problem? Actually, once set up, it works anywhere, under any sea conditions and in deep or shallow water.

Deepsix

 

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[ScubaFinder]

Interesting...as you know a mag anomoly's Gamma reading is determined primarily by the distance to the target. I've always lived by the theory that it doesn't much matter how close you are, so long as you know how to interpret what you are seeing (unless you are looking for very small objects). I float mags all the time here, because the smart people understand that most shipwrecks probably occured on a reef or something that was within a few meters of the surface.

I use the PVC tube method myself, if you make two of them exactly the same, and add a little surface area to the lower fin of the mag, she'll fly straight and true in most seas. I have (in my head) devised a system using a forward looking depth sounder and a PIC board that could effectively control the depth of the mag to a set altitude above the actual bottom. Basically a mag with an elevator lke you see on an aircraft that is controlled by a depth sensor in the front of the mag. Great plan, but about $10K to do it effectively...hence my problem. I think on a simple, usable level...floating the mag on the surface and adjusting your Gamma reading to the actual depth makes more sense. With a lot of money and time, I could solve the problem electronically, but in todays world most treasure hunters don't have an abundance of either. If you've got a better idea, you might be a millionaire soon, and I for one would love to hear about it....hint hint....PM me, really....I'm your buddy.

Interesting topic to say the least, thanks!

Jason

 

[mad4wrecks]

While I don't think this was the solution you and Aquanut came up with, one of the advantages of very shallow water is that you don't need the mag very close to the bottom. In fact, you don't even need it in the water. A degree of success has been achieved using helicopters for magging shallow water.

http://www.terraplus.ca/products/airborne/helicopter-gsmp-35a-v7.0.pdf

Tom

ps. I see Jason and I responded within minutes!

 

[ScubaFinder]

Oops, up late anticipating tomorrows success.

 

[aquanut]

This is no big deal. Simply tie your fish to a SMALL body-surf type boogie-board. It keeps the fish from hanging up on the reefs.
Aquanut

 

[deepsix47]

This is no big deal. Simply tie your fish to a SMALL body-surf type boogie-board. It keeps the fish from hanging up on the reefs.
Aquanut

Well, obviously he doesn't mind. Take a boogie board type body board (not one of the cheap Styrofoam boards. They will break up on you). Drill a bunch of small holes a few inches from the edges and all along the rim of the board. Slide the fish into a totally nylon mesh divers bag then lace the bag to the board with parachute cord.

That's it. It will tow true behind the boat in any sea condition and at any speed and stays on the surface.

Deepsix

 

[diverlynn]

Jason,
Didn't you have a jet ski set up also to run your mag? I thought it was a great idea.

diverlynn

 

[SFLOcenEng]

This looks like the type of device that would solve your problem and might be of some interest to you and others.

If you Google JHU/APL and Paravane you should find the following.

Surface-Operated Profiling Paravane
Anderson, C.
Johns Hopkins University, Laurel, MD, USA;

This paper appears in: OCEANS
Publication Date: Sep 1984
Volume: 16, On page(s): 1020- 1023
Current Version Published: 2003-01-06

Abstract
A surface-controlled paravane system was built to serve as a submerged platform for towing a buoyant cable. APL modeled the paravane after a helicopter-towed minesweeping vehicle designed at the David Taylor Naval Ship Research and Development Center. The APL system allows a shipboard operator to direct the vehicle to hold a constant depth, to change depth, and to change between port and starboard tow-off directions. In addition to running the paravane at constant depth (as in the cable test), the system can operate in a mode wherein the depth is continuously changing. Such operation could be useful for oceanographic surveys if the paravane were instrumented with environmental sensors. Several profiling test runs were made at tow speeds from 5 to 11 knots over a 25 m vertical aperture. Climb/dive angles of about20degwere typical when averaged over two or more profiling cycles. A maximum angle of38degwas measured during the climb leg at 9 knots.

 

[ScubaFinder]

Neat stuff SFL, thanks.

Lynn, I had a Humminbird Sonar on my JetSki, I had a plan for a Aquascan Mag but never aquired one before I left for the DR. I found things with the Humminbird, and it woulod have been great with the mag added. Plus the way I had it set up it was a great little dive platform. On my budget, you'd be hard pressed to build a better search vehicle.

Jason

 

[Galleon Hunter]

We had a good deal off success in the Keys just wrapping the fish with a couple of lifejackets. Life jackets were all successfully employed in moving anchors. We didn't had our anchor boat and after a couple of days of manually hoofing a pair of 75 pound anchors across the bottom several hundred yards we decided it was much easier to simply tie a couple of life vest to the anchors, leasurely snorkel them out away from the boat and at a signal from the boat we were in the fight position, untie to jacket. It sure beat the old way walking the anchor across the bottom, popping up every few feet only to be told move father out or to the left of right, swim back down, an try to move the anchor again until we we close to the right spot. I'm surprised none of us drowned or had a heart attack in the process. Not only was that way quicker and easier, who ever would take the anchor out often used up a tank of air in the process before we could even start blowing any holes.

Life jackets have a multitude of uses.

GH

 

[aquanut]

Yeah Galleon Hunter, they're real lifesavers...
Aquanut

 

[bronzecannons]

That's correct.. sometimes its a real pain to do a proper maggie survey and pinpoint the mag hits on or near a shallow reef.

What has worked best for me to exactly pinpoint these hard targets is first I would anchor the boat nearby the survey area to perform a detailed hand-pulled Maggie pinpointing survey.

Once the boat was anchored in position using both bow and stern anchors, tie two small buoys on the mag to make it float and keep it off the reef (one on the front and the other on the back). The zodiac would then be used to carry the magnetometer out approximately 70 meters from the boat in various compass directions. After which the magnetometer would then be slowly hand-pulled back towards the survey boat. This method provides exact pinpoint accuracy in detecting small or difficult to locate magnetometer targets (see attached Mag Pull Survey drawing below).

Your mag cable should be marked off with electrical tape so you would know the distance it is out from the boat at all times.

Good luck!
TW

 

[deepsix47]

Hi bronzecannonb> Great idea!!!! The issue with pinpointing in very shallow water is a big one. Many years ago in the Bahamas I was magging with an old timer along a particularly nasty section of reef. All his mag would do is ping a hit but he had no chart, GPS, etc. He used a pretty cool technique.

When the mag sounded off we tossed a buoy then made another run on a reverse course. Again we dropped a buoy when the mag sounded. Many times a quick look underwater at a center point between the buoy would show us the target. If not, we would repeat the process at right angles to the first. It never failed that about the center point between all of the buoys the target would be there.

It's a bit time consuming but when you're working on a very limited budget (virtually 0....lol), using an inflatable, fanning the bottom with ping pong paddles (anyone here old enough to remember doing that....lol!!!!), floating goodies up on tire tubes, etc, and totally determined that you were going to find and salvage your wreck, it works....lol. Oh yea, you can add to that managing to eat on what you could bring up from the bottom and find growing wild on the island (hey, don't laugh, any money had to go for gas). It made for many life long memories that no fiction writer could never dream up.

Deepsix

 

[bronzecannons]

DeepSix,

Yes, you're correct. Its very time consuming also to keep running the boat and towing the mag in different directions when trying to exactly pinpoint a mag target (especially if its a small one).

This hand-pull mag survey can pretty much eliminate those frustrations. If you want you can even let the 'boys' in the zodiac hang back about 40 feet or so and follow the mag being pulled in so you can immediately shout to them to shoot over there and throw a buoy on the 'target' when you get the hit. Since you can easily see the two floating buoys and know exactly where the mag is at all times this isn't a problem at all. Then the diver can jump in with his metal detector and find this target within minutes.

Using this method has saved us tons of time and is especially great for the reef stuff where we couldn't risk taking the boat cause it would be kind of embarrassing for us to also become a shipwreck while out surveying! lol

TW

 

[ivan salis]

vessels of long ago are similar in one way to todays vessels in that most vessels don't just "break up" at sea due to structural failure --- most vessels have to strike something to cause a large amount of "pressure" stress which then causes the vessel's hull l to break up --things like hitting reffs --or bottom bouncing in shallow waters --banging their bottoms (often repeatedly) on the ocean floor while "trapped"in shallow waters during in a storm and unable to get off shore to the safety of deeper waters - if this happens the vessel was just beaten to death.

these facts plus the fact that shallow water wrecks are easier to find (and work on) is why to date most of the wrecks that have been found are fairly "shallow water" wrecks .

anything that makes scanning gear work well in thin water conditions is good -- often some of these areas due to folks being stuck in "normal" searching modes have not been checked out in the past as well as they could have been -- but new ideals require that one think a bit "outside of the box".

 

[ScubaFinder]

Thanks TW! I'm betting I'll be using a slightly modified version of your technique as soon as the weather clears up here in the Dominican Republic. We've got a reef covered with cannon and anchors, and a large sand spit behind it that we have been dredging holes in blindly for several weeks. Finally found some timbers a week or so ago, but it's just impossible to get a mag in there. Most of the reefs break the surface, and there isn't much room to maneuver either, so a mag survey of the sand spit was out of the question...until now.

You never know what you might pick up on TNET. Thanks again....I'll get some HD video of the process.

Jason

 

[bronzecannons]

My pleasure ScubaFinder.

BTW - are you working with Lee Spence there in the DR?

Tony

 

[ScubaFinder]

Lee is no longer directly involved in the project, but yes this is the same lease covering the western half of the north coast. It certainly keeps us busy.