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	Under Sea Adventurers Dive Club

Locating Your Favorite Dive Spot, AGAIN!

Ray McAllister

This little exercise is for the diver who wants to return to a good dive spot without the help of a chartered dive boat, without complex and expensive electronics; a method requiring only one good Mark 1, Mod 1 eyeball, in functioning condition. There are a few other requirements too. There must be objects on land that stick up above the houses on the beach; objects like water towers, church steeples, tall buildings and radio or TV antennas. In addition you must be within sight of these objects. I'd say two to three miles away is about the limit in flat country but in Bermuda, which had hills, we used it as far as 5 to 6 miles out.

In South Florida, north of the Keys, it is exceptionally useful. Because many of the Florida Keys are low and not very wide, the method is only useful near some of the bigger, more built up Keys. It worked very well for me in Bermuda, before Loran and GPS were available. I've used it on the Great Lakes, in Southern California and in the Bahamas, always subject to the conditions stated above. Where it works it is better than Loran, ordinary GPS and often better than Differential GPS in accuracy.

Lets start with a couple of basic rules of geometry which many of us learned in high school. First: only one straight line can be drawn thru any two distinct points. That is not hard to see with a pencil, ruler and a sheet of paper. The second rule states that two different straight lines can only cross at one place in the world. That, too, is easy to prove. Now we are ready to locate ourselves at sea, within sight of land and land objects.

When you are anchored on a good diving spot, shorten scope on your anchor to get nearly directly above the spot. Now look ashore and find two objects that touch each other. Try to pick objects that are permanent like big buildings or lighthouses. Next in usefulness are church steeples, water towers, and various antennas. Last in utility are telephone poles, chickees and other structures which are easy to move if streets get widened, etc.

Line up the two objects and sketch them on a three by five card. The better and more complete the sketch, the better your return to the spot. (Telephoto photographs are, of course, better!) Then look up and down the beach and choose two more objects in line, preferably 90 degrees from the first set and draw them. The illustration below, for the statue of King Neptune, off the Breakers Hotel in Palm Beach, Florida, shows a good set of "marks", as fishermen often call them, or ranges, as they are called by most mariners.

Note the exact position of the Florida Power and Light stacks on the white beach buildings in front of them. Also note that the black "Darth Vader" building, as locals call it, lines up with a beach building with prominent windows.

To return to the good spot, run up the coast till the first set of marks lines up. Turn and run along that line and watch to see if the other mark gets better or worse. If worse turn and run the opposite direction along the line until the second set of marks lines up. Immediately drop a marker or your anchor on the desired spot.

How good is this technique? Many fishermen and lobstermen use it to find their spots or traps on a wide ocean, where a lobster buoy can only be seen for a couple of hundred yards.

Indeed, the Palomares H-bomb, dropped off the coast of Spain, when an American bomber blew up at high altitude, was found because a Spanish fisherman lined up marks for a silvery object he saw falling from the sky. He got a gold watch for his efforts.

The following rules and observations summarize the procedure which I use for publishing two books on diving spots off the Southeast Florida coast.

Marks or ranges can be used to find a point at sea with very great accuracy if you follow the the rules and suggestions below.

Rule 1. Only one straight line in all the world can go through two different points. Put in different words it says that if you line up two chosen points so that they touch or merge, you are on a very specific line. This line is also called a "range".

Rule 2. Two straight lines can cross at only one point. So, if you line up a second set of points, the new straight line, crossing the one in Rule 1, determines your exact location. (See illustration).

Other helpful rules based upon geometrical considerations, etc. are:

Rule 3. For maximum accuracy, be sure points chosen are sharp and clear, for example, the peak of a roof, the side of a building, a radio antenna, tree trunk, or water tower leg.

Rule 4. Wherever possible, chose two points which are widely separated. The farther apart they are, the better defined is the straight line they determine. Usually, the best combination is an object near the beach over one well inland.

Rule 5. Maintain an angle of 60 to 120 degrees between the two lines or ranges for greatest accuracy.

Rule 6. Be meticulous about your marks. If you are exactly on your marks you are exactly over your fishing and diving spot.

To use marks, for instance, note the two points indicated on the North Mark below. Line up these two points exactly. Now, keeping the marks exactly as shown in the photograph, imagine running in or out until the other set of marks looks just exactly like the South Mark photo. At that point you would drop a small buoy or anchor, as desired.

A few more suggestions may help:

1. In choosing new marks of your own, run past a good spot which you have buoyed. Note which objects on land appear to move fastest in relation to each other. Use fast moving marks where possible, for they are farthest apart. See Rule 4 above.

2. Take your own marks. They are better than anyone elses, except for photo marks as in the illustration.

3. If you lose a range behind a new building, travel out the other range until a depth sounder or towed diver sees the ledge or reef. In addition sometimes a less prominent object will line up and help recover a lost mark.

4. A length of line wound on a gallon bleach bottle, with a small anchor at the end, will unwind rapidly and makes a good buoy.

5. The farthest mark will travel in the same direction as your boat!

Remember this suggestion for it will be very useful.

How accurate is this procedure? To test it off our coast I put a fiber barrel hoop about 3 feet on diameter on the bottom in 60 feet of water, one mile offshore. Using six small practice bomblets (mortar shell shaped, with fins) I went to the marks and dropped one over the side. I circled well away from the spot and came in again five more times and dropped a bomblet. We togged up and went down to see the results. Four bomblets were in the circle. One just touched the rim and one was three feet away. Of course I am experienced in doing this and publish two books of marks so I should be able to do a good job, but it shows how good the location can be if the marks are good and one is careful using them!

Loran C, which costs several hundred dollars, will get you somewhere between 60 and 120 feet from the spot if you got your own Loran numbers. Ordinary GPS, considerably more expensive, will do a little better, but not much. Differential GPS, very expensive, can get you somewhere between 12 and 50 feet depending on your set and the satellites in range at the time. Optical (eyeball) is cheap, better and dependable. If you have Loran or GPS, use them to get close and use the marks to get right on. In poor visibility it will save many a dive.

If you lose something over the side, or drop your anchor line to go pick up divers in a current, get marks and come back and salvage your lost equipment. It has saved me several weightbelts, masks, one dive watch and several anchors.

One last story and I'll quit! I had a dive shop in the late 60's. We gave a new set of marks to anyone that wanted to come in and pick it up every month. After a time an older lady came in every month and picked up one mark. We finally asked her what she was doing with them, for at that time few older people were diving and she definitely did not look like she could stand up with a tank on. She swore me to secrecy. "My husband and I moved to Florida to retire and fish. We caught almost nothing. One day I heard about your marks so I got one and memorized it. When we were not catching much I told my husband I had a hunch we could catch fish at a spot a little ways away. He humored me, with some disgust, of course. I went to one of the dropoffs you published and we caught fish. Periodically I'd get a new mark. He thinks I made a pact with the devil, but we caught fish on most of the spots." Why not? Good diving spots are usually good fishing spots as well. That's why we go there.

Good luck. Try this technique. It may help you a lot.