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Sunday, March 16, 2008

Sunday Ship History: MoBoard


Let us begin, brethren, with a couple of odd notes, one of which might be explained herein, and the other of which will remain a mystery.

Picture the bridge of a destroyer which is plodding along in an area of the Pacific Ocean somewhere below Guam and near the equator, well off major shipping lanes, the Captain and the Navigator are both on the bridge, the CO bored and semi-dozing in his bridge chair, the Navigator also being the Officer of the Deck. The ship was on a classified mission and is on a course, roughly, of 340 degrees at 10 knots. Suddenly, the watch standers in the Combat Information Center report to the bridge that they have an intermittent contact ("skunk alpha") with a "constant bearing and decreasing range (CBDR)" with a "closest point of approach (CPA)" of close aboard (meaning that the destroyer and the unknown object were going to collide if neither changed course). The CIC crew reported the "skunk" was on a course of 160 degrees and traveling at a speed of 10 knots with a closing rate of 10 knots. The CO, since the mission had been classified, had his interest piqued about the possibility of an interloper. The Navigator questioned whether the object had any speed at all. Why?

When Admiral Raymond Spruance went to war, he had an odd practice, described here:
Spruance carried a rolled-up twenty-inch-square maneuvering board [a printed form used for solving relative motion problems], fastened by a paper clip. He was never without it, and when he entered the flag shelter he would casually toss it upon the book rack. There it remained until he retrieved it upon leaving. No one asked him to explain his mysterious maneuvering board.
Why would a surface warrior tote around a maneuvering board?

In fact, what the heck is a "maneuvering board?" Here's an explanation by description:
There is a bit of magic in a maneuvering board. It is nothing more than a pad of paper, with worksheets on it. It is about twelve inches on all sides. It has a circular “bullseye”drawn on the paper with graduated markings. Just what a radar screen looks like. A person needs a pencil, a pair of dividers, and parallel rulers to do maneuvering board problems. Real high tech stuff.
***
It also tells you whether or not another ship out there, sailing nearby, is going to pass close to you or even collide with you.

Think of it this way. You are driving your car along a road and you are approaching an intersection. You can see across the flat, level field. There is a car on another road headed towards the same intersection. You hold your left arm out the open window and point your finger at the approaching car. A few minutes later you do the same. If the approaching car is still at the same angle it was a few minutes before, and neither of you slow down or stop at the intersection, you will be able to touch that car with your outstretch hand shortly. That is also called a two car accident. The same principle applies to two ships at sea. We use a radar to get the distance to another ship. We use a compass mounted on a pedestal to take bearings to the other ship. The maneuvering board lets you plot the approach of another ship and determine how close it will come to your ship.

Back to the formation steaming I mentioned earlier. Let me put it another way. You are on a parade ground. There is a marching band in the middle of that parade ground.. You are a majorette. There are five of you in a line up front. There are five more baton twirlers in the back and four more along the side of the band as it marches down the field. You come to a point where the drum major orders everyone to turn to the left at once. When the formation makes that turn you and all the majorettes and baton twirlers are expected to be in the same position relative to the band that you were before the turn. You are supposed to be at the front of the band formation again. The same applies to ships in a formation at sea.
How to avoid collisions and sea and how to get into the right place in a formation can be explained by the proper use of a maneuvering board (I would suggest reading all of Mr. Sparkman's post to get a feel for some concerns that are raised when using a "moboard.")

A more compelling review of a failure of skill (or perhaps anticipation) or maneuvering board practice comes from the findings of the investigation into the collision between USS Frank E. Evans (DD-754) and the Australian carrier HMAS Melbourne in 1969:
Translated: ""At some stage during the "Form Column" maneuver, LTJG Ramsey attempted a maneuvering board solution but abandoned it because he thought it was impracticable, due to the close range"

On the other hand, use of the maneuvering board is complicated enough for some to have suggested that an automated system would be much better:
The U.S. Navy currently bases the majority of our contact management decisions around a time and manning intensive paper-based Maneuvering Board (MOBOARD) process. The use of Maneuvering Boards is a perishable skill that has a steep learning curve. In order to overcome inherent human error, it is not uncommon to have up to four people simultaneously involved in solving just one maneuvering problem. Additional manning requirements are involved on many Naval Ships in order to accurately convey the information to the Officer of the Deck (OOD) and/or the Commanding Officer. When given situations where there exist multiple contacts, the current system is quickly overwhelmed and may not provide Commanding Officers and OODs a complete and accurate picture in a timely manner.

The purpose of this research is to implement a stand-alone system that will provide timely and accurate contact information for U.S. Navy Commanding Officers, OODs, and CIC watch teams. By creating a reliable, automated system in a format that is familiar to all Surface Warfare Officers we will provide the Navy with a valuable decision-making tool, while increasing ease of data exchange and reducing current redundancies and manning inefficient practices.
You can judge for yourself whether the MoBoard is all that complicated by reviewing NVPUB 217, the Maneuvering Board Manual, a pdf document you can download for free by going to gCaptain here and in the column titled "Publications" selecting "Maneuvering Board Manual -Pub 217." In fact, gCaptain points to a number of free (and some pay for) nautical tools. Many of them are actually available from the National Geospatial Intelligence Agency website.

Not that the MoBoard solves all problems. As Captain Wayne Hughes explains, he had to work out some additional formulae for maneuvering:
MIKE GARRAMBONE: You talk about maneuver as a major planning process that you have to think about well in advance. It appears you were concentrating on the dynamics of movement you encountered at sea?
WAYNE HUGHES: Yes. After my tour at the Naval Academy, I was the Operations Officer of another destroyer that operated with a hunter/killer group. There were lots of times when you would go after a submarine in what was called a search attack unit with a couple of ships to try and find and destroy an exercise submarine. After simulating our attack, we would have to rejoin and take our station. If you come back and take station from “ahead,” then you may have to do a turn that is approximately a hundred and eighty degrees. Well, imagine the time it takes to turn a ship. It takes about two and one-half minutes. During the turn, the movement of the rest of the formation is substantial and so is your own transfer, which is the off-access (axis?)movement, and it can be substantial too. It is as big as a turning circle of the destroyer. The “maneuvering board” we used doesn’t solve that problem. The maneuvering board tells you what course and speed to take when you’re going directly into the station without accounting for advance and transfer.
MIKE GARRAMBONE: What did you do in these special cases?
WAYNE HUGHES: I developed a little algorithm I called the turning ellipse. It was all geometric, no mathematics at all. But it worked like a charm and I taught everybody in my wardroom, then wrote it up and had it published in one of the tactical pubs. When I got here to the Naval Postgraduate School years later I decided maybe I ought to see what the mathematical formula really was. It turned out that I was describing a mathematical cycloid. Its proper name would’ve been the tactical cycloid, but that didn’t have any buzz to it.
So, back to the earlier questions...why did the Navigator disagree with CIC? If you turn to the second example in Pub 217, you will find a method for determining another ship's course and speed using the MoBoard. You take three bearings and ranges on the other ship at specific time intervals and plot them on the board:
EXAMPLE 2 COURSE AND SPEED OF OTHER SHIP
Situation: Own ship R is on course 150°, speed 18 knots. Ship M is observed as follows:
Time Bearing Range Relative Position
1100 255° 20,000 M1
1107 260° 15,700 M2
1114 270° 11,200 M3

Required:
(1) Course and speed of M.

Solution:
(1) Plot M1, M2, M3, and R. Draw the direction of relative movement line (RML) from M1 through M3. With the distance M1 M3 and the interval of time between M1 and M3, find the relative speed (SRM) by using the TDS scale: 21 knots. Draw the reference ship vector er corresponding to the course and speed of R. Through r draw vector rm parallel to and in the direction of M1 M3 with a length equivalent to the SRM of 21 knots. The third side of the triangle, em, is the velocity vector of the ship M: 099°, 27 knots.

Answer:
(1) Course 099°, speed 27 knots.
That's a classic MoBoard solution. Now, in the case of "Skunk A," the wise old Navigator had a a simpler approach. If you are thinking about relative motion of two objects headed at each other on reciprocal courses (340 and 160 being reciprocal or 180 degrees different) then the speed at which they are closing should be the sum of their speeds, that is, the speed of Skunk A (10 knots as reported by CIC) and the speed of the destroyer (known to be 10 knots) would yield a "closing rate" of 20 knots (10+10=20) (again, like cars on the road- if you are driving 70 mph and on-coming cars are at the same speed, the closing rate is 140 mph, which is one reason head on wrecks at highway speeds are so deadly).

But CIC was reporting a closing rate of only 10 knots -meaning that one of the objects in the picture had no speed. Since the Navigator knew his ship was moving, the unknown object had to be stopped or "dead in the water." Sure enough, the ship's radar had picked up a drifting coconut tree log and CIC had made a simple MoBoard mistake. All motion on the maneuvering board has to be relative to some known object. Generally, it's relative to our own ship.

As to why Admiral Spruance carried around a maneuvering board? I suppose it's just one of those mysteries. Unless, during his earlier career he had discovered that it was always a good idea to have one on hand...and became a matter of habit.

It should also be noted that the maneuvering board does not require radar, as some sources seem to imply. Visual observations can be plotted, too. Tools needed might include a compass, maybe a sextant, a watch or chronometer, and a stadimeter.

Other MoBoard problems might include wind conversion:
By the mid-20th century, generations of U.S. Navy cadets had learned to compute True Wind using the equations derived by Bowditch. "Wind Problems," as they were called, could be solved graphically using the familiar Maneuvering Board. In addition, a slide rule instrument called the "wind computer" became popular with navigators and aerographers for solving wind problems. Use of the Maneuvering Board and the Wind Computer became essential to mission planning.
Getting the wind exactly right across the flight deck for helicopter operations is one of the challenges faced by SWOs in the past using the MoBoard. Much cursing generally ensued.

Then there was the Battenberg Course Indicator.

There. Would you like some more mud thrown on the subject? Check out Pub 217 and Pub 1310 for more fun with the MoBoard.

And, if any of you happens to discover the person who first set up the maneuvering board as we know it today, please let me know.

UPDATE: More on maneuvering board here (pdf version of Chapter 11 of Operations Specialist 2 (NAVEDTRA 10106) and Operations Specialist 3 (NAVEDTRA 10105)). And an electronic MoBoard downloadable here, though you should always check for viruses and things.

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