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October 22, 2008

On Design Constraints

Donald Pittenger writes:

Dear Blowhards --

I never studied engineering in college. This was realistic on my part because I lacked the mathematical skills and the temperament a good engineer needs. On the other hand, I missed something really important -- something it took years for me to attain willy-nilly as I experienced life. Too bad I didn't get it rammed into my skull when I was 19 or 20.

I'm alluding to the matter of constraints.

Sure, one deals with constraints from the time he's hatched. But most constraints are minor or simply part of the environment, so they aren't given much thought. It's not all that often that people have to think through constraints in a formal sense. But that's what engineers and others who do almost any kind of technical work have to deal with a lot.

People whose trade is ideas and words face far fewer and less critical constraints than, say, the designer of a battleship.

So to make matters more concrete, let's consider some of the many constraining factors for battleship design. The last true battleship was commissioned in 1946 (HMS Vanguard), only 40 years after the completion of the first modern (all big-gun) battleship HMS Dreadnought. That's a pretty short run, but a well-documented one. My favorite source on battleship design is this book by Norman Friedman.

A highly important constraint is cost. Battleships were hugely expensive items in an era where the world was less rich and government shares of economies were much less than they are now. Politicians who had the responsibility of proposing naval budgets or voting on them were torn between adequately defending the nation and other demands on the treasury. As a rule of thumb, the better battleship is the bigger battleship in a number of ways including survivability. (For instance, the largest battleships ever built, Japan's Yamato class, were extremely hard to destroy.) But another rule is that cost is almost always proportional to size; at some point, even the most bellicose politicians will draw the line at more spending.

Another constraint is the number and characteristics of battleships in fleets of potential enemies (and even allies). It makes little sense to build ships that would be quickly destroyed in a fight; your battleships should be superior to or, minimally, competitive with those of your foes.

After the Great War ended, a naval race between the U.S.A., Britain and Japan loomed. Its potential cost was so high that politicians instead used the device of a treaty that limited the number of ships (via total tonnage by type of ship), their size (in terms of displacement) and how large their main armament could be.

Regardless whether the ship's displacement was limited by treaty or budget, the designers had to honor that limit and essentially allocate various features of the ship according to shares of the total displacement weight. Friedman suggests that a good rule of thumb is that around 60 percent of the displacement of a battleship can be devoted to propulsion, armor and weapons -- the remaining 40 percent is used up by the ship's structure and all the other bits that go into it.

That weight budget for arms, armor and propulsion makes life interesting for the designer.

(The "designer" at this point isn't necessarily a naval architect. "He" is a committee of seasoned officers who consider capabilities of proposed ships in light of operating doctrine and conditions of their own navy as well as current and likely future characteristics of potential enemy battleships. For example, during the pre-Great War naval race between Britain and Germany, German designers didn't need to allow as much space for fuel and crew quarters as did the British because the Germans could safely assume that their ships would be fighting in the North Sea and wouldn't have to steam very far. The British had a world-wide empire that required ships to range far from home.)

Here are the basic elements of the weight-budgeting game. The faster the ship is supposed to go, the greater the weight for propulsion systems. But that means sacrificing some armor or weaponry. Jacky Fisher, First Sea Lord during an important part of the Anglo-German arms race, very much liked the idea of fast ships. He held that a fast ship (or in practice, 3-5 ship unit) would control the initiative in battle; they could engage the enemy or break contact at will. Since he wanted these ships to be able to destroy enemy ships, armament couldn't be stinted; what had to go was protection. So part of the British fleet in 1914 was comprised of fast, battleship-gunned but lightly armored vessels called battlecruisers. They were and remain controversial. The British lost three of them at Jutland in 1916. That might have been due to a design or procedural flaw related to ammunition handling. Battlecruisers have their defenders, but even navies with such ships had a doctrine that battlecruisers were to avoid slugging it out with actual battleships if possible.

The American navy opted for protection over speed. The idea was that one or two well-placed shells could drop the speed of a fast ship (or any ship, for that matter) and, at that point, its most important need was survivability in terms of adequate armor protection. The Germans also followed this philosophy.

Some South American countries also engaged in a pre-Great War arms race. But the battleships they ordered from (mostly British) shipyards emphasized armament -- perhaps more for show than conflict. For example, Brazil's Rivadavia and Minas Gerais class battleships sported 12 12-inch guns whereas the contemporary British Bellerophon, St. Vincent and Colossus classes, designed to deal with strong German opposition, had but ten 12-inch guns per ship.

Battleship designers in those days were seriously concerned about the danger posed by torpedoes launched from small, fast ships, the solution being secondary quick-firing four or five inch guns for defense. Until the war, such guns were placed in casemates strung along the upper part of the ship's hull. But with the battleship at speed in any but the calmest seas, many of the guns couldn't be operated dues to splashing water. The obvious solution was to mount the guns higher, on the main deck itself. But this would raise the ship's center of gravity, making it less stable and seaworthy. After the Great War most navies plated over the casemates and did move the guns higher, but that required some compensating weight-shifting and perhaps making beams wider. (A constraint for U.S. designers was the width of Panama Canal locks. If battleships were to be quickly moved between the oceans, their beams had to be narrow enough to pass through the locks. Sizes of land-based and floating drydocks also constrained ship designers.)


U.S. battleship Texas as seen in 1919. The secondary armament in casemates can be seen at the top of the hull. The casemates were plated over during a refit and new casemates built atop the main deck in the middle third of the hull.

Placement of armor also was constrained. Only so much of it could be carried, so the question became: What parts of the ship should be protected? Up until the very early 1900s, ships' guns were comparatively short-ranged. This meant that the trajectory of the shell at maximum range was, comparatively again, flat and that the target ship would be struck someplace on the side of its hull or superstructure. So the sides of battleships were armored, but not the decks. By 1910 the range of big guns extended to several miles and shells at such ranges plunged onto decks and upper surfaces of superstructures. This meant that placement of armor had to be reallocated. The ultimate American solution, one that was later accepted by other navies, was "all-or-nothing" protection. Rather than putting armor plating along the entire length of the hull, the U.S. Navy started building battleships with armor concentrated to protect vital parts. Such parts include: magazines, turrets and ammunition-handling systems; smoke uptakes from the engine rooms and the rooms themselves; control stations, the conning tower especially; and enough of the hull to retain buoyancy. On the other hand, bow areas were unprotected.

I could go into a lot more detail, but this posting is plenty long already. The point I am trying to make is that technical work such as designing battleships is necessarily a highly disciplined task subject to strong constraints requiring a good deal of compromise or trade-offs. Minds subjected to such discipline tend to operate differently than other minds. I know that my own style of thinking changed after I found myself having to design and program software systems -- especially in those distant days when my computer could only address 640 kilobytes of memory which was diminished by the needs of the operating system and programming language, not to mention the data I had sitting there already. In other words, I spent a lot of time counting bytes and adjusting my programs to what memory was still available.

The result was a more disciplined way of looking at things in general. Too bad I was 43 years old at the time and not 20.



posted by Donald at October 22, 2008


A pretty entertaining little marketing book came out a couple of years ago called The Houdini Solution, by Ernie Schenck.

He argued that facing up to constraints is the beginning of the creative process, and much of its inspiration as well. Or, as the subtitle says, Put Creativity and Innovation to Work by Thinking Inside the Box.

In Houdini's case, it was rather extreme, and literal.

Posted by: Reg C├Žsar on October 22, 2008 6:32 PM

Fascinating posting about a topic I knew less than zero about. Beyond battleships, the topic of constraints is such a good one. In art and entertainment, some creative people and talents seem to thrive on a "go wild" approach to things, though that often doesn't last long. It burns itself up and then there's nothing left. But most people seem to do best when they subject themselves to maybe five years of classical-traditional training. Seems to confer tons of life and creative skills, as well as to develop character and depth. Then, once you've mastered beginning and intermediate skills, why not start having some fun?

But that would probably be much too loosey-goosey for the engineering field, let alone the battleship field.

Posted by: Michael Blowhard on October 22, 2008 11:06 PM

There is an old saw which states that you need essentially two teachers; one firm taskmaster who holds your feet to the fire and teaches you to stick to the rules, another who teaches you to look beyond the rules, outside and up. But -and here is the catch - they have to come in that order.
I suppose the Beatles might be a good example of this.
After 30 years of journalism I began to be exasperated by the thinking styles of myself and those around me.
We were lost in blue sky speculations and totally detached from practical application. I've no doubt this is part of the reason for the heterogenous thinking styles.

Posted by: Barry Wood on October 23, 2008 4:39 AM

An exercise for you, Donald. Try writing a two stanza poem, each stanza consisting of four lines, lines one and three and two and four rhyming, lines one and three eight beats, lines two and four six beats. The poem can be about any subject that genuinely interests you (in your case that might be politics or American history or Seattle or architecture or classic cars). Lastly, the poem has to make sense and the rhyming has to be unforced. Then come back and tell me that only those on the technical side of the equation deal with constraints.

Posted by: ricpic on October 23, 2008 6:26 AM

ricpic -- I wasn't categorical. And if every poem had to have the structure you propose or else had to be a haiku or a sonnet -- and nothing else was allowed -- then indeed poets would have to ply their trade severely constrained.

But that's not the way it is: Poets can do whatever they please these days (they aren't forced to write sonnets), while technical workers will forever remain shackled in many respects.

But here's an example of constraints in the arts: stage set designer. He's only got so much real estate to deal with. There are sightlines to consider. Ease of set changing. Stage features -- any turntables, trap doors, etc. The play or opera itself and its minimal staging requirements. There is a budget to consider. And deadlines. Not to mention the whims of the director who demands that Die Fledermaus be staged in a Nazi concentration camp setting.

Posted by: Donald Pittenger on October 23, 2008 9:57 AM

I just finished reading my son's college application essay. He discusses music composition, the pleasure he gets out of composing a piece using the baroque or classical era rules, and then intentionally breaking those rules. Sounds familiar!

Posted by: Julie Brook on October 23, 2008 12:02 PM

Donald - in your last paragraph of the previous comment (about the stage designer) you just described the process of architects' and interior designers' work.
Only our job involves a)more technical constraints b)administration of more trades c)clients that -on principle- avoid getting educating about those constraints d)legal responsibility where welfare of the public is concerned, as in - somebody can (and do) go to jail for faulty design that resulted in injury.

Generally, I find engineer/designer type much prefereable to deal with than the "artsy" types. These people know responsibility.

Posted by: Tatyana on October 23, 2008 12:14 PM

This is such a wonderful post! I was unaware of Friedman's book (and his others on similar subjects) and will definitely add them to my Christmas list.

Everything in warship design involves tradeoffs. Push in here and it pushes back there. There's no free lunch. Pile on more armor and the ship becomes more survivable but the speed goes down and fuel consumption rises. Larger guns give more hitting power but increase topside weight and may lead to poor handling or even capsizing if damaged. Overall draft is limited by harbor depths.

Trading off armor for increased speed turned out to be risky business. The HMS Hood was a powerful ship with 15" guns, but she was destroyed rather easily by plunging fire from the Bismarck and Prinz Eugen. Her extra speed was of little avail.

One of the most interesting (and almost last) of the battleship clashes was the second naval battle of Guadalcanal (November, 1942), when the Americans under Admiral Lee took on the Japanese. The Americans had the powerful battleships Washington and South Dakota, while the Japanese had the battleship Kirishima and some cruisers. Both sides had some destroyers (all of the American destroyers were sunk in the battle). The battle took place at night, and the Japanese were experts at night fighting. But the Americans had radar, which the Japanese didn't know about. This decisively trumped the Japanese advanatge in night actions.

The South Dakota was knocked out early in the action by an electrical malfunction, leaving the Washington to face the Japanese fleet alone. The Japanese flagship, the Kirishima, embodied Japanese naval design. She had 14" inch guns (to the American 16") and was faster than the American ships. But the newer American ships had all the other advantages - firepower, radar, maneuverability, and vastly superior armored protection. The Washington spotted the Kirishima at a short range of 8,400 yards and in just a few minutes used her radar-controlled 16" batteries to reduce the Japanese battleship to a burning hulk. In one of the final battleship clashes, the American ships prevailed decisively.

Posted by: Ned on October 24, 2008 4:16 PM

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