July 5, 2011

Readers write back

IT’S TIME for some reader input. One reader, Dave Donkers, must have been experiencing a major crisis. He has deliberately expelled himself from the Silent Fan Club.

“Greetings, John,” he says, “OK, I’m breaking the Fan Club rules, but here goes. I first ran into your Black Box Theory in The Practical Mariner's Book of Knowledge, and have shamelessly used it in the USPS Boating course I teach. I believe I have found a corollary to the theory: The Box Is Leaky!!! Those who don't keep putting points in it always appear to run out of luck sooner than even the Average Sailor.”
— Dave Donkers, 30-foot houseboat Nuffernau, Illinois River.

► Well Dave, I’m sorry you had to humiliate yourself in public like this. Most people are pretty careful never to praise me or my theories, not wishing to jeopardize their privileged membership in Vigor’s Silent Fan Club.

But you are right. The Black Box is leaky. In fact I have always advised people to begin earning more points as soon as possible after making a big withdrawal. To quote from the delightful book you mention: “Those with points to spend will survive — but they must start immediately to replenish their savings, for the sea offers no credit.”

Meanwhile, on a completely different subject, loyal reader Oded Kishony wants to know: “How is the 'comfort index' calculated for a catamaran? Does it apply in the same way? I've read that cats have a more jerky motion in the water.”

► Oded, I don’t believe naval architect Ted Brewer had catamarans in mind when he invented the comfort ratio. He was thinking only of comparisons between monohulls. Cats are animals of a different stripe, although I must say in my limited experience with them I’ve never noticed a great increase in jerkiness. Their hulls are finer, less buoyant at the bow, so they don’t react as violently to oncoming waves as a mono would. Furthermore, their great beam tends to stabilize them to a certain extent from individual waves approaching at right angles. But I suspect that there are different courses for different cats, depending on their displacement and hull shape. So, actually, what I’m trying to say, without really admitting it, is: I don’t know.

Incidentally, Ted says in his excellent book, Understanding Boat Design, that he “dreamed up” the comfort ratio, tongue-in-cheek, for a magazine article some years ago. He says that “corkiness” is determined by two main factors: the beam of the hull and the area of the waterline.

Ted’s formula, for enquiring minds, is: Displacement divided by [65 x (0.7LWL + 0.3LOA) x B1.333]

Today’s Thought
O my good lord, that comfort comes too late;
’Tis like a pardon after execution;
That gentle physic, given in time, had cur’d me;
But now I am past all comforts here but prayers.
— Shakespeare, Henry VIII

Boaters’ Rules of Thumb, #218
How much open water is needed for waves to reach their maximum height? The old rule is that a fetch (a stretch of deep water unaffected by land masses) of about 600 miles is required. The wind must blow in the same direction for a certain minimum time for the sea to become fully developed, and the rule here is that the time, in hours, equals the wind speed in knots. That is to say, a 20-knot wind will take about 20 hours to form its biggest waves, and so on.

Number Three said to Number Two: “Hey gorgeous, let’s get together and multiply.”
“Forget it,” said Number Two, “you’re just a six maniac.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

1 comment:

DPurpleTerror said...

John --

Without trying to sound like I'm flogging a lame horse, not only do boaters need to build up a store of points on a new boat and replace "used" points, they can NOT rest once they have what they consider a sufficient store of points, as they will dribble out and be lost.

I believe that the Box has an infinite capacity for points - it never hurts to put more of them in.

I don't know how many Stinkpotters like myself read your infinitely educational and entertaining blog, but we do have as much to take care of, it's just different stuff that can ruin an outing.

Regards, Dave