August 19, 2010

Faster under water

IT HAS COME TO MY ATTENTION that certain scientists are now studying animals that have been moving through fluids like air and water for millions of years. They want to know, for instance, why a dolphin can swim faster than a yacht. Well, actually, they may also want to know how to make planes and missiles and torpedoes and warships go faster, but it’s the yachts that should interest us most.

We suspect that dolphins swim so fast because their skin has special properties. But we can’t build boats like dolphins because ... well because we don’t know how to; and besides, I don’t know if you’ve ever seen the inside of a dolphin but it’s not the kind of place you’d like to inhabit for long. It’s kinda messy and smelly down there.

If you’re looking for a faster sailboat, I believe the answer is a submarine yacht. As you undoubtedly know, when a conventional displacement yacht gets up to hull speed it becomes trapped in a large hollow wave. It can’t climb out. And large hollow waves go very slowly. Grandma can pedal faster on her tricycle.

Now, there is no wave under water. Well, there is, but it’s a different sort of wave. We all know that submarines can go much faster under water than on the surface. So what comes to mind immediately is a submarine yacht with a mast and sails.

Aha, you say in your usual perspicacious way, but what about stability? Won’t the submarine yacht just roll over on its side? Well, on the surface, a yacht’s center of buoyancy steps out sideways as the hull heels, restoring equilibrium by shoving upwards to counterbalance the center of gravity shoving downwards. But what keeps a submarine upright? The usual suspects: buoyancy on top and ballast down below. But it must be neutral buoyancy, of course, otherwise the submarine will either pop out of the water like a balloon, or drop to the seabed like a stone.

But never mind that for the moment. Here’s the real thing – is there a submerged sea animal with a mast and sails that the scientists can study? Well yes. As a matter of fact, there is. How about the humble Portuguese man-o’-war, then? Yes, yes, I know. It’s kinda slow and can’t sail upwind. But it’s a good place to start. And it might be better to start slow with submarine yachts, anyway. After all, submarines can’t see where they’re going, which is very worrisome when you’re doing 40 knots under water.

Today’s Thought
The best scientist is open to experience and begins with romance — the idea that anything is possible.
— Ray Bradbury, LA Times, 9 Aug 76

Boaters’ Rules of Thumb #85
Size distortion in fog. With visibility in fog between 30 and 150 yards, vessels and other objects appear twice as large as normal. This illusion also doubles their speed of approach, which greatly raises the heart rate of the skipper

“She told me you told her the secret I told you not to tell her.”
“Aw gee, I told her not to tell you I told her.”
“You did? Well for goodness’ sake don’t tell her I told you she told me you told her.”

1 comment:

Aaron Headly said...

Boring scientific elaboration (so I'll keep it short): Fish-like things that swim can beat their 'hull speed' (without planing) because they 'flick' the resulting vortices away from their body with every power-stroke of their tail. (A lot of 'hull' drag comes from these vortices.)

They built a robot tuna at MIT and found out a lot about this. More here.