May 11, 2010

Talking about engines ...

A READER IN SAN DIEGO says he’s noticed in his travels around the world that almost all commercial fishing boats have just one diesel engine. “Why not two — for safety reasons?” he wants to know.

Well, the simple fact is that two engines are rarely twice as good as one. Twin-screw installations are comparatively wasteful of power. They cost more to start with, of course, they need bigger fuel tanks, they require twice the amount of servicing, and they weigh far more. Two engines side by side are usually very cramped and have poor access, which almost guarantees poor maintenance.

It’s true that the commonest reason for twin engines is safety, but it doesn’t always pan out that way because many planing powerboat hulls are almost unmanageable under one engine in heavy weather.

A boat with two 100-hp engines cannot make the same use of all the available power as a boat with one 200-hp engine. You pay dearly for the added weight, added friction in drivetrains, and added drag from extra struts and rudders. In fact, it’s commonly taken for granted that a twin-screw installation wastes about 20 percent of available power, compared with a single engine of comparable horsepower.

One well-maintained engine is better in many ways than two poorly maintained engines, but if safety is the prime issue, then one big diesel backed up by an outboard “kicker” of 9.9 hp or so is a reasonable compromise for pleasure powercraft.

Today’s Thought
Power, like a desolating pestilence,
Pollutes whate’er it touches.

— Shelley, Queen Mab

Boaters’ Rules of Thumb, #50
Designing new yachts. The general rule is that in any new design nine-tenths is 90-percent borrowed from existing plans and 10-percent adapted. Of the remaining tenth, 9 percent seems to fit in place by luck, 1 percent is genuine inspiration or “art,” and 90 percent is pure trial and error.

Two monkeys found a loaf of bread.
“Great,” said one, “let’s make toast.”
“How are we gonna do that?” asked the other.
“Simple, I hear that you just stick it under the gorilla.”

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