December 8, 2013

Go gently on the helm

IT’S OFTEN SAID that anyone able to handle a sailing dinghy well ought to be able to steer a much bigger boat with equal ability, whereas the reverse is not the case. But this idea is pooh-poohed by Douglas Phillips-Birt, the renowned British designer and author in his book Reflections on Yachts (Nautical Publishing Company).

He says the chief feature of the modern dinghy is her extreme lightness.  She loses way in a moment and picks it up again equally quickly. “She can only be handled by rapid and considerable helm movements capable of putting her about before a sea stops her, or of keeping her moving by a process of weaving through seas which she lacks the power to trample down.”

But that situation is reversed in a bigger, ballasted yacht, says the author. “The most effective way of applying the brake is to swing the yacht abruptly from one course to another.”

Why should this be? Well, think about what happens when you turn the rudder. “The fact that the rudder is put over to a certain angle when altering course creates a little resistance, but that of the rudder alone is a trifle. The effect of the rudder is to give the whole hull a sheer or angle of yaw — it is analogous to the angle of leeway when sailing to windward. The whole yacht, in fact, starts moving obliquely. The water pressure set up on the hull thereby, and not the rudder, is what ultimately turns the yacht.”

It’s obvious that this sideslipping through the water must entail a large increase in resistance to forward movement.  Phillips-Birt estimates it’s something like an additional 10 percent for each degree of yaw established.

“So, when a few spokes of the wheel are applied, the head swings this way or that only because the hull has first been set into an oblique manner of advance, which is very much more resistful than advance straight ahead.

“You pay a great deal in added resistance for a few degrees of luffing up or bearing away.”

Every time the helm is moved, he adds— easy though the movement may seem, and harmless — it initiates a train of events introducing far bigger forces than those applied by the helmsman, and these tend to stop the ship. “The best helmsman,” he concludes, “is the one who does not seem to be steering.”

Today’s Thought
We spend our lives in learning pilotage,
And grow good steersmen when the vessel’s crank!
George Meredith, The Wisdom of Eld

“The tolerances in this engine are very fine ­— we aim at no more than three thousands of an inch.”
“Wow! How many thousands are there in an inch?”
“Gee, feller, I dunno. There must be millions of them.”

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


biglilwave said...

John, unfortunately many of us that started as dinghy sailors learn this the hard way the first time we park a large yacht into a small slip after making a 90 degree turn too late.

Bill said...

My first lesson only cost me approximately $1000 on both my charter boat and the other poor guy's power cat.