January 26, 2016

Tricky question from lame brain

MY BRAIN HAD A QUESTION for me in the middle of the night: How does a rudder rud?

“We know how a writer writes and how a singer sings,” it said, “but how does a rudder rud?”

My brain thinks it’s quite funny on the quiet but in fact its sense of humor is quite warped. Nevertheless, as I had the rest of the disturbed night to think about it, I did start considering the question.

I seem to remember learning that it’s not the rudder alone that steers a sailboat. It’s all very vague now, but apparently the rudder just starts the boat turning, and the hull, now being at an oblique angle to the boat’s forward progress, is forced off to one side or the other. So I’m not exactly sure how the rudder ruds, except that it’s a hydrofoil that generates lift in either direction, according to how you turn it.

Nevertheless, it’s the action of the rudder that you feel when you’re slicing along to windward on a lovely day in a calm sea and all is wonderful around you. A couple of fingers on the tiller is all that’s need to keep your little beauty running straight and true — until a sudden gust of wind comes along, and you find yourself tugging the tiller up under your chin. It’s the dreaded weather helm, of course. Even on boats where the sail plan is nicely balanced with the keel plan, weather helm will show its ugly face, and it’s not hard to see why.

If you take a model yacht, place it in water (your bath will do), and use a finger behind the mast to push it forward, the boat will tend to go straight as long as the mast is upright. But if you heel the yacht over and push in the same place in the same direction with the same finger, you’ll find that your finger, the source of forward power, is now out to the side of the boat. You’re creating an off-balance push from one side of the boat. Naturally, the boat will try to turn toward the opposite side. You will have to counteract that tendency to round up into the wind by turning the rudder.

Now the rudder is a very effective brake. On sailboats it needs to be a large hydrofoil because it moves through the water comparatively slowly. Various designs of rudder make brakes of greater or lesser efficiency, but they all slow the boat down, some considerably, when they are turned. That is why it pays to reef the sails when the boat is heeling too much. The mast, being more upright now, creates less weather helm for the rudder to deal with.

This is all very simplistic, of course, suitable for a lower-class brain to absorb. It’s presuming that the driving force is transmitted at one point through the mast, which is convenient but not true. You can tell that because of how the mainsheet pulls when you’re on the run. There are forces on the shrouds and stays, too, all driving the boat forward.

It’s also presuming that the rudder is working upright in optimum conditions in calm water, which is not always the case. We all know that a rudder is less effective the more the boat heels, and hardly works at all in the foaming water left by a wave breaking under the stern. So it’s all really highly complicated and, I regret to say, too esoteric for a brain like mine.

Today’s Thought
He who will not be ruled by the rudder, must be ruled by the rock.
— Isaac D’Israeli, Curiosities of Literature

Words of wisdom from Scotland:
“A weel-bred dog gaes oot when he sees them preparing tae kick him oot.”

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


Tillerman said...

It's rudimentary dear Vigor.

It's ruddy obvious.

Have you never heard of Ruddles ale?

A rudder doesn't rud it ruddles on the puddles as the skipper muddles along until he's totally befuddled.

John Vigor said...

Wll I'll be ruddled. I should have known a tiller man would know all about rudders.
And no, I don't know about Ruddles ale. I shall ask my brain to investigate.


John V.

Alden Smith said...

Forthsooth, just how DOES a Rudder Rud? If one knew that you would be able to untangle that old conundrum of just how doe an Udder Udd? If you solve these two great philosophical questions you will of course simultaneously solve the meaning of the universe and everything - Good luck.

John Vigor said...

Alden, I was told long ago, when I was the greaser's peggy on a British Union-Castle liner, that "she was only a farmer's daughter, but she liked her 'Uddersfield." I hope this helps.


John V.

Alden Smith said...

John - LOL - You obviously know how an Udder udds and are half way to knowing the meaning of the universe and everything - good work. When you attain the knowledge of how Rudders rud you will obviously become an Enlightened Being LOL