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Want to see how much you know? Want to show everyone else h

much you know? The first three people to submit the correct ans

to the following question will win a Westlawn tee shirt and cap, a

will also receive a Know It All certificate. The answer and winners

be published in the next issue of

Who Will Be The June 2010

Know It All Winner?

Email your answer to:

title of “Know It All,” with all the rights and privileges pertaining

thereto. Westlawn tee shirts, caps, and—of course—distinguished

Know It All certificates are on the way to each of our brainiacs.

The complete answer to the March 2010 Know It All question is

as follows:

Of Cycloids and Gravity:

Researchers studying waves and ship motion (particularly Wil-

liam Froude) discovered that—without other influence, like shoal

waters or interfering wave patterns—ocean waves follow a form

known as “cycloidal.” Also called “gravity waves,” the individual

particles making up each wave followed the path of a single

point on the rim of a circular ring rolling along a flat surface.

Naturally, there’re are all manner of combinations of these roll-

ing patterns, and many cycloids will interact with each other, but

it was a very useful discovery.

Any regular motion can be reduced to mathematical expression.

In our case, for seawater on planet Earth, we learned the length

(L) between wave crests is equal to 5.12 times the wave’s period

(P) squared. (The period is the time it takes for two crests to pass

the same point.) We also found the speed (S) of the wave crests

is equal to 3.03 times the period. A little algebraic manipulation

gives the classic hull-speed formula as shown in the sidebar.

In reality, boats do go faster than hull speed. Such vessels lift up

and skim over their bow wave—they can plane. To do this, lots of

power is needed along with a properly formed hull. Alternately,

light and/or slender hulls can knife through the bow wave, with-

out having to climb up it and so exceed classic hull speed.

For fairly heavy boats that must push a lot of water out of the

way, the classic hull-speed formula works (at least reasonably

accurately), and so it has been accepted as “gospel.” According

to gospel, no non-planing boat can go faster than this hull speed.

We now know that this isn’t really so. We’ve discovered that hull

speed—at least classic hull speed—isn’t truly accurate and the

1.34 constant isn’t constant, but actually varies as a function of

displacement/length ratio. This is covered in detail on pages 12

and 13 of the

June 2008 issue of

Where:

L = wavelength

P = period

S = speed

2

2

2

2

2

2

2

2

L = 5.12 x P

and

S = 3.03 x P

or

S

P =

3.03

So, substituting . . .

S

L = 5.12

3.03

S

L = 5.12 x

3.03

S

L = 5.12 x

9.1809

L = 0.55768 x S

L

S =

0.55768

S = 1.7931 x L

S = 1.7931 x L

S = 1.34 x L , The classic hull speed formula

You have a well-constructed, fiberglass-composite, 46-foot sailing catamaran,

. Beam overall is 26 feet and

displacement is 6 tons.

’s cutter rig has a sail area, with 100% fore-triangle, of 1,100 square feet. The mast and

rigging are rugged and properly stayed. Chainplates are strong and correctly aligned. Sail-handling gear is well thought

and sized appropriately. The center of effort of

’s sailplan is 29.4 feet above the DWL.

With regard to stability and sail-carrying power, is

suited to offshore cruising and why or why not?