[Rhodes22-list] What's in a Number?

[Bob Keller]

Hello all,
The current (April) edition of Sail magazine has an interesting article 
titled "Crunching the Numbers."  It explains the commonly used numeric 
calculations to define and compare different boats and designs. The article 
discusses some of the shortcomings of these values, but also tells how to 
calculate them.

So, I ran the numbers for the Rhodes 22, and the conclusion is that the R-22 
is a moderate displacement, tender boat with a low-powered sail plan that 
does not point to windward well at all.

Here's how the calculations were done:

D/L (displacement/length ratio) = (displacement/2,240)/(0.01 x LWL)3 (third 
power) = (3,200/2,240)/(0.01 x 20)3 = 1.43/0.008 = 184 - this puts it in the 
"moderate" category.
I used 3,200 displacement as a guesstimate for my 1995 boat with motor, 
three batteries, marine head, water tank, etc, etc.

SA/D (sail area/displacement ratio) = sail area sq ft/displacement cu ft 
(displacement lb/64) = 300/50 =6 this is considered low, with 15 being the 
the upper end of the low range!
I used 300 sq feet considering IMF main and 175 genoa.

BR (ballast ratio) = ballast weight/displacement = 700/3200 = 0.22 this 
falls into the tender category with anything below 0.3.  This means 
(according to the article) that the boat is tender with limited upwind 
capability.

L/B (length to beam ratio) = 22/8 = 2.75 the article states that "a wide 
beam increases stiffness, which in turn reduces the ballast required, 
enabling lighter construction to be used all around."  Also, "lightweight, 
beamy boats often perform poorly to windward in choppy conditions because 
they get thrown all over the place."  The author looks for a L/B of 3.0 or 
higher.

Some of this seems to be off the mark, but I can identify with some of it, 
as well.  In particular the last comment about going to windward in choppy 
seas.

Comments anyone?
Bob K
Yankee Clipper

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