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

[Wally Buck]

For another sail calculator -

http://image-ination.com/sailcalc.html

I would think that most pocket cruisers wthout full keel would have similiar 
results. Our boats are more tender and don't point as well as a full keel 22 
footer, no surprise here. They are much easier to get on and off a trailer 
though. :-)








>From: "Bob Keller" <r22yankeeclipper at hotmail.com>
>Reply-To: The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
>To: rhodes22-list at rhodes22.org, rhodes-list at sailnet.net
>Subject: [Rhodes22-list] What's in a Number?
>Date: Thu, 25 Mar 2004 11:33:51 -0500
>
>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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