Read the current issue of Sail. There is a good article that explains this.

John

"Jeff Morris" wrote in message
news
Dale wrote:
Roger Long wrote:

It's like the question of when they go from being a boat to a ship.
There are some commonly agreed on displacement length numbers but they
shift with time and fashion. The scandalously light of fifty years ago
would be a heavy tank today. Where will it ever end?

Yes, but I see many posts where people refer to HD vs MD with no
discussion on what these are, which tells me that there are some general
ideas about them. So what are the commonly agreed upon numbers for our
current fashion?


Disp/LWL is probably the most direct measure, though SA/Disp takes into
account the ability to make use of the low displacement.

As for "commonly agreed upon numbers," you won't find specific agreement.
For instance, another poster said "medium" was 225 to 275; that would make
a Nonsuch 30 (at 216) a "Light Displacement" boat. Also, lots of C&C's,
Freedoms, Pearsons, Tartans, etc. are under 225 but many people wouldn't
think of them as "light."

The best thing to do is to use a program like sailcalc to see how boats
that you're familiar with measure up.

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