SA/D

cruisers/index.md.html

@@ -1,6 +1,6 @@
         <meta charset="utf-8" emacsmode="-*-markdown-*-"><link rel="shortcut icon" type="image/png" href="../compass-rose.png">
                         **Selected Cruising Sailboats**
-                Published 2023-01-08; Last updated 2025-01-27
+                Published 2023-01-08; Last updated 2025-02-12
 
 
 ![The Valiant 42 is a classic bluewater cruiser.](valiant42.jpg width=500)
@@ -35,7 +35,7 @@
  | [Jeanneau Sun Odyssey 350](https://www.jeanneau.com/boats/sailboat/2-sun-odyssey/700-sun-odyssey-350) | Weekend | ![](exterior/jeanneau-350.webp class="icon") | | 2024 | 10.40 | 9.38 | 3.59 | 22.71 | 2.04 | 17.68 | 1.98 | Mid-Boom Bridle | Bolt-on Fin Bulb | Dual Spade, Dual Helm | Fractional Sloop | Upgraded layout from the 349
  | [Hanse 348](https://www.hanseyachtsag.com/hanse/gb/yachts/hanse-348/ "Hanse 348") | Coastal | ![](exterior/hanse-348.jpg class="icon") |   | 2018 | 10.40 | 9.55 | 3.55 | 26.19 | 1.91 | 17.51 | 1.98 | Mid-Boom Bridle | Bolt-on Fin | Dual Spade, Dual Helm | Sloop |   |
  | [Hanse 350](https://hanseyachts.com/us/historical-models/hanse-350/) | Coastal | ![](exterior/hanse-350.webp class="icon") | | 2007 | 10.59 | 9.60 | 3.55 | 25.36 | 1.94 | 19.25 | 1.92 | Mid-Boom Bridle | Bolt-on Fin Bulb | Spade | Fractional Sloop | Still listed because the newer 360 has much nicer accomodation but is slower and less sea kindly
-<big>♥</big>| [Sirius 35 DS](https://www.sirius-yachts.com/yachts/35ds/ "Sirius 35 DS") | Bluewater | ![](exterior/sirius35.jpg class="icon") | TRUE | 2010 | 10.60 | 9.70 | 3.53 | 30.08 | 1.80 | 18.92 | 1.55 | Boom End Binnacle Block | Bolt-on Dual, many other options | Partial Skeg | Solent | Metrics w/ performance rig and performance dual keels; SA/D is 15.39 with the standard rig.</comment>| 
+<big>♥</big>| [Sirius 35 DS](https://www.sirius-yachts.com/yachts/35ds/ "Sirius 35 DS") | Bluewater | ![](exterior/sirius35.jpg class="icon") | TRUE | 2010 | 10.60 | 9.70 | 3.53 | 30.08 | 1.80 | 16.46 | 1.55 | Boom End Binnacle Block | Bolt-on Dual, many other options | Partial Skeg | Solent | </comment>| 
  | [Linjett 34](https://www.linjett.se/en/linjett-34/ "Linjett 34") | Weekend | ![](exterior/linjett34.jpg class="icon") |   | 2012 | 10.66 | 9.30 | 3.45 | 23.23 | 1.97 | 19.48 | 1.84 | Mid-Boom Traveller | Bolt-on Fin | Spade | Sloop | |
  | [Dehler 34-3](https://www.hanseyachtsag.com/dehler/gb/boats/dehler-34/) | Weekend | ![](exterior/dehler-34-3.jpg class="icon") | | 2015 | 10.70 | 9.60 | 3.60 |	23.42 | 2.00 | 20.07 | 1.95 | Boom End Before Helm | Bolt-on Fin Bulb | Spade | Fractional Sloop | |
  | [Beneteau Oceanis 34.1](https://www.beneteau.com/oceanis/oceanis-341) | Weekend | ![](exterior/beneteau-oceanis-34.1.jpg class="icon") | | 2021 | 10.77 | 9.50 | 3.57 | 21.70 | 2.05 | 16.20 | 2.00 | Mid-Boom Bridle | Bolt-on Fin | Dual Spade Dual Helm | Fractional Sloop | |
@@ -372,12 +372,19 @@
 
 ## SA/D 
 
-This is referred to as "Sail Area / Displacement", but is not a direct ratio.
-The equation is:
+This is referred to as "Sail Area to Displacement", but is not a direct ratio.
+The equation, using upwind sail area, is:
 
 \begin{eqnarray}
 \nonumber
-\mbox{``SA/D''} &=& \dfrac{\mbox{sail area} ~ [\mbox{ft}^2]}{\left(\mbox{displacement} ~ [\mbox{ft}^3]\right)^{2/3}} = \dfrac{\mbox{sail area} ~ [\operatorname{ft}^2]}{\left(\frac{1}{64} \mbox{displacement}~[\operatorname{lbs}]\right)^{2/3}} \\
+\mbox{"SA/D"} &=& \dfrac{\mbox{sail area} ~ [\mbox{ft}^2]}{\left(\mbox{displacement} ~ [\mbox{ft}^3]\right)^{2/3}} \\
+\nonumber\\
+\nonumber
+&=& \dfrac{\mbox{sail area} ~ [\operatorname{ft}^2]}{\left(\frac{1}{64} \mbox{displacement}~[\operatorname{lbs}]\right)^{2/3}} \\
+\nonumber\\
+\nonumber
+&=& \dfrac{\mbox{sail area} ~ [\mbox{m}^2]}{\left(\frac{1}{141}\mbox{displacement}~[\mbox{kg}]\right)^{2/3}} \\
+\nonumber\\
 \nonumber
 &=& \dfrac{\mbox{sail area} ~ [\mbox{m}^2]}{\left(\mbox{displacement}~[\mbox{m}^3]\right)^{2/3}}
 \end{eqnarray}
@@ -422,11 +429,21 @@
 Note that all monohulls in displacement mode (and laden cruisers don't
 plane upwind) have an effective maximum
 [hull speed](http://staging4.wavetrain.net/2010/03/26/crunching-numbers-why-longer-is-faster/)
-in knots through the water of $1.3 \sqrt{\operatorname{LWL}~[\mbox{ft}]} = 2.4 \sqrt{\operatorname{LWL}~[\mbox{m}]} = \sqrt{\frac{\operatorname{LWL}~[\operatorname{m}] \times g}{2\pi}}, g = 9.81~\operatorname{m}/\operatorname{s}^2$. 
-This will be 7-8 kts for any mid-sized cruiser. The performance questions are
-largely how much wind is needed to reach that hull speed (which SA/D
-helps indicate) and how high the boat can point (which is indicated by
-a polar or track tacking angle).
+in knots through the water of 
+
+\begin{equation}
+1.3 \sqrt{\operatorname{LWL}~[\mbox{ft}]} = 2.4 \sqrt{\operatorname{LWL}~[\mbox{m}]} = \sqrt{\frac{\operatorname{LWL}~[\operatorname{m}] \times g}{2\pi}} \approx 8 \mbox{kts},
+\end{equation}
+
+where $g = 9.81~\operatorname{m}/\operatorname{s}^2$. This hull speed
+will be 7-9 kts for any mid-sized cruiser listed on this page in the
+range 9-14 meters of waterline. So, in 15 kts of breeze, more sail
+area, less weight, or another foot of waterline isn't going to make
+any practical difference between these boats in boat speed. Therefore
+the performance questions are largely how much wind is needed to reach
+that hull speed (which SA/D helps indicate), how high the boat can
+point (which is indicated by a polar or track tacking angle) and how much leeway
+it makes, and how fast the boat is in _light_ wind.
 
 ## Comfort Ratio