Limit of Positive Stability

[Les Luzar]

I recently read the report following the Chicago - Mac race where the Kiwi 35 "Wingnuts" blew over in 60 knot sustained winds and capsized. That brought about a lot of discussion about the Limit of Positive Stability for various yacht designs and apparently most cruising/racing boats have a LPS of between 110 degrees and 120 degress. Wingnuts had a LPS of between 74 degrees to 100.7 degress! Does anyone know what the Limit of Positive Stability is for a C-34? 

[2ndwish]

This link gives an approximation... LPS=Angle of Vanishing Stability

http://www.sailingusa.info/cal__avs.htm

My best guess at the specs in their tool puts it in the ~125 deg range...
T

[rondegroot]

When I purchased my C34 back in 2005 I asked Catalina for the stability figures.

They advised
Limit of Positive Stability 127 degrees
STIX  36.25

cheers
Ron
Mundora 1726 (2005)

[scotty]

WWhen I did the VAS calculation I got 133.  Another interesting source of information is the Catalina 34 FAQ, Measures of Seaworthyness: www.c34.org/faq-pages/faq-quantitative.html#CAPSIZE%20RISK
I really think that the main consideration for offshore capability has to do with preparation, not stability.  One interesting thread is: www.c34.org/bbs/index.php/topic,4378.0.html   Another is:  www.c34.org/bbs/index.php/topic,2034.0.html

I have read (but couldn't find it to give you the link) that a particular concern is that the scantlings and hull thickness of the Catalina 34 are such that there is an unaceptable amount of oil canning", or flexing, that occurs in the hull on prolonged ocean passages.  This can lead to a variety of problems, and is something that would be hard to fix.

Is the Catalina 34 a stable platform for offshore (or Chicago to Mac) passages?  Seems to depend on three factors:  Good preparation, Good seamanship and Good luck (Acts of God).

[Ken Heyman]

That's interesting Scotty, because I have often seen the Catalina 34 referred to as a "stiff" boat albeit generally not recommended for long ocean passages without modification.That said others have sailed the 34 on long ocean passages and evidently have had a combination of good preparation and good luck. BTW what are "scantlings" ?

Thanks,
Ken

[tonywright]

Despite all empirical evidence to the contrary, I see that everyone is using the "design weight"  of 12,550 in these calculations, rather than the actual measured weight of 16,000-17,000 lb.

It seems to me this has to have a significant impact on the rating! Depending on what numbers you put in for hull draft below the waterline (note that this has to exclude the keel), and how much weight you ascribe to the keel (presumably this exceeded its design weight goal as well), you can come up with a much higher stability number (upwards of 150). This would explain the stiffness of the boat.

Please stop using the 12,550 lb number. It simply does not reflect reality. Does Gerry have a revised number for the keel weight, or should we just add 25-30% in line with the general increase in weight?

On a similar note, we maybe need to be more careful to warn new owners about the real weight. It affects trailer and towing specifications, winter cradles, the size of a crane needed to lift it, etc. All of which could lead to dangerous situations if undersized. How about creating  a revised spec sheet?

Tony

[Ken Juul]

I don't think the keel weighs much more than the specified weight, the weight of lead is known.  I think the extra comes from the solid fiberglass/resin used in making the hull.

[scotty]

I used a 1500 lb figure to plug into the formula (that's why the number I got was 133).  From wikipedia:  "In shipbuilding, the scantling refers to the collective dimensions of the various parts, particularly the framing and structural supports."  I've always thought of this as the bulkheads, frames  and stringers making up the skeleton of the boat.  Particularly important is the manner in which they are attached, or tied together.  Catalina often refers, with some pride, to the structural "grid" that is the basis for hull integrety (look at the Catalina Yachts homepage).