[PUP] PUP PPM *Stability*

[Scott E. Bulger]

Perhaps this is better as a subset of a broader DESIGN category, but since
its generated significant comment, lets discuss it, and use this topic as
a way to further define how we will discuss the issue and reach conclusion.



First, lets start with a broad statement of the issue:





Stability:  A Passagemaking vessel is likely to encounter conditions that
are significantly more challenging than boats operating closer to local
harbors and ports.  Distance from port, fast moving hemispherical weather
systems or rapidly developing (not forecasted) weather systems may be
encountered at sea, where there is no opportunity to seek refuge.  Therefore
we need to define the stability requirements the vessel will be designed
around.  Rather than re-invent the wheel,  I would propose we research what
standards exist for various levels of seagoing classifications for
commercial vessels.  Understanding what international design standards are
applied to commercial vessels will enable us to assess the applicability of
those standards to our target market, and select the most appropriate level
of stability, then incorporate that into the design standard.



Roll Over Survivability:  Obviously a vessel can be constructed to survive
complete 360 degree roll overs and continue operations.   USCG Lifesaving
boats are a good example of this capability.  However, significant
compromises and cost are incurred by holding a vessel accountable to this
degree of stability or roll over survivability.  Perhaps we should ask the
following questions:



a.        Are there ANY current production Passagemaking trawlers that will
survive a 360 roll over and be able to continue operations?

b.      Are there ANY current sailing vessels that achieve this objective?
Most capsizes I have seen result in loss of the sailing rig, but perhaps the
vessel can continue under power?  Are there standards that describe the
components necessary to achieve this design goal?

c.       As a group, do we believe it is a REQUIREMENT to have a vessel
survive a capsize in an operational state?



As far as Im concerned Id summarize my feeling this way:  If the vessel
can be designed to a high degree of stability at a reasonable cost I would
rather put money into that effort than to put funds into survivability that
might cost 2 or 3 times more than making the boat more stable.  In other
words Id rather put in a pound of prevention than 10 pounds of cure.  Our
only experience with significantly rough conditions was our broaching in
Nicaragua.  We attempted to enter a harbor but the channel has moved about =
mile along the beach.  We were caught by a set of significantly higher than
average period waves and the boat broached.  As the bow buried in the
trough, the stern swung parallel to the trough and the boat healed over to
about 45 to 50 degrees.  As the wave moved under us the boat snapped back
from the roll and we easily turned back out to sea before the second and
third waves arrived.  Had we been another few hundred yards inshore and the
wave had been fully breaking rather than just foaming on top I believe the
boat would have capsized.  Regardless this demonstrates to us that a high
degree of roll stability is desirable.  At what point it becomes an effort
of diminishing returns is not clear, I just dont have enough experience.



I would like to go read what Dashew  has contributed on the subject, because
he clearly has decades of experience to draw from.



In  summary, comments on the degree of stability needed, and the amount of
effort that should be expended on roll survivability should be contributed
and summarized to reach a consensus.