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Of
particular interest is the floatation level of hatches, dinghies,
and the companionway door into the saloon. Note that except for
the leeward coamings and the vent cowls attached thereto (which
have closure plates operable from inside the boat) the rest of the
gear and openings are well above the floatation waterline.
Of
equal interest is the flotation plane of the bow and stern. The
stern is still significantly more immersed than the bow, and given
the fact that the center of resistance of
the deck edge and house are aft of amidships, we expect that the
hull would still maintain a favorable bias of bow down the wave.
Our
best guess is that unless we messed up with a truly horrendous breaking
wave - a maximum case of operator error coinciding with being at
the wrong place at the wrong time - we're not likely to ever see
more than a 90-degree heel angle (we'd be a lot happier with a maximum
of 20-degree heel too!). The odds of being totally upset, to the
point of vanishing stability, we think are minuscule. Still, we
like to plan for the worst. Towards that end we study what the boat
looks like in a fully capsized condition. In the next series of
images we've got the boat at a 135-degree flotation plane.
Let's
get the worst of this over with at the beginning. We've seen photos
of fishing boats in this attitude, before they went down. It is
enough to send the shivers down anyone's spine. Yet we want to know
that we can capsize to this position, and with a little luck come
back upright with the boat still watertight.
The
first concern we have is with the engine room vents. You will recall
that these are located in the breakwaters at the aft end of the
deck. Take a close look at the submerged corner of the hull, and
then follow the waterline up the transom. Notice how the top edge
of the breakwater, closest to the centerline (to the right of the
image) is just barely submerged. The down pipe for the air vents
runs deep down into the engine room, towards the hull bottom, and
in this heel angle is many feet above the flotation plane. Bottom
line, we would not expect any more than a couple of buckets of sea
water in the engine room (and the vents are sealable in bad weather).
Another
question is the depth of submergence for the door into the saloon
and deck hatches. The deeper they sit, the more hydrostatic pressure
they are going to feel. You can see that the water tight door into
the saloon at this angle has a maximum depth of three to four feet
(900 to 1200mm). That's a minimal amount of hydrostatic pressure.
The depth of the deck hatches is even less.
Checking
the bow/stern trim relationship again we still have more resistance aft than forward,
especially when you consider the twin wing masts, which are now acting as huge
daggerboards. So we would expect that the bow would still be preceding the stern
down the face of the wave. 
In
spite of all the preceding images and copy you've just read, we
do not dwell on these issues when we're cruising. We make them the
bottom line in our approach to yacht design, so that we don't have
to be concerned when we're offshore.
After
writing and reviewing this section the two us began to compare (again)
the heavy weather capabilities of this design and that of Beowulf
and Sundeer. We think the Unsailboat will be a lot easier
to handle - no sails to change, trim, or worry about. Slow speed
steering characteristics, while heading into breaking seas, should
be substantially better. Off the wind, running with the waves, our
control will be at the very least probably better than Sundeer,
and equal to or maybe a hair less than Beowulf. And in a
capsize scenario, we think the new design will do a lot better.
Of course, we've done everything possible to give us the tools to
avoid capsize risks in the first place.
In
closing we'd like to ask you to keep in mind that dangerous weather
is rare. If you practice good seamanship, stay ahead on maintenance,
and take care in choosing your passage weather, the odds are minimal
of hitting condition that could cause real problems. In all of our
cruising to date, we've been exposed to less than 24 hours of weather
that could potentially pose a danger to this boat if it were disabled
or mishandled. We like these odds a lot more than what we face coming
back from the movie on a Saturday night and worrying about drunk
drivers.
For
related info, see Surviving the
Storm pages 608-621 (Design Factors), and pages 628-631 (Powerboat
Design). Also see Offshore Cruising
Encyclopedia pages 407-421 (Cruising Design).
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