Vessel Stability
Try this for size in the recent thread on this topic.
Assume a hard chine trawler (often referred to as semi-displacement) w/no
external or internal ballast. We could call these the GB types.
Assume a soft chine, full displacement vessel with some amount of internal or
external ballast. We could call these Willlard, Krogen or Nordhaven types.
WKN's for short
Assume a 50 or 60 degree roll induced by whatever.
Given the above the GB types are going to turn turtle and assume a relatively
stable inverted position. The crew are going to perish.
The full displacement w/ballast types are going to return to an upright
position. The crew big eyed and speaking in tongues are going to hit the nearest
bar/church.
The point in all this is that the GB types really, really, really want to
avoide rolling greater than 45 degrees.
Perhaps somewhat simplistic but 'quite' accurate. Also largely supported by
the numbers that I so dearly have come to love.
Rolling On,.
chuck
I've not done any calculations on my Krogen 42, but the specs say she's
self-righting from 110 degrees. I feel pretty good about that, and hope I
never have to prove it!
Keith
__
If you think there is good in everybody, you haven't met everybody.
----- Original Message -----
From: SVWindigo@aol.com
Assume a 50 or 60 degree roll induced by whatever.
Given the above the GB types are going to turn turtle and assume a
relatively
stable inverted position. The crew are going to perish.
The full displacement w/ballast types are going to return to an upright
position. The crew big eyed and speaking in tongues are going to hit the
nearest
bar/church.
SVWindigo@aol.com
At 06:53 PM 11/28/04 -0500, you wrote:
Perhaps somewhat simplistic but 'quite' accurate. Also largely supported by
the numbers that I so dearly have come to love.
Anyone who plans on rolling their rig to some really extreme degree should
go have a quiet think somewhere and contemplate the strength of the
cabinetry. For even if the boat should achieve the not quite inverted
configuration and recover, you may still be awash in loose cannons.
In the Fastnet 79' disaster, many of the boats that were abandoned, did so
because of the equipment and interiors that had broken loose.
It does little good to prepare for a rollover by increasing righting
ability if the interior won't be livable after the fact. And the former is
easier to fix than the latter. What you can assume is that no matter how
well the interior is constructed there is always something that has been
overlooked, even in the best built and designed boats. Unfortunately
there are some very expensive rigs that have some presence in the
marketplace, whose interiors would not stand up to any seriously close
inversion. Still, it is a worthwhile mental exercise to think these
processes out.
Regards,
Mike
Capt. Mike Maurice
Tualatin(Portland), Oregon
"Keith" kemmons@houston.rr.com
At 06:02 PM 11/28/04 -0600, you wrote:
I've not done any calculations on my Krogen 42, but the specs say she's
self-righting from 110 degrees. I feel pretty good about that, and hope I
never have to prove it!
This 110 degree stuff assumes the vessel hull, cabin and windows remain
intact and that insufficient downflooding (water ingress) occurs before the
righting potential is compromised.
I once had a boat that took 21 breakers clear over the top of the flying
bridge. If any one of them had broken out so much as a handful of window,
the boat's upright stability would have been destroyed in under 60 seconds.
I think that if it came down to a live or die situation and the tradeoff
was increasing vanishing stability versus improvements in structural
integrity of cabin, windows and prevention of down flooding I think I would
go for the latter. It's the total picture, not any one single math formula
that counts. I have had the 42' Krogen out in about 50 knots of headwind
and it is one tough boat, but I would worry about the windows. In any event
if you get into a bind and the boat has any specific weakness that makes it
vulnerable the prudent seaman is obligated to take steps to protect that
vulnerability. If practical, maneuver to avoid strikes upon the vulnerable
locations.
Regards,
Mike
Capt. Mike Maurice
Tualatin(Portland), Oregon
On Sun, 28 Nov 2004 18:02:30 -0600, Keith kemmons@houston.rr.com wrote:
I've not done any calculations on my Krogen 42, but the specs say she's
self-righting from 110 degrees. I feel pretty good about that, and hope I
never have to prove it!
Keith
The FAQ at http://www.his.com/~vann/KrgStuff/42trwlr.htm lists
as "range of positive stability" a figure of 85 degrees.
That is what I've always bragged about. :-) Where did the 110 degrees
come from?
--chuck
KK42-152
"Tusen Takk"
--
The only maxim of a free government ought to be to trust no man
living with power to endanger the public liberty.
- John Adams
Well heck. I don't know where that 110 degree figure came from... it's just
been stuck in my head for years. Two different sites confirm the 85 degree
number, so I stand corrected. Still a pretty good number that I hope not to
test personally!
Keith
__
There are three simple rules for making a smooth return to your slip.
Unfortunately no one knows what they are.
----- Original Message -----
From: "Chuck Shipley" shiplech@gmail.com
The FAQ at http://www.his.com/~vann/KrgStuff/42trwlr.htm lists
as "range of positive stability" a figure of 85 degrees.
That is what I've always bragged about. :-) Where did the 110 degrees
come from?
--chuck
KK42-152
"Tusen Takk"