[PUP] Scelenes vs Nordhavns

[Mark Tilden]

All good points and there's a great deal of difference between the
theoretical limit of positive stability in flat water and a boat in the
typical dynamics of even a relatively small sea.

The comments about protecting the large windows and securing things in the
cabins are also key because it doesn't matter how much righting arm a boat
has if it gets flooded from breaking out a 5-square foot window in the side
of the saloon and filling the boat up with water.

Several years ago, Bruce Schwab, who sailed the 60' "Ocean Planet" around
the world had to do a required righting test on the boat. They took the mast
off the boat and then with him inside and the cabin closed up, they
intentionally inverted the boat with a crane and straps wrapped around the
keel. They got it completely turtled in flat water in the Alameda channel.
The test required Schwab to be able to single-handed right the boat using
the moveable water ballast. Ocean Planet had a huge fin keel with a bulb and
an enormous limit of positive stability--in excess of 140 degrees. Yet, the
boat sat very nicely stable in a completely inverted position for at least
30 minutes (I don't remember the exact amount of time).

No boat will right itself in those conditions, but those conditions are not
typical because they were in absolutely flat water with nothing to encourage
the boat to begin to roll back over and develop righting arm. In typical
conditions, the waves and wind would roll the boat around enough to get it
righted very quickly.

The point is that, once again, there is a substantial difference between a
theoretical limit of positive stability and the conditions under which the
boat will actually right itself. I find it hard to believe that any modern
production trawler has a limit of positive stability even in the same
ballpark as ocean racing sailboats--most of which have stability ranges
around 120 - 140 degrees. That does NOT mean that the boat is guaranteed to
invert and stay turtled in anything over its LPS. It just means that's the
point at which the righting arm goes to zero and starts to be negative.

Just a bit of clarification on my previous note...

Mark




-----Original Message-----
From: passagemaking-under-power-bounces@lists.samurai.com
[mailto:passagemaking-under-power-bounces@lists.samurai.com] On Behalf Of
Keith
Sent: Tuesday, April 03, 2007 10:37 AM
To: Passagemaking Under Power List
Subject: Re: [PUP] Scelenes vs Nordhavns

The Krogen 42, at least my 1986 vintage is advertised to be self-righting 
from 110 degree knockdowns, e.g., the mast in the water. I personally have 
been over 45-50 degrees more than a few times. Has quite the tendency to 
scramble things around and show you how well you prepared (or didn't) for 
that trip. Other than that, she pops right back up.


Keith
_____
There are occasions when the Mate's opinion of sailing has some truth to it.
----- Original Message ----- 
From: "Scott E. Bulger" <scottebulger@comcast.net>

>
> I don't believe my 40 would survive a knock down (90 degree) roll and
> "recover".  Perhaps I'm not giving the boat enough credit, but the forces
> that would be at work on the superstructure, exhaust stack and mast,
> windows, engine vents, contents of the interior of the boat and so forth 
> are
> scary to consider.  I guess the righting moments are there in the 
> stability
> data, but physically what would happen inside the boat is really the
> concern.  Maybe someone can comment on the most extreme situations they 
> have
> encountered?
_______________________________________________

Passagemaking Under Power and PUP are trademarks of Water World Productions,
formerly known as Trawler World Productions.

To be removed from the PUP list send an email with the
subject "unsubscribe" (no quotes) to the link below:

mailto:passagemaking-under-power-request@lists.samurai.com

Passagemaking-Under-Power Mailing List