hi guys
my design accounts for the need to mount additional equipment and
possible salvage with the ballast requirements. Depending on the weight
being lifted and the depth option for blowing fdw soft ballast tanks or
dropping disposable ballast. the only time that the design became unstable
was when the soft tanks where too low in a surface condition and the
emergency ballast was dropped. rule one keep the weight low and the
flotation high. rule two soft ballast tank that are above water line do
nothing but suck HP air. for every one in the design stage, weight and
balance, center of displacement, running submerged and surface. is a
constant trade off.
one subject that has not been here for awhile positioning of stern
mounted thrusters. to avoid a pitch up or down condition under power. by
draging a tank model that is neutral buoyant hinged at the center of
buoyancy. one can determine the where to place the thrust center line.
rick m
----- Original Message -----
From: "Sean T. Stevenson" <cast55@telus.net>
To: <personal_submersibles@psubs.org>
Sent: Friday, March 03, 2006 6:43 AM
Subject: Re: [PSUBS-MAILIST]
Metacentric height can be explained in a pretty simple manner. If you
imagine a line drawn through the center of your vessel which passes
through CG, as your ship rolls, CB shifts outboard. If you subsequently
draw a vertical line through CB, it will intersect the first line (hull
centerline). This intersection is known as the metacenter, and the
distance between the metacenter and the vessel's CG is the metacentric
height. This is not a constant value, but rather a function of both the
angle of roll of the vessel and the shape of its hull. Metacentric
height is a useful measure for describing the amount of stability a
surface vessel has for any given angle of roll. For a submarine in the
submerged condition, it has less meaning, since CB is higher than CG and
the position of CB does not change, and hence the metacentric height is
constant, and equal to the distance between CB and CG.
-Sean
Jay K. Jeffries wrote:
In naval architecture terms, you are attempting to establish a low
center of gravity and and a high metacentric height (don't ask me for a
definition, its been years since I had the class ;-) ). You need to be
careful with George's explanation when the sub comes out of the water as
it might still roll over with the center of gravity just below the the
waterline as the metacentric height and center of gravity switch
positions. Buoyancy is no longer in the equation. You should strive
for a large separation between center of gravity and the meta centric
height.
Respectfully,
Jay K. Jeffries
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