This post is on popular demand --
Instead of re-inventing the wheel, i will just put an actual email to my company.
You read what follows and everything becomes clear.
Be careful, most inspectors ( PSC / Vetting etc ) who come on board
to test your knowledge on Damage Stabilty are themselves ignoramuses
on this subject.
-----
From: XXXX MASTER
Date: Sat, 2 Oct 2010 19:48 +0100 Msg: A03153-23810
Subject: XXXXX/ DAMAGE STABILITY THOUGHTS
gentlemen,
i need to step in - as we are getting paranoid about damage stability --
we do INTACT stability calculations on board merchant ships -- most
important for ships whose cargo can shift -- like copper ore
concentrates and grain.
to prevent grain from shifting -- ship is allowed MOLOO ( more of less
owners option ) by charter party , so that ship can avoid slack holds.
DAMAGE stability comes into play in case ship's hull gets a HOLE due to
an accident/ grounding .
ETAS calculates "survival capabilities" of ship -- if master will tell
them :--
1) where the hole is
2) which all compartments sea water can ingress .
damage stability is NOT like grain loading intact stability calculations
, we do for AMSA and NCB prior loading cargo -- for the WORST
condition where all slack holds cargo has shifted to its max extent --
on any chemical tanker there will be about 40 load intact CONDITIONS --
as is usual in the ship's stability book.
now--
for each of above CONDITIONS there will be atleast 30 DAMAGE
CASES --
example -- assumed grounding damage CASES :
case no 1:- bottom raking damage and ingress to forepeak and no 1 cargo
tank port side
case no 15:- side damage at bridge front to no 10 COT port , ballast
pumproom
case no 22:- side and bottom damage to ER ( with permeability ) and HO
tank port
case no 29:- bottom damage to after peak tank , and steering gear.
etc etc
this amounts to several hundreds of permutations and combinations for a
ship without a class approved damage stability programme in the
loadicator --
for damage stability ballast conditions are NOT considered.
this info is what we send to Class ETAS after every dep load port--with
permeability's . for ETAS to use their software and calculate :--
1)residual dynamical stability ( area under curve > 0.0175 m rad )
2)righting lever range ( min range 20 deg beyond posn of equilibrium
plus GZ >0.1 mtrs within 20 deg range )
3)max angle of heel due to unsymmetrical flooding ( < 25 deg or 30 deg
in case no deck immersion happens )-- and assess survival capabilities
and give advise.
ONLY WHEN THE HULL GETS A HOLE -- read this twice--
ONLY WHEN THE HULL GETS A HOLE --
if you insist to Class that you want damage stability calculations ,
without a hole -- this will be greatest joke of the century for them --
they will have a nice laugh over saki and sushi--
we stick to approved loading patterns or CONDITIONS given in the
stability book-- on usual ships --but NOT parcel tankers.
ON "PARCEL" TANKERS --
AAA) WE ARE CAREFUL WHEN THE CARGO IS OF VERY HIGH
DENSITY -- GREATER THAN DENSITY 1.7 .
i had once carried dead sea drilling brine salts of > 2.0 density for
XXXX --if you are NOT careful ship will capsize or even
break her tanks during rolling.
BBB) WHEN TOO MUST CARGO IS LOADED TO ONE SIDE OF
THE CENTRE LINE -- THAT WE DO NOT HAVE ANY
POSSIBILITY TO CORRECT THE LIST WITH BALLAST ,
AS ALL COUNTERACTING BALLAST TANKS ARE ALREADY
USED UP. AND YOU CANT EVEN JETTISON CARGO DUE
TO ITS NATURE--
this is the reason why in the stowage plan attached-- i PERSONALLY check
out the LIST created by cargo-- to caution the mate-- when he gets it
all wrong due to tunnel vision.
having said all this -- the botttom line is -- you need a blessed hole
to DAMAGE an INTACT ship.
brgds
capt. ajit vadakayil
MASTER
XXXXX
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