Draft Survey _ Basic Concepts Part 1

Introduction to draft survey Basic Concepts

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Closed Caption:

welcome to this video about drafts away
well job services used to calculate
cargo loaded or discharge if it is
conducted in a right way the accuracy
can be within 0.5 percent of the cargo
well a job serving involves careful
reading of jobs taking into account all
the prevailing circumstances now let us
first understand about hydrostatic and
draft well draft at the center of
floatation is called hydrostatic draft
the center of floatation is the point
about which the ship trims so here this
is the vessel and this is the point here
about which the vessels trims so we can
say the vessel trends like this at some
point so the hydrostatic draft is the
draft at center of floatation and this
is very very important because all the
hydrostatic particulars like
displacement tpc that is turns per
centimeter MC pc that is moment to
change the trim by one centimeter lcb
longitude no center of buoyancy lcf
longitudinal center of floatation kb
that is center of buoyancy from key and
that is matter center transmeta center
and this one a longitude no matter
center so all the hydrostatic particular
in a ship stability booklet are
tabulated against the hydrostatic draft
and that is the draft at the center of
floatation and center of floatation is
the point where the ship trims so if the
vessel is that in key trim is 0 and the
draft is the
hydrostatic draft so in case of in kill
it is pretty easy to find initial
hydrostatic draft and from the table we
can also find the initial displacement
if you look at this table here suppose
drafts 3-meter we can find the
displacement as 5478 done similarly if i
have the initial hydrostatic draft so i
can easily find the initial displacement
know if I have some cargo and I load the
cargo like this the ship goes like this
so i have final hydrostatic draft and
similarly i can find the final
displacement all I know now that if i
have the initial displacement and I add
something which is the card why have
loaded or subtract if any i have
conception or I add something like if I
loaded some ballast also or loaded some
bunkers also i have the final
displacement and this equation is very
very useful i can easily find the
quantity of cargo loaded with this
equation and that is the basic principle
of drafts away so over object to is to
find the hydrostatic draft
well we need to read the draft from all
six positions and that means on the
forward port side and starboard side of
the ship port side and starboard side
and after also port side and the
starboard side the draft are read to the
nearest a centimeter that is that can be
seen
so these drafts are connected to the
center line so if i have the port side
draft and starboard side drive so i need
to take the mean of that
similarly if i have the port side draft
of midship and starboard side draft of
the midship so i need to take the mean
of that
and similarly to the art draft also
basically we need to correct the
opposite draft to the center line
however we have one more challenge that
draft marks are not exactly located at
forward perpendicular after
perpendicular or amateur due to the
shape of the vessel they are slightly
displaced sideways so for example here
is the forward perpendicular well
forward perpendicular is a reference
line and the dr mark here they artists
they are sideways displaced similarly
the off perpendicular is also a
different line the draft marks may not
be located off perpendicular but
slightly displaced laterally and the
midship marks are also not exactly at
midship so we need to apply Corrections
accordingly so the first collection is
called stem correction which needs to be
applied to forward raft so forward draft
must be dead
precisely at a forward perpendicular