447 / 868
N
A
v
I
G
the \Vaot of due care at ,he hel" by not keeping her
1I<.Jy, bu, (u!f<ring her to yaw and fall o!f; {uddcn
fiorms, when no accaunt can
b~
kept.
6c.
j
[he latitude
by ",couo! frequently di!fers from ,he lati,ude by obfer–
vatioo; and when chat happcns,
it
is evident (here mun
be (ome error in lhe reckoning; to difcover which, and
wberc
it
líes, and alfo how
tO
correa
lhe
rcckoning, you
may ob(erve ,he following rules_
1
n,
Ir. che Ihip raíl
atar
(he
meridian, or
within
2
or
2{
points
the~eof;
lhen
if
(he Jatitude
~y
aCCDunl
diCa·
grees wi,h ,he lati,ude by obferva,ion, i, is moll likely
lhac (he error lies in che difiance ruo ; for
it
is
plain
chat
in tbis cafe
it
wilJ
require a very (enúble error in
che
courre
[O
make any confiderabJe error in lhe difference
of la,i,ude, whieh eaonot well happen if due eare be
ta–
ken a' ,he helm, and proper allowances be made for t'he
lee-way. variatioo, \ and currents. ConfequeotJy
ir
Ihe
courre be pretty otar lhe trurh, and the error in the diC.
tallee run regularly ,brough the whole, we may, from ,he
lati.ude ob,ained by obf<rva,ion, correa ,he diltanee aDd
depart.reby aeeount, by ,he following aoalogies,
fJiz_
As
th~
di!fereoee of latitude by aeCOUD'
i,
to
lhe lrue
difFerence
of
Jatitude.
fo is ,he departure by aecouot
to
lhe true
departure.
and fo i. ,he direél dinanee!>y aeeOODI
to ,he true d ireét dinance_
The reafon ofthis isplain: for le\ AS
(N
0_.
33 .)
de–
note the meridian of ,he l)1ip a! A, and fuppofe ,he fuip
fails upon ,he' rhomb AE near .he meridian, till by ae–
coum fue is found in C, and eÓDfequendy her di!fereDee
of latitude by aceount is AS; bu, by ob(erva,ioo Ibe is
found iD the parallel -ED, and Co her true di!ferenee of
Ia,itude is AD, her Irue diflaDee Ar:, and her Irue de–
par,ure DE; then finee ,he triangles ABC ADE are
limilar, it will be AS : AD : : BC : DE, aod AS : AD
:: AC: AE_
EXAMPLE_ 5uppofe a ffiip from the lati,ude of
45~
~o'
north. after having f2iled
upon
fev,eral
co~rfes
near
the meridian for 24 l1ours, her difference
of
Jqlitudo is
compu'ed 'o be upon the whole 95 miles fou,herly, and
her departure
34
miles eaHerly; bu, by ob(er••,ioD Ibe
is
found
tO
be in
Ihe latilude of
430 10' nonh.
and
COD·
fequen,ly her Irue dilrerenee of latitude i. '30 mile. fou–
therly; ,hen for the <rue departure, i, will be, As ,he dif–
ference of latilude by 'accounl 9
S
is
10
Üle
!rue difference
of la,i,ude '30, fo i. the departure by aeeoun' 34'0 ,he
true departure 46 ,52, .nd fo is ,he dillanee by aeeount
100.
9
to .he true diílance '38-
2dly,
If
the eourfes are for .he moll part Dear ,he paral–
leI of eaíl and well, .nd ,he direél eour(e belwi,hin 5i- or 6
points of the
meridiao;
lhen if
lhe latitude
by
aceount
d'iffers from ,he obferved la,i,ude, it i. moíl prob.ble ,ha!
lhe (fror Hes in lhe courre.
or
difhnce,
or
perh"ps
both;
for in
this
clfe
it
is
evident ,
the
depanure
by
aceount
will be very nearly Irue; and ,heDee by ,he help of this.
and
Ihe true difference
oC
Jatitude. may
the
true cJurfe
and direél
di~anee
be readily found by
Cofe
4-
of
Plain
S.iling_
VOL.IrI N° 85-
t
A ToN.
39"
EXAM PLE . Suppo(e albip from tbe lati'ucle of 43 ° 50'
north,
ah a
havlng (diJed upon
fever21 courCes near the
porallel of eaH and well, for ,he fpaee of 24 hour., is
found by dead reekoning 'o be in ,he la,i,ude of
420
4
s'
nonh, and to
have
made ] 60
miles
of
weCling;
but
by a good obfe rva,ion ,he Ibip i. fouod 'o be in ,he lati –
tude of
420
3)'
north : R equired ,he "ue eourfe, and
di,eél dilhnee [ailed_
Wi,h ,he !rue diiferenee of latitude 75
mile.~.nd
de–
parture 160 miles, \Ve
0,,11
find (by
Ca/e
4-
o[
PlaillS.iI–ing) .the 'rue courfe ,obe
5640
53 '.W,
an¡l .the direl1
ddtal'ee
116-7
miles_
3dly, lf ,he eourfesare for ,he mon pu, nearthemid.
die of the qnadran" ·and ,he direél: eourfe wi'llin 2 and
6
points of
(he meridian; lhen the uror
lllay
he either
in
the
,::ourfe.
or
iq rhe diíhnce,
oc
in both. which will
cau(~. an
error bo,h in ,he di!ferenee of latitude and dep.r–
ture
i
to
correa: whicb, haviog (ound the true difference
of lati,ude by obferl'.tion, with-,bis, and ,he direél
di–
lIaDee by dead reekonióg, find a new departure (by
C.fe3.
of
Ploin Sailing;)
,ljen.haIL the fum of 'his.departure,
and ,ha! by dead reekoning, \ViII be nearly equal
'o
,he
Ulle
depanure
j
aod
eoofequently
with
this,
and the
true
di!ferenee of latitude, we may (by
Cafe
4,
o[
Plaln ,Sail·
ing)
fiDd ,he <rue eourfe and diHanee_
EXAMPLB _Suppofe .lbip,from the la,i,ude Df
44038'
nortb,
fails
between
routh and eaCl upon, fel'eraJ
courfes,
nearthemiddle "f,hequadrant, for the (pace oC 24 nours,
and is ,hen fouod by dead reekQniDg_'o be in
th~
lalitudt>
of 42°
J
5'
north, and 'o have made of ea.íling -136 miles;
bu, by obfervationnle i. found 'o-be in ,he lati,ud..-of 42.
04' porth: Required her true eou rfe
aD~ dill~nee.
Wi,h the !rue diltaDce of lalitude .)
S
4
miles,. Qnd <he
direa diílanee
by
dead reckoDing t
97 _
4, you \Vill6nd (by
CoA
3-
o¡'Plain Sailing)
,he new departure to be 123-4,
and haJf the
(um.oc.,hi. and ,he departure
by
c;le,iJ ree·
koning will be t 23 -7 ,he "ue departure
I
(he. witb ,his,
and the <rue di!ferenee of latitude, you will finQ·(gyf.''!fo
4-
of
PI.inSailing)
,he Irue cour(e tO be
S'
3")0-00' E.
and ,he d..eél dill.oee 198.2 miles_
7
In keeping • nlip'.. .recko.ning
ot
fe., Ihe common
metllod is ' o take .from the 'IDg-board tHe feveral eourfe.
and
diíla~ee
• .lI.emmed by ,he Ibip
1.11
24 hQurs,
~nd
,o
tran,fer ,hefe ,ogethei wi,h the mofi remarkable oecur·
reneu in,o the log-book,-into which .al(o ale inlerted ,he
courfes eorreéled, and ,he dilferenee of lati,ude 'Dd dif–
ferenee of longi'ude
m.degood upon eaeh ; ,heQ ,he whole
day's ,'ork being finilbed in ,he log-book, if the la,i,ude
by
account agree
wilh
lhe
latilude by
obfervalÍon,
the
Chip'.
place will be ,ruly determined; if no" then .he r«kon–
ing muíl be eorreéled aeeordinl: 'o ,he preceding rulea, and
pl aeep in the jourD.I.
The form of ,he Log-book and 10urnal, logether wi,h
an example of 2 days work; you have here fubjoined _
Note, To expre(s ,he day. of the w«k, ,heyeom–
monly u(e the eh.raélers by whieh ,he (un and plaDe"
are expreíTed.
,lizo
0
denotes
SUlJda)
,
C.
Mondt1),
c!
Tuifdoy,
~
Wednefdoy ,
'l/.
Thur[d.),.
!j!
F,iday,
and
9
denotes
So/urday.
5 F
The