2(36 
NAVIGATION, 
1. It the velocity of the current is lev? 
than the velocity of the ship, then the ship 
will get so much ahead as is the difference 
of these velocities. 
2. If the velocity of the current is greater 
than that of the ship, then the ship will fall so 
much astern as is the difference of these ve- 
locities. 
3. Lastly, if the velocity of the current is 
equal to that of the ship, then the ship will 
stand still, the one velocity destroying the 
other. 
Case III. If the current thwarts the course 
of the ship, then it not only lessens or aug- 
ments her velocity, but gives her a new di- 
rection, compounded of the course she steers 
and the setting of the current. 
The method of keeping a journal at sea, and 
fi:nv to correct it ; by making proper allow- 
ance for the lee-way, variation, jc. 1 . Lee- 
way is the angle that the rhumb-line, upon 
which the ship endeavours to sail, makes with 
the rhumb she really sails upon. This is oc- 
casioned by the force of the wind or surge of 
the sea, when she lies to the windward, or is 
close hauled, which causes her to fall off and 
glide sideways from the point of the compass 
she capes at Thus let NES'W (fig. 22.) re- 
present the compass ; and suppose a ship at C 
capes at, or endeavours to sail upon, the 
rhumb C a ; but by the f ree of the wind, apd 
surge of the sea, she is obliged to fall off, and 
make her way °;ood upon the rhumb Ch; 
then the angle aCb is the lee- way ; and if that 
angle is equal to one point, the ship is said to 
nuke one point iee-way ; and if equal to two 
points, the ship is said to make two points lee- 
way, &c. 
2. File quantity of tins angle is very uncer- 
tain, because some ships, with the same quan- 
tity of sail, and with the same gale, will make 
more lee-way than others; it depending much 
upon the mould and trim of the ship, and the 
quantity of water that she draws. The com- 
mon allowances that are generally made for 
the lee-way, areas follow: 
(1.) If a ship is close hauled, has all her 
sails set, the water smooth, and a moderate 
gale of wind, she is then supposed to make 
little or no lee-way. (2.) If it blows so fresh 
as to cause the small sails to be handed, it is 
usual to allow one point. (3.) If it blows so 
hard that the top-sails must be close -reefed, 
then the common allowance is two points for 
lee-way. (4.) If one top-sail must be hand- 
ed, then the ship is supposed to make be- 
tween two and three points lee-wav. (5.) 
When both top-sails must be handed, then 
the allowance is about four points for lee- 
way. (b.) If it blows so hard as to occasion 
the fore-course to be handed, the allowance 
is between bk and 6 points. (7.) When both 
main and fore-courses must be handed, then 
0 or tj| points are commonly allowed for lee- 
way. (S.) When the mizen is handed, and 
the ship is trying ahull, she is then com- 
monly allowed about 7 points for lee-way. 
3. Though these rules are such as are ge- 
nerally made use of, yet since the lee-wav 
depends much upon the mould and trim of 
the ship, it is evident that they cannot ex- 
actly serve to every ship; and" therefore the 
best way is to find it by observation. Thus, 
let the ship’s wake be set by a compass in the 
poop, and the opposite rhumb is the true 
course made good by the ship ; then the dif- 
ference between this and the course given by 
the compass in the binacle, is the lee-way re’- 
quired. If the ship is within sight of land, 
then the lee way may be exactly found by 
observing a point on the land which conti- 
nues to bear the same way; and the distance 
between the point of the compass it lies upon, 
and the point the ship capes at, will be the 
lee-way. d hus, suppose a ship at C is lying 
up NhW (fig. 23) towards A ; but instead of 
keeping that course, she is carried on the 
NN E line CB, and consequently the point B 
continues to bear the same way from the 
ship; here it is evident that the angle ACB I 
(or the distance between the N6\V line that ' 
the ship capes at, and the NNE fine that the ! 
ship really sails upon) will be the lee-way. 
4. Having the course steered and the lee- 
way given, we may from thence find the true 
course by the following method, viz. Let your 
face be turned directly to the windward ; and 
if the ship has her larboard tacks on board, 
count the lee-way from the course steered 
towards the right hand ; but if the starboard 
tacks are on board, then count it from the 
course steered towards the left hand. Thus, 
suppose tiie wind at north-, and the ship lies 
np within six points of the wind, with her lar- 
board tacks on board, making one point lee- 
) va } ' heie it is plain that the course steered 
is LN E, and the true course E6N : also sup- 
pose the wind is at NNW, and the ship lies 
up within 6f points of the wind, with her star- 
board tack on board, making ]i point lee- 
a) , it is evident that the true course, in 
this case, is WSW. 
^ e this general rule for finding the 
ship s true course, having t he course steered 
and the variation given, viz. Let your face 
be turned towards the point of the compass 
upon which the ship is steered ; and if the 
variation is easterly, count the quantity of it 
from the course steered towards the rmht 
hand, but if westerly towards the left hand ; 
and the course thus found is the true course 
steered. Thus, suppose the course steered 
is NnE, and the variation one point easterly, 
then the true course steered will be NNE; 
also suppose the course steered isNE/jE,’ 
aim the variation one point westerly, then in 
this case the true course will be NE: and so 
of others. 
Hence, by knowing the lee-way, variation, 
■and course steered, we may from’thence find 
the ship’s true course ; but if there is a cur- 
rent under foot, then that must be tried, and 
proper allowances made lor it, as lias been 
shown in toe section concerning currents 
fiom thence to find the true course. 
6. After making all the proper allowances 
lot finding the snips true course, and making 
<i> just an estimate of the distance as we can ; 
yet by reason of the many accidents that at- 
teim a snip in a day’s running, such as differ- 
ent rates of sailing between the times of heav- 
ing the log, the want of due care at the helm 
by not keeping her steady but suffering her 
to yaw and fall oh, sudden storms when no 
account can be kept, Sic. the latitude by ac- 
count frequently differs from the latitude by 
observation; and when that happens, it is 
evident there must be some error in the reck- 
omng : to discover which, ^id where it lies, 
and also now to correct the reckoning, you 
may observe the following rules: 
1st. if the ship sails near the niei’klian, or 
within S or 2$ points thereof, then if the lati- 
tude by account disagrees with the latitude 
by qbsej vation, it is most likely that the error 
lies in the distance run ; for it is plain, that in 
this case it will require a very sensible error 
in the couise to make any considerable error 
in the diffeience ot latitude, which cannot 
well happen it due care is taken at the helm, 
and proper allowances are made for the lee- 
way, variation, and currents. Consequently, 
if the course is pretty near the truth, and the 
e:ror in the distance runs regularly through 
; the whole, we may, from the latitude oblain- 
j ed by observation, correct the distance aud 
j departure by account, by the follow ing ana- 
i logies, viz. 
As the difference of latitude by account 
is to the true difference of latitude, 
So is the departure by account 
to the true departure, 
And so is the direct distance by account 
to the true direct distance. 
The reason of this is plain ; for let AR, fig, 
24, denote the meridian of the ship at A; and 
suppose the ship sails upon the rhumb AE 
near the meridian, till by account she is found 
in C, and consequently her difference of la- 
titude by account is AB ; but by observation 
she is found in the parallel ED, and so her 
true difference of latitude is AD, her true 
distance A E, and her true departure DE; 
then, since the triangles ABC, ADE, are simi- 
lar, it will be AB : AD •• BC * DE, and 
AB ; AD ;; AC i AE. 
Example. Suppose a ship from the latitude 
^4 45 20 north, after having sailed upon se- 
veral courses near the meridian for 24 hours, 
her difference of latitude is computed to be 
upon the whole 95 miles southerly, and her 
departure 34 miles easterly; but by observa- 
tion she is found to be in the latitude of 43° 
t0‘ north, and consequently her true differ- 
ence of latitude is 1.30 miles southerly ; then 
for the true departure, it will be, As the dif- 
ference of latitude by account 95, is to the 
true difference of latitude 130, so is the de- 
paituie by account 34, to the true departure 
4b.52, and so is the distance by account 
100 9, to the true distance 138. 
near the parallel of east and west, and the 
dilect course is w ithin 5-| or 6 points of the 
meridian; then if the latitude by account 
differs from the observed latitude, "it is most 
piobable that the error lies in the course ov 
distance, or perhaps Loth ; for in this case it is 
evident, the departure by account will be 
very nearly true ; and thence by the help of 
tim, and the true difference of latitude, may 
the true course and direct distance be readily 
found by case 4. of plane sailing. 
1 he form of the log-book and journal, to- 
gelhet w ii.h an example of a day’s w ork are 
here subjoined. 
I o ex pi ess the days of the w eek, we com- 
monly use the characters by which the sun 
and planets are expressed, viz. 0 denotes 
buiulay, ^ Monday, $ Tuesday, $ Wed- 
nesday, 1 hursday, 9 Friday, h Satur- 
day. ‘ 
