The New York herald., 1878-02-10
LECTURE SEASON.
PROFESSOR A. CAREY SMITH ON NAVAL ARcHI-
TECTuRv

froiessor A. Carey Smith gave his third lecture on
i"Naval Archtecturs' At Dslmonico's last evening,
before the members OF the seswanhsks Yacht Club
and their riendz This OF lectures u incrsas-
Ing In popularity every day, aud there was quite
l'rge attendance last evening Professor Carey
Smith, by way OF Introduction stated the subject
Tor the evenings lecture would 90 the calcust'ons
oil the areas aud centre OF effort Of saila Alter
briefly reviewing the remarks In the previous lecture
relating 10 displacement, centre OF gravity OF dis
Placement, centres OF gravity OF immersed ana
emersed wedges at ten degrees Of inclination
and lateral resistance, Mr. smith said:-"ro
make the system complete want 10 get the centre
OF effort Of salts nearly the lateral resistance Of
the huh Experience teaches that the centre o effort
Of sails should be forward Of the centre Of lateral resist
Ance from per cent to hGh lour per cont OF
length in small and wide boaIs. The of this
ls that the wider tho boat the more the water
line changes when inclined. and consequently the
more pressure the lee bow, which acts TO turn tho
boat from q straight course. On looking at the plan
before you Hnd that the sails are divided into
triangles by lines drawn from 10 the other,
all these calculations made by means oil TIL
angles First. 6nd the area OF a triangle by
multiplying the base by one-half the perpendicular,
Second, we and centre OF gravity OF triangle by
bsecting the base; producing line froin the biscc-
ton to the apex one-.hrd of the distance from
the dissection il the centre Of gravity centre OF
effort, as we call It when speaking OF sails. Third,
TO lind the centre OF gravity OF series OF bodies We
got the each and the centre OF gravity of each
multiplying the area OF each by the distance OF It's
centre OF gravity from point; that product Is
called the moment. The sum OF tho moments d.
vdod by the sum of the gives the common GEN.
ire OF gravity from the ixcd point This is precisely
ike finding the centre OF gravity OF displacement
cept that multiply the Of each by the
tnen multiply ths product by the distance between
the sections. This gives the same result with much
less figures, but the principle is the same"
CENTRE OF EFFORT OF SAILS.
Mr., Carey then said:-We will now pr occod 10 make
the calculation OF the centre OF effort the sails. Ho
then went over the pan showing how to get the
the jib and mainsail He then found The centre OF
effort OF the b, and from that explained how
tho moment OF the jib Alter obtaining the centres
effort OF the tranglcs on the mansa he drew lines
connecting these centres and showed at the point OF
tho centr OF effort OF me malnsuiL Mr.
Smith then said. "We now multiply the Of the
mainsa by the distance of the centre OF effort from
tho perpendicular the stem, and thus obtain the
momenl." AIter finding the area aud moment oil the
vide the sum Of the moments by the sum oil the
ana we have the common centre oi effort OF
The SAILS Next We multiply the urea Of each sail by
The perpendicular distance Of Its centre OF effort from
the water line the OF the moments divided by tho
sum OF tho urcas gives Us the height OF the centre OF
eIort from tho wafer line. The Of the suils mu-
tiplied by the height Of the entire effort from the
water IIne called the moment OF sails ana s very
useful IN proportioning sails, as We may make a high
nnu short ris low and long rig with the samo
momeIt, and in this way we know that the iorce
erted cureen the boat will be the samo III both
eases We may row 20 on and proportion the cuntre
OF eilort OF the reeed sails IN tho sane way as to
preserve the balance o. sail. This should always bo
done ana then we know that the boat will work
when it may be very dangerous try
experiments ana when the certainty OF knowing that
the boat Will work under short sail, will be worth
all tho trouble expended. When going through these
calculations jib we find the proper size OF the
bonnet r,cf and also fnd that the inboard end
OF the bonnet or rect must be higher than the
board end IN order that the sheet may pull at the
angle whom rceled when full sail is When
designing sails IN this way we shodid know where the
best place Is 70 put the mast as moving the mast u
short distance forward aft exerts great influence
the OF effort oil SAIL aui If put the mast
ait by the ordinary method-that Is tho mast must
be many feet from the bow because some other
boat has her mast III that position-we must make
up our minds 10 put very long ana consequently
heavy bowsprit to balance It when the thinxing
yachtsman makes calculation oil the moment oil u
nwsprilthat Is, the weight OF II multiplied by the
distance vi the centre OF gravity o IRON the
OF gravity oil splacement OF the 0oat-he Will hnd
that to the mast AFT over certain limits, be
add on The end OF the bowsprt about enough bal.
ance IT, ana is not surprised wnen he hnds that the
pitching movement oil the boat IL nearly much II
wus before he moved the mast AFT need not dwell
tact that long Uowsprt the most trouble
some thing in the boat ,oduKs care OF. We now
the wisdom OF the EastePh fsnermany who puts his
musts well forward, thereby gettbg u small jib aud
snort bowsprt, together with much larger area OF
sail on The same spars HIS mainboon may have the
sings right IN the middle, but that end OF the boat
easy 10 take care oil.
TRIMMING SHEETS
We now come u The proper method Of trimming
anced we will lose the advantage gained # not
get the sheets trimmed to proper angle. On the
deck plan We lay down angle OF Twelve degrees for
jib aud the forestaysAi II used, ought 70 be lald
down ut nine degrees The reason Tor this The
jD takes the true Wind and Will stand uIl the
Ioresay SAIL at the same angle VIII not be full therc
tUrc have TO bring II In. Tho mainss, being on q
traveller, can be trimmed 70 SUIT the jbs. In this
way know that tho sails trimmed q certain
auge ard can vary from experience teaches US.
Next We come to- the place where the sheet should
LEAD in order TO draw on both lssches alike, when
this not the the sail gets pulled too
much on one leech and slack on the other
~ where We think the Jb viii stretch
the stay, which Will be about tnroc the
length, ana do the samo on the loot allowing the
same percentage Describe arc with the len 9Th
the eech, with her percentage added as radius and
using tho tack Tor centre then describe another arc
with the length of the loot, with percentage added
radius aud head OF the ji0 as the contro, and from
where these arcs interscct Draw line a to pass
through the point wncre the clew will come when
stretched, and continue tho line to the sail deck,
and We have the proper line. II this line CONE out
Side Of the sail II marks the eDd oil the 0utrigger. Do
THIS Tor all the sails set on stay nnd we know that
our sails will stand wear alike. Where there two
parts to the Josheet TINS hnc should pass just be-
tween them, TO change the drec-
tion OF the pun. THIS method also applies TO gan.
topsais, sail, that hard to make by guess
work The distance from the jaws OF The gan " the
head Of the topnast Is blseced; line drawn IRON the
dissection to the place whore the topsaIl sheet 20
marks the ending vi the cew. This OF course Tor a
working topsail thai does not beyond the
gan next one-third OF the distance from tho
topmast head to the tOpsail sheet marx IL. line
drawn this POINT tue Of the mast, narks
tho line OF the tack. This arrangement ke the
tack aud sheet pull equally and draw eech as
tight q drum allow the other TO nutter and
worry the man at the helm. These remarks ay seem
out OF place here, but the speed OF Ooat depends on
her sails US much on the model, and no trouble
should bo spared TO make them perfect
Alter the lecture, which was thoroughly enjoyed by
the amateur sailors present, the party sat down
supper and finished the evening In sociabie aud
pleasant manner.
COLONEL INGERsoLL ON SKULLS.
Colonel Robert G. lngerso lectursd last evening at
Gilmore's Garden on 'Skulls: or, Liberty for Man
Woman and Child" 1t was tho same lecture with q
different titlo which the speaker delivered two
weeks ago In Chckering Hail. There more
Ihan TWO huudred persons present
Many people. said tho speaker, did not agree with
him, which simply proved he did not agree with