THREE DIMENSIONAL
LIFEBOAT LAUNCHING
A Thesis Presented for
the Degree of Bachelor
of
Science
in
Naval
Architecture and Marine
Engineering
By
Arthur Lewis HasklnB
Renata
Paul
Iodice
Class of 1935
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
Cambridge, Massachusetts-MAy
16, 1935
TABLE OF CONTENTS
Page No.
Letter of Transmittal - - - - - - - - - - - - - - Acknowledgements _0_
2
Introduction -
3
Purpose -
3
Method Persued - - - -
3
1
History - - -
5
Application -
7
Design - - - - - - - - - - - - - - - - ~ ~ - - - -
12
Theory - - - - - - - - - - - - - - - - - - - -
12
Choice of ~oat - - -- - - - - - - - - - - - - - 13
General Layout - - - - - - Motion - - - - - - - - - - - -
- - -
13
- - - - - -
14
-------Tension in Cables --- -----Bending Moments - -------Twisting Moments - - - -Compression in Arms - - - - -----Diameter of Arms - - - - - - - - - - - - - - -
Load on Arms
Size of Cables - - - - -
14
15
15
15
16
16
- - -
10
Results - - - - -
- - -
18
Conclusions - - -
- - - - -
19
- - - - 21
Data - - - - - - - - - - - Bending Moments - - -
--------
21
Twisting Moments - - - - - - - - - - - - - - -
22
Compression and Tension in Arms - - - - - - -
25
Tension in Operating Cables -
27
Calculations - - - - - - - - - - -
- - - - - -
28
TABLE OF CONTENTS (CONTINUED)
Page No.
Load on Arms - - - - - - - - -
- - -
28
Tension in Fixed Length Cables - - - - - ~ - ~
31
Arm Diameters - - - ~ - - - -
32
Plates and Bending Moment Diagrams
- - - - - - -
- - -
Appendix
1.
Mass. Institute of Technology
CambrIdge, Massachusetts
May 16, 1935
Professor James R. Jack
Mass. Institute of Technology
Cambridge, Massachusetts
Dear Sir:
In accordance with the requirements in application for
the degree of Bachelor of Science in Naval Architecture and
Marine Engineering, we are presenting a thesis which we have
truly entitIed "Three Dimensional Lifeboat Launching •.
"
We wish to call your attention to the radical change in
method of launching whinh the title indicates, the complications of design which it involves, and the difficulties in
lifeboat launching which it overcomes.
Though we claim no credit for the fundemental idea, the
three dimensional principle, the design, when taken up as
thesis work, had no foundation but its fundemental idea and
the principles of engineering mechaniBs.
The degree of fine-
ness to which the design is carried was Bubject to restriction
due to limited time, though the attempt was made to complete
all working plans.
Sincerely yours,
<
,!
\
\
j
12,
ACKNOWLEDGEMENTS
We are'grateful to the following men for aid given
during the preparation of this thesis:
To
Mr. F. Forrest Pease for the fundmmental
principle on which the thesis is based,
Mr. C.B. Palmer for making available the
clippings from the Boston Transcript files
on Marine disasters,
Professor Evers Burtner for miscellaneous
technical information.
A.L.H.
R.P.I.
INTRODUCTION
INTRODUCTION
PURPOSE.
The purpose of this thesis is to introduee
to the naval architectural world the value, principle, and
design of the Pease Lifeboat Launching Crane.
METHOD PERSUED.
Herein is briefly outlined the method
used in the working out of the design.
A more detailed
explanation is found in the section under Design.
Before starting the actual design work, it was necessary
to determine how much had been done before us.
to be nil.
This proved
Therefore, to have a practical basis , a thorough
perusal of all clippings from the Boston Transcript files
on marine disasters was undertaken.
~rom these were taken
the faults of the present equipment which were listed as
factors to be eliminated in the new design.
As tn8 type of lifeboat launching equipment cannot be
a stock unit, but must be custom built, it next remained to
choose a boat for which to design the apparatus.
The S.S.
Colombia, a Ferris design, was chosen both because of its
common type and because of the adaptability of the apparatuB
to it.
In order to give the initiate to this new principle a
clear idea of how it works, a drawing was made of the midship portion of the Colombia, showing the launching of a
lifeboat in three views, accompanied by a fourth supplementary
diagram. (See Plate I)
Due to the extreme complications in direction of cables
and arms, it was considered advisable to draw in fouu views
the complete motion of
a
single arm, and as far as possible,
obtain all data graphically from these drawings (See Plate
II).
This plan was carried out in obtaining all the forces
and moments "inthe arms and cables.
The bending moments were taken or resolved into two
perpendicular planes and combined. into a resultant benling
moment, which was in turn combined with the twisting moment
by Rankine's theory.
The result, along with the total
compression and an assumed fiber stress, was used to get
the varying diameters of the arms.
United states Standard tables in Mark's handbook were
used to estimate the size of cables.
HISTORY
HISTORY
The idea behind the Pease Lifeboat Launching Crane is
not a brainstDrm brought on by recent marine disasters.
It
followed six years of sea experience from 1909 to 1915.
In
the latter year the idea was presented to leaders in marine
fields and received considerable encouragement.
WilliansAnthony
Dr. Alfred
of Lewiston, lmine was desirous of backing
it and had the money to do so.
To make sure of the ground
on which he trod, Dr. Anthony requested Professor Peabody
of the Massachusetts Institute of Technology to look into
the idea.
Professor Peabody's report showed the idea to be
sound and wxtremely worthy of development.
With Mr. Pease as engineer and Dr. Anthony as manager,
the idea grew.
A
steamer at Portland was chosen as a suit-
able subject, and designs were started for installation
when Mr. Pease was forced to abandon the work due to illness.
By 1916, Mr. Pease was again on the trail of a backer
for the idea.
This led him to the Fore River plant of the
Bethlehem Steel Corporation.
Rush of war construction pre-
vented any immediate action on the lifeboat launching crane,
but Mr. Pease was taken on as superintendant of apprentices
in the yard.
Soon after, the United States Shipping Board
ordered him to Philadelphia, not to return until after the
War.
In 1921, Fore River again attacked the lifeboat launching
problem.
The technical staff was instructed to examine the
idea, and considerable amount of study and preliminary plans
were made.
The investigation showed that a great deal of
money was needed for experimentatio~ and the management, though
realizing the value of the idea, decided that it didn't care
to go into the development.
From then on, ,the idea bounced. from shipyard to ship
owner, fromshlp
owner to Steamboat inspection ~ervice, and
from Steamboat Inspection Service back again.
The shipyard
couldn't develop the apparatus for lack of money.
They were
willing to install one should the owner desire it, but only
under that condition could they see the value to themselves.
The shipowner was satisfied with the existing equipment as
long as it was passed by the Steamboat Inspection Service,
and the latter had no money or authority to do the developing.
They said that they would gladly pass judgement on the
apparatus if it were installed an some ship.
This leaves only two sources of backing for the idea,
the government and a private investor.
The latter is looking
for a minimum of risk with a maximum of return, and the very
nature" of the apparatus fails in this qualification.
At present, the government is extremely interested.
Recently, Mr. Pease demonstrated his model and showed moving
pictures of this model launching model-lifeboats
experimental tank of the Massachusetts
into an
Institute of Technology
before the members of the United states Steamboat Inspection
Service.
They were greatly impressed, and Mr. Pease now
awaits a report from the chairman, l~. Dickerson Hoover, as
to the success they have had toward getting appropriations
for the project.
Assisting 1~. Pease in Washington is
Congressman Wigglesworth who is an enthusiastic advocate.
In addition, the newspapers have been big aids in helping
the idea to gain the approval of the public and professional
men which it now has.
APPLICATION
7
APPLICATION
The Court of Inquiry Report on the Titanic disaster,
made in August 1912, stated that at sea there was but one
death in every 800,000 passengers carried.
This does not
impress us with anything but its insignificance as a figure,
but its insignificance is confined to the field of mathematics and does not trespass on the human side of the question.
When nine out of ten of these deaths 'are due to faulty
machinery or inadequate machinery, it remains for the engineer to answer the cry of the indignant public.
The public cry is naturally heard the loudest immediately
following a spectacular disaster.
It rose in volume following
the sinking of the Titanic in April 1912.
Two years later,
the collision of the Empress of Ireland and a Danish tramp
with a consequent loss of life of more than 1000 persons
gave rise to another public outburst.
In May 1915, it was
the sinking of the Luisitania, in 1928 it was the Vestris,
today it is the recent Ward Line calamities that have roused
humanity.
As engineer~we
are interested in the lesson from each
of these calamities.
From the Titanic disaster, we learn
that it is perfectly feasible to launch all boats safely
under perfect conditions with the ordinary boat davits.
This
is important as a contrast to the success of the operation
under distress conditions.
When the Titanic sank, the sea
was perfectly calm and the ship sank by the head without
listing and slow enough to give everyone plenty of time to
get away in the boats.
The greatest reason for loss of life
in this case was the lack of sufficient lifeboats and reluc-
8
tance of passengers in leaving what they were lead to believe
was an unsinkable ship.
Excellent conditions are abnormal
rather than norma~ and as we are looking for difficulties to
overcome, the sinking of the Titanic is not of such importance.
Though no detailed information is available on the fate
ofthe Empress of Ireland's complement, it is suspected that
this disaster can be classed with the Titanic.
When the Luisitania was torpedoed off the Irish coast,
the American public was too busy directing its indignation
toward the Imperial German Government to ask why, when given
15 minutes to abandon ship, nearly 1200 persons found no
means of safety at hand.
Here we learn the lesson of speed
and efficiency that is not associated with the age old block
and tackle principle used in existing lifeboat davits.
In the sinking of the Vestris off the Virginia Capes in
1928, we learn several things about lifeboat launching.
weather was extremely bad.
The
The ship had a list of about 150
as the boats were being lowered.
The Vestris carried 14
boats, plenty to accomodate a~l 328 persons aboard from
either side of the ship.
T~e following table, showing what
happened to each boat, gives an impressive pfcture of what
this thesis is trying to eliminate.
-Port side
Boat #2 - Stayed on deck and sank with ship.
#4 and #6 - Lowered part way with women and children
but never &aunched, and went down with ship.
#8 - Launched but sank because of damage in launching.
#10 - Successfully launched with all passengers and
no crew.
Tackle ch~pped.off block because of
entanglement.
9
#12 - Remained on deck and sank with ship.
#14 - Remained on deck and floated off as ship
sank and remained afloat.
-Starboard side
Boat #1,3,5,7,11 - Successfully launched.
#9 - One end lowered before the other and sank.
#13 - Floated off deck and remained afloat.
Out of the total of 14 boats, 8 got away safely with
218 people.
Of these 8, two were never launched but floated
off the ship empty as it sank, and still another had to be
chipped loose from the blocks as it hung loaded from davits,
and was thus prevented from beiug dragged down with the ship.
The port side was the windward and high side.
The effect
of list is plainly shown by the table, but eKen on the low
side, two of the boats failed to get away.
It took two hours
to launch the boats on the high side.
Trouble with the releasing gear was shown in a statement
by the chief engineer, Mr. Johnson.
He said that the releas-
ing equipment broke in two instances and that there was no
instance when it operated successfully.
Now we come to the present, the recent Ward Line calamities,
of which the burning of the Morro Castle is the most striking.
Out of 12 lifeboats, each with a capacity of from 50 to 80
persona, only 8 got away, some of them carrying as few as six
people, mostly crew.
We find here that the windward side of
a burning ship is the only possible side from which to launch
lifeboats.
When tremendous seas hurl their force from that
quarte~ the problem of boat launching becomes exceedingly
difficult.
These few major disasters cause but a small part of the
10
toll of deaths at aea, however.
They are the ones we read
about in the newspapers, but we do not look behind the scenes
of smaller incidents of the same sort where numbers of persons
are lost in one sweep.
Captain Fried lost two men and five
boats attempting to rescue the crew of the Antinoe in January 1926.
He stood about 80 hours before daring to launch
a single boat.
'Vhen the Monroe and Nantucket crashed in
January 1914, 49 men drowned because ten minutes were not
sufficient to launch the lifeboats.
A whole fleet of ships,
standing by the Volturno in ~d-ocean
all day, October 13,
1913, watching her burn to the water's edge, unable because
of the high seas to be of any assistance.
136 lives were
lost, all of which were lost in attempts to get away in the
ship's boats.
And so on through volumes and volumes with always the
same story
"calm water enables all boats to get away
safelyr or
"heavy sea conditions prevented proper mani-
pUlation of launchlng eqUipment."
In other words, the
design of launching equipment should include all the factors
possible for the elimination of each of the defects in present
davits.
The most important of these factors are listed
below:
1. Long outreach to enable launChing on windward side
and against a list.
2. Single motion with one man operation for efficiency
and speed in operation.
3. Launching under motion for immediate steerage way.
4. Capacity to handle large boats for greater seaworthiness and for greater confidence from the passengers.
(This also enables more boats to be carrled on each
JI
side of the ship where desired.)
5. No rigid fastenings to llfeboats for immediate and
synchronous release when waterborne, and also to
enable boat to float free of sinking ShlP were it
not launched.
All of these factors, along with convenience, beauty,
and economy have been considered in the following design,
though compromises were inevitable in Borne instances.
DESIGN
I~
DESIGN
THEORY.
The motion described by the Pease Lifeboat
Launching Crane can be outlined very simply.
First, consider
as a horizontal plane, the plane of rotation (Plate II), with
a line perpendicular to it.
Around this line, rotating in
a semi-circle are two other lines in a plane perpendicular
to the p~ane of rotation which meet the latter plane in the
Bame point, one of which intersects the plane at an angle of
16° and the other at about 40°.
The 16° line is a steel
arm, and its angle with the plane of rotation is termed the
"droop" of the arm.
The 40° line 1s a fixed length cable
which holds the arm from drooping further.
Nww, take this
whole unit and place it alongside a vessel with the plane of
rotation perpendicular to the side, tip it up so that the
~lane of rotation makes about 45° with the surfac~ of the
water, and we have the motion described by one of the three
arms of the appa~atus.
Three of these unite with parallel
planes of rotation, and with the outer ends of the arms
rigidly connected, make up the launching device.
If the
description has been followed up to this point, the picture
now ie that of a parallel ruler in three dimensions, where
the rules are the ship and the rigid arm connection (Fig. 3,
Plate I).
The latter is the cradle in which the boat rests.
To control the motion of the apparatus, three operating
cables in the planes of rotation are fastened from the outer
end of the arms through sheaves and around a drum on deck.
The drum is operated by a winch to return the apparatus after
launching a boat.
It is also fitted with a hand or centrifugal
/3
brake to check the boat in launching.
To keep the cradle upright, nothing more than three
parallel pins is necessary.
These are perpendicular to the
plane of rotation and pin the arms to the cradles.
They
are the outer swivels of the parallel ruler.
Instead of using pins at the ship's side, a universal
joint is employed to allow the cradle to rise straight up
with a heavy sea in launching rather than twist off the pins.
CHOICE OF BOAT.
The S.S. Colombia was chosen as subject
for the design of the equipment for several reasons.
She
has a small enough complement of passengers and crew to
enable all to be accomodated in a single large lifeboat.
Her
freeboard is not so extreme but that the arms can be conveniently butted and swivelled at the ba~elof the superstructure.
This allows the arms to lie inside the outermost beam
of the vessel and prevents damaging from other boats or from
a wharf.
Also, the farther from the load line that the arms
are swivelled the longer they must be to properly place the
boats on the water.
GENERAL LAYOUT.
It was first desired to keep the arms
for this installation perfectly straight and about 40 feet
long.
However, it was found that straight arms would neces-
sitate cutting into all three of the upper decks to set the
boats inboard.
To eliminate this trouble the arms were
curved for about 8 feet of their length so that only the
boat deck had to be cut away under the lifeboat.
Were the arms limited to 40 feet in length, the angle
of launching would have been excessive.
Considering 450
/4
as a reasonable angle at which to launch, the arms were
drawn to about 47 feet in length.
The droop of the arms is determined by the height of
the arm butt at the ship from the load line.
The higher
this point is, the more droop is necessary in order to have
the boat waterborne at the outermost point of the curve.
A slight compromise was necessary here in that if the boat
were waterborne at exactly the outermost point, an arm 60
feet long would be necessary, other factors remaining the same.
The boat actually floats off the cradle at about 100 past
position #4 with the 47 foot arms.
In order to keep the twisting moments inthe arm at a
minimum, and angle of
450
was constructed between the plane
of the curved arm and the ship's side in #1 position (See
Plate II).
This causes the plane of the curved arm to be
perpendicular to the water in the waterborne position.
MOTION.
Plate II, showing the motion of a single arm,
explains itself, though it is rather complicated descriptive
geometry.
All N-B lines represent the fixed length cables;
all O-B-A lines, the arms; all B-B lines (Fig. 4 only), the
operating cables.
N-O shows the slant of the cradle pins
and the center-line of rotation.
LOAD ON ARMS.
There are three sources of load on the
arms: a static load, a dynamic load due to rollmng of the
ship, and a dynamic load due to checking the boat before
reaching the water.
These three were calculated for the
worst possible conditions and a resultant vertical load of
6.41 tons was determined.
The load was assumed constant,
though it actually was slightly less at the extremities of
/S'
the motion.
Several assumptions were made for the calculations
on the dynandc forces, but the forces themselves are so
· small in relation thethe resultant vertical load that Tariations in these assumtions hwe little effect on the result.
TENSION IN CABLES.
Plate III shows the settup for obtaining
the tension in the fi~ed length cables.
It is simply a case
of taking moments around the butt of the arm in position #1.
The tension in these cables is constant.
The stress diagram for finding the tension in the
operating cables is shown in Plate IV.
This is a settup
of moments in the plane of rotation, and due to the changing
angle between the cable and the arm, this cable varies in
tension.
#7 position was eliminated at this stage because
of an infinite tension in the operating cables.
stops
would prevent the arms from reaching further than #6 position.
BENDING MOMENTS.
With all the forces known, the next
step was to figure the bending moments due to each force for
different positions along the arm and for each position.
This was done so that all moments obtained lay either in
the horizontal or vertical plane. (The horizontal plane
here referred to is the plane of rotation.)
A plot of
vertical and horizontal bending moments was made and a
resulta~t bending moment diagram obtained by taking the
square root of the sum of the equares of the vertical and
horizontal oDminates.
a representative
The force diagram used is shown by
sketch in Plate IV. and also in Plate. III.
TWISTING MOMENTS.
Due to the curve in the arm, there
is a varying twisting moment set up by the load on the end.
Figure 3, Plate II, shows the true arm for the twisting
moment, but it was necessary to construct the auxilary
Ib
diagram to get the angles at which the load acta.
COMPRESSION IN ARMS.
In PlateI~
it can 'be seen that
the triangles O-B-B are isoceles in every position.
We
know the length of the arm to the cable fastening and can
measure the length fif the cable.
With these we can find the
base angles and therefor the compression in the arm due to
these cables.
Straightforward resolution of the tension in the fixed
length cables along the arm in Plate III gives the compress10n from this source.
theoompression
An ~uxiliary diagram was used ~o obtaim
and tension due to the load.
Algebraic addition
of the three forces gave the resultant compression.
DIAMETER OF ARMS.
Rankine's formula for combining twist-
ing and bending moments was used to obtain an equivalent
bending moment.
The theoretical value given by this equation
Is that sImple bengIng moment which, if applied to a beam at
the point in question, will give a fIber stress equal to that
due to twisting and bending both.
It was calculated for
every point of probable maximum as shown by the bending
moment diagrams.
Assuming a steel of yield point around 60,000 pounds per
square inch and a safety factor of two, the diameter of the
arm for every 15 feet of its length was calculated, using the
maximum equivalent bending moment.
The results are shown in
Plate V.
SiZB 6F CABLES.
It is noted that the tension in the fixed
length cables is 11.8 tons and in the operating cables, 12.1
tons.
This would call for aboat the same si~e cables, but
/7
but the fixed length cables must partially support the lifeboat as it is stowed and are not wound on any drum.
For
these reasons, a heat-treated steel cable is used.
The operating cables, on the other hand, take no load
until the boat is being launched and must be flexible enough
to wind on the winch drum.
cable.
This calls for an annealed steel
RESULTS
RESULTS
1. Details of Arm.
a. Hollow steel, Y.P. 60,000 Ibs./sq. in.
b. See Plate V.
2. Fixed Length Cables.
a. Plow steel, heat treated.
b. Carbon content, .90.
c. Diamete~ 1 inch.
d. Ultimate Btrengt~50
tons.
e. Safety factor, 4. (Based on ultimate strength.) -
3. Operating Cables.
a. Monitor. plow steel, annealed.
b. Carbon content, .82.
c. Diameter, 1 inch.
d. Ultimate strength, 50 tons.
e. Safety factor, 4. (Based on ultimate strength.)
CONCLUSIONS
,
.
'7
CONCLUSIONS
The three factors for presentation by this thesis are,
as stated in the purpose, the value, principle, and design
of the Pease Lifeboat Launching Crane.
It was essential to
cover the first two thoroughly before attempting the last.
As a result, the last was left dangling near the end.
However, the hard part of the design is done, the part
that takes the ~settin' and thinkin'
It.
With the arms defined
both in siz~ and motion, it is but a routine machine desIgners job to layout
drawings for fittings, and to make up a .
suitable cradle.
With no basis for comparison, it is hard to define the
limits of reason, but the dimensions as calculated for arms
and cables seem to lie within this range despite the lack of
any parent design from which to work.
Where so many consider-
ations are necessary, mistakes or omissions are not impossible
either in assumptions or calculations.
There are many special considerations.
One is a ram on
the promenade deck at the position of the buffer as shown in '
Plate II to force the 'apparatus outboard against a list, and
to hold it there in spite of the ship's rollIng.
Another is
a catch device to take the load as the boats are stowed.
In
other words, there are any number of refinements that are
out of pkace in this pioneering paper, but will develop' with
the idea.
Itremains that the three dimensional principle applied
to lifeboat launching has all the advantages neceasary to
Supplememtary Conclusiens
I.'addi tieD to the cGlIcluaisns abo'Ye, there" are 'Yarim s
eensideratiens as to applieation aad operations. Te i.stal
this apparatus abeard a ship er the t1:MorroCastle" type
with her extremely high sides, it w~uld'be .eeessary to
built the arms dowa en her shell plates. This weuld be eut
of the questi,ollas the apparatus would be 'Yery easily
damaged by a ship eoming alongside Gr even by a d04k waeR
tRe ship .emes ta
A selutioR'for this preblem might
be to set these arms inte the null. This would eatail
breaking the cORtenuity ef the shi.s strength members.
Whea startiRg from scratch this .Guld be taken iato ••• sideratien by iBdelltiag.the hull at the plaee where the apparatus
is goiJlg te be eRstalled. It is ob\1ieus'to the'Raval arehitect
waat am added expense this WQuld be. To take the 1ife boat
off a deok ~s high as the boat deck of a medern transoceanic
ii.er would be Qigh1y improbab1e, as the arms would be in
vicinity' er ore hud:re d t'eef., in 1eagth and kbouttw. feet 1ra
diameter. Of ceurse a mGre accessible plaee rerotha life
belats "euldbe
e. a lower dectkj if this c<ouid be aceomplished
tbe lifeboateeuld
easily earry out its missi.n. But even SG,
if the boats were ~lfty feet abeve the water, an arm er about
seventy feet in length and eighteen imches 1D diameter would
be necessary. This h0wever Is not out .1 preportien t. a lifeboat sixty feet in le~gth aRd havimg a capacity er approximately
fonr hundred persons.
,£ccnrved arm was designed 1m the thesis so as t. elimlRate
cuttiag int. the decks above the butt er the arms. It added
a few complicati.ns tG> the design, but we feel that its
superierity ever the straight arm 1s so great as ~. make it
alm0s~ imperltive. True, the straight arm weuld have simple
beDding, tensiQn, and eompreSSiQR te wlthsta~dj ,and the
curved arm has ene more beading m~ment aDd a twisting moment
due to its curvature. These twe added items imerese the size
er the arm; but this disadvantage is more than .frset by
maki~g the applieatie. of the apparatus ~norm.usly simpler.
Wehave often been confronted with the questien,"H.w are you
goiJlg to pick up these boats after they are laulllched?"The
answer is;"who wan-ts to put lifeboats back en a disabled
ship?" This statement assumes that the lifeboats are j',ebe
used i. tbeship!s own emergency. 1m calm water it would
b~~t~epiek up boats with this apparatus, but in heavy weather
it would be impossible. "Can the CORventienal type of lifeboat
launching appar~tus pick up a boat in rough water,or does it
wait till the seas subdue?" Another objection that has come
up eccasionally is that the huge arms pr0trudiJl1Bfrem the
side of the vessel act in tme same maaner as did the bowsprit ef the aId square riggers,- under water and Gut. This
claim completely forgets that a ship does not pit.h~back
a_d forth traRsveresly but lells back and f~rth sl~wly.
Whem full of water, it dGes not even do much of that.
p.~.
The time of launching eould easily be chosen at the most
opportune time ef the roll.
When several of these iRstallatl.ns are put ORa ship,
it is possible, but Rot prebab1e that one set after launching
w.uld interfere with another while it was launching. With a
little foresight iR the design, this trouble could easIly
be avoided.
When the preseat day apparatus fails te launch its lifeboat on the high side of the vessel, 'this new apparatus is
abl~ t. de so with little difficulty. There is a llmit,ef
course, a~ to the anglo of list against which it will launch
a boat. But, due t. the natura Gf the design G~ this apparatus,
the lifeboat is launched with'it's keel'a1ways parallel tD
the keel of the vessel itself. So, to go te the extreme,if
the ship were trimmed by the stern by an angle Gf ferty five
degrees witl:1the norizontal, the lifeboat would never be
launched- it would simply m.ve im a horizo~tal plaDe. In
0ther wGrds the plane sf retatiom would become a horizontal
plane. But dQes one wait till the ship is trimmed to such
aR excessive angle before launching a lifeboat?"The answer
is obviously no. It is Revertheless ome of the biggest dlsadYa~tage if aot the biggest. But if care is taken to launch
the boat aScSOOll as the ship is in danger ef takiRg a
perma~ent a~d dangerous trim, or even if the ship is brought
back to almQst •• rmal trim by floodi~g compartments, it
w0uld practically eliminate this trOUble. It of course
reguires fast and straight thi~kimg on the part ef the
cemmamder.
we have purposely left the question of weight and cost
till last. It is im our epi»iQn the least important of all
the questions discussed. It gees without saying that the
weight and Qost .r this new apparatus exceeds that .~ the
preseRt type; but not by a- amount t. make it prghibitive.
therefQre, since it is mot so much in excess to present day
equipmeRt, aRd if the ultimate geal is te endeaver to make
the passenger's lire a little safer, then why debate the ,.'
questieR .~ cost and weight?
I. weighimg the advantages and disadvantages of this new
apparatus and comparimg it with present day equipment, we
have aome to the cORclusien that it does give the remava1
of passengers from a siRking ship a greater element of
security than eQuId be ebtaiRed with the conventioRal type
"f davit. It nm.st be kept ill mind, hewever, that we are not
insiRuatiRg that it is a teo1proof apparatus; but it does
make the life of the passenger a little safer in case Gf
emergency; aRd after all this the ultimate purpose of any
lifesaviRe apparatus.
DATA
TABLE OF TWISTING MOMENTS
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TABLE OF TENSION IN WORKING CABLES
,
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