THREE DIMENSIONAL LIFEBOAT LAUNCHING
A Thesis Presented forthe Degree of Bachelorof Science in NavalArchitecture and Marine
Engineering
By
Arthur Lewis HasklnBRenata Paul Iodice
Class of 1935
MASSACHUSETTS INSTITUTE OF TECHNOLOGYCambridge, Massachusetts-MAy 16, 1935
TABLE OF CONTENTS
Letter of Transmittal - - - - - - - - - - - - - - -Acknowledgements _0- _Introduction -
Purpose -Method Persued - - - -
History - - -Application -Design - - - - - - - - - - - - - - - - ~ ~ - - - -
Theory - - - - - - - - - - - - - - - - - - - -
Page No.1
2
3
3
3
5
7
1212
Choice of ~oat - - -- - - - - - - - - - - - - - 13
Load on Arms - - - - - - - - -Tension in Cables - - - - - - - - - -Bending Moments - - - - - - - - - - -Twisting Moments - - - --Compression in Arms - - - - - - - - - - -Diameter of Arms - - - - - - - - - - - - - - -
Motion - - - - - - - - - - - -General Layout - - - - - - -
21
- - - 13- - - - - - 14
141515151616
- - - 10- - - 18
- - - - - 19- - - - 21
- - - - - - - -Bending Moments - - -
Size of Cables - - - - -Results - - - - -Conclusions - - -Data - - - - - - - - - - - -
Twisting Moments - - - - - - - - - - - - - - - 22Compression and Tension in Arms - - - - - - - 25Tension in Operating Cables - - - - - - - 27
Calculations - - - - - - - - - - - 28
TABLE OF CONTENTS (CONTINUED)
Load on Arms - - - - - - - - -Tension in Fixed Length Cables -Arm Diameters - - - ~ - - - -
Plates and Bending Moment Diagrams
Page No.- - - 28
- - - - ~ - ~ 31- - - - - - - 32
- - - Appendix
Mass. Institute of TechnologyCambrIdge, MassachusettsMay 16, 1935
Professor James R. JackMass. Institute of TechnologyCambridge, Massachusetts
Dear Sir:In accordance with the requirements in application for
the degree of Bachelor of Science in Naval Architecture andMarine Engineering, we are presenting a thesis which we havetruly entitIed "Three Dimensional Lifeboat Launching •."
We wish to call your attention to the radical change inmethod of launching whinh the title indicates, the complica-tions of design which it involves, and the difficulties inlifeboat launching which it overcomes.
Though we claim no credit for the fundemental idea, thethree dimensional principle, the design, when taken up asthesis work, had no foundation but its fundemental idea andthe principles of engineering mechaniBs. The degree of fine-ness to which the design is carried was Bubject to restrictiondue to limited time, though the attempt was made to completeall working plans.
Sincerely yours,<!,\\
j
1.
ACKNOWLEDGEMENTS
We are'grateful to the following men for aid givenduring the preparation of this thesis:
ToMr. F. Forrest Pease for the fundmmentalprinciple on which the thesis is based,
Mr. C.B. Palmer for making available theclippings from the Boston Transcript fileson Marine disasters,
Professor Evers Burtner for miscellaneoustechnical information.
A.L.H.R.P.I.
12,
INTRODUCTION
INTRODUCTION
PURPOSE. The purpose of this thesis is to introdueeto the naval architectural world the value, principle, anddesign of the Pease Lifeboat Launching Crane.
METHOD PERSUED. Herein is briefly outlined the methodused in the working out of the design. A more detailedexplanation is found in the section under Design.
Before starting the actual design work, it was necessaryto determine how much had been done before us. This provedto be nil. Therefore, to have a practical basis , a thoroughperusal of all clippings from the Boston Transcript fileson marine disasters was undertaken. ~rom these were takenthe faults of the present equipment which were listed asfactors to be eliminated in the new design.
As tn8 type of lifeboat launching equipment cannot bea stock unit, but must be custom built, it next remained tochoose a boat for which to design the apparatus. The S.S.Colombia, a Ferris design, was chosen both because of itscommon type and because of the adaptability of the apparatuBto it.
In order to give the initiate to this new principle aclear idea of how it works, a drawing was made of the mid-ship portion of the Colombia, showing the launching of alifeboat in three views, accompanied by a fourth supplementarydiagram. (See Plate I)
Due to the extreme complications in direction of cablesand 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 PlateII). This plan was carried out in obtaining all the forcesand moments "inthe arms and cables.
The bending moments were taken or resolved into twoperpendicular planes and combined. into a resultant benlingmoment, which was in turn combined with the twisting momentby Rankine's theory. The result, along with the totalcompression and an assumed fiber stress, was used to getthe varying diameters of the arms.
United states Standard tables in Mark's handbook wereused to estimate the size of cables.
HISTORY
HISTORY
The idea behind the Pease Lifeboat Launching Crane isnot a brainstDrm brought on by recent marine disasters. Itfollowed six years of sea experience from 1909 to 1915. Inthe latter year the idea was presented to leaders in marinefields and received considerable encouragement. Dr. AlfredWilliansAnthony of Lewiston, lmine was desirous of backingit and had the money to do so. To make sure of the ground
on which he trod, Dr. Anthony requested Professor Peabodyof the Massachusetts Institute of Technology to look intothe idea. Professor Peabody's report showed the idea to besound 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 installationwhen Mr. Pease was forced to abandon the work due to illness.
By 1916, Mr. Pease was again on the trail of a backerfor the idea. This led him to the Fore River plant of theBethlehem 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 apprenticesin the yard. Soon after, the United States Shipping Boardordered him to Philadelphia, not to return until after theWar.
In 1921, Fore River again attacked the lifeboat launchingproblem. The technical staff was instructed to examine theidea, and considerable amount of study and preliminary planswere made. The investigation showed that a great deal ofmoney was needed for experimentatio~ and the management, though
realizing the value of the idea, decided that it didn't careto go into the development.
From then on, ,the idea bounced. from shipyard to shipowner, fromshlp owner to Steamboat inspection ~ervice, andfrom Steamboat Inspection Service back again. The shipyardcouldn't develop the apparatus for lack of money. They werewilling to install one should the owner desire it, but onlyunder that condition could they see the value to themselves.The shipowner was satisfied with the existing equipment aslong as it was passed by the Steamboat Inspection Service,and the latter had no money or authority to do the develop-ing. They said that they would gladly pass judgement on theapparatus 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 lookingfor a minimum of risk with a maximum of return, and the verynature" of the apparatus fails in this qualification.
At present, the government is extremely interested.Recently, Mr. Pease demonstrated his model and showed movingpictures of this model launching model-lifeboats into anexperimental tank of the Massachusetts Institute of Technologybefore the members of the United states Steamboat InspectionService. They were greatly impressed, and Mr. Pease nowawaits a report from the chairman, l~. Dickerson Hoover, asto the success they have had toward getting appropriationsfor the project. Assisting 1~. Pease in Washington isCongressman Wigglesworth who is an enthusiastic advocate.In addition, the newspapers have been big aids in helpingthe idea to gain the approval of the public and professionalmen which it now has.
APPLICATION
APPLICATION
The Court of Inquiry Report on the Titanic disaster,made in August 1912, stated that at sea there was but onedeath in every 800,000 passengers carried. This does notimpress us with anything but its insignificance as a figure,but its insignificance is confined to the field of mathema-tics and does not trespass on the human side of the question.When nine out of ten of these deaths 'are due to faultymachinery or inadequate machinery, it remains for the engi-neer to answer the cry of the indignant public.
The public cry is naturally heard the loudest immediatelyfollowing a spectacular disaster. It rose in volume followingthe sinking of the Titanic in April 1912. Two years later,the collision of the Empress of Ireland and a Danish trampwith a consequent loss of life of more than 1000 persons
gave rise to another public outburst. In May 1915, it wasthe sinking of the Luisitania, in 1928 it was the Vestris,today it is the recent Ward Line calamities that have rousedhumanity.
As engineer~we are interested in the lesson from eachof these calamities. From the Titanic disaster, we learnthat it is perfectly feasible to launch all boats safelyunder perfect conditions with the ordinary boat davits. Thisis important as a contrast to the success of the operationunder distress conditions. When the Titanic sank, the seawas perfectly calm and the ship sank by the head without
listing and slow enough to give everyone plenty of time toget away in the boats. The greatest reason for loss of lifein this case was the lack of sufficient lifeboats and reluc-
7
tance of passengers in leaving what they were lead to believewas an unsinkable ship. Excellent conditions are abnormalrather than norma~ and as we are looking for difficulties toovercome, the sinking of the Titanic is not of such importance.
Though no detailed information is available on the fateofthe Empress of Ireland's complement, it is suspected thatthis disaster can be classed with the Titanic.
When the Luisitania was torpedoed off the Irish coast,the American public was too busy directing its indignationtoward the Imperial German Government to ask why, when given15 minutes to abandon ship, nearly 1200 persons found nomeans of safety at hand. Here we learn the lesson of speedand efficiency that is not associated with the age old blockand tackle principle used in existing lifeboat davits.
In the sinking of the Vestris off the Virginia Capes in1928, we learn several things about lifeboat launching. Theweather was extremely bad. The ship had a list of about 150
as the boats were being lowered. The Vestris carried 14boats, plenty to accomodate a~l 328 persons aboard fromeither side of the ship. T~e following table, showing whathappened to each boat, gives an impressive pfcture of whatthis thesis is trying to eliminate.
-Port sideBoat #2 - Stayed on deck and sank with ship.
#4 and #6 - Lowered part way with women and childrenbut 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 ofentanglement.
8
#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 with218 people. Of these 8, two were never launched but floatedoff the ship empty as it sank, and still another had to bechipped 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 effectof list is plainly shown by the table, but eKen on the lowside, two of the boats failed to get away. It took two hoursto launch the boats on the high side.
Trouble with the releasing gear was shown in a statementby the chief engineer, Mr. Johnson. He said that the releas-ing equipment broke in two instances and that there was noinstance 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 80persona, only 8 got away, some of them carrying as few as sixpeople, mostly crew. We find here that the windward side ofa burning ship is the only possible side from which to launchlifeboats. When tremendous seas hurl their force from thatquarte~ the problem of boat launching becomes exceedingly
difficult.These few major disasters cause but a small part of the
9
toll of deaths at aea, however. They are the ones we readabout in the newspapers, but we do not look behind the scenesof smaller incidents of the same sort where numbers of personsare lost in one sweep. Captain Fried lost two men and fiveboats attempting to rescue the crew of the Antinoe in Jan-uary 1926. He stood about 80 hours before daring to launcha single boat. 'Vhen the Monroe and Nantucket crashed inJanuary 1914, 49 men drowned because ten minutes were notsufficient 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 becauseof the high seas to be of any assistance. 136 lives werelost, all of which were lost in attempts to get away in theship's boats.
And so on through volumes and volumes with always thesame story "calm water enables all boats to get awaysafelyr or "heavy sea conditions prevented proper mani-pUlation of launchlng eqUipment." In other words, thedesign of launching equipment should include all the factorspossible for the elimination of each of the defects in presentdavits. The most important of these factors are listedbelow:
1. Long outreach to enable launChing on windward sideand against a list.
2. Single motion with one man operation for efficiencyand speed in operation.
3. Launching under motion for immediate steerage way.4. Capacity to handle large boats for greater seaworthi-
ness and for greater confidence from the passengers.(This also enables more boats to be carrled on each
10
side of the ship where desired.)5. No rigid fastenings to llfeboats for immediate and
synchronous release when waterborne, and also toenable boat to float free of sinking ShlP were itnot launched.
All of these factors, along with convenience, beauty,and economy have been considered in the following design,though compromises were inevitable in Borneinstances.
JI
DESIGN
DESIGN
THEORY. The motion described by the Pease LifeboatLaunching Crane can be outlined very simply. First, consideras a horizontal plane, the plane of rotation (Plate II), witha line perpendicular to it. Around this line, rotating ina semi-circle are two other lines in a plane perpendicularto the p~ane of rotation which meet the latter plane in theBame point, one of which intersects the plane at an angle of16° and the other at about 40°. The 16° line is a steelarm, and its angle with the plane of rotation is termed the"droop" of the arm. The 40° line 1s a fixed length cablewhich holds the arm from drooping further. Nww, take thiswhole unit and place it alongside a vessel with the plane ofrotation perpendicular to the side, tip it up so that the~lane of rotation makes about 45° with the surfac~ of thewater, and we have the motion described by one of the threearms of the appa~atus. Three of these unite with parallelplanes of rotation, and with the outer ends of the armsrigidly connected, make up the launching device. If thedescription has been followed up to this point, the picturenow ie that of a parallel ruler in three dimensions, wherethe 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 operatingcables in the planes of rotation are fastened from the outerend of the arms through sheaves and around a drum on deck.The drum is operated by a winch to return the apparatus afterlaunching a boat. It is also fitted with a hand or centrifugal
I~
brake to check the boat in launching.To keep the cradle upright, nothing more than three
parallel pins is necessary. These are perpendicular to theplane of rotation and pin the arms to the cradles. Theyare the outer swivels of the parallel ruler.
Instead of using pins at the ship's side, a universaljoint is employed to allow the cradle to rise straight upwith a heavy sea in launching rather than twist off the pins.
CHOICE OF BOAT. The S.S. Colombia was chosen as subjectfor the design of the equipment for several reasons. Shehas a small enough complement of passengers and crew toenable all to be accomodated in a single large lifeboat. Herfreeboard is not so extreme but that the arms can be con-veniently butted and swivelled at the ba~elof the superstruc-ture. This allows the arms to lie inside the outermost beamof the vessel and prevents damaging from other boats or froma wharf. Also, the farther from the load line that the armsare swivelled the longer they must be to properly place theboats on the water.
GENERAL LAYOUT. It was first desired to keep the armsfor this installation perfectly straight and about 40 feetlong. However, it was found that straight arms would neces-sitate cutting into all three of the upper decks to set theboats inboard. To eliminate this trouble the arms werecurved for about 8 feet of their length so that only theboat deck had to be cut away under the lifeboat.
Were the arms limited to 40 feet in length, the angleof launching would have been excessive. Considering 450
/3
as a reasonable angle at which to launch, the arms weredrawn to about 47 feet in length.
The droop of the arms is determined by the height ofthe arm butt at the ship from the load line. The higherthis point is, the more droop is necessary in order to havethe boat waterborne at the outermost point of the curve.A slight compromise was necessary here in that if the boatwere waterborne at exactly the outermost point, an arm 60feet long would be necessary, other factors remaining the same.The boat actually floats off the cradle at about 100 pastposition #4 with the 47 foot arms.
In order to keep the twisting moments inthe arm at aminimum, and angle of 450 was constructed between the planeof the curved arm and the ship's side in #1 position (SeePlate II). This causes the plane of the curved arm to beperpendicular to the water in the waterborne position.
MOTION. Plate II, showing the motion of a single arm,explains itself, though it is rather complicated descriptivegeometry. All N-B lines represent the fixed length cables;all O-B-A lines, the arms; all B-B lines (Fig. 4 only), theoperating cables. N-O shows the slant of the cradle pinsand the center-line of rotation.
LOAD ON ARMS. There are three sources of load on thearms: a static load, a dynamic load due to rollmng of theship, and a dynamic load due to checking the boat beforereaching the water. These three were calculated for theworst possible conditions and a resultant vertical load of6.41 tons was determined. The load was assumed constant,though it actually was slightly less at the extremities of
/4
the motion. Several assumptions were made for the calculationson the dynandc forces, but the forces themselves are so
· small in relation thethe resultant vertical load that Taria-tions in these assumtions hwe little effect on the result.TENSION IN CABLES. Plate III shows the settup for obtainingthe tension in the fi~ed length cables. It is simply a caseof 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 theoperating cables is shown in Plate IV. This is a settupof moments in the plane of rotation, and due to the changingangle between the cable and the arm, this cable varies intension. #7 position was eliminated at this stage becauseof an infinite tension in the operating cables. stopswould prevent the arms from reaching further than #6 position.
BENDING MOMENTS. With all the forces known, the nextstep was to figure the bending moments due to each force fordifferent positions along the arm and for each position.This was done so that all moments obtained lay either inthe horizontal or vertical plane. (The horizontal planehere referred to is the plane of rotation.) A plot ofvertical and horizontal bending moments was made and aresulta~t bending moment diagram obtained by taking thesquare root of the sum of the equares of the vertical andhorizontal oDminates. The force diagram used is shown bya representative sketch in Plate IV. and also in Plate. III.
TWISTING MOMENTS. Due to the curve in the arm, thereis a varying twisting moment set up by the load on the end.Figure 3, Plate II, shows the true arm for the twistingmoment, but it was necessary to construct the auxilary
/S'
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. Weknow the length of the arm to the cable fastening and canmeasure the length fifthe cable. With these we can find thebase angles and therefor the compression in the arm due tothese cables.
Straightforward resolution of the tension in the fixedlength cables along the arm in Plate III gives the compres-
s10n from this source. An ~uxiliary diagram was used ~o obtaimtheoompression and tension due to the load. Algebraic additionof 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 equivalentbending moment.
The theoretical value given by this equationIs that sImple bengIng moment which, if applied to a beam atthe point in question, will give a fIber stress equal to thatdue to twisting and bending both. It was calculated forevery point of probable maximum as shown by the bendingmoment diagrams.
Assuming a steel of yield point around 60,000 pounds persquare inch and a safety factor of two, the diameter of thearm for every 15 feet of its length was calculated, using themaximum equivalent bending moment. The results are shown inPlate V.
SiZB 6F CABLES. It is noted that the tension in the fixedlength cables is 11.8 tons and in the operating cables, 12.1
tons. This would call for aboat the same si~e cables, but
Ib
but the fixed length cables must partially support the life-boat as it is stowed and are not wound on any drum. Forthese reasons, a heat-treated steel cable is used.
The operating cables, on the other hand, take no loaduntil the boat is being launched and must be flexible enoughto wind on the winch drum. This calls for an annealed steelcable.
/7
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
CONCLUSIONS
The three factors for presentation by this thesis are,as stated in the purpose, the value, principle, and designof the Pease Lifeboat Launching Crane. It was essential tocover 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 partthat takes the ~settin' and thinkin' It. With the arms definedboth in siz~ and motion, it is but a routine machine desIgn-ers job to layout drawings for fittings, and to make up a .suitable cradle.
With no basis for comparison, it is hard to define thelimits of reason, but the dimensions as calculated for armsand cables seem to lie within this range despite the lack ofany parent design from which to work. Where so many consider-ations are necessary, mistakes or omissions are not impossibleeither in assumptions or calculations.
There are many special considerations. One is a ram onthe promenade deck at the position of the buffer as shown in 'Plate II to force the 'apparatus outboard against a list, andto hold it there in spite of the ship's rollIng. Another isa catch device to take the load as the boats are stowed. Inother words, there are any number of refinements that areout of pkace in this pioneering paper, but will develop' withthe idea.
Itremains that the three dimensional principle appliedto lifeboat launching has all the advantages neceasary to
'7
Supplememtary ConclusiensI.'addi tieD to the cGlIcluaisns abo'Ye, there" are 'Yarim s
eensideratiens as to applieation aad operations. Te i.stalthis apparatus abeard a ship er the t1:MorroCastle" typewith her extremely high sides, it w~uld'be .eeessary tobuilt the arms dowa en her shell plates. This weuld be eutof the questi,ollas the apparatus would be 'Yery easilydamaged by a ship eoming alongside Gr even by a d04k waeRtRe ship .emes ta p.~.A selutioR'for this preblem mightbe to set these arms inte the null. This would eatailbreaking the cORtenuity ef the shi.s strength members.Whea startiRg from scratch this .Guld be taken iato ••• sidera-tien by iBdelltiag.the hull at the plaee where the apparatusis goiJlg te be eRstalled. It is ob\1ieus'to the'Raval arehitectwaat am added expense this WQuld be. To take the 1ife boatoff a deok ~s high as the boat deck of a medern transoceanicii.er would be Qigh1y improbab1e, as the arms would be invicinity' er ore hud:re d t'eef., in 1eagth and kbouttw. feet 1radiameter. Of ceurse a mGre accessible plaee rerotha lifebelats "euldbe e. a lower dectkj if this c<ouid be aceomplishedtbe lifeboateeuld easily earry out its missi.n. But even SG,
if the boats were ~lfty feet abeve the water, an arm er aboutseventy feet in length and eighteen imches 1D diameter wouldbe necessary. This h0wever Is not out .1 preportien t. a life-boat sixty feet in le~gth aRd havimg a capacity er approximatelyfonr hundred persons.
,£ccnrved arm was designed 1m the thesis so as t. elimlRatecuttiag int. the decks above the butt er the arms. It addeda few complicati.ns tG> the design, but we feel that itssuperierity ever the straight arm 1s so great as ~. make italm0s~ imperltive. True, the straight arm weuld have simplebeDding, tensiQn, and eompreSSiQR te wlthsta~dj ,and thecurved arm has ene more beading m~ment aDd a twisting momentdue to its curvature. These twe added items imerese the sizeer the arm; but this disadvantage is more than .frset bymaki~g the applieatie. of the apparatus ~norm.usly simpler.
Wehave often been confronted with the questien,"H.w are yougoiJlg to pick up these boats after they are laulllched?"Theanswer is;"who wan-ts to put lifeboats back en a disabledship?" This statement assumes that the lifeboats are j',ebeused i. tbeship!s own emergency. 1m calm water it wouldb~~t~epiek up boats with this apparatus, but in heavy weatherit would be impossible. "Can the CORventienal type of lifeboatlaunching appar~tus pick up a boat in rough water,or does itwait till the seas subdue?" Another objection that has comeup eccasionally is that the huge arms pr0trudiJl1Bfrem theside of the vessel act in tme same maaner as did the bow-sprit ef the aId square riggers,- under water and Gut. Thisclaim completely forgets that a ship does not pit.h~backa_d forth traRsveresly but lells back and f~rth sl~wly.Whem full of water, it dGes not even do much of that.
The time of launching eould easily be chosen at the mostopportune time ef the roll.
When several of these iRstallatl.ns are put ORa ship,it is possible, but Rot prebab1e that one set after launchingw.uld interfere with another while it was launching. With alittle foresight iR the design, this trouble could easIlybe avoided.
When the preseat day apparatus fails te launch its life-boat on the high side of the vessel, 'this new apparatus isabl~ t. de so with little difficulty. There is a llmit,efcourse, a~ to the anglo of list against which it will launcha boat. But, due t. the natura Gf the design G~ this apparatus,the lifeboat is launched with'it's keel'a1ways parallel tDthe keel of the vessel itself. So, to go te the extreme,ifthe ship were trimmed by the stern by an angle Gf ferty fivedegrees witl:1the norizontal, the lifeboat would never belaunched- it would simply m.ve im a horizo~tal plaDe. In0ther wGrds the plane sf retatiom would become a horizontalplane. But dQes one wait till the ship is trimmed to suchaR excessive angle before launching a lifeboat?"The answeris obviously no. It is Revertheless ome of the biggest dls-adYa~tage if aot the biggest. But if care is taken to launchthe boat aScSOOll as the ship is in danger ef takiRg aperma~ent a~d dangerous trim, or even if the ship is broughtback to almQst ••rmal trim by floodi~g compartments, itw0uld practically eliminate this trOUble. It of coursereguires fast and straight thi~kimg on the part ef thecemmamder.
we have purposely left the question of weight and costtill last. It is im our epi»iQn the least important of allthe questions discussed. It gees without saying that theweight and Qost .r this new apparatus exceeds that .~ thepreseRt type; but not by a- amount t. make it prghibitive.therefQre, since it is mot so much in excess to present dayequipmeRt, aRd if the ultimate geal is te endeaver to makethe passenger's lire a little safer, then why debate the ,.'questieR .~ cost and weight?
I. weighimg the advantages and disadvantages of this newapparatus and comparimg it with present day equipment, wehave aome to the cORclusien that it does give the remava1of passengers from a siRking ship a greater element ofsecurity than eQuId be ebtaiRed with the conventioRal type"f davit. It nm.st be kept ill mind, hewever, that we are notinsiRuatiRg that it is a teo1proof apparatus; but it doesmake the life of the passenger a little safer in case Gfemergency; aRd after all this the ultimate purpose of anylifesaviRe apparatus.
DATA
TABLE OF TWISTING MOMENTS
\ .. ' , . , ,
Pes. F (J-90)e.s. (J 90) FC.s.(J-90~ t FCes.(J-90)f.......
1.. 6.41 32 .866 5.56 5.0 27~8
2 " 24: .914 5.85 2.80 16.40~. .. ' .~
3 • 9 .988 6.33 .80 5.06
4 " -11 .982N.t. lftAa ~l1l"ah" •
5' ft -32 .848 ..
6 n -52 616 3.95 :...50 5.93
-
/
,....~.......
c:Q0• 0• tt) .~ 0 0
tM • •{I) CO ....IX.t
CX) 10 It) 0bO • • •tt') C\! ....
t:Q
• roIIC fD U).... (0 It) 0 0
{I) • •r-IIXt
t:Q en to-• It) ro• C\! 0 0 0.,.. • •
{I)
t:Q to It) 0 0....
r-Ir:. .... = I: c•
(0
U It) t"- It) OJ• • • •... It)
I CO t"-.... ~ .... ....
~ r-I, .... ~ 0t"- O) t\l 0. • • •tQ
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CALCULATIONS
CAL,C(/~/-lT/CJ/VS F"O~
LOA 0 ON'.A ~/'t?S
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A V.o5"'~ A y.-c: Yv.7= P.e-R. PE"~:So/'V
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= 73.CJ r:-T.
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6-
MAXIMV/\7 P-O"<CE C>Ue- TO CHE"C~//'Vy.
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"~"= P/S7"t/,/CE TRA.VE:4L,£""Z> l;)(;1"?,//,/y- BR"V*(//Yy.
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V£"RT/CA ~ CO/V7 p(//V.c:/'y/~ . ~ox.?t:J7-- .<;;'.<70/',/$
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ADOE'D FO~CE L;;JVE To ~aL-L.,//'V9 0;:- .s¥/p.
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to::: A/VGV'&AR' VEL,OC/ry
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LET C ::.AIVC;-L£ /5£,vve-s/'./ T/-,L£" TOTAL,
L OAO [6.~/TO/y's] ".q/YO THE PL,A/'v'E" o,e::- ~O'-A'/O/Y.
t 1,= 45D FOA< AL, L, POS/;r/ON..5,
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NOR/V7AL- .,~ PLA,/"',/E" OF RtCJrAT/(,)/'Y A/'/D
A L So //V THE" PL,A/V£ or=- ROTA T/ON.
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P/,4?ENS"/C)N Or- ARMS
POS/T/()/Y /VO.1
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TH/.::s ~r~ES.:s /.3SAr/.:srAC7"O~)o- T#e~E,.e.-O"'L~ THE
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:: ~.s FT TtJNS
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O/~ECT sr~~ss =- /~.<s TO/"l/S //V' Co/"? P.
PIt)S/7/~/V /'Yo. ~
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TOA F//'V /S# 0//VCttS:' O/VC /S A REPREservrAT/v6
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PLATES
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