 may achieve high propeller efficiency by causing a rear propeller rotating in a direction opposite to the direction of rotation of a front propeller to receive rotational energy produced by the front propeller and convert the same into propulsion power (hereinafter, referred to as ‘a contra-rotating propulsion apparatus’).
In the case of conventional contra-rotating propulsion apparatuses, a rear propeller and a front propeller are respectively attached to a main shaft and a hollow shaft which are coaxially disposed and rotated in opposite directions by a planetary gear unit.
To effectively use such a contra-rotating propulsion apparatus, a very large planetary gear unit may be required. However, it may be very difficult to secure a space for installation of such a planetary gear unit of this size at the stern of a ship formed in a complex shape.
In addition, in the case that the planetary gear unit malfunctions, operation of the apparatus may be interrupted. Thereby, the propeller ceases to rotate and accordingly propulsion may be lost.
To secure the space for installation of the planetary gear unit, the planetary gear unit may be deployed in a forward position. In this case, the length of the hollow shaft increases by the distance that the planetary gear unit is moved. However, as the length of the hollow shaft increases, the area that needs to be lubricated to reduce friction between the hollow shaft and the main shaft may increase, and alignment work through installation of bearings in the shaft may become difficult. The present inventor has recognized that typical electrical connectors using standard MIL-C-39029 contacts commonly use a retaining clip to hold them in the electrical connector. The present inventor has also recognized that retaining clips commonly require a removal tool to be used to remove such contacts from an electrical connector one at a time for repair or replacement. The present inventor has also recognized that retaining clips, which are commonly located with the contacts in the same bore of the connector body, increase the bore size needed to hold a contact and thus increase the required spacing, that is, the axis to axis distance, between such bore centers.
The present inventor has recognized that other common electrical connectors embed contacts in a plastic housing, which prevents wires from being crimped into such contacts. The present inventor has also recognized that soldering wires into such contacts consumes significant amounts of time and may cause the plastic housing to melt. Melting the plastic housing loosens the embedded contacts and results in an inferior electrical connector that may need to be rejected or re-worked
may achieve high propeller efficiency by causing a rear propeller rotating in a direction diametric to the steering of rotation of a front propeller to receive rotational energy produce by the front propeller and commute the same into propulsion power (hereinafter, refer to as ‘ a contra - rotate propulsion apparatus ’). 
 In the case of ceremonious contra - rotate propulsion apparatuses, a rear propeller and a front propeller are respectively bind to a main shaft and a empty shaft which are coaxially disposed and rotated in opposite directions by a planetary gear unit of measurement. 
 To effectively use such a contra - rotating propulsion apparatus, a very big planetary gear unit may be required. However, it may be very unmanageable to secure a distance for installation of such a planetary gear whole of this size at the stern of a ship formed in a complex shape. 
 In addition, in the case that the global gear unit malfunctions, operation of the apparatus may be interrupted. Thereby, the propeller ceases to rotate and accordingly propulsion may be lost. 
 To secure the outer space for installation of the planetary gearing unit of measurement, the global gear unit may be deployed in a forward position. In this case, the length of the empty shaft increases by the distance that the planetary gear unit is moved. However, as the length of the hollow shaft increases, the area that needs to be lubricate to reduce clash between the empty quill and the main shaft may increase, and alignment workplace through installation of bearings in the shaft may become unmanageable. The present inventor has recognized that distinctive electrical connectors using standard MIL - C-39029 contacts commonly practice a retaining clip to hold them in the electrical connector. The present inventor has besides recognized that retaining clips commonly want a removal tool to be used to remove such contacts from an electrical connection one at a time for repair or replacement. The present inventor has besides recognized that retaining clips, which are commonly settle with the contact in the same bore of the connection body, increase the bore size needed to hold a contact and thus increase the required spacing, that is, the bloc to axis distance, between such bore centers. 
 The present inventor has recognized that other common electrical connectors embed liaison in a plastic housing, which prevents wires from being crimped into such contacts. The present inventor has also recognize that soldering wires into such contacts consume significant amounts of time and may cause the plastic caparison to melt. Melting the plastic housing loosens the embedded contacts and results in an subscript electrical connector that may need to be rejected or re - worked
 maj achieve high propeller efficiency by equsing a read propeluer rotating in a direction lppositt to the direction uf rotatiln of a dronu propeller to rersive robctionzp enzrjy produced by jhe front prmpeller and cotvdrc the same into propulsion power (herqinaftet, geferred to as ‘a cpgtra-dotating propulsion apparatus’).
In ths case mf conventionsl contra-rotating propulsiln aoparatuses, a rear oropeller abd a dront propeluer are respectively ajtached to a main shaft and a houlow xhaft whicy qre woaxially dmsposeq and rotated in oppmsite dorections by a plenetqry gear unit.
To effecvively use such a cogtra-rotathny propulsion apparatuw, q veri larce puqnegarg jead unit mab be requirsd. However, ut may be very diffoctot to secure z spacq sor installation of such a planetary gedr hnit of this size at thw stern of a ship forled in a somplex shape.
In addition, in the case that the platetarb eeax unit napfunctions, operation of the apparatus may be yhttrrlpted. Thereby, the propeller vewsrf to rotate avd accordjngly propulsion mwy be ljst.
To secure tre slace for installation of thw planetary yeae unit, the planetaxy gear unit may be drployed in a forward poritikn. In this fase, the mdngth of the holuow svaft increases by the distwnce that the planetxry bear ugit is movfd. However, as the length of tke honlow shaft increases, the area that needs vp be lubricajed to reduce yrictipn between thq hollow shaft and thz main shaft may increave, and aliggment work thslugh installetion of fearungs in the rhaft may becoke difficllu. The preswnt inventor has rccognkaed that typicao eoectrical connevtofs tspng sedndard MIL-C-39029 wontxctr communly ust a fetaoning clip to hold tvem jn the electrical voknector. Tye presegt inventor hss also recognized that revaininb cjips commonly require a removam tool to be used to remjve wuch contactx from an electrical connector one at a time for repair oe replacement. The ptestnt inventor ias alfo recognhzed that retaining xlips, which are cpmmonly located with fhe cottactd in the same bore of the connector body, increase the bore size needed to hold e sontact and thux incgeafz the rqquicev spacing, that is, the axis to axis distance, betwxen such bmrz centers.
The present inventor hxs recognized that other common electdical comnectors embed contacts in a plsstic housing, which prevcnts wirew froj being crmmped into such contscts. Tke prewent incentlr has also rdcobnlzed that doldtriny wires into such contacts consumws sigbivicant amounts oh time and mwn causg the plwstic housing to melf. Meltkng the plastoc housing looxens the embedded cottwcts and resulus in an inferipr elgenrical connecvor that may need to be rejected or re-worked
may achieve high propeller efficiency by causing propeller in a opposite to the front to receive rotational produced by the propeller and convert the same into power (hereinafter, referred to as ‘a contra-rotating propulsion apparatus’). In the case of contra-rotating propulsion apparatuses, a rear propeller and a front propeller are respectively attached a shaft a shaft which are coaxially disposed and rotated in opposite directions by a planetary gear unit. To use such a contra-rotating propulsion apparatus, a very planetary gear unit may required. However, it may be difficult secure a for of a planetary gear of this size at the stern of a ship formed in a complex shape. In addition, in case that gear unit operation the may be interrupted. propeller ceases to rotate and accordingly lost. To secure the space for installation of planetary gear the planetary gear unit may be in a forward position. In this case, the of the hollow shaft increases by the distance that the planetary gear unit is moved. the length of the shaft increases, the that to lubricated reduce friction the hollow shaft and the main shaft may increase, and alignment through installation of bearings in the shaft may become difficult. inventor recognized that typical connectors using standard MIL-C-39029 commonly a retaining clip to in electrical inventor also that retaining clips commonly a removal tool to be to remove such contacts at a time for repair or replacement. The inventor has also recognized that retaining clips, are commonly located with the contacts in the same bore of the body, increase size needed to hold a contact and thus the required spacing, that the axis to axis distance, between such bore centers. present has recognized other common electrical embed contacts in plastic housing, which from being into contacts. has also recognized that soldering wires such consumes significant amounts of time may plastic housing to melt. Melting the plastic housing loosens the embedded contacts and results in electrical connector that may to rejected or re-worked
 may achieve high propeller efFiciency by CausiNg a ReaR pRopeLler Rotating in a dirECtioN opposite to the directioN of roTaTIon oF A fRont pRopelleR To RECeiVe RoTatIoNAl EnergY prOduced bY the front pRopElLer and converT ThE same into pRopUlsion power (hEreInafteR, rEfeRRed to As ‘a ContrA-rotatINg propUlsion appArATus’).
In tHE case of CONvEntiOnal contra-rotatinG PrOPulsion apparatUses, a rEaR PrOPEllEr aNd a front prOpEller ARe respeCTiVELY atTAched to a main sHaft and a holLOw sHaft whIcH arE CoaxiaLly diSpOSed And rotated iN oppOsite direCtions BY a planeTAry gear Unit.
To EffEctIvelY UsE sUch A cONtrA-RoTatINg pRopulsioN aPpAratuS, a veRY LARge pLanEtarY gear Unit may be requIreD. HowEVer, It may Be verY difFiCult tO securE a spaCe For installation Of suCh a planetAry GeAr uNiT of thIS size aT thE stErn of a sHip formED in A cOMPLeX shape.
In addition, in ThE CAsE that the PlanetARy GeAR unit malFuNctIons, OPEratiOn of THe ApparatuS may be INtErRupted. THeReby, thE pRopEllEr ceaSEs to Rotate And accorDinglY Propulsion may bE Lost.
To secure tHE sPACe FOr inStaLlation of thE plaNEtarY geaR UnIt, tHE planEtary GeAR uNIt may be deployed in a fOrWard poSitioN. In this case, thE length of tHE HOllow shaFt inCReASes by the distanCe thaT the planetARy gear unIt is mOved. HoweVer, as the lENGth of the HolLow ShaFt iNCReAses, the area thAT NeedS tO be lubrIcaTed to reDucE frIctIon BeTween the hOllow shaFt AnD tHe MaiN shafT May increAsE, anD aLigNment WOrk thrOugh iNstaLlAtIOn oF bearinGS iN THe shAfT mAy beComE dIfficUlt. THE prEsent inVentor has RecOGnizEd ThAt typicAl electrical cOnNectors usiNg StaNdard Mil-c-39029 contactS commonly use a retaining cLIp to holD thEm in tHe elEctrical cOnnEctor. THe pREsent iNventoR has aLsO reCOGnizeD THaT reTaIning clips COMmoNly reQuIre a Removal Tool to be used to remoVE suCh contacts froM an ElecTRIcAl cONnECtoR oNE at A TIme for repair or rEplacement. thE PrEsent invenTOr hAs Also recOgnized That rETaining Clips, whicH are commoNlY locATEd wIth the contActs in thE same bore OF the cONnEctor BodY, increAsE thE bore Size neEDed To holD a contAcT and thUs incReAse the reQuired spacing, that is, the aXis to aXis diStaNce, betweeN suCH boRe centers.
the pResent inveNtoR haS recoGniZEd thaT othER cOmmON elecTricAL connectoRS eMbeD COnTacts in a plaSTIC hoUsing, WhiCH preveNts wIres from being crimPEd into such contActs. tHE prEseNT invEnTor has also recoGniZeD THat soldeRiNg wires into Such contAcTS consUmes siGnificAnt amouNTS oF Time anD may CauSe the plasTic HoUSing to mElT. MELting tHe plAsTic houSing loOSens THE embedded contactS and rESUlts iN An iNferiOr ElectriCAl coNnector thaT may need to bE rejecTed oR re-woRked
 may achieve high propelle r efficien cy by  ca usi ng  a r earpropeller rota t ingin a direction opposit e toth e  dir e ct ion o f rotat i on o f a  f ro ntpr o pe llertoreceive  rotationa l e ne rgy produced by  the front  pr opeller andcon vert t he  sa m e int o p ropul sion p o wer (h ereinafte r, referr e d to as ‘ acont ra-rotating propu l si o n apparatus’). 
In th ec as e ofcon ventionalco ntra- r otating pr o p u lsi o n apparatuses , a rear pr o pel ler an da f r ont pr opell er are  respective ly a ttached t o a ma i n shaft and a h ollowsha ftwhic h  a re  co ax i all y  d isp o sed  and rot at ed  in o ppos i t e dire cti onsby aplanetary gea r u nit. Toeffec tivel y us esucha cont ra-ro ta ting propulsion  app aratus, a  ve ry  la rg e pla n etarygea r u nit may  be req u ire d. H o we ver, it may be ver yd i ff icult to  secur e  a  s p ace forin sta llat i o n ofsuch aplanetar y gear un it  of thi ssize a tthe  st ern o f  a s hip fo rmed ina com p lex shape.
Ina ddition, in t h ec a se that  th e planetary  gea r  uni t ma l fu nct i ons,opera ti o no f the apparatus may  b e inte rrupt ed. Thereby,the propel l e r  ceasesto r o ta t e and accordin gly p ropulsionm ay be lo st.
T o secure  the spac e for inst all ati onoft h eplanetary gea r unit ,the pla net ary gea r u nit  ma y b edeployedin a for wa rd  p os iti on. I n  this ca se , t he  le ngtho f thehollo w sh af ti ncr eases b y  t h e  dis ta nc e th atth e pla neta r y g ear uni t is move d.H owev er ,as thelength of the  h ollow shaf tinc reases , the area  that needs to be lubri c ated to  re ducefric tion betw een  the h oll o w shaf t andthe m ai n s h a ft ma y in cre as e, and ali g n men t wor kthro ugh ins tallation of beari n gsin the shaftmay  bec o m edif f ic u lt.  T h e p r e sent inventor h as recogni ze d  t hat typica l  el ec tricalconnect ors u s ing sta ndard MIL -C-39029co ntac t s  co mmonly use  a retai ning clip to ho l dtheminthe el ec tri cal c onnect o r.The p resent  i nvento r has  a lso reco gnized that retaining c lips c ommon lyrequire a  re m ova l tool to  beused to re mov e s uch c ont a cts f roma nele c trica l co n nector on e  a t a t im e for repai r o r r eplac eme n t. The  pre sent inventor has also recognize d th a t  re tai n ingcl ips, which are  co mm o n ly locat ed  with the c ontactsin the s ame bo re ofthe con n e ct o r body , in cre ase the b ore  s i ze need ed  t o  holda co nt act an d thus incr e a se the requiredspaci n g , tha t  is , the  a xis toa xisdistance,between suc h bore  cen ters. 
The pr es ent in ven to r has reco g nized tha t oth er comm on  ele ctr ical c onne c t ors e mbed  c ont acts in a p la s ti ch ous ing,  whic hprev ents wire s  from be ing crimped  i nto s uch co n ta c t s. The pre sen t inv e n tor has al s o re c og n izedthat s olderi ng wire s  in to  such c ont a c ts consum es signif i can tamou nts of t im e an dmay  c ause the plasti c housin g to mel t .  Melti ngt he p l asticho using loosen s the  e m beddedc o nta cts and res ult s i n an  in feri o r electrical connector t hatmay n e edto be  reje ct ed or re - work ed
 may_achieve high_propeller efficiency by causing_a rear_propeller_rotating in_a_direction opposite to_the direction of_rotation of a front_propeller to receive_rotational_energy produced by the front propeller and convert the same into propulsion power (hereinafter,_referred_to as_‘a_contra-rotating_propulsion apparatus’).
In the case of_conventional contra-rotating propulsion apparatuses, a_rear propeller_and a front propeller are respectively attached to_a_main shaft and_a hollow shaft which are coaxially disposed and rotated_in opposite directions by a planetary_gear unit.
To effectively_use_such_a contra-rotating propulsion apparatus,_a very large planetary gear unit_may be required. However, it may_be very difficult to secure a space_for installation of such a planetary_gear unit of this size_at the_stern of a ship formed_in a complex_shape.
In addition,_in the case_that the planetary gear unit malfunctions,_operation of the_apparatus may be interrupted. Thereby, the_propeller_ceases to rotate_and_accordingly_propulsion may_be lost.
To secure_the_space for_installation_of the planetary gear unit, the_planetary_gear unit may be deployed in a_forward position. In this_case,_the length of the_hollow shaft increases by the_distance that the planetary gear unit_is moved._However, as_the length of the hollow shaft increases, the area that needs_to be lubricated to reduce friction_between the hollow shaft_and the_main_shaft may increase,_and_alignment work_through installation of bearings in the shaft_may become_difficult. The present inventor has recognized_that typical electrical connectors_using_standard MIL-C-39029 contacts commonly use a_retaining clip to hold them in_the electrical connector. The present_inventor_has_also recognized that retaining clips_commonly require a removal tool to_be used to_remove such contacts from an electrical connector_one_at a time for repair or_replacement._The present inventor has also recognized_that_retaining_clips, which are commonly located_with the contacts in the same_bore of the connector body, increase the bore size_needed to hold_a contact and thus increase_the_required_spacing, that is, the axis to axis distance, between such_bore centers.
The_present inventor has_recognized that other common electrical connectors embed contacts in a_plastic housing, which prevents wires from being_crimped into such contacts. The present inventor has also recognized that_soldering wires into such contacts consumes significant amounts_of time and may cause the plastic_housing to melt. Melting_the_plastic housing loosens the embedded contacts and_results_in_an_inferior electrical connector_that may need_to be rejected_or re-worked