Tech­ni­cal: The elec­tri­cal ship

Superyacht - - WHAT’S ON - By An­drea Man­ci­ni

Hy­brid pro­pul­sion, Hy­brid ya­ch­ts, elec­tri­cal pro­pul­sion: the­re’s of­ten a great deal of con­fu­sion on what should be un­der­stood by this wor­ding. Not to men­tion the pro­pa­gan­da whi­ch at ti­mes is car­ried th­rou­gh when swit­ching from “hy­brid” to “elec­tric” to mean “green” or eco-friend­ly, eco su­stai­na­ble, ore­ven en­vi­ron­men­tal im­pact and so on as if they are all the sa­me thing. “Green”, “hy­brid”, “elec­tric”, are cer­tain­ly words whi­ch link wi­th one ano­ther, but are not sy­no­nyms, nor are they used to mean the sa­me things. Let’s start from the be­gin­ning: what does hy­brid mean, or bet­ter what does hy­brid pro­pul­sion mean? In na­tu­re the term “hy­brid” is used to si­gni­fy union bet­ween two di­ver­se spe­cies.when tal­king about “hy­brid” in na­val pro­pul­sion terms, we mean the­re are dif­fe­rent ways of get­ting pro­pel­lers to ro­ta­te: an elec­tric en­gi­ne and a die­sel one are no doubt the mo­st po­pu­lar sy­stems in­stal­led on board.the sa­me goes for the au­to­mo­ti­ve in­du­stry when tal­king about hy­brid cars sin­ce they too de­ploy two en­gi­nes: an elec­tric one and a four stro­ke pe­trol one whi­ch de­ve­lop a wor­king sy­stem set wi­thin de­fi­ned pa­ra­me­ters whi­ch de­fi­ne the le­vel of their hy­bri­di­sa­tion.

In­stead when the en­gi­nes are not wor­king to­ge­ther the cor­rect de­fi­ni­tion for this mo­de is: die­sel elec­tric whe­re the die­sel (ge­ne­ra­tor set) sup­plies suf­fi­cient ener­gy to work the elec­tric en­gi­ne whi­ch ma­kes pro­pel­lers ro­ta­te. This sy­stem is com­mon­ly found on crui­se ships whe­re a po­wer hou­se, ma­de up of a se­ries of gen. se­ts sup­plies nee­ded ener­gy to work all the on board sy­stems, ser­vi­ces and abo­ve all the elec­tric en­gi­nes. The elec­tric en­gi­nes’ hi­gh ef­fi­cien­cy means they’re mo­stly ex­ploi­ted sin­ce they can per­form over ve­ry long pe­riods abo­ve the 90% mark wi­th a max. tor­que cur­ve clo­se to ze­ro rpm. Fur­ther­mo­re the­re is no need for se­pa­ra­te dri­ve uni­ts as they can ea­si­ly work from gen. se­ts or from en­gi­nes. It is al­so a kno­wn fact that ther­mal 4 stro­ke en­gi­nes are not equal­ly ef­fi­cient at low rpm. and their ef­fi­cien­cy is ra­ted at about 35% on­ly. By wor­king the­se two en­gi­ne ty­pes ac­cor­din­gly to­ge­ther or, in the ca­se of a hy­brid pro­pul­sion unit by wor­king them to­ge­ther it is ho­we­ver pos­si­ble to re­du­ce fuel con­sump­tion and con­se­quent en­vi­ron­men­tal pol­lu­tion whi­ch trans­la­tes in­to a se­ries of ad­van­ta­ges whi­ch en­han­ce ver­sa­ti­li­ty, and fle­xi­bi­li­ty of use and the qua­li­ty of li­fe on board. The sy­stems to ma­ke the two work to­ge­ther are di­ver­se ju­st as mu­ch as and mo­re im­por­tan­tly so are the ones de­ployed to ma­na­ge and mo­ni­tor. He­re is whe­re un­der­stan­ding how a gi­ven hy­brid sy­stem real­ly works be­co­mes mo­re dif­fi­cult and we fall in­to the kind of con­fu­sion we men­tio­ned in the be­gin­ning. We in­vi­ted Al­ber­to Ami­ci foun­der of Au­xi­lia Elec­tric Pro­pul­sion na­me­ly RTN’S brand ( a com­pa­ny whi­ch has been de­si­gning and de­li­ve­ring pro­pul­sion sy­stems for ships for 50 years) and has been en­ti­re­ly in­vol­ved in sup­ply­ing ships’ on board elec­tric pro­pul­sion sy­stems for ten years, to shed so­me light on this to­pic. This com­pa­ny has al­so been de­li­ve­ring ve­ry im­por­tant hy­brid and /or die­sel elec­tric in­stal­la­tions to lar­ge and small ya­ch­ts.

Mr. Ami­ci, let’s start by clea­ring the fir­st point: is elec­tric pro­pul­sion a sy­no­nym of green, mea­ning that it al­ways gua­ran­tees a les­ser en­vi­ron­men­tal im­pact?

Well let’s start by asking our­sel­ves the fol­lo­wing que­stion: “How will the ener­gy nee­ded to run the ship be sto­red?”. Wi­th the avai­la­ble tech­no­lo­gy, to­day we ha­ve th­ree dif­fe­rent ways of doing so. Li­quid forms, (die­sel fuel, pe­trol, LPG, na­tu­ral gas, Gas forms, (me­tha­ne gas, hy­dro­gen) or bat­te­ry banks (dry cell, deep cy­cle, li­thium etc.) In the fir­st two ca­ses Li­quid and gas forms) the sup­ply is de­li­ve­red by trans­fer­ring the pro­duc­ts from land ba­sed sta­tions to ships (in the fir­st ca­se wi­th pumps, and wi­th com­pres­sors in the se­cond). In­stead as for bat­te­ries they’re po­we­red up or fil­led by elec­tri­ci­ty from quay si­de sho­re li­nes or from on board gen. set plan­ts. This pre­mi­se is im­por­tant in an ef­fort to cla­ri­fy things. If I we­re to pro­du­ce elec­tri­ci­ty on board th­rou­gh the de­ploy­ment of a ge­ne­ra­tor set (a die­sel en­gi­ne cou­pled to an al­ter­na­tor) whi­ch then is ca­bled th­rou­gh to pro­pel­ler via an elec­tric mo­tor, even if elec­tric ef­fi­cien­cy is hi­gher when elec­tric de­vi­ces are used the loss of ener­gy pas­sing th­rou­gh the ca­bles is sum­med, I will lo­se ef­fec­ti­ve ef­fi­cien­cy (and then will in­crea­se die­sel fuel con­sump­tion to ma­ke up for the loss) by com­pa­ri­son to tra­di­tio­nal me­cha­ni­cal dri­ve sy­stems whi­ch are in the main ma­de up of in li­ne shaf­ts ac­cor­din­gly cou­pled to me­cha­ni­cal gear bo­xes. The­re­fo­re al­low me to be pro­vo­ca­ti­ve, elec­tric pro­pul­sion can be a so­lu­tion whi­ch in fact in­crea­ses fuel con­sump­tion and is mo­re pol­lu­ting ( less eco friend­ly) than tra­di­tio­nal in li­ne dri­ve shaf­ts. On­ly thanks to wor­king in­tel­li­gent sy­ner­gy bet­ween a die­sel en­gi­ne wi­th an elec­tri­cal one is it pos­si­ble to pro­du­ce ener­gy in a co­st ef­fec­ti­ve and eco friend­ly way on board ship wi­th the no­ta­ble ad­van­ta­ges that go wi­th it in the li­kes of fuel re­duc­tion, ex­tra com­fort and less noi­se. As for the en­vi­ron­ment (less NOX and SOX or pos­si­bi­li­ty of ad­van­cing in ZEM mo­de (Ze­ro Emis­sion Mo­de). This has been the main rea­son that has spur­red us to de­ve­lop our AU­XI­LIA sy­stem.

The fi­gu­res show loss of ef­fi­cien­cy (gra­ph be­low) that oc­curs when ex­ploi­ting con­ven­tio­nal me­cha­ni­cal dri­ves (fig 01 a), a “full” die­sel–elec­tric sy­stem (fig 01 b) whi­le con­si­de­ring a hy­po­the­ti­cal po­wer of 1000KW. A “full” die­sel-elec­tric sy­stem as can be seen will in the end yield less than a con­ven­tio­nal me­cha­ni­cal en­gi­ne and dri­ves.

Al­ber­to Ami­ci, RTN ow­ner anf foun­der of AU­XI­LIA ELEC­TRIC PRO­PUL­SION (www.au­xi­lia-pro­pul­sion.com)

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