This so­lar- pow­ered pro­duc­tion yacht has the space, range and lux­ury to chal­lenge its diesel ri­vals

Motorboat & Yachting - - Contents -

Is the Silent 55 hy­brid a glimpse into the fu­ture of mo­tor­boat propul­sion?

If your idea of an elec­tric boat is a skinny, river launch with a sin­gle-fig­ure top speed and a painfully lim­ited cruis­ing range, pre­pare to think again.

Silent Yachts’ lat­est craft is a 55ft ocean-go­ing mo­tor cata­ma­ran with un­lim­ited range, a top speed of 14 knots and all the space and lux­ury you could wish for.

The key to un­lock­ing the usual lim­i­ta­tions of an elec­tric boat is the ar­ray of 30 high-ef­fi­ciency so­lar pan­els spread across the fly­bridge and hard top. To­gether they can gen­er­ate up to 10 kw of to­tally free, silent and con­tin­u­ously re­new­able en­ergy. Not only does this over­come the prob­lem of fi­nite bat­tery ca­pac­ity but it means you can run all the boat’s do­mes­tic sys­tems in­clud­ing air-con­di­tion­ing, fridge freezer and cook­ing fa­cil­i­ties with­out ever hav­ing to start up the gen­er­a­tor.

Think about it – a boat you can cruise all day and all night in near si­lence while burn­ing no fuel then an­chor in a quiet bay with­out hav­ing to shat­ter the peace with the noise and smell of diesel. It of­fers all the ben­e­fits of a sail­ing boat with­out the rig­ging, has­sle and wind re­liance. If this all sounds a lit­tle too good to be true, it’s not en­tirely with­out com­pro­mise. That 10 kw of so­lar power is a peak fig­ure gen­er­ated in ideal con­di­tions and even then it’s only suf­fi­cient to run the two 135kw elec­tric mo­tors at around 4% of their rated max­i­mum. That equates to a con­tin­u­ous cruis­ing speed of just 4-5 knots if you’re in­tent on leav­ing the bat­ter­ies’ 140kwh in re­serve for cruis­ing all night too. In re­al­ity most own­ers are likely to cruise at 6-8 knots dur­ing the day us­ing a mix­ture of so­lar and bat­tery power. This should still give around 10 hours of silent cruis­ing be­fore a recharge of some kind is re­quired.

backup plan

When con­sis­tently bad weather pre­vents the so­lar pan­els from reach­ing their full po­ten­tial there is a diesel gen­er­a­tor fit­ted. This is not the usual 10-15KVA genset but a much more pow­er­ful 100kw Volvo gen­er­a­tor that burns 33lph and is fed by two 300-litre tanks. This can power both elec­tric mo­tors di­rectly for a con­tin­u­ous speed of 12 knots, or more typ­i­cally be used for shorter pe­ri­ods to pro­pel the boat at its usual pace while si­mul­ta­ne­ously recharg­ing the bat­ter­ies. This gives you the op­tion of cruis­ing at 6-8 knots for 8 hours of silent run­ning fol­lowed by an hour of gen­er­a­tor use to top up the bat­ter­ies or main­tain­ing a faster speed of 10 knots by us­ing the gen­er­a­tor for two hours on and two hours off.

The max­i­mum speed of 14 knots can only be achieved when draw­ing power from both the gen­er­a­tor and the bat­ter­ies at the same time, and is there­fore not sus­tain­able for very long. In fact the ac­tual top speed is closer to 20 knots but this sprint mode uses so much power that it is only likely to be used for demon­stra­tion pur­poses, a bit like the Tesla Model S’s ‘Lu­di­crous’ mode.

It sounds com­pli­cated but the whole sys­tem is man­aged by a sim­ple au­to­mated con­trol panel that uses max­i­mum power point track­ing (MPPT) to reg­u­late the so­lar charg­ers and keep the lithium bat­ter­ies in peak con­di­tion. The set up is claimed to be more re­li­able and re­quire less main­te­nance than a con­ven­tional dieselpow­ered craft with all its fu­elling and cool­ing sys­tems. In the event of bat­tery fail­ure the en­tire bank can be iso­lated and the elec­tric mo­tors run di­rectly from the so­lar pan­els or gen­er­a­tor.

All this would be of lit­tle in­ter­est if the boat it­self were un­able to match the lev­els of com­fort, con­ve­nience and style of­fered by con­ven­tional power cata­ma­rans. From what we saw of the Silent 55 on dis­play at Cannes, it has no con­cerns here. The hull is built in China to the Aus­trian com­pany’s ex­act­ing stan­dards us­ing car­bon re­in­forced vac­uum-in­fused GRP mould­ings, while all the tech­ni­cal fit­tings are in­stalled in Eu­rope. The in­te­rior lay­out is also very ef­fec­tive with a 40m ² main deck that in­cor­po­rates the gal­ley, saloon, din­ing area and lower helm in a sin­gle so­cia­ble space. The view ahead is slightly com­pro­mised by the height of the for­ward bulk­head, but the pay­back is a won­der­ful mas­ter cabin that spans both hulls and en­joys ex­cep­tional light, space and pri­vacy. This still leaves space for three or four more dou­ble en­suite guest cab­ins in the two hulls. The fly­bridge has a fold­ing helm sta­tion and hard top that seals off the en­tire area when not in use, so no need for cov­ers.

In fact, the 55 is avail­able with five dif­fer­ent lay­out op­tions and four dif­fer­ent power con­fig­u­ra­tions. The one on show at Cannes is called the E-power model and uses the tech­ni­cal set up de­scribed here, but you can also opt for a Cruiser ver­sion with smaller 30kw elec­tric mo­tors or a Hy­brid Power model that uses twin 220hp Volvo D3 en­gines and a pair of 14kw elec­tric mo­tors for shorter stints of elec­tric-only cruis­ing. The fi­nal op­tion is a Sailor model that com­bines any of the above three with a mast and sails.

The com­pany also makes a 64ft so­lar pow­ered cata­ma­ran, pre­vi­ously sold un­der the So­lar Wave name, and is de­vel­op­ing a 79-footer too. It claims to have sold 14 boats so far, in­clud­ing 5 of the new 55s. Keep an eye out for a full sea trial of the Silent 55 in a fu­ture is­sue of MBY.

Con­tact www.silenty­

30 high-ef­fi­ciency so­lar pan­els gen­er­ate up to 10kw of free, silent and con­tin­u­ous power A clever open-plan lay­out cre­ates a so­cia­ble space The spa­cious, pri­vate mas­ter cabin spans both hulls

ABOVE LEFT The panel above the wheel shows how much power is be­ing gen­er­ated and used ABOVE RIGHT One of the four en­suite guest cab­ins

The bank of lithium bat­ter­ies can power the boat all night

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