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