POWERTRAIN
elements. Without these, any moisture that gets into the bearing will cause rapid corrosion and deterioration. Although this is a logical route to take, users must be aware that this approach can greatly increase bearing torque, hindering performance. When assessing the suitability and quality of bearings, it is also important to look beyond the external aesthetic. Users who have 440 grade stainless steel bearings in their electric boats may start to see signs of corrosion on the outside of their bearings. However, while the instant reaction may be to assume that this will cause the bearings to fail, external corrosion may have no eff ect on the bearing’s internal rollability and general performance. Inside however, marine bearings
must be protected from ingress of contaminates. Wherever there is potential contact with salt, water and the elements, bearing material choice is extremely important. Although full ceramic bearings are more expensive due to the greater diffi culty in machining to precision tolerances and the cost of the raw material, they are an excellent choice for electric boats due to their impressive corrosion resistance properties, even when fully submerged. Bearing lubricants work by simply
reducing friction and dissipating heat to stop elements from overheating — the two most basic types being oil or grease. Regardless of which you choose, extreme temperatures can dramatically aff ect the eff ectiveness
Complex outboard motors with ignition coils could soon be a thing of the past
of a lubricant. Operating in reduced temperatures, without the correct lubricant, will result in a higher viscosity lubricant, which can increase frictional torque signifi cantly. Where marine bearings are
immersed in water however, there may be very little heat build-up, so lubrication is not always necessary - particularly with full ceramic bearings. Fortunately, if lubrication is required, there are water- and saltwater- resistant lubricants available, even for submerged bearings. Many of the dilemmas faced
when choosing bearings for electric
boats apply to all marine applications - should load rating or corrosion resistance be the priority? It’s a fi ne balance that must be achieved by considering the long-term demands of the bearings, as well as the harsh environment they will be used in. Either way, electric boats are on the rise, and with pioneers and major companies committing to reducing emissions, the future is electric. ●
The author is managing driector of marine supplier SMB Bearings,
www.smbbearings.com
All features great and small
Electric boats came under the spotlight last summer when climate activist Greta Thunberg crossed the Atlantic in one. Her ride, the Malizia II negotiated the 3,711 nautical mile trip in two weeks. With the power density
of cells and the space constraints onboard a ship one might be forgiven for
assuming small vessels such as that are the limit of electric power on the water. MBNA Thames Clippers,
providers of London’s River Bus disagree. After Transport for London (TfL) paused the proposal to build a bridge between Rotherhithe and Canary Wharf due to its escalating cost, the company has proposed a
large electric ferry capable of carrying 150 passengers per trip, half of which could bring bikes onboard. Total capacity would be 2,250 people per hour, per direction. The cost is estimated to be
around £30 million, which looks cheap considering the bridge option is around 20 times more expensive. TfL is considering it.
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