These spin round on a rotating ring driven by electro magnets for minimum resistance and drag. Electric drivetrain manufacturer RAD Propulsion tried a similar set-up for its own electric outboard and found it very efficient at lower speeds but not so good at faster speeds.
Because the BlueSpin Outboard system is only designed for low-speed cruising between 6 and 10 knots this makes perfect sense, maximising its electric-only range.
Retractable drives
Ultimately, the range will depend on the size and number of batteries fitted but BlueNav reco*mends 6 LFP batteries of 7.2kWh each for a total of 43kWh. These can be installed anywhere inside the hull and should give 2-3 hours running time at 7-8 knots – around 20nm.
Like an outboard motor, steering is achieved by vectoring the thrust from side to side but, unlike an outboard, these drives can rotate through 360 degrees, enabling them to operate in astern by spinning 180 degrees or act as unusually powerful stern thrusters by pushing sideways in tandem at 90 degrees.
Bespoke throttles and software give independent control of the electric drives to minimise interference with the main engines
In fact, with the help of a suitably powerful bow thruster, it should be possible to move the whole boat sideways onto or off a pontoon without any assistance from the main engines.
The usual disadvantage of having an extra set of drives hanging off the transom, namely the drag created by the propellers when they aren’t being used, has also been neatly side-stepped by making the unit retractable.
When not in use the rim-drives simply lift up into the housing on the transom, keeping them out of the way of the waterflow passing under the hull. The only thing this might affect is the positioning of the trim tabs, which are usually mounted in roughly the same place on the transom.
This aside, BlueSpin Outboard looks like a very convenient solution for boat builders or owners wishing to retrofit a hybrid drive solution to a new or used boat without having to change the existing engine set up.
According to BlueNav, in most cases “installation requires no alteration to the existing propulsion system or the boat’s structure, providing hassle-free transition to electric power.”
Alternative options
At the moment the BlueSpin Outboard model is limited to 15kW per side and needs to be installed in pairs due to the offset mounting positions, but a 30kW (40hp) version is under development as well as a smaller 8kW (11hp) drive.
BlueNav also offers a retractable Inhull design and a Stationary fixed version. The Inhull one is designed to be fitted further forward on the centreline of a boat and retracts to leave a flush-fitting plate in its place.
A typical installation on a 30-45ft twin outboard day boat
This looks best suited to flat-bottomed craft like sailing yachts or perhaps a round-bilged motor boat. The Stationary version is a fixed solution that is designed to sit under the hull of slow moving displacement boats where drag is not as much of an issue.
BlueNav is being a little coy about revealing retail prices to the press, saying only that prices are available on request. We’ve not yet had a chance to see or experience it in action but as a quick fix solution to creating a hybrid drive option on an existing boat, it certainly seems like a very neat idea.
First published in the October 2023 issue of MBY.
If you enjoyed this…
Be first to all the latest boats, gadgets, cruising ideas, buying advice and readers’ adventures with a subscription to Motor Boat & Yachting. Available in both print and digital formats, our monthly magazine will be sent directly to your home or device at a substantial discount to the usual cover price. See our latest offers and save at least 30% off the cover price.
Source: BlueSpin Outboard retrofit system makes switching to hybrid power easy (http://ht**://www.mby.c**/features/bluespin-outboard-retrofit-system-hybrid-boats-128915)
Topic: BlueSpin Outboard retrofit system makes switching to hybrid power easy 
