Choose an Electric or Hybrid Engine for your Boat
By Tom Burden, Last updated: 6/16/2021
Working for a Blue Future
The author testing an early Torqeedo in 2007. Although we liked the original version, it was pretty klugey in appearance, compared with the current generation of electric outboards.
West Marine is committed to making boating more environmentally sustainable, and with recent reports showing that greenhouse gasses are being added to the atmosphere at an alarming rate, there is a lot we can all do to make this global situation better. If you want to make a difference for cleaner boating, consider these actions:
- Get rid of that two-stroke outboard: Four-stroke outboards, like the models by Mercury Marine that we offer, run quieter, are cleane and are much more fuel efficient than two-stroke engines. We also offer propane-powered outboards by Mercury Marine which are cleaner and more efficient than gasoline-powered models.
- Consider an electric or hybrid alternative: We’ll look at this maturing technology below. If you’re considering a new engine in your older boat or planning new construction of your dream vessel, a hybrid or all-electric option makes sense.
Electric Outboard Engines
Torqeedo Electric Outboards: After testing Torqeedo outboards for years, we are believers in the product. So are our customers, including the man who posted the following review on an earlier generation Torqeedo motor:
Torqeedo Travel 1103 Outboard
“Fantastic Gas Outboard Alternative! Impressive quality and engineering. I use it on a Watertender 9.9 and my expectations have been exceeded. Range and speed are very good. I replaced a 4hp four-stroke and really like a gas-/oil-free 30lb. motor. I ran it several hours, approx. 2-4 miles and got home with 50% battery remaining. I am planning on adding a solar panel to extend the range and recharge while at the sandbar. Considering its weight at 29.5 lbs. and range of 2-16NM depending on speed, no oil changes, water pump impellers, thermostats, tune-ups, flushing, not having to start and warm-up, not having to reach back to shift F-N-R, only twisting the throttle. This is the perfect outboard for 2-4hp applications. I Love It!”
Torqeedo Travel Outboards feature an integrated lithium-ion battery. With efficient operation, they are a great alternative to small gasoline-powered outboards. The Travel 1103 model can do everything a 3 HP outboard motor can, but is lighter, cleaner, quieter, and more convenient. Torqeedo Travel outboards can easily propel tenders, dinghies and day-sailers up to 1.5 tons. Torqeedo Travel outboards include an on-board computer with GPS-based range calculation as standard which can be accessed from a smartphone app.
Torqeedo Cruise Outboard
Torqeedo Cruise Outboards are powered by an external battery and include a choice of tiller- or remotely steered models. The photo (below) of the inflatable moving smartly along on a full plane shows a Cruise system in operation. A planing electric-powered boat is a huge breakthrough for the technology, as the conventional thinking used to be that the batteries were too heavy. With lightweight Lithium batteries, e-propulsion is beginning to make sense for runabouts, and not just for train locomotives, sailboats, container ships or submarines.
Pure Electric Inboards
The most successful electric propulsion retrofits have happened on inboard boats, with drop-in electric motors that directly replace your old, dead gas or diesel engine. Remove your old Atomic 4 or diesel, clean out the toxic leftovers, remove the old fuel tanks, adapt the engine mounts, and install the electric drive using your existing prop shaft and prop. Next, add a controller, battery charger, and lots of batteries!
You’ll typically remove about 500lb. of an engine, transmission and fuel tankage on a 30' boat and replace them with a lightweight electric motor, and most of the rest of the weight in battery banks.
Last year, Alerion Yachts began offering electric propulsion on their new production boats, with a Mastervolt electric pod drive as a “no charge” option on their popular Alerion Express 28 sailboat model, substituting for the normal 14hp diesel saildrive. Here is their August 29, 2011 blog entry, presenting a great overview of the benefits (and caveats) of pure e-propulsion:
As most of you know, a typical day sail with a diesel motor consists of checking oil, opening seacocks and starting the old “iron”. These trusty motors sputter and come to “life” with a gurgle and spray of raw water from the exhaust thru-hull. We shove off from the marina or mooring, hoist the sails and enjoy a fulfilling day of Alerion sailing.
The Alerion Experience is different with electric propulsion. With this technology, a turn of the battery switch and a nudge of the throttle trigger instant, silent thrust. The boat moves eerily along while onlookers pause and wonder how an Alerion can move so silently without sails. The transition from power to sail is graceful and smooth. With sails filled, the DC current changes direction; the spinning propeller steadily regenerates current and slowly charges the batteries.
Our RIB 310 inflatable boat on a plane, powered by the Cruise 4.0 outboard and a lightweight lithium battery bank
The benefits of electric propulsion are numerous: completely sealed systems, low maintenance, silent operation, increased maneuverability and simplicity. The benefits easily outweigh the costs for most sailors’ lifestyles. However, with great breakthroughs, there are always other considerations. Currently, the system designed for the Alerion Express 28 is optimized for boats that are stored in marinas. Although there are solar and prop regenerating options, a good old shore power cable ensures a fully charged system every time you step aboard. The basic system specified for the Alerion Express 28 has a range of approximately 5-7NM depending on speed and weather conditions. For most this is sufficient for a typical day sail. There is room and capacity for more batteries/range on the Alerion Express 28 but there are obviously cost and weight compromises to consider.
One of our existing electric propulsion owners loves the system for many reasons. The biggest reason is that he finds himself sailing more and not defaulting to auxiliary power as much. During the testing phase our design team was startled by the simplicity and silent transition from power to sail and back to power.
Maybe sailors will use this technology on those glorious sunset evenings when there’s no wind in the same spirit of a classic Elco launch. No wind, no noise, just the sound of a pretty boat moving through the water. Pure and Simple.
Video of an e-boat
Here is a YouTube video about an electric Alerion Express 33, which gives you a glimpse of why we love e-propulsion for sailboats. This vessel is powered by an inboard DriveMaster Ultra 7.5kW system, powered by two Mastervolt lithium 24/160 batteries with a total of 320Ah of energy at 48V.
You can see how the near-silent power instantly comes on, without waiting for a diesel to rev up. We have enjoyed the same experience during the last eight years while ghosting along in our Torqeedo-powered Ultimate 20.
Parallel Hybrids (like the HybridMaster, available from Mastervolt) combine an electric motor with a combustion engine, and represent some of the coolest new technology. Use silent battery power to get out of the harbor, and fire the diesel up if you need to fight against a big current or wind. Running the combustion engine recharges the batteries using the electric drive. The HybridMaster also has “regenerative charging” potential too, so it feeds power back into the battery bank while you’re under sail. Owners of hybrid autos, like the Prius, will feel at home with this technology.
Serial hybrids use an electric motor as the full-time propulsion engine, with a gas or diesel generator to replenish the battery banks (like submarines, diesel/electric locomotives and ships).
Size of an e-drive compared to a gas or diesel
One key difference between gas and electric engines deals with torque; with a gas or diesel engine, the torque increases rapidly when RPM goes up. Rev the engine to get lots of “oomph.” An electric engine has a flat torque curve, meaning you get all available torque at even the lowest RPM—when you most need it. Thus a small electric motor can actually replace a much larger combustion engine. One rule of thumb that seems to work is that you need about 1000 watts from your electric motor for every ton of displacement of your boat. An e-drive’s shaft horsepower (shp) rating needs to be about one third to one half the brake horsepower (bhp) of the combustion engine it replaces.
Motoring hours vs. battery size
The number of electric motoring hours depends on your battery bank combined with any generated capacity (from solar, wind, regen or other sources). According to Mastervolt, for six to eight hours of operation, you need 4.6 times the motor’s power output in kWh. Example: 4.6 x 3.5kW = 16.1kWh; this is the battery capacity required for six to eight hours of e-powering.
What type of battery should I choose?
There are four categories:
Flooded lead acid: most affordable are 6V deep cycle batteries, often used in electric golf cart, with a typical capacity of 200-250Ah. They are economical and are built for deep discharges. They need to be mounted upright and receive regular addition of distilled water. They also emit hydrogen gas when recharging.
AGM batteries are fully sealed, maintenance-free, handle high recharging current and can be mounted in any position.
Gel cells are sealed, maintenance free, with a long lifespan allowing a large number of charging and discharging cycles. They are excellent as a service battery for medium and large systems.
Lithium-ion batteries are top quality but most expensive, with highly advanced technology. They have a high energy density and are perfect for deep cycling applications. Compared to traditional lead-acid batteries, Lithium-ion batteries offer savings of up to 70 percent in volume and weight, while the number of charging cycles is three times as large. Delivering 104Ah from a weight of only 44lb., Torqeedo’s Power 26-104 features four times the energy per pound of battery weight compared to conventional gel or AGM batteries.
What is the lifetime of the battery pack?
With proper care, a battery pack can provide five to seven years of clean, reliable service.
Mastervolt offers a wide selection of options, in serial and parallel hybrids and pure electric systems, which are shipped directly from the manufacturer. Contact our Product Advice department at 1-800-BOATING and we can work with Mastervolt to customize a propulsion system for your boat.