Alternatives in Marine Engines

Published: Thursday, February 17, 2011 7:00 am
By: Tom Burden

Are you shopping for an engine? If you're in the market for an outboard to push your dinghy, inflatable, pontoon boat or small sailboat, West Marine has the traditional choice from Mercury Marine, as well as the "green" choice if you want to go electric.

Need to re-power your larger, inboard-powered vessel? Here's where exciting new technology has arrived that echoes the Chevy Volt, Nissan Leaf and the ubiquitous Toyota Prius automobiles. Read below for a brief survey of some new options that are changing the way we power our boats.

Gasoline Outboard Alternatives

2-Stroke DFI engines: Much cleaner than old-style 2-stroke engines, lighter but not as efficient as 4-strokes. Reduced oil consumption (by 50%) over conventional 2-stroke engines. They're available in horsepower ratings above about 75hp.

4-Stroke outboards: 4-strokes have been around for about 40 years and are the most popular small-sized gas outboards, with more torque at lower RPM, quiet operation and smoothe ridling, so they're great for trolling and make good kicker motors for small sailboats. Cleanest gas-powered motors, and currently available in the entire range of horsepower ratings. The intake and exhaust valves in 4-stroke engines are never open at the same time, so they are efficient gas consumers, unlike dirty and fuel-wasting old-fashioned 2-strokes that blow about 30% of their unburned gas directly out the exhaust. 4-strokes run on regular unleaded gasoline, so you don't need to mix in oil with the gas. The "greenest" alternative in gasoline power.

Alternatives to Gas or Diesel

Electric propulsion now provides a real choice, one that more powerboaters and sailors are embracing.This is especially true for sailboats, which use ballast to counteract the windpressure and the towering rig. The weight of a battery bank can be optimally distributed; boats that have replaced their worn-out inboard with an e-drive often see improved performance under sail, as a lightweight electric motor substitutes for engine, transmission, exhaust system and fuel tanks. Batteries can be centered fore-and-aft and located down low.

Of course, electric power for displacement powerboats is not news either. For years, hobbyists and backyard inventors have tinkered with electric motors, and professionals like the Duffy Electric Boat Company have been building electric launches for decades. We recently heard from Mastervolt about a new electric power cruiser that splashed last year in Europe, and garnered an award at its first boat show. The 34' (10.5 meter) Delphia Escape 1050 EKO is equipped with an electric drive developed by Mastervolt, the 7.5kW Silent Prop, with eight 12V/160Ah AGM batteries. A Whisper 3.5 generator provides power to supplement the battery bank. More on this project at www.mastervolt.com/product-news/delphia-yachts-goes-electric.

Battery technology advances too, with flooded batteries being replaced by AGM, lithium manganese and lithium iron phosphate (LiFePO). We have probably reached a technological tipping point, and it is no surprise that we'll soon be seeing electric autos like the Volt and Leaf on the highways.

Thrust vs. Horsepower

Perhaps you're considering the alternatives in gas and electric engines, but how do you compare the two types? Can you relate electric engine output power in Watts to ratings for gas engines expressed in Horsepower? Well, you can't, at least not with the elegance of a formula. 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 workis that you need about 1000 Watts from your electric motor for every ton of displacement of your boat.

Electric Engines with Shore Power Recharging

Torqeedo 1003 Electric Outboard: the German-manufactured Torqeedo outboard is now in Generation II, and while the original 801 model was a bit of a VW Beetle in look, sound and designes thetics, the new 1003 has more of the BMW ethos. At the 2010 Annapolis Boat Show the Torqeedo reps were offering rides on a J24 sailboat (weight 3,100lb.), and we've easily propelled our friend's Antrim 27 using a 1003 outboard.

At a recent round-the-buoys race at our club, we showed up with our Ultimate 20 sportboat with our Torqeedo1003 electric outboard hanging on the transom bracket, but we weren't the only electric-powered sportboat in attendance. An Open 5.7 was also motoring about with the 1003 model. We talked to the owner, who was happy with his decision to "go electric".

The Torqeedo 1003 is manufacturer-rated to run up to 16 nautical miles on the energy equivalent of 1.2oz. of gasoline. It can propel tenders, dinghies and day sailors up to 3,000lb. The table below shows its performance specs:

Speed in knots Range in NM Run Time (Hrs)
Slow Speed 1.5-2.0   12.0-16.0 8:00
Half Throttle 2.5-3.0    6.5-7.8 2:40
Full Throttle    4.5-5.0    2.0-2.2     0:26

Cruise Electric Outboards are remotely powered, and the OR versions are remotely steered with cables. Wewould love to try a pair of remotely-steered Cruise 4.0R on a pontoon boat.They accept standard Teleflex cables, so a retro fit would be a snap.

Pure Electric Inboards or Saildrives

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. In 2009, West Marine introduced the first widely-available inboard replacement, the Mastervolt HybridMaster 2.5. Remove your old Atomic 4 or diesel, clean out the toxic leftovers, remove the old fuel tanks (using only Green disposal methods, of course), adapt the engine mounts, and install the electric drive using your existing prop shaft and prop. Next, add a controller, battery charger, and lotsof batteries!

You'll typically remove about 500lb. of engine, transmission and fuel tankage, and replace them with a lightweight electric motor, and most of the rest of the weight in battery banks.

Last year we read about a new Alerion Express 33 sailboat on the excellent www.Panbo.com marine electronics site, powered by a system of off-the-shelf Mastervolt components (search for "Geek Green" on Ben Ellison's blog). It uses two 24V 160Ah LiFePO batteries,60A ChargeMaster battery chargers, powering a 7.5kW DriveMaster saildrive motor.

This brief quote from the new owner echoes our own experiences with electric sailboat propulsion:

"I get lots of quizzical looks from people in the marina as I glide by in silence while maneuvering. Getting into and out of my very tight slip has become easy now, even single-handed. The intuitive and instantaneous response of the throttle is perfect in these spots. I can stop the boat on the dock within inches of my target, and just step off with a line in hand. Motoring longer distances has been easy too. Range is sufficient, but does require some attention to budgeting the battery, if one needs to go more than 12nm at a stretch. Slowing down to 4 knots extends range substantially, if needed. Noise is a little greater at cruising speed of 5 to 6 knots, but is just the low rumble of the prop noise. The motor itself is truly silent."

Hybrid Systems

Parallel Hybrids (like the HybridMaster) 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. The HybridMaster also has "regenerative charging" potential too, so it feeds power back into the battery bank while you're under sail.

Serial hybrids (like the Delphia 1050 EKO referenced above) 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). Mastervolt offers a wide selection of options, in serial and parallel hybrids and pure-electric systems.

Contact our Product Advice department at 1-800-BOATING and West Marine can work with Torqeedo or Mastervolt to customize a propulsion system for your boat.

Tom Burden, Senior Technical Editor for Creative Services, writes and edits the West Advisor articles in the West Marine Annual Catalogand website. With over 40 years experience sailing, building boats, racing, rigging and writing about sail and powerboats, Tom owns a collection of boats, including an Ultimate 20 sportboat a Laser and several El Toros.