Where are we with hybrid drive for powerboats?

by philg

Twelve years ago I wrote a post asking why there weren’t Prius-style powerboats. I was out the other day on a friend’s sailboat (“it was like time had stopped”) and it occurred to me to check up on this concept.

Here’s what I have found:

It seems as though we still don’t have a Prius-of-the-waves, i.e., a mass-produced boat where the propeller is sometimes driven by the internal combustion engine and sometimes by an electric motor. Matt O’Toole’s comment on the 2003 posting was “Modern generator sets are really quiet, and electric motors are very small, simple, and reliable, and don’t require a separate gearbox — just a switch to go backwards. I think the way to go about this is to forget the Prius (which has a much different set of service requirements), and use a standard marine generator set, a big bank of deep cycle batteries, an off the shelf marine charging system, and an electric motor of your choice.”

Is it as simple as this mournful chart of energy density? Is the extra weight of batteries in a boat more of a hindrance than the extra weight of batteries in a rolling vehicle such as a car? Why should weight be bad when a lot of boats (sailboats at least!) have lead ballast in the keel. Why can’t batteries at the bottom of the hull be the source of stability? (The German battery holds 40 amp-hours at 345V. They say that an 80 hp push can be sustained for about 30 minutes with two of these batteries (range chart) or a slow cruise can be maintained for hours.)

Is the problem complexity and the harsh marine environment? In some ways it is hard to beat the simplicity of a shaft bolted to the back of a diesel engine, though presumably the lack of moving parts in a solar-powered system could make it more reliable than anything where the source of energy was combustion.

19 thoughts on “Where are we with hybrid drive for powerboats?”

  1. Submarines have been diesel/ electric hybrid drive since forever.

    Many modern cruise ships use diesel/electric propulsion. The diesel engine drives a generator and the electricity produced is used to spin an electric motor attached to the prop (as well as to provide lighting, etc. on the ship) . However, they skip the batteries entirely. This way the diesel can operate at a constant speed where it is most efficient.

    So all of these concepts are doable. The question is whether they are economical and make sense in the context of a pleasure (or other) boat. As it is, a Prius makes little sense for most drivers, but most pleasure boats travel much less than the 12,000 miles/year people put on their cars, so the payback period for all this extra hardware in order to save a few gallons of fuel is forever.

  2. The points you make are probably valid for the power/high speed boats. With the sailboats the engine is so sparsely used that many owners are worried about not burning through a tank of gas (or diesel) in one season and having it go stale. As far as the ballast on – you’d want a light hull with the weight as deep as possible below the waterline. Someone should invent a keel with a built in maintenance free lead acid battery.

  3. If you look at tugboats, harbor boats, and short haul ferries you will find more. The hybrids tend to be more complex, more capital cost, cleaner, quieter, and lower operating cost. Right now hybrid short haul ferries and in-harbor boats are more cost effective in countries with strict emission controls. Air pollution controls on diesels add cost and shift the balance.

    For example, a recent harbor boat delivered to Amsterdam uses the batteries when sitting at dock or holding position without a load. The diesels turn on when moving, pushing, or pulling a load.

  5. Phil,

    Think sailboats! They are true hybrids and most of the time do not use a drop of oil!

  6. Many reasons. All boats operate in the water – but the missions differ greatly. The Elco is perfect for a quiet, stately river cruise, but all other boating pursuits indicate a different power/weight/range profile. For example, sportfishing boats have deep vee hulls below the water line to go fast on the plane in heavier seas, but this mission requires a great deal of engine power. A 50 foot sportfish will have 800 to 1000 or more HP – but there is still a need to keep the weight down (batteries not practical) to attempt to minimize the fuel burn.

    Irregardless of the size or mission, for the most part, a boat is operated at a constant load. This type load is just right for diesel engines, and to some extent, gasoline engines can be included. So the conventional marine power train is already delivering the efficiencies associated with a constant load; needing no electrical components.

    The reason cruise ships are moving to electric propulsion (google on azipods) is because of the staggering electrical loads exclusive of propulsion found on cruise ships.

    The last negative is complexity. Quality boats are already expensive, and adding batteries, electric motors, and controls don’t really get you much of anything over the simple diesel engine propulsion systems when the additional construction and maintenance costs are figured in. Prudent owners also place a premium on reliability, seen as much enhanced with a diesel engine just turning a propeller.

    For specialty applications (we have a tender with an electric trolling type motor and a lithium power pack) electric (as a part of a hybrid system or batteries only) makes good sense. As noted by previous posts, there are specialty missions where hybrids work great, but IMHO, use by recreational boaters in the US is a long way off – waiting for the magic battery like everyone else.

  8. Check out setsail.com. Steve and Linda Dashew are veteran sailors who now build a line of powerboats in New Zealand that range from 67 to 110 feet (premium build quality, premium price).

    Steve, in 2010:
    “For our service where reliability is an absolute requirement the yacht level diesel electric is problematic at this time. It is also much more costly, and our genset needs are so minor that this is not a benefit (we have the required DC/AC power now with our big alternators and inverters. But we keep watching this. Maybe a few years down the road.”

    They definitely believe in solar panels, though, and it really makes sense on a properly designed boat. Solar not only reduces carbon output (who cares) but more importantly reduces noise pollution. The sound a generator makes while anchored in a nice quiet bay can carry a great distance.

    http://www.setsail.com/fpb-97-efficient-at-anchor-and-underway/

    That FPB 97-1 is their latest boat and I think it’s a gorgeous, practical boat.

    http://www.setsail.com/fpb-97-code-name-wicked/

  9. Solar panels + darrieus wind turbine + battery pack is interesting for boats in constrained channels like the intracoastal waterway where tacking sucks. On a boat already with a gasoline/diesel engine I can’t imagine the added complexity is worth it.

  11. Internal combustion engines are most efficient (energy produced/fuel used) at the RPM that delivers peak HP at wide open throttle. Peak HP is generally limited by the volumetric efficiency of the engine. Depending on camshaft duration, lift, and timing, intake restrictions, exhaust restrictions and sound wave tuning, more efficiency can be had by turning at a higher RPM. Higher RPMs increase friction, leading to diminishing returns. Diesels don’t have throttles and vary power by the amount of fuel injected, thus they have no throttling losses. Gas engines run at a fixed air fuel ratio and control power by restricting the air intake with a throttle.

    To get the best highway fuel efficiency from a car with a gas engine, you want an engine spinning high in the RPM range (at the HP peak) at wide open throttle (WOT). This car that was operating at peak efficiency going 70 mph might require 60 hp, but it would take forever to accelerate to that speed. Instead manufacturers build engines with much more power than is required for travelling at 70mph. These engines are then heavily throttled (read inefficient) going down the highway, but especially when cruising along at 30 mph.

    The Prius increases fuel economy by using a much smaller engine, and assisting that engine with a battery for acceleration. Thus the Prius gas engine spends much more of it’s life at WOT. The fuel efficiency of a Prius is comparatively much better at city driving than it is a highway driving when compared to a conventional gas powerplant with equivalent total power output.

    None of this matters for most power boats. Powerboats spend a much larger proportion of their life at WOT than passenger cars. They also don’t accelerate and decelerate like passenger cars, so there isn’t a chance to supplement the gas motor run at narrow throttle openings with an electric assist.

  12. Paddy’s analysis is excellent. It raises the question of why Americans don’t just buy diesel cars, which are just as efficient as hybrids without all that expensive electrical equipment. In Europe this is considered a “no brainer”. In businesses where fuel consumption is a vital question of economics (trucking), fleets switched to diesel many decades ago. I guess aside from a few preeners who want to show off their environmental consciousness by driving Priusi, most Americans really don’t care about saving a few $ in fuel every week. That GM once sold the world’s worst automobile diesel engines and thereby ruined the reputation of the diesel car in America didn’t help either, nor does the fact that diesel fuel sells at a premium to gasoline and that German mfrs charge an arm and a leg for their few diesel offerings in the US.

  13. I think that diesel cars are not popular in US for few reasons main of which are noise and extra maintenance required as well as limited choice of diesel cars from car manufactures. Was looking to by a diesel and found out that some German cars designed not to start if urea tank has not not been refilled. It is a good idea to maintain car regularly but this is an extreme I do not want to test. Also there is a premium to be paid for diesel engine in a small car that negates or eats into savings at the pump depending on mileage. If diesel engine replaces gasoline engine diesel price is bound to grow as well…

  14. Knowing several former German diesel owners in USA, I know other reasons that Americans don’t buy them. When they fail (like a VW TDI did w/i 40k miles), *no one* around here can fix them. Dealers, specialists, mechanics from other states, they all replace the same few incredibly expensive parts, and it still barely runs. Forget about driving it over 10 mph.

    I know some will claim that diesel sold here is impure or whatever, but American-made diesel trucks run forever on it, so that is an incomplete explanation.

  15. Anonymous new diesel trucks sold in USA are the same way with respect to the urea solution. It’s cheap at the truck stop, so it’s not really a problem.

  16. Had no idea urea could be replaced at any truck stop. Now if VW TDI quality record was better I would consider it for my next vehicle, not really ready to spend on Mercedes bluetech diesel for mostly daily commute use. Does anyone know why GM, Ford and Japanese automakers are down on diesel engine in small to medium cars?

  17. Does anyone know why GM, Ford and Japanese automakers are down on diesel engine in small to medium cars?

    They are not really “down” on them – they sell tons of them in Europe (about half of all cars). It’s the American consumer that doesn’t demand them. Car makers are very responsive to demand (whatever is selling well among their competitors). If SUV’s are selling well for say Jeep, then EVERYBODY starts making SUV’s to steal their sales – even Porsche, even though it makes no sense for them as a brand. To hell with brand identity – Money talks. So if American consumers were demanding diesels, we’d be getting them up the wazoo just like you can get every conceivable brand and flavor of SUV today. But Americans don’t want them.

    Regarding urea, you don’t expect your car to run if it is out of oil or gas or coolant. For a modern diesel, urea is considered essential to their (clean) operation, so why should you expect your car to run without it?

    The urea fluid tank on a Passat for example, holds 5 gallons and lasts for around 10,000 miles. Several thousand miles before it goes dry, a light comes on so you have plenty of time to top up. About $25 worth will fill the tank for another 10,000 miles. To me, this is no reason not to buy the car but you can see that people will invent all sorts of excuses to rationalize their decisions. Modern diesels are NOT noisy or smelly. I drove a Ford minivan with a diesel engine in Europe for several weeks and it was indistinguishable from a gas powered car, except that a tankful of fuel lasted an incredibly long time.

  18. And anyway VW and Mercedes seem to sell diesel cars states-side, apparently not very reliable vehicles to boot in case of VW. It is a big question one anyone would buy car that breaks at 40K miles when larger Hondas and Toyotas that drive 300K + miles without issues and get just under 40 miles/gallon are available at significantly lower price. My guess that the fact that small diesels sell well in Europe is that Europe protects its car makers. I once worked with an European who had no idea how civics and corollas drive. Once he found out he bought a Japanese compact car and never looked back.

  19. Diesels break down because people don’t know how to drive them. Yes, they are more complex than the basic petrol engine. If you only ever do short trips with a cold engine you will destroy the DPF filter (and other things like EGR valve) in no time. Stick to petrol or hybrid for such use. Diesel loves longer trips. Also, if you don’t let the turbo cool down it’s going to go soon (OK, that’s relevant for any car with a turbo).

    Urea is a non issue. I didn’t even know my fathers car used it for 7 years he was driving it. The warning message only came on once, 2 months before he sold it. Turned out it was simply refilled at every regular service interval. Even if it happens in the middle of a huge trip you can still refill yourself at nearly any gas station.

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