I recently published a video walkthrough of the Greenline Hybrid 39. This is a production cruising vessel that is offered with a hybrid drive system built into its primary propulsion system. In short, the hybrid system allows the vessel to cruise at 4.5 knots for 20 miles on its fully charged lithium batteries, or conventionally under diesel power at speeds ranging from displacement to semi-displacement. The batteries are charged either from the solar array on the cabin top, the engine driven generator or shore power when available. While the 20 mile range is fairly small, the system is useful for entering and exiting harbors, or quietly exploring small coves close to shore. One additional benefit of the combination of a large battery bank and charging capacity, is that prodigious electric power is available through an inverter to run all of the boats house systems including the AC, silently without a need for a generator running. This makes time on the hook quite and comfortable.
Today, hybrid/electric options for boats are somewhat limited. The issue, of course is the size and weight of the batteries versus the power consumption. Unlike a car, which uses a lot of power to accelerate up to cruising speed, and very little to stay at that speed allowing EVs to offer range similar to internal combustion vehicles, boats use power accelerating and maintaining a given speed. There is no coasting and the drag resistance created by moving through the water is fairly consistent. Once a car is rolling, it takes far less energy to keep it rolling then it does a boat.
There have been significant advancements in small electric outboard motors from Torqueedo and others to a point that they are competitive with auxiliary outboards up to 3.5hp with built in batteries and up to 80 hp with batteries in the boat. While these offerings are more costly than their internal combustion cousins, they are a very good alternative for dinghies and small craft.
Similarly, there are inboard offerings for small boats and auxiliary sailboats that offer that same kind of quiet green alternative to burning fuel. With any electric power plant, range is always the issue due to the fundamental difference in the amount of energy that is stored in a gallon of gas or diesel v. The equivalent weight in a battery cell. For the time being, range is the achillies heal of electric power plants. As battery technology improves, so will range for boats.
Hybrid drives like the aforementioned Greenline vessels, are very viable alternatives in that they allow long distance cruising under diesel power usually at displacement or semi displacement speeds from a modest size engine and then shorter range on all electric power. The added benefit of superior electric power for house systems is just a bonus.
At this writing, Greenline is the only manufacturer of production hybrid vessels. They occupy a niche market at the moment but given that there really are no compromises by adopting such technology, other manufacturers may step in. According to one owner of a 39, Greenline has manufactured hundreds of their various models which is a good indication of the acceptance of the technology. It helps that the boats are high quality, stylish and very reasonably priced. The 39 starts at $395,000 including the hybrid drive system according to their website. Under diesel power alone, the 39 can cruise 1,000nm at 7.5 knots on 185 gallons. That is pretty efficient cruising. The boats are made in Slovenia which may contribute to their value pricing.
Will hybrid.electric boating be part of the future, at some level yes. As EVs become more commonplace on the road and people become more use to seeking alternatives to internal combustion power, the demand for this type of power in boats will increase. As battery storage technology improves, and all electric range approaches distances typically travelled in a single days boating, 50-100 miles, we will see greater acceptance and proliferation on our waterways.