#1: The most obvious and common choice is a pair of 55hp diesel engines on shaft drives. These have a lot of advantages, but the biggest one is price. These will cost something like $30,000, or more, less than the other three choices. That is a lot of money! Diesels also have the advantage of using a very energy dense fuel, diesel. This means, pound for pound, diesel has more potential energy than what you can put into a battery (which the other three systems all use). Now for the downsides.
#2: A Hybrid Diesel / Electric system. This consists of two electric motors (sail drives most likely) and two diesel generators. Now, you could go with only one generator, but then you would be sorely underpowered for any lengthy motoring situation where you need all their thrust. Let's start with the good stuff. Anytime you are doing short passages, it is unlikely you will even need those generators, so you can make such a passage on zero diesel fuel. The electric motors need no time to warm up, so they
#3: Parallel Diesel / Electric system. Here, you have two 45 hp diesel engines with an electric motor attached between the diesel and the shaft drive that leads to the prop. The system can run on just the diesel or switch to the electric motor. Now you have the option to be a diesel boat, with all those advantages, or an electric boat, with all those advantages. But there is more! If you add a clutch to the
#4 Combo Parallel Engine and 20 kw Electric motor. In this configuration, we have a parallel engine in one hull (see above) and an electric motor in the other hull. Both use shaft drives. Because there is only one diesel, we increase the size of the engine to get 110 hp. That makes it equal to the diesel boat and more than the parallel boat. In the other hull, we put a single 20 kw electric motor that produces up to 28 hp, full out, or 22 hp for long periods. if you add that to the diesel, your total horsepower is 138, more than any of the other options! Better yet, you are getting rid of one diesel engine, meaning you
In the end, we will burn 2,600 gallons less fuel, smell and hear a diesel engine running 6,000 hours less, do shorter passages without burning a single gallon of fuel, have extended range on long passages, including endless electric power from solar and regeneration. And all that, while shedding well over 500 pounds of weight compared to a Diesel boat!
That is why we are going with a Combo propulsion system on S/V Lynx. Right now, we are considering which parallel engine and which electric motor to purchase, though we have some front runners. We want both to have 20 kw electric motors that run at 48v. That limits our choices as many 20 kw motors run at a higher voltages. However, there are some choices available, we just have to decide on which one!
If you would like to see a more detailed comparison of these systems, including a bunch of example passages comparing fuel usage, follow this link to the pertinent page on the S/V Lynx website
Or, just go to www.SVLynx.com later.