Good points Adelie. Good reminders. In my enthusiasm I had forgotten how efficient some mechanical drives can be made to be, and how inefficient it is to convert energy from one form to another.
There are lots of efficiencies: total cost of operation per thrust, weight vs thrust, size vs thrust, etc.. Low maintenance
costs and high torque of DC motors are distinct advantages. Total cost of operations are not always immediately obvious in a system such as the propulsion and electrical
generation systems of a boat, and are worth considering.
I don't use an engine much and would usually only need docking
power. 110 amps at 48v would propel me at hull speed
for over an hour, and a couple of hours at reduced speed. A DC motor that can also be a generator when the prop is dragged through the water would allow recharging any time the wind
is blowing enough for the drag not to matter. Batteries and Diesel or gas generator could be located anywhere convenient, or helpful to stability. They would not have to occupy some of the best part of the vessel inboard installations often do, nor the other frequent option of being crammed into a maintenance
As for do-gooder solar nuts... During the 1970s oil
crisis there was lots of discussion about oil
, how much left, etc., etc.. I did a calculation based upon the rate of growth of energy consumption
since the discovery of oil to 1970, and projecting that growth rate out to infinity assuming that every particle of earth could be converted to energy as efficiently as oil can be in order to answer the question, how long before every particle of earth would be gone. Answer: approximately 500 years. The world has to move from fossil fuels to renewable forms of energy and the sooner the world does so the more freedom of the seas us cruisers will continue to enjoy, and the less chaos, death, and destruction there will be (Oil grows food
. Nations exist or fail based on whether they can feed their people or not. We've seen the problems created by just a couple of failed states.)
I can only justify the continued use of my ecologically horrible 2 cycle outboard because it gets very little use and I spill more oil changing the oil in my car than pours through its exhaust
. Given current reality I will probably replace it with a 4 cycle outboard, because a feasible electric option is not immediately obvious. But until I do buy a new outboard, I am not done exploring the possibility of electric drive. For those needing to replace an inboard drive there apparently are viable cost and performance options (see the link in my prior post).