I understand you're asking Scott, not me. I'm going to chime in anyway having some experience studying the use of hybrid diesel electric propulsion and deciding against it. I was tasked with helping decide if hybrid was a good propulsion system for an oceanographic research boat. Let me say up front I am not a design engineer, electrical engineer, naval engineer (with respect to design, not operation) or a naval architect. So I drew upon those experts to help decide. To do the calculation and devise a cost benefit decision matrix. Let me say also that this was almost 7 yrs ago and things advance quickly in this field.
First, how a hybrid performs well. And what it doesn't do well. Think Prius. The design's success is that it captures otherwise wasted energy. Dynamic regenerative braking being primary. It also uses a somewhat under powered fossil fuel power plant. It takes advantage of the fact that even that power plant is often not asked to output anywhere near it's full power. Further the system keeps the gas engine at optimal operating temperature to minimize tail pipe emissions, if the engine is asked to run just to keep itself warm, use it to recharge batteries. So when the gas engine is running excess power is being used to recharge the batteries. So the upshot is a Prius excels at urban driving. On the highway it is like Scott's boat. It quickly depletes the batteries and then runs on fossil fuels. In simple terms, the Prius concept is great at stop and go. Not so good on go without stopping.
How does that apply to boats? One of the remarkable sucess stories at the time, I belive it is still so, was Foss Towing's diesel electric tugs. They were an engineering marvel. But the design only works well for harbor assist tugs. A harbor assist tug spends a lot of time loitering waiting to assist a ship docking and un-docking. In loiter mode, or transiting light boat to it's next job it needs only enough HP to move or keep position. When pulling a ship off the dock or laying alongside the dock it needs
LOTS of hp. They were designed with massive battery banks, huge electric propulsion engines and multiple gen sets. When loitering and running light if the batteries have sufficient charge they are all electric. If a little more power is needed or the batteries need to be charged more diesel gen sets come online. As much as is needed for the task at hand. When in ship assist mode and the capt calls for full power the batteries give full power to the electric propulsion motors while the full suite of diesel gensets spin up and come online. Of course it's more complex than that but that's the simple version.
Keep in mind this only works for ship assist tugs. Long haul tugs would barely get off the dock, their tows behind them and batteries would be depleted. Then it's all diesel to the destination or hand over.
re the oceanographic boat. It's the inverse of the harbor assist tug. A local research boat will charge from one research site to the next but spend most of it's time on station requiring minimal power. The thought was that a modest gen set capacity of multiple gen sets could be designed to work like a Prius in reverse. Without the dynamic regenerative braking. Make enough power between research stations to run the boat and recharge the batteries. On station, battery power alone. Quiet, clean, efficient was the dream. It didn't pan out. The interior volume required to house the batteries, controls, electric motors, multiple generators etc took up far more space than fuel tanks. Even if we were willing to sacrifice the space the cost payback was longer than the design life of the vessel.
So, one heck of a long winded post here. I'm sure with your back ground you'll understand what I'm saying. If you want an all electric boat or a diesel / electric hybrid then go for it. Not because it will save you $0.01 in operating costs. Not because it will increase your range. But because it interests you and you want to do it.
I'm interested in this concept. I'm also interested in cruising the remote areas of BC and Ak. All budgetary considerations aside I just don't think it will work for me. Scott talks about time to recharge at a dock so he can get the first few miles on electric. If I were hopping dock to dock with relatively short runs per day I might consider diesel electric hybrid. But I want to cover longer distances, anchor out at night. Be in a marina maybe 1 day in 10. If I were happy with what Codger2 is doing in his Duffy, and I may be in 10 years, I'd go all electric.
Ah, but this isn't all about me. It's about you and your boat. So, in my opinion, beyond your as yet not stated intended use of the boat, I don't think yours is a good candidate for conversion. She's a converted or adapted gill netter. Scott's is designed from the keel up to be a diesel electric hybrid. Until batteries and charging systems improve the boat has to be designed from the keel up and the intended use has to be suitable for diesel electric hybrid.
A couple more thoughts before I bore you and everyone else to tears. If Foss's diesel / electric hybrid tugs were a huge sucess there would be lots of them and in more fleets than Foss. But there aren't.
One idea I'm interested in following is all electric short haul. Think ferry. Charge across from one side to the other on batter. Slip in to the dock and plug in. While unloading and loading put some juice in the batteries. There would be a slow loss throughout the day but as the wee hours approach and time at dock increases or the boat even shuts down for the night?
Scott,
Thanks for posting up real world numbers on your boat, very interesting.
I think: could a boat (hull) like my present boat be a practical candidate for conversion?
Your boat is expressly designed for low drag, is fantastic in that regard, beats the crap out of my hull form. Weighs in about 5000# less than mine at full load.
The hybrid approach makes sense in your boat, but not sure I would have room for diesel and e-motor (& many additional batteries). I have looked at a couple aftermarket drivetrains like that, so far is a bridge (or boat) too far for me.
The no engine noise part really appeals to me, that is of huge value to me. Like sailing without the sails.
I used to design stuff for automated guided vehicles and involved with other battery powered equipment/motorcycles, so I have an appreciation for what they can/can't do.
Maybe I will cross paths with a Greenline next summer up here, there are a few around. Solar panels on my boat work great, good use of a boat buck.
