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Old 02-02-2021, 15:58   #1
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energy storage density, electric propulsion and safety

from my perspective the issue of energy density isn't so much about sustainability per se. It's more about safety.

Diesel is about 10Kwh per litre, and as a stable liquid fuel it's easy to manage. you can work out the range of a vessel with a 400L tank for a certain cruising speed or rpm, and be aware of how far you'll get against bad weather.

Electric motors will probably convert more KWh from their fuel that an I.C.E but regardless, the point is that most of the time, you will never need that stored energy, however when you do it may be critical to survival.

So how can you get to a similar level of safety margin with electric propulsion? 4000 KWh in a 400L diesel tank, would take several tons of batteries, or what size fuel cell stack?
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Old 03-02-2021, 11:20   #2
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Re: energy storage density, electric propulsion and safety

You do it by having a large enough battery bank to handle most conditions, plus a solar or wind generator sufficient to charge the batteries under most conditions. Then you have a genset sufficient to propel your boat without the batteries for your OMG moment, which you rarely use. So far, no one has come up with a battery that can store as much energy as a fuel tank, or a way of refilling a battery in a few minutes as you would refill a fuel tank. Electric cars have the same problem.
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Old 03-02-2021, 11:53   #3
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Re: energy storage density, electric propulsion and safety

Quote:
Originally Posted by barrymac View Post
So how can you get to a similar level of safety margin with electric propulsion? 4000 KWh in a 400L diesel tank, would take several tons of batteries, or what size fuel cell stack?
Why do you need to store 4000Kw of power? How about trying 14Kw, that's 12 x Group 31 batteries and seems quite achievable if you take the diesel engine out.

This guy has just done a cirumnavigation of the North Atlantic. You could watch to see how he go along without an engine.

If you have a yacht and don't need to sail to a time table so being back on Sunday night to go to work on Monday morning, then a number of yachts have proven its quite possible. A trawler might be a problem and a Miami Vice Cigarette 50, well your stuffed.

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Old 08-02-2021, 18:48   #4
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Re: energy storage density, electric propulsion and safety

I really like this guy's style, I aspire to such a state of zen. Of course with the right type of boat no engines are necessary. I sailed on one such boat for a time, he did tow a genny to keep the beer cold. I enjoyed the minimalism.

It's a very different experience to a modern fast catamaran of course. I wondering what people consider a safe amount of motor propulsion runtime to be carrying, on a boat that would depend on mechanised propulsion in some circumstances.
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Old 09-02-2021, 04:20   #5
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Re: energy storage density, electric propulsion and safety

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Why do you need to store 4000Kw of power? How about trying 14Kw, that's 12 x Group 31 batteries and seems quite achievable if you take the diesel engine out.

This guy has just done a cirumnavigation of the North Atlantic. You could watch to see how he go along without an engine.

If you have a yacht and don't need to sail to a time table so being back on Sunday night to go to work on Monday morning, then a number of yachts have proven its quite possible. A trawler might be a problem and a Miami Vice Cigarette 50, well your stuffed.


the point here is you have an engine as comfort and added security when the **** hits the fan.


To compare apple with apple I fully agree with barrymac.
I wouldn't take 400l but 200-300l if you are in a 3 day storm is easyly used when engine runs day&night to safe your ass.

72h by 4l/h (45ft/60hp engine runs on higher RPM, not comfortably motorsailing)= 288l, lets go in the middle say 250l = 2500KW in the batteries

And this is what you have bluewater sailor have to count with on a long range passage.


So its 2500KW that need to be stored in batteries or fuel cell, to be 100% comparable and have the same security then with a diesel and a 250l tank.



Lets face it and be honest, every electric boat that kinda works well out there is

- very lightly build, with high efficency hull, spartan interieur with a lot of compromises in liveability to safe weight=> and if you would put a diesel in that boat in can be half size (eg 20hp instead 40hp in a 40ft) and uses min 50% fuel less then a conservative bluewater comparable one (so 2l/h instead of 4l/h. So reduced emissions already by half. And to this you need to compare then to the electric boat (not the heavy bluewater cruiser with double engine size to be fair and 100% comparable). But how much energy&pollution does the production of the carbon fibre you use to make it very light causes? A lot and how does the total co2 balance look like, deep red
today and near future, with same(!) safety and comfort as a diesel engine (with around +30% higher purchase price then diesel boat):
- full electric daysailing => a clear yes
- classic med full electric sailing, habour to habour day sails and occassionally 2 or 3 days trip but you could stop daily at habour if you need. => a clear yes

- bluewater sailing, weeks over open ocean and a strom or other event can happen where you need your ironhourse for several days straight or simply the use the panama canal (obligation to be able motor for 3 days with 6kn to be able to use it) on your way around the world=> a clear NO, no energy concept avaliable that can store the needed 2500kw on a 45ft sailboat.


same story with cars: i was forced to have a tesla Model S as company car last year. I warned our CEO before...doing 60000km/year with a Tesla impossible especially with my tide scedule. Well it lasted a week, where I got picked up 4 times by a tow truck because the 300km+ range shown ended up in reality less then 180km range with no charger nearby plus forced breaks to recharge missed 8 customer meetings and 80k turnover, maybe more because don't know if there would be additional business. Driving overall was horrible, yes nice torque for excelleration but
constant watching of the dreaded battery level was stress pure. And that compares to bluewater sailing.

A week later I had my BMW 335xd that I had requested (instead a 520d, i like smaller and more hp for german highway) and all was fine...
I owned privately a electric Renault twizzy myself, to go to my 5km away workshop, quickly shopping in the area etc for that it was perfect, fitted upfront our house on the motorbike parking spot and was heavly incentivised so it cost me less then a motorbike.
Nothing against electric where it makes sense...


quit, sold everything and 100% bluewater cruising on a 40ft longkeeler pilothouse ketch (soon a 36 Mahe evolution i hope)
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