serious discussion about electric power in large boats

[misfits]

Originally Posted by SwellGuy

I'm not sure "days" describes it properly.

Even if we use your 5 horsepower figure (which is obviously inadequate for a ship this size, but what the hell, let's be optimists) we are talking

5hp * (745 watts per hp) = 3725 watts of power

Now if we use your trip time, and optimistically assume that this 5hp motor is somehow going to move this ship 100 miles in 15 hours, we are up to

3725 watts * 15 hours = 55875 watt*hours of energy

Now we've got 260 watts of solar, so we hook up our magic, 100% efficient solar charger, and it'll still take 55875 watt*hours / 260 watt = 214 hours of direct sunlight.

Figuring optimistically that we get the equivalent of 8 hours of direct sunlight on those panels per day, it'll take 26 days to charge up.

I did say days, just didn't say how many I have no idea what this guys plan is. Not sure where the 5 HP came from, didn't come from me.

I've got 10kw electric drive on my little boat. Can I motor forever, No. Do I take predicted wind direction & tides into account if planning a 20+ mile hop, Yes. If I need to wait for cooperative wind & tides, I wait. Even if I had a diesel I suspect my M.O. would be the same because it's afterall a sailboat. What's the point of slogging along under power at 6 knots, talk about wanting to be put to sleep...

Many times I can putt along at 3-3.5 knots & only consume 15 AH. That's 750 watts at 48 volts or 1 HP. How can you hate that?

If you positively, absolutely need to be somewhere, electric is not for you. Come to think of it, a sailboat probably isn't either. Just saying.

[waterman46]

To those who did all the real life calculations, thank you! You clearly showed the futility of electric engines for cruising boats and it remained, as the OP asked, an "adult" discussion.

[benvanstaveren]

I wouldn't change out for electric, mostly because with your desired range you're never going to get there unless you tow a raft of battery banks behind you. Second, to bring up Sailing Uma, they've had a few close calls IIRC (I recall at least one) where having had a diesel would've turned it into a total non-issue.


But then again I know nothing

[ramblinrod]

Originally Posted by benvanstaveren

I wouldn't change out for electric, mostly because with your desired range you're never going to get there unless you tow a raft of battery banks behind you. Second, to bring up Sailing Uma, they've had a few close calls IIRC (I recall at least one) where having had a diesel would've turned it into a total non-issue.


But then again I know nothing

And after they declared all of their “green” reasons for going electric, they bought a larger than necessary gasoline powered outboard for their dinghy, spent who knows hose long racing about in an abandoned marina, and repeatedly strap their gasoline powered dinghy to the main boat to propel it where they need / wish to go.

More than a little hypocritical me thinks.

Also note that they declare their solution is not a substitute for a proper diesel, it is merely a substitute for a sculling oar.

[benvanstaveren]

Originally Posted by ramblinrod

And after they declared all of their “green” reasons for going electric, they bought a larger than necessary gasoline powered outboard for their dinghy, spent who knows hose long racing about in an abandoned marina, and repeatedly strap their gasoline powered dinghy to the main boat to propel it where they need / wish to go.

More than a little hypocritical me thinks.

Also note that they declare their solution is not a substitute for a proper diesel, it is merely a substitute for a sculling oar.

I've seen them do the dinghy thing but I think that's more a case of the electric engine still not being powerful enough to propel the boat at a safe speed - or that's what I took away from it, at any rate.



Whether or not it's hypocritical, eh, depends. I'd like to think they got into it with the idea of being ecologically friendly, but encountered reality where it just turned out that at this time, it won't work. In the future when battery packs are cheaper and more powerful it may just be the way to go...

[jmschmidt]

Assuming you have a proper solar array to charge batteries during daylight underway or parked you should know that a wind generator operating underway simply extracts power from your sails or your engine. The wind generator should be used in the marina or at anchor (day or night) to charge batteries. Nobody believes that but its true. There ain't no free lunch in life or physics.

"I can explain it to you, but I can't make you understand" – Author Unknown

[john61ct]

Hard facts: in order to push the boat with an electric motor, which

you will need to feed it from a big diesel genset.

Batteries will only store enough for a few hours' worth of time-shifting.

Alternative energy sources are tiny, insignificant from a practical POV, only valuable for Green PR purposes, and then only impressive to the ignorant.

Do-able? yes. Practical? no.

In the end **much** less fuel efficient than directly powered by a diesel engine.

And of course a **lot** more expensive.

[Jammer]

Originally Posted by tom jones

Our criteria: at least 100 miles cruising distance between charges
recharge capacity using 2 Kyracera 130s and Carib WindGenerator
and occasional Honda 2000i portable generator

any insight appreciated as well as experienced/knowledgable forums
its disappointing the lack of actual information and experience onhand.
thanks Tom Jones s/v Blue Trust
tj5035@gmail.com 443 454 4871

Hi Tom


I like to think in terms of L16 batteries for applications like this.
Around 120 pounds each. $200 or so in quantity if you shop
2 kwh
12 x 7 x 17" high


Minimum horsepower you would want to plan for is 20 HP which would realistically give you 4 knots. Figure 25 hours to make your distance. Motors are 90% usually about efficient


20 hp * .746 kw/hp * 25 hours / 90% = 414 kwh needed


With no reserve that would be 207 batteries or about 20,700 pounds and $41,000 worth. A 2:1 reserve is usually recommended.


Fancier batteries (LiFePO) would cut the weight in half but increase the cost.



Recharge with the Honda generator would take about 10 days.


Electric propulsion makes the most sense where much shorter periods of operation are contemplated. If you figure 4 hours with a 2:1 reserve then you can almost make it work.


But electric propulsion is generally not cost competitive with diesel on boats that large even then.


Fair winds

[sanibel sailor]

Originally Posted by jmschmidt

you should know that a wind generator operating underway simply extracts power from your sails or your engine. The wind generator should be used in the marina or at anchor (day or night) to charge batteries. Nobody believes that but its true. There ain't no free lunch in life or physics.

Doesn't it depend on point of sail? Upwind or motoring- yes, wind generator creates drag and decreases forward propulsion. However, if I am sailing dead downwind for instance, wind generator puts out power and the drag actually might (theoretically) increase my speed. There actually is occasionally a free lunch in physics. Identifying and effectively harnessing it usually makes somebody very wealthy.


Electric boats are at the stage electric cars were 30 years ago, a science project for pioneers, impractical with enormous compromises in performance. And I've put 10k miles on my electric car this year.

[GordMay]

Originally Posted by sanibel sailor

Doesn't it depend on point of sail? Upwind or motoring- yes, wind generator creates drag and decreases forward propulsion. However, if I am sailing dead downwind for instance, wind generator puts out power and the drag actually might (theoretically) increase my speed. There actually is occasionally a free lunch in physics. Identifying and effectively harnessing it usually makes somebody very wealthy...

I'd need some definitive proof of those counter-intuitive concepts.
- Drag increasing speed.
- Free lunch.

[waterman46]

Originally Posted by GordMay

I'd need some definitive proof of those counter-intuitive concepts.
- Drag increasing speed.
- Free lunch.

He meant to say, wind resistance, downwind sailing, increases speed.

Yes there is a free lunch, equipment not included. All of us get free power from the wind each time we sail.

[sanibel sailor]

Or free lunch like using a pump-free cooling system -thermal siphon like on old Model T engines- to cool your solar panel, increasing their efficiency and using the waste heat for warm showers. No idea if it’s feasible but there are ways in physics/engineering to profit at opposite ends of a problem

[Cpt Pat]

While focusing on road vehicles, this may be informative for comparing the energy desities of various combustion fuels: https://www.eia.gov/todayinenergy/detail.php?id=9991

You won't come close to the energy densities of gasoline or diesel fuels without resorting to using Lithium Cobalt battery formulations (like used in Teslas). But charge and discharge of Lithium Cobalt batteries must be very carefully managed. Failures of these batteries can result in intense and explosive fires that can not be practically extinguished. If they catch fire - you will lose your boat. Of course the same can be said of gasoline, but we have a century of experience with handling its hazards and, unlike Lithium Cobalt batteries, it won't spontaneously combust without an ignition source. Diesel is even safer yet.

Lithium Iron Phosphate (LFP) batteries are far safer that Lithium Cobalt and are gaining wide use as house batteries, but they have only about half the energy density of Lithium Cobalt.

Here's a good comparison of the various lithium battery formulations: https://batteryuniversity.com/learn/...of_lithium_ion

I can't imagine using lead acid batteries for powering propulsion. Not unless you intend to tow a barge full of batteries behind your boat!

Assuming you have a displacement hull, the drag produced by water-impeller generators is irrelevant after your boat has accelerated to hull speed. The same can be said about the induced and parasite drag from a wind turbine. Not to minimize the importance of keeping aerodynamic drag low, but In my experience, the windage of the average high-sided cruising boat with all its various stuff on deck creates the vast majority of the aerodynamic drag. A dodger will add more drag than a wind turbine. And leaving up too much sail instead of reefing will add enormous amounts of induced drag. I frequently outrun much larger sailing vessels that are fully canvased, while I'm flying my storm jib and main taken in to the second reef.

Except when your hull is surfing, your speed is constrained by the hull speed limitation. I see no change in speed when deploying my water-impeller generator (Hamilton Ferris) at hull speed - even with my smaller (7.5 K pounds) vessel. And when surfing in following seas, I see a slight improvement in yaw stability caused by the impeller's drag astern. It behaves like a very small trailing drogue.

[john61ct]

Originally Posted by Cpt Pat

I can't imagine using lead acid batteries for powering propulsion.

Done all the time, these lithium batteries have only been gaining ground the last decade or so.

Checking out a Tartan next weekend, been using a Thunderstruck 48V 8.5 kw kit, been completely reliable for 9+ years now, put in the second set of 8V Trojan T890 batteries about 3 years ago.

Just used for getting in and out, but about 4 hours run time if needed.

[Cpt Pat]

Originally Posted by john61ct

Done all the time, these lithium batteries have only been gaining ground the last decade or so.

Checking out a Tartan next weekend, been using a Thunderstruck 48V 8.5 kw kit, been completely reliable for 9+ years now, put in the second set of 8V Trojan T890 batteries about 3 years ago.

Just used for getting in and out, but about 4 hours run time if needed.

Well yes, or course, you're right. Diesel-electric submarines have been using lead acid batteries from the start. But even in that application, they're switching over to lithiums: https://www.defensenews.com/industry/techwatch/2018/11/16/new-battery-can-double-the-operational-time-of-submarines-says-south-korea/.

So I will revise my statement: I can't imagine buying new lead acid batteries today to power a new propulsion system (which I believe the OP was discussing) because, for a given amount of power, they weight twice as much, degrade rapidly if not fully and promptly recharged (sulfation), and last one-fourth as long (at best) when perfectly cared for.

But, except for potentially outgassing hydrogen and the risk of turning your boat into Sailing Vessel Hinderberg, they don't catch fire and blow up as readily (although they too are vulnerable to thermal runaway - the effect isn't as dramatic). If you're looking for safe and cheap propulsion, oars were used by the Vikings for propulsion much longer ago. They allow you to travel much greater distances - and they operate on only food and water.