Propellor for charging batteries using electric motor

[Adelie]

Originally Posted by Fore and Aft

Thanks StuM for the maths and I assume those calculations are for healthy batteries and the maths only gets worse as the batteries get older?
Adelie I only think its a choice most people would'nt make until it finally works perfectly. Then I imagine most people will happily make the change. But we are still a long way from that and will we ever reach that stage? You are saying change is coming but just how far can batteries and recharge systems go? Sometimes things can only be improved so much, look at car tyres as an example. When is one set of tyres going to last the life of my car?

Cheers

If by perfectly you mean the performs same as an internal combustion engine, that ain't ever going to happen. Even if it were people still wouldn't be happy about changing exactly because it's not a combustion engine, "It performs just as well as what I've got so why would I spend money to change?"

When the negative effects of climate change really start kicking in what's available to engine a boat will change and eventually fuel supplies will become harder and more expensive to get. Long ways away (50yr maybe) but doesn't mean it's not coming.

The reality is the loss of a sense of control is what is going to drive more folks away from cruising, they can't just turn on the engine whenever they want, they need to think about it.

[wingssail]

Originally Posted by Adelie

If there are 12hr of sun, by tracking you should be able to get full capacity almost from the time the sun comes up. I accept that for 15m or so at sunrise or sunset the insolation is attenuated by the extra atmospheric distance, but you will still be looking at over 11hr full output.

In practicality it probably won't be that good.

Today, for example (lat 20) the sun came up around 7:30. It is a beautifully clear day and no haze, clouds, or smog. At 8:00 I rotated my panels to be perpendicular to the sun. There is no shade on either panel. It's perfect.

At 8:00 I was getting about 30%. At 08:45 I was getting 50%, by 9:00 I am seeing 66%. I know from experience that I will get 100% by 10:00 AM and that will continue until abound 6:00 PM (if I rotate the panels). So in the best conditions I am getting full power for 8 hours. A lot depends on the direction of the wind because if my boat swings the wrong way the mast shadow can cut one panel at least in half.

In my experience with a pretty good set-up (but only moderate sized panels) I can expect, at best, about 1300kw per day. Keep in mind that even good solar panels will actually only produce about 50% of the watts that the manf rates them at. (some commenters here have said 33%).

So, with 450watts, in a very good installation, fully able to change the angle, one could expect a total of 2000kw. That's pretty good! Ignoring any other electrical loads (in most use cases the refrigerator is the biggest user, but we can all go without refrigeration) you can run your 800watt motor for 2.5 hours.

I have to say I am skeptical of the speeds you hope to get from an 800watt motor. That is about 1HP. I think most folks would think that is insufficient to move even a 20ft boat at 3-4 knots. However, if it could, you would get less than 15 miles. Travelling slower (using only 400watts) you might increase that distance.

So, is it possible? Yes. Is it practical for most cruisers? No, I don't think so.

A few weeks ago I asked EWOL to provide some numbers (he's in the business of selling props for this type of use) and he declined. I think the reason is that they don't work out.

In the future, maybe. For someone willing to travel primarily by sail, OK. For most folks, not yet.

My numbers: Please correct them if you will.

Assume: 45’ cruising yacht with 36’wl. Hull speed = 7.8, 75% hull speed = 5.8kts
Size electric motor to drive at 5.8 kts = 20kw
Power use at 5.8 kts = 16kw
4 hours of powering = 56kwh
Battery size LifePo4 = 4x300AH 48v (1200lbs, 18cu ft, approx $40,000) (check me here!)
Diesel:
Size diesel motor to drive at 7+ knots = 36hp (27kw)
Power use at 5.8 kts 20hp (16kw)
Fuel use per hour = .65 gal diesel
4 hours powering = 2.6 gallons (62kwh)
Fuel tank size = 2.6 gallons .5 cu ft
Solar:
1000w solar = 6kwh /day maximum
Six days to replace 4 hours of powering
Wind:
12 amps = 144 watts
16 days of wind to produce power for 4 hours of motoring
Regen:
256watts (22amps) optimistically, at 7kts speed, optimized, reduced speed due to drag not calculated.
9+ days of sailing to produce power for 4 hours of motoring

BTW, people who live on solar, without motoring on an electric motor, often have more than a 1000watts, which is a lot of panels.

[john61ct]

Originally Posted by wingssail

So, with 450watts, in a very good installation, fully able to change the angle, one could expect a total of 2000kw

Yes, consensus from real-life measurements over time is 450W in ideal conditions yields "about a third" or 150Ah per day into a 12V bank.

[Shawn67]

Originally Posted by wingssail

Keep in mind that even good solar panels will actually only produce about 50% of the watts that the manf rates them at. (some commenters here have said 33%).

Where does this number come from? I have a $110 Renogy 100w panel on my boat. It is 4 years old and I am regularly seeing it put out more than 50% of its rating. I recently swapped to a Victon charge controller but per its data I'm averaging 69.2watts peak over the last 37 days. And that is including the cloudy days. This is in Rhode Island on a flat mount. See attached. My daily load was small. For most of that it was a Dometic CF25. From day31 it is running a Isotherm GE-150SX in my icebox.

Shawn

[wingssail]

Originally Posted by Shawn67

Where does this number come from? I have a $110 Renogy 100w panel on my boat. It is 4 years old and I am regularly seeing it put out more than 50% of its rating. I recently swapped to a Victon charge controller but per its data I'm averaging 69.2watts peak over the last 37 days. And that is including the cloudy days. This is in Rhode Island on a flat mount. See attached. My daily load was small. For most of that it was a Dometic CF25. From day31 it is running a Isotherm GE-150SX in my icebox.

Shawn

Shawn, looking at your attachment I see an average output per day of, say, around 224 Wh. Over an 9 hour day that is 25watts per hour, or slightly over 2amps. I'm just not sure how Victron calculates all of this stuff but that does not seem like 69% of 100. It's less than 33% of 100watts.

Anyhow, if you can run your refer on that 2amps that is really good.

[Shawn67]

Originally Posted by wingssail

Shawn, looking at your attachment I see an average output per day of, say, around 210 Wh. Over an 8 hour day that is 26watts per hour, or slightly over 2amps. I'm just not sure how Victron calculates all of this stuff but that does not seem like 69% of 100. It's less than 33% of 100watts

Look at max PV output. It averages 69w.

You can't calculate the panels output based just on the yield, unless you are in bulk charge the entire day. Yield depends upon need. If there is no need for the controller to put anything out it doesn't. If the batteries aren't in bulk charging (and there aren't other loads running at the time) the controller is limiting the solar output. If this wasn't happening it would cook the batteries otherwise. If I am in full sun with fully charged batteries the PV output might only be a couple of watts for float. When the fridge cycles on then the PV output would jump up, and be counted toward the yield. The Victron shows this all in real time including the +/- into the battery itself as it is also measuring load.

The way you worded it it sounds like you were saying manufacturers overstate the watt output rating of panels. That is what I was responding to. My 4 year old panel is averaging a peak output of about 69% of its rating, including the cloudy days. If that isn't what you mean they were are probably on the same page in that what the panel will put out will of course vary during the day.

EDIT: And yes, the 100w panel is running my fridge just fine. You can see that by looking at minimum battery voltage per day and that on most days I am back to float meaning the batteries (2 group 24 deep cycles) have recovered from the night before. I'm going to add more insulation to the icebox to see if I can reduce the daily need. The lid isn't really insulated at all. You can also see the relationship between consumption and yield here too. When I switched over to the Isotherm my consumption increased as did my daily yield.

Shawn

[u4ea32]

Originally Posted by Shawn67

If your propulsion power needs are that low (half refrigeration) I guess I wonder why bother with the expense of trying for more regen at all? I just converted my icebox to a fridge (without adding additional insulation) and over the past 11 days my average consumption is 264wh. The yield of my 100w panel averaged out to 315wh. The charging averaged 201 minutes of float time each day so it is keeping up. With 160 or 200w of solar you should be fine for your needs.

Shawn

Shawn, I agree, and I may well just use solar panels.

It just seems that since I have a motor with a controller that supports regeneration, my boat sails at least 7-8 knots in just about any condition, and my current prop is simply old, very inefficient especially in reverse, and unbalanced, I want to replace that old prop anyway.

It **seems** that a feathering prop will work well enough, but there are expensive and wide spread advertisements for folding props for regeneration and that does not work at all, not even close. So I am hesitant to "just trust the vendor" and buy an expensive prop, and then discover that it really does not help.

So I am hoping for some wisdom that is built upon direct experience.

I have found some first hand reports: the Autoprop was effective on an early (maybe first?) all electric catamaran. I don't want one of those because (it seems) the blades don't fold until the boat is going quite fast, so low speed (under 10 knots or so) drag will be very high. I don't want to slow my boat down when not charging, and I expect to not need to charge often.

Another used a fixed prop with my same electric motor and it worked very well on passages, maintaining 100% battery charge essentially all the time.

My boat has no liner or interior insulation, its 100% balsa cored, so it is like a guitar: any noise in the hull is pervasive. The "shaft rumble" is not all that loud, but it is offensive compared to the sound of the water passing the hull. So I don't want a constant shaft rumble, so no fixed prop.

[u4ea32]

Originally Posted by barryglewis

Just had a look, i think you might have misread their pitch (pun intended).
The propellor has different positions according to what the use is, so when feathered for sailing it is not also generating.
When set for generating it is not simultaneously feathered.
Similarly when driving or in reverse it is set for that purpose.
This looks very exciting to me.
I have and use a SailGen , but if i ever went to an electric motor i would certainly look very closely at the OceanVolt.

Barry
sv Risky Business

I think their assumption is that the prop will spin at very high speed when regenerating, to enable the prop to stay open, like when powering in reverse.

In actual experimentation with my boat and my prop, this is not even close to what happens: the prop simply and immediately folds when propulsive throttle is reduced, regardless of direction of thrust.

My prop is not theirs. Maybe some differences between mine and theirs make theirs work. So maybe they are not lying.

But drag is needed to spin a prop for regeneration. Drag causes folding props to close. So I don't see the physics of it working. That does not mean it will not work. Software and control makes a big difference compared to fixed physical configuration.

[u4ea32]

Many people say things like "You must be able to motor XX hours or XX miles" whereas I own a sailboat to sail. Its the freedom, the nature, the endless possibilities, the peacefulness, that attracts me to sailing.

I do enjoy powerboats too.

I do see that some people have time constraints that require them to even go boating with schedules. I have schedules for lots of things in my life, but I don't apply schedules to my boating. Out of choice. I choose to structure my life so my boating is not limited by schedules. I have been able to do this since I was a young boy, and have never given up this prioritization when I have sailboats. Powerboats, sure. Schedule everything, no real problem. But sailboats are a different experience, at least for me. I like the sailing itself. I sail to sail, not to get somewhere at a specific time.

In my 60 years of boating, I have powered a sailboat to or from Catalina Island exactly zero times out of perhaps a thousand times. I have powered a powerboat to Catalina perhaps a thousand times. Both are a lot of fun. Viva la difference!

[wingssail]

Shawn, You're doing really great with your system, but...

Originally Posted by Shawn67

Look at max PV output. It averages 69w.

You can't calculate the panels output based just on the yield, unless you are in bulk charge the entire day.

Shawn

Your minutes of bulk charge indicate over 9 hours a day, with a flat panel, so your yield is close to bulk charging all day.

Originally Posted by Shawn67

The way you worded it it sounds like you were saying manufacturers overstate the watt output rating of panels.

Yes, that is exactly what I am saying, and many other commenters in this thread have said that too, and I actually think your own numbers also say that. Your yield, over 9+ hours of bulk charging is less than 33% of the manufacture's claim. Look, most manufacturers rate their panels by multiplying the maximum voltage, say 21 on an open circuit, against the maximum amps, say 5 on a dead short, giving, in this example, over 100 watts, yet these two conditions never coexist.

Originally Posted by Shawn67

Yes, It is running my fridge just fine.

Well, that is fantastic! Because most figures quoted for these compressors is around 5-9 amps and the duty cycle varies with the ambient temperature and the quality of the insulation. Even in Maine I am surprised that you can run your refer 24 hours on 160Wh, which is 13Ah, which is average of about .5 amps over the course of a day. That is 10 times better than the manufacturer claims.

[wingssail]

Originally Posted by u4ea32

In my 60 years of boating, I have powered a sailboat to or from Catalina Island exactly zero times out of perhaps a thousand times. I have powered a powerboat to Catalina perhaps a thousand times. Both are a lot of fun. Viva la difference!...

...whereas I own a sailboat to sail. Its the freedom, the nature, the endless possibilities, the peacefulness, that attracts me to sailing...

You have actually been to Catalina 2000 times in 60 years? That is 32 times a year and never missed a year! Wow, you must like the place.

Actually, I am glad you like sailing. I do too. And if you come to Mexico like you say you might, with your electric drive and depending on solar and regen, it will be a good thing that you do, because there ain't much wind here a lot of the time. The last guy I knew who came here in an Olsen 40 (a keen sailor) went home after one year because the sailing was so bad. On the other hand I think it is pretty good, but I have, and use, my motor when I need to.

And look us up when you get to Puerto Vallarta, I'd like to see how it is actually doing, plus, with your fantastic speeds sailing with that boat you will enjoy joining the racing scene, you will absolutely clean up, nobody else's 40 footer goes like that, even Double take, the J145, won't be able to touch you!

[Adelie]

I’ve been there once and it was great. I could see going there repeatedly every year.

I’m pretty sure he was exaggerating for emphasis. But you knew that didn’t you WingSail and were just being a little snarky weren’t you?

[wingssail]

Originally Posted by Adelie

I’ve been there once and it was great. I could see going there repeatedly every year.

I’m pretty sure he was exaggerating for emphasis. But you knew that didn’t you WingSail and were just being a little snarky weren’t you?

Yeah, couldn't help myself.

[Brewgyver]

Originally Posted by Adelie

If I were to get 4-160W panels ...

I'd love to know where you're going to put 40 square feet of ADDITIONAL solar panels on a Cal 20.

[Adelie]

Originally Posted by wingssail

Yeah, couldn't help myself.

Yeah, I understand. I like poking at people prone to exaggeration myself.