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Old 22-08-2015, 00:01   #61
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Re: Electric Inboard

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Originally Posted by Wireless1 View Post
I'm seeing the info on the graph just fine, but I don't get what you are seeing that makes TacomaSailor "right" and what? Me wrong? I'm using the Electric Yacht Systems 10.5Kw PMAC motor. It's slightly over sized for my 8,900 Lb. displacement Freedom 32. So what do you see that is not right about my system? What am I missing here?
BTW, my LFP battery pack is oversized at 21kWh capacity and per their chart more typical of a 45 foot boat installation. So would you mind sharing what is wrong with any of this in your opinion?

Thanks!
Wireless1, you have to ask the right question to get a useful answer. The objections stem from trying to save the OP from themselves, a common theme on this forum. So it has to be proven (easy enough to do) that pure Electric isn't useful to the "average cruiser", which the OP is assumed to be (and probably is).

You are not the average cruiser, so their arguments do not apply to you, you simply showed up and wedged yourself in the middle. Let the beatings begin.

Pure electric, LiFePo etc is still bleeding edge here in cruisers forum. We have a ton of sailors who cannot imagine not motoring 50 miles a day. You know that isn't possible on pure electric. That is what they want / need. The fact that it is not what YOU want / need is irrelevant.

So do not expect to "win" any electric / diesel argument. Just enjoy your electric boat which does exactly what you desire. There are a handful of others out here, the badly beaten silent minority who also have electric boats.

I find the subject fascinating. Someday I may well do a conversion as well.
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Old 22-08-2015, 00:08   #62
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Re: Electric Inboard

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Originally Posted by TacomaSailor View Post
“And on a long passage, power regeneration under sail with a spinning prop shaft, (3 to 4 AH using the motor controllers regen mode ) plus the 600 watt solar panels (72 volts @ 8AH using MPPT chg reg.) can take their own sweet time charging the 48 volt propulsion battery pack to 100%. Thus it's possible to arrive in port with full batteries.”


Here is another example of wishful thinking that ignores physical reality. Numbers do not lie!

I have a Ferris towed generator that produces 180 watts at 7-knots or 15 amps at 12V at 7-knots boat speed. That power production slows the boat about ¼ knot. However, at 5-knots boat speed the Ferris only delivers 3 amps and slows our 40’ sailboat almost 0.4 knots. I have big solar panels and have used them at sea for over 6,000 NM. I know the reality of these processes.

Let’s assume you run the motor for 12-hours during a 5-day passage. Assuming the boat needs 4-HP (3 Kw) to move while at sea then a 48V motor would pull about 62-amps per hour or a total of 750 amp hours.

The regen process can provide 72 Ah per day or 324 Ah for the 4.5 days the electric motor is NOT providing power.

If the 600-watt panels average 50% power for 10-hours a day they produce 62 Ah per day or 310 Ah for the five day voyage.

If we assume the boat used 18 AH (48V) per day while under way for radar, lights, autopilot, refrigerator, radio then 375 Ah are consumed during the five day voyage.

Here is the result of a 5-day ocean voyage where you sail at least 4-knots for 90% of the time (everything is in 48V Ah):

-750 Ah motoring
- 90 Ah boat operations
+324 Ah motor regen process
+310 Ah Solar panel output

At the end of five days the batteries are down 205 amp hours or about 25% discharge on an 800 Ah battery bank.

Is there anything wrong with the calculations above?

Please remember I have lived with solar panels providing all the boat energy for 15-years including 6,000 NM at sea and over three years full time living at anchor. I have also skippered two other boats with big solar arrays for over 4,000 NM at sea.

I love alternate energy systems and that is why I am so obsessive about details and numbers.
Well, you asked; "Is there anything wrong with the calculations above?"

Yes TacomaSailor, regarding that guy with the system you were belittling and quoting, there is something very very wrong with your post. Why? because based on what you quoted it's been a total waste of your time, and related to that guys quote; your entire post is...well, irrelevant.

See folks, here is yet another example of a nay-sayer assuming all sorts of things and quoting someone (ME!) without bothering to ask about any details of the system in question, before being blinded by their overzealous chance to prove someone wrong and shoot their mouth off about all they know and their wonderful experience. Well, now TacomaSailor is about to find out that this was a pretty foolish assumption on his part.

TacomaSailor? Are you sitting down? I am, and I'm laughing as I type this. You were not only rude by quoting me and saying I have wishful thinking and my system has nothing to do with physical reality, but you were SO anxious to nay-say about my charging system that you assumed WAY to much and forgot to ask yourself one simple question, and that question is this; "Hey, what if this guy with the wishful thinking and no grasp on reality has a completely separate charging system for his 48 volt propulsion system and his 600 watt panels and his Sevcon motor controller in regen mode ARE ONLY USED for charging his STANDALONE 48 volt propulsion system, because maybe he has a completely separate standalone solar panel powering his 12 volt house battery system". DOH!!! Yes, that's the setup I have. My propulsion system is TOTALLY separate from my house system.

You trashed yourself pretty good on this one pal. And you know what? I don't care how you work your numbers because like I said; on a LONG passage my 600 watt panels and my regen mode Sevcon controller are NOT BEING USED FOR ANYTHING OTHER THAN CHARGING MY PROPULSION BATTERIES. SO THERE! GOT IT?? There, I feel better after yelling at you for being a nitwit. Now go check out your other thread where you worked up the numbers where I can only get 16 nautical miles range out of my electric propulsion system, oh and take a look at the numbers supplied by the factory that built my system. They have over 300 installations behind them, one of which is in a boat exactly like mine. Their data shows your numbers are pretty looney.
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Old 22-08-2015, 00:37   #63
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Re: Electric Inboard

Again, Your numbers do not work out! Sorry - you are just spouting emotion but not using arithmetic!

"TacomaSailor? Are you sitting down? I am, and I'm laughing as I type this. You were not only rude by quoting me and saying I have wishful thinking and my system has nothing to do with physical reality, but you were SO anxious to nay-say about my charging system that you assumed WAY to much and forgot to ask yourself one simple question, and that question is this; "Hey, what if this guy with the wishful thinking and no grasp on reality has a completely separate charging system for his 48 volt propulsion system and his 600 watt panels and his Sevcon motor controller in regen mode ARE ONLY USED for charging his STANDALONE 48 volt propulsion system, because maybe he has a completely separate standalone solar panel powering his 12 volt house battery system". DOH!!! Yes, that's the setup I have. My propulsion system is TOTALLY separate from my house system. "

If you dedicate all your solar and regen power to recharging the propulsion batteries then take the 90 Ah I applied to boat operations and apply them to the propulsion recharge. You are still down 116 amp hours at the end of five days of voyaging. Or, did I get something else wrong?

I think you guys need to get a grip!

I am not denying the attraction of new technology or the benefit of quiet and clean motoring. That is why I have a large solar array and never plug into shore power and never run my propulsion engine to charge the batteries. I am all in on the solar revolution and have been for 15-years.

That is also why I spent a small fortune on light air sails and hardware. I sail my boat anytime I can move at 3-knots. I have chosen a different route to quiet movement of my boat.

I am just running the numbers as I see them and asking you where the numbers are wrong. I would love to have someone show me where my formulas and arithmetic are in error. But, so far all I get is emotional reactions and stories about some other boat did some other thing.

Please, give me formulas and numbers to show me where I am wrong.

Why is there so much emotion associated with a topic that is highly technical and has many well understood formulas with which to calculate answers?
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Old 22-08-2015, 00:40   #64
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Re: Electric Inboard

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Originally Posted by TacomaSailor View Post
"So, the big question is range. There were some funny range numbers posted here, but let me say this; If I can get my 4 knots at 20 amps, (fingers crossed),"

I think I found a fundamental error in your calculations. That boat (with two passengers and some water onboard) needs almost 5 HP (3.8 Kw) to move at 4 knots rather than the 1.2 HP (0.96 Kw) you are using for range calculations. Following is a well tested calculation.

Freedom 32
32' 9" LOA
25' 3" LWL
12' 3" Beam
8,500 pounds with no cruising load

Every calculation I do shows that boat would need 4.7 HP at the prop to move that boat at 4 knots. Both Bebe and Gerr formulas predict the same thing.

If you add 500 pounds of equipment and liveaboard stuff (real cruiser?) you then need 5.0 HP at the prop to move 4 knots.

Using the light load (no operator, no water, no clothes...etc) your batteries would need to deliver 3.5 Kw power or FOUR (4) times your estimate of 0.96 Kw (20 amps x 48V). Range is a linear function of power consumed so your range would drop by a factor of four (4).

How in the world did you calculate a 4 knot power demand of 1.3 HP for a 32', 4 Ton sailboat?

And, no power system is 100% efficient. Looking at a more realistic case with 96% efficient power system and 500 pounds load on the boat your batteries must deliver 3.9 Kw to move the boat at 4 knots in still water. Your calculated range of 50 NM drops to less than 12 NM.

What happens when you have a 5-knot head wind or a 1 knot adverse current.

It still does not make sense!

Here is an online power/speed calculator for sailboats:
Boat Speed Calculator
I think you would be wise to look into the differences in torque that the electric motor provides, also the adjustable pulley reductions you can tune. I don't see you calculating the torque advantages of electric propulsion swinging large oversized props. Also, take a look at the data numbers supplied by the factory in my other post. Your worries seem to be unfounded based on the data they are getting. And besides, I get what I get. If I don't make 4 knots at 20 amps draw after I tweak my 3 blade variable pitch prop...so what? I'll at least be close. Their data already shows my boat moving 3.2 knots at 20 amps. And that is for a 15" fixed blade fixed pitch prop. I have not installed it yet, but I have switched now to a 16.5" three blade Kiwi feathering prop. The factory would have suggested a larger prop because the torque will turn it, but they were unsure of the clearance on the Freedom 32. There is a friend cursing over in Indonesia with a the same 16.5" Kiwi prop on his Freedom 32 and it's turned it into another boat when motoring. BTW, the Freedom's underbody is more like a race boat than a cruiser; deep thin fin keel, very deep spade rudder. Nay say all you want. I'm fine with how it works out because there are more important things I like about electric propulsion and overall range is nice, if I can get more, but there is more to it than that for me; like the quiet, oh yes...the quiet! And the incredible torque at low speed maneuvering, less smelly diesel maintenance and on-going cost headaches. Now, go ahead and pick apart every single thing I've said that I like...as I'm starting to see a pattern here. Now, what if I said I like racing road bikes instead of mountain bikes, or Shimano better than Campagnolo...LOL...
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Old 22-08-2015, 01:10   #65
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Re: Electric Inboard

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Originally Posted by jwcolby54 View Post
Wireless1, you have to ask the right question to get a useful answer. The objections stem from trying to save the OP from themselves, a common theme on this forum. So it has to be proven (easy enough to do) that pure Electric isn't useful to the "average cruiser", which the OP is assumed to be (and probably is).

You are not the average cruiser, so their arguments do not apply to you, you simply showed up and wedged yourself in the middle. Let the beatings begin.

Pure electric, LiFePo etc is still bleeding edge here in cruisers forum. We have a ton of sailors who cannot imagine not motoring 50 miles a day. You know that isn't possible on pure electric. That is what they want / need. The fact that it is not what YOU want / need is irrelevant.

So do not expect to "win" any electric / diesel argument. Just enjoy your electric boat which does exactly what you desire. There are a handful of others out here, the badly beaten silent minority who also have electric boats.

I find the subject fascinating. Someday I may well do a conversion as well.
Hmm? Just what "right question" did I not ask? I see the chart, I see the system I am using, all looks well to me. And yet there is supposed to be something on that chart that shows one poster is right, and I am wrong? Still don't get that. Oh well, as to the OP; I just thought what I was installing would be of interest to anyone considering going all electric. As to saving the OPs? Never even considered it. As to "wedging myself into this thread?" That's a bit pompous of you isn't it? Really? It is titled "Electric Inboard" isn't it? Well then excuse me for posting. I guess the next time I see "Electric Anything" I'll be sure and run the other way! LMOA!
As to not being able to motor 50 miles? My numbers are projected to possibly do that...but it would be WAY TO SLOOOOOOOOW to be practical...like maybe 2 knots? And there had better be zero wind and the water like a big pond out there.
As for winning any diesel versus electric argument? I really have had none. I've stated what I like about electric and I've stated what I don't like about my old smelly diesel. So what. I've said in numerous posts that what I am doing is not for everybody, and yet the diesel addicts still love to pick apart anything one is trying or exploring with electric propulsion. I guess that's human nature as sailors do tend to look at anything new with great suspicion. Oh well...so be it. I'm having fun with this and nobody is going to take the wind out of my sails on this project---that is for sure! If I end up not getting the expected range? So be it. All the range I really need is to get out of the harbor for a day sail, or a sail out to the local islands for a week or so. So there yah go. Now, I guess someone will jump in here and beat me up for wanting that!
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Old 22-08-2015, 01:29   #66
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Re: Electric Inboard

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Originally Posted by TacomaSailor View Post
Again, Your numbers do not work out! Sorry - you are just spouting emotion but not using arithmetic!

"TacomaSailor? Are you sitting down? I am, and I'm laughing as I type this. You were not only rude by quoting me and saying I have wishful thinking and my system has nothing to do with physical reality, but you were SO anxious to nay-say about my charging system that you assumed WAY to much and forgot to ask yourself one simple question, and that question is this; "Hey, what if this guy with the wishful thinking and no grasp on reality has a completely separate charging system for his 48 volt propulsion system and his 600 watt panels and his Sevcon motor controller in regen mode ARE ONLY USED for charging his STANDALONE 48 volt propulsion system, because maybe he has a completely separate standalone solar panel powering his 12 volt house battery system". DOH!!! Yes, that's the setup I have. My propulsion system is TOTALLY separate from my house system. "

If you dedicate all your solar and regen power to recharging the propulsion batteries then take the 90 Ah I applied to boat operations and apply them to the propulsion recharge. You are still down 116 amp hours at the end of five days of voyaging. Or, did I get something else wrong?

I think you guys need to get a grip!

I am not denying the attraction of new technology or the benefit of quiet and clean motoring. That is why I have a large solar array and never plug into shore power and never run my propulsion engine to charge the batteries. I am all in on the solar revolution and have been for 15-years.

That is also why I spent a small fortune on light air sails and hardware. I sail my boat anytime I can move at 3-knots. I have chosen a different route to quiet movement of my boat.

I am just running the numbers as I see them and asking you where the numbers are wrong. I would love to have someone show me where my formulas and arithmetic are in error. But, so far all I get is emotional reactions and stories about some other boat did some other thing.

Please, give me formulas and numbers to show me where I am wrong.

Why is there so much emotion associated with a topic that is highly technical and has many well understood formulas with which to calculate answers?
You still don't get what I am doing do you? Look, I said my 12 volt house system has nothing to do with my electric propulsion system. My 12 volt house system has it's own 150W solar panel over the davits and does not contribute to the propulsion system at all. Now, pay attention; the propulsion system will have two 300 watt 72 volt panels in series to supply solar to the propulsion batteries and has nothing to do with the house system. Got it this time? The two separate solar installations have nothing to do with each other. I do not know how to make it any more simple than that. Now, YOU made the wrong assumption the house was partially powered by the propulsion panels, and worked up more numbers like I was partially using my propulsion solar panels and my LifePO4 motor batteries for my house system. I am not doing that. You wasted your time calculating all this energy coming out of my propulsion batteries for the house stuff like radar, radian, etc. Again; I don't do that. The two systems are separate and not related at all. Got it this time? Or am I being too emotional, wishfully thinking and not based in reality? OK, just to make sure; solar panel for house only, solar panels for electric propulsion only. The two are not shared, connected, or related, but two entirely different systems. Whew.... I hope you get it this time. Good luck!
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Old 22-08-2015, 02:50   #67
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Re: Electric Inboard

"Now, pay attention; the propulsion system will have two 300 watt 72 volt panels in series to supply solar to the propulsion batteries"

I guess I am dumb or really misunderstand electricity!

600 watts at 48V (that is your battery bank - right?) is 12.5 amps max power provided by the solar panels. Or, is there way to get more power out of the panels than is their power rating? At 72V the 600 watt panels produce 8.3 amps or do I have that wrong?

Assume you get full power four hours a day as I did with my 500 watts at 23 N and you get 50% power for another 6 hours a day (wildly optimistic). That is (at 48V) 50Ah+37.5Ah or about 88 Ah a day you are putting back into the batteries.

Your regen process provides another 72 Ah per day for a total of 160 Ah a day put back into the batteries.

All of the above assumes your panels are 100% efficient, the mast or boom never shadows the panels and pitching/yawing has no impact on panel power production. My 15-years experience with a lot of panels says otherwise, but lets assume best case.

Did I get it right this time?
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Old 22-08-2015, 03:24   #68
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Re: Electric Inboard

"I think you would be wise to look into the differences in torque that the electric motor provides, also the adjustable pulley reductions you can tune. I don't see you calculating the torque advantages of electric propulsion swinging large oversized props. "

Torque is only a force but it is power that moves the boat.

HP = (torque x RPM) / 5252
Torque = HP x 5252 / RPM

If you double the torque with gear or pulley ratios you slow the RPM and the horsepower stays the same.

Increasing torque by decreasing RPM (that is what gear ratios do) does not increase the HP and HP is what moves the boat.

Torque is measured in foot pounds (at least in the US) so if you move 550 pounds one foot you've exerted 550 foot pounds of torque. But, that says nothing about the time taken to move that weight that distance.

Horsepower measures the energy produced/consumed per unit of time and ONE Horsepower is the power needed to move 550 pounds one foot in one second. One HP is equivalent to 746 watts of electrical energy.

So I can move that 550 pounds one foot in one second while using 1 HP or I can take 10 seconds to move it and use 1/10 of a horsepower.

So - you can have very high torque, as shown in a stalled electric motor, but produce no horsepower because there is no shaft rotation and nothing moves - but there is still the torque (force) available.

You can change the gear and pulley ratios all you want but the power needed to move the boat will remain the same.

A boat has weight and drag and to move that weight and overcome that drag will always require the same force at any given boat speed. You can increase the torque (force) but if you do that only with gear ratios you will decrease the RPM and therefore the power (energy per time unit) will remain constant and the boat speed will remain constant.

If you increase the torque and maintain the RPM then the power required will increase at the same ratio as the gear ratio.

Using a bigger prop makes the prop more efficient but as you increase the prop efficiency you also let it put more power into the water thus requiring more power from whatever drives the prop shaft.

You can not gain boat speed except by applying more power thru the prop to the water and that power has to come from somewhere.

You can not make any additional power, just by changing gear ratios and prop sizes without adding watts (amps x volts) delivered from the battery.

Power and Force have always confused me and if you find something wrong in what I have written above - please let me know 'cause I copied most of it from some physics books.
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Old 22-08-2015, 03:44   #69
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Re: Electric Inboard

Let me preface this post with a clear statement of my admiration and respect for those trying to advance the engineering and technology of electric propulsion in power boats. I love technology and love numbers. My questions and comments are an attempt to understand how the leaders in the new frontier of electrical propulsion plan to overcome what most of us thought were well established limitations based on solid physics and electrical engineering.

Please do not think I am trying to stop folks from moving forward - I just really want to know how you plan to overcome these limits.

"I hope the numbers below will give you some food for thought in your calculations. Here you go >> (it's from a graph so I will interpolate as best I can).
Motor: 10Kw PMAC @ 48 Volts
Shaft HP: 9 with 40:24 reduction
Prop: 15" x 12" (I have gone up to a 16.5" variable pitch Kiwi feathering prop)

Amps vs. Speed Graph
10 amps - 2.4 knots
20 amps - 3.2 knots (hoping to squeeze another .8 knots our of my variable prop?)
40 amps - 4.5 knots
65 amps - 5.0 knots
80 amps - 5.5 knots
120 amps - 6.3 knots
180 amps - 7.0 knots "


I am always glad to learn new things and play with new numbers. Some of what you report above is confusing.

The high efficiency motor you cite is 10 Kw and 9 shaft horsepower. But, 10 Kw is actually 13.3 HP at 100% efficiency. Your reported 9-shaft HP is only 67% efficient. What do I misunderstand here?

10 amps at 48V is 0.63 HP and you say that will move your 8,900 pound boat at 2.4 knots? How can that occur? My ½” Milwaukee drill ( 660 watts or 0.88 HP) is geared for 0 to 950 RPM and I am pretty sure it can’t move an 8,900 pound boat at 2.4 knots.

Dave Gerr is a very well respected Naval Architect and has published a great deal of technical professional information about calculating power to move vessels. Here is a link to an article about the formula and it’s application in the professional journal published by the Westlawn Institute of Naval Technology.
http://www.westlawn.edu/news/Westlaw...d06_June08.pdf

Gerr says you need 2.06 Kw (2.76 HP) or 43 amps at 48V to move the boat at 2.4 Knots rather than the 0.63 HP your data reports.

You claim to move the boat at 5.5 knots using 3.84 Kw (80 amps) but the Gerr formula says you need 7.11 Kw.

How do you propose to overcome the formulas used by professional boat designers? Those formulas predict you need more than four (4) times the shaft horsepower to move the boat as you are citing.

I am not making up any numbers! I am just applying the numbers you provide to standard formulas. Are you saying that you and the other electric boat advocates know how to overcome the power issues that have plagued naval architects since the first propeller driven ship?

I have reviewed the E-Boat modeling spreadsheet used to calculate power needed to move a boat thru the water. I see that sheet predicts the same power requirements you cite above.

Looking at the E-boat formula for hull drag I see a simple linear function that seems to ignore the exponential characteristic of drag as a function of speed.

So – a fundamental difference I find in our positions is the calculation of power requirements.

A big difference I see in the formulas are probably the cause of our vastly different estimations of required power.

The Gerr formula is exponential in respect to drag increase with speed increase. The E-boat formula for drag is linear and specifically excludes calculations below an S/L of 1.0 or 5 knots in your case.

The E-boat spreadsheet also assumes a fixed 55% efficiency factor the transmission of power to the water by the prop. But, we know that most prop curves are cubic in nature and the prop puts very little power into the water at low RPM. For example, a 20HP Yanmar 3GM makes 9 SHP at 1800 RPM but the prop only puts 2.5 HP into the water for an efficiency of 28%. At 2200 RPM those numbers are 12, 3.5 and 29%. The engine has to be turning 2900 RPM for the prop to put 50% of the 14 SHP into the water.

As far as I know – electric motors turning a propeller in the water suffer the same cubic prop curve. The E-Boat model ignores the inefficiency of the prop at low RPM compared to total RPM.

The results of the spreadsheet equate shaft horsepower in a direct and linear fashion to propulsion power. I am pretty sure than is not the way it works.

Is there something unique about the new motors and controllers that allow them to move boats thru the water with less power than all previous boats powered with diesels?

I have applied the Gerr and Bebe formulas to my Caliber 40 and find them, when using the Yanmar prop curve charts, to be very accurate at predicting boat speed in still water. That is - the Gerr prediction for a given HP needed agrees almost exactly with the prop HP delivered at a particular RPM and a measured speed. I would be totally gob-smacked if someone told me the Gerr, or Bebe, formulas are incorrect.

Those formulas also work very well with a Tartan 42/Perkins 4-108 that I operated for several years and thousands of miles.

That is the reason I am so curious about the predicted HP needed to move electrically powered boats - it differs by a factor of 3 or 4 from what I measure in my real life.
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Old 22-08-2015, 04:49   #70
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Re: Electric Inboard

Thread is getting intresting

keep reading and calculating...

p.s. 2000 cycles at 50n\m each= 100.000 nm...how much would you spent on fuel to travel 100.000 miles? (2000 cycles and 50n\m each) being conservative
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Old 22-08-2015, 09:21   #71
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Re: Electric Inboard

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Originally Posted by jwcolby54 View Post
Do you have something to prove? Do you feel challenged by this conversation? You don't want electric, we get it. You seem very determined to convince people who already use it that it doesn't work for them.



</Soapbox>

Let the beatings resume.
If stating facts is having "something to prove"...yeah, I'm OK with that.

The ones who seem to have something to prove are the ones claiming magical abilities of electric drivetrains. I find it an interesting engineering discussion and hopefully steer the less informed into looking at reality before they buy into the magical abilities.

I would love to be proven wrong but the capabilities are not even close.

Why do the electric drivetrain advocates not want to openly admit the sever limitations of their systems, do you think?

We have someone claiming 20amps is enough to get their boat going 4kts and it defies the laws of physics.

If they are happy with their systems, good for them but some of the statements made are outright false. Hopefully it is just misunderstanding on their part and not intentional misrepresentation.
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Old 22-08-2015, 11:40   #72
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Re: Electric Inboard

Here is very easy to understand document explaining the concepts and formulas needed to understand hull design, drag calculations, force and power needed to move a boat through the water:

http://www.sponbergyachtdesign.com/t...n%20ratios.pdf

Start at page 42 if you want to jump directly to the calculations of hull drag, force, and power needed to move a boat thru water. NA Sponberg dissects the Gerr "HP Required Formula" and shows in easy to understand detail how to apply them to your boat.

The article which was written by a naval architect. He explains how he did the design work on several different sailboats. The article I reference is a compilation of his class notes used to teach student naval architects the basics about the fundamental design parameters.

Here are a couple quotes:

"We don’t care at the moment what the constants or coefficients are; we only care that Force is proportional to speed squared. Vessel resistance is a force—it has the same units, pounds—and so it is proportional to speed squared. We also know from our discussion of displacement-length ratio that resistance is directly proportional to displacement. "

Any formula that calculates HP needed to move a boat that does not account for the Force is proportional to speed squared is very suspect.

You are welcome to plug your numbers into the reported formulas or to use the online calculator at PsychoSnail that implements the formulas in a instructive and easy to use format. The output displays graphs of various parameters for the boat whose data you enter into the calculator.

Boat Speed Calculator <== click here and enter your boat values

Final output will show Kw needed to move a boat at a given speed.

Try it - You'll like it!

I hope one or more of the electric propulsion proponents can show us where these well established naval architects have erred in their calculations and application of the standard formulas.
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Old 22-08-2015, 13:27   #73
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Re: Electric Inboard

Boat - SolarWave

29.000lbs cat 2x10 kw , ONLY with 8kw solar goes 4 kts on calm water...

I think a lot is how expensive is the fuel around the world, above all the pros and cons of the electric vs diesel...

i calculate that in my case i would need less than 3 years as return of investiment if cruising only in italy (1.70 euro liter diesel), while calculating same everything but paying fuel 0.80 euro liter..(like usa, canada)...lot more..oman or dubai at 0.20 euro liter...century need to came back to the investment)

in my case , from Venice, to go to egypt ( there 0.40 euro/liter) it would be an investment just get all solar and make the 800n\m slowly, very slowly and all electric...it will get payied by itself..only to do this way, and then i'll keep an engine as redundant system over the diesel engine, a big home battery (even the same for the house load)
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Old 22-08-2015, 15:24   #74
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Re: Electric Inboard

SolarWave is actually a pretty good example of how good design can change the numbers.

Drag is proportional to the L/B ratio (leingth/beam) or more technically the froude's number. Basically as a hull gets longer and thinner it produces less drag. On a monohull there is a practical limit to this since the hull also has to contain the living space. On a multihull the living space can be pushed to the bridge deck and the hulls can be made very long and very narrow.

This is exactly what SolarWave has done. Where a typical monohull has a L/B of about 2.5:1 SolarWave is about 7:1. This means the hulls are incredibly easily driven compared to a monohull, thus needs less power for the same speed. To use it as a comparison we would need a 45' monohull that is about 6' wide at the waterline. You could certainly design such a boat and it would take very little power to move, but it would be a pain to sleep on.

This is why all the prop-speed formulas have a disclaimer that they don't work for catamarans BTW. but there are separate formulas that do.
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Old 22-08-2015, 15:31   #75
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Re: Electric Inboard

Quote:
Originally Posted by TacomaSailor View Post
"Now, pay attention; the propulsion system will have two 300 watt 72 volt panels in series to supply solar to the propulsion batteries"

I guess I am dumb or really misunderstand electricity!

600 watts at 48V (that is your battery bank - right?) is 12.5 amps max power provided by the solar panels. Or, is there way to get more power out of the panels than is their power rating? At 72V the 600 watt panels produce 8.3 amps or do I have that wrong?

Assume you get full power four hours a day as I did with my 500 watts at 23 N and you get 50% power for another 6 hours a day (wildly optimistic). That is (at 48V) 50Ah+37.5Ah or about 88 Ah a day you are putting back into the batteries.

Your regen process provides another 72 Ah per day for a total of 160 Ah a day put back into the batteries.

All of the above assumes your panels are 100% efficient, the mast or boom never shadows the panels and pitching/yawing has no impact on panel power production. My 15-years experience with a lot of panels says otherwise, but lets assume best case.

Did I get it right this time?
No, I made a mistake in quoting what the open circuit no load voltage of the 300 watt panels are---more of a brain fart so to speak. They are 36 volt panels and approx. a little over 8 amps each as you state. So in series of course they are 72 volts @ 8+ amps. Since you and I have both lived on solar, we know you rarely get that, and if you do, maybe only for a few hours. My panels will be fixed and in place of the bimini and parallel the water thus always rocking around. In my case I am lucky. My boat is similar to a cat boat with the mast farther forward and therefore no boom shadows over the bimini unless the sun is near to directly on the bow in which case everyone gets shadowed. Or, I could throw one of my bridle lines with a chain hook on it and pay out some chain from the windlass, swinging around stern to for the afternoon, then release and swing back for sunrise. But...I'm probably to lazy to do that because late afternoon is margarita time. Also, being a Freedom, it's a free standing carbon spar with no rigging wires to shadow the panels as well.

Oh, you asked if there was a way to make more solar power than the rating of the panels. Yes there is. I chose 72 volt panels for a reason. I don't need 72 volt panels to get my 54.72 final charge voltage, but here's why I picked 72V panels. I wouldn't state that you can make an 300 watt panel into a 400 watt panel, but in the real world using a MPPT (maximum power point tracking) solar charge controller (some called a boost controller) will get you more current into your batteries as the excess voltage that is over what you need gets converted into more current (dc to dc conversion). Some users report as much at 15% to 18% more, so maybe figure that into your calculations---I didn't in my example below. (Being a solar guy you must have known this already, but just throwing MPPT out there if others are unaware of these controllers). So, wildly and optimistically dreaming 8.3A + 18% MPPT boost = 9.3A panels...beyond their rating!

Secondly, you are using 48 volts as my propulsion battery voltage. Hopefully I never have to see 48 volts. My LVC (low volt cut) per cell is 3.10 volts. 48 volts would be a LVC of 3.0 VPC. Now, I'm sure you realize a 12 volt battery is hardly ever 12 volts---same with 48 volt batteries. I will charge my prismatic LFP battery bank to exactly 54.72 volts, and I mean exactly! (3.42VPC) at HVC (hi volts cutoff is extremely important with LFP). Many others charge their LFP cells to 3.6 or more. Not me. My charge curve will never reach the hockey stick part of the LFP curve. There is no sense in nearing the destruction voltage of the cells as there is little AH capacity residing in that part of the curve anyway. My LVC will be 49.60 volts (3.10VPC) measured under a short timed recovery no load. In an emergency situation where I need more range I can take them down to 2.5 volts LVC per cell and my bench top testing using my CellPro PowerLog 8 Battery Workstation, combined with the CSS control/graphing software, shows I will have approximately another 20+/- AH if I have to discharge this low in an emergency, though it's on the very steep waterfall part of the discharge curve (a place LFP doesn't like to go for longevity). The EV car guys do worse, sometimes taking their LFP battery packs down to zero volts. (just the thought makes me cringe at $110 to $200 PER CELL retail). So if you care to, you'll have to work up your numbers again using 54.72 volts (3.42 VPC) and the MPPT charge rate. But again, this is a "take what I get" system, so what works for me, and what I am OK with may not work for you, or anyone else for that matter.

Incidentally LFP batteries are not only great for propulsion they obsolete lead acid (LA) batteries for the house system as well. When configured as a 12 volt pack they have an unbelievable and nearly straight line discharge curve. In other words you'll have well over 13 volts before they hit the drop-off knee and it is time to recharge. No more sub 12 volt problems. Running lights are bright all the time, refrigeration is colder, water makers produce more water output per run time, anything really increases it's efficiency during the entire discharge of the battery (especially inductive loads). It's as though your house system now has a constant voltage DC power supply instead of an 11.5 volt dead LA battery that only has about 50% useful amp hour capacity to begin with, instead of 80% to 90% useful capacity with LFP. And it's the same with prolusion. The guys that try and save a buck using AGM or golf LA cart batteries with their propulsion setups are really missing out on quite a lot of performance both in terms of power, range and efficiency, not to mention they have hundreds of pounds more lead in their boats.

Now, go ahead and work up your numbers on my propulsion solar charge system. (Oh, I am not considering prop regen here...just sitting at anchor say in a sunny Catalina anchorage) I am well aware that at even at a guestimate 40AH per day, it's going to take some time to get them fully charged. In a week or so they'd be back to about 240AH or 70% capacity, and maybe around 8.5 days they would arrive at 340AH and considered at 100% SOC. Do these figures work OK for you? Hope so. Because it's a great excuse to stay the island longer! Ha! Or... I could just recharge enough to make the next leg of the trip with a little reserve figured in and then the charge process continues at the next anchorage (and even during the trip). After all, it's a sailboat. Sometimes nay-sayers want to forget the sailboat part of the equation.

Now...how about a scenario here. I think you like those. Here's one of mine---YNMV. It's not worst case, but say I limp into Isthmus Harbor near Catalina Island's west end and my propulsion batteries are nearly depleted. Say I have about 20AH left in my bank, or around (340AH/20AH = 5% SOC on a 380AH pack). So I sit there for a couple of days. Do I have to wait a week or more to fully recharge them before I leave? NO. They are not lead acid batteries. They don't care what state of charge they sit at, they just stay there (for years!). Now, it's been sunny and on those two days at anchor and with my solar panels, and using your numbers I was able to put 80AH back into the batteries. I decide I'd like to go check out Marina del Rey and hang at the park dock there for a few days. I've got 80AH in the batteries and 20AH reserve before LVC hits (80AH+20AH = 100AH or 340AH/100AH = 29% SOC. So, after two days I motor out from the anchorage and set sail for MdR and put my motor into regen mode. It's a great day to sail and under fully batten large roach mains'l I'm making a solid 6 knots. I could go a little faster, but I've chosen to use my regenerating prop along with my 600 watts of solar so there is a little prop drag, probably around 1/4 to 1/2 knot My regen readout shows I'm getting on average 3AH to 4AH into the batteries. It's about 30 miles from the Isthumus to MdR (I like round numbers), so during that 5 plus hours of sailing I may get 3x5=15AH from my reg prop. My solar shows I'm getting approximately 50% of their capacity and I'm only getting 4 amps from the panels (gotta throw a low factor in for fun). So I'm getting 15AH from regen and 4AHx5hrs = 20AH from the panels. 15AH regen + 20AH solar = 35AH into the propulsion batteries for this trip. So leaving the anchorage my total LFP pack's SOC was 29% (80AH solar + 20AH reserve = 100AH/340AH total = 29% SOC.). Now I add in the trip charging; 100AH at anchor +15AH regen + 20AH solar, or 135AH into my batteries arriving at the end of the trip. I arrive at the Harbor Patrol dock, pay for my stay, then electrically and quietly, I motor over the the park dock and tie up. Once at the dock I get out my shore power cord and plug in. I go down below and switch on my 30A LFP battery charger. Since I arrived with 135AH back into the batteries from being at anchor two sunny days, and then the sail over, and my 100% SOC is around 340AH (on my 380AH system) I have to put back 340AH - 135AH = 205AH to reach 100% SOC. At a 30AH charge rate (no absorption, bulk, or Float BS with LFP batteries---hit them as hard as you want up to 3C to 5C)....so at 30AH charge rate 205AH/30 = 6.83 hours or 6 hrs 49 minutes to reach 100% SOC. So if I arrive MdR around 4:00PM or so, then a little before 11:00 PM my system arrives at 100% state of charge. I can sleep well with this scenario and I hit the sack with a full tank of "fuel". Not scientifically accurate, and maybe even some mistakes in there, but for my purposes? Close enough, not too far off from typical and it will do.

So no biggie really and please remember; this solar array is not intended to solely propel the boat by itself at all, (impossible anyway, except maybe at sculling speed if no wind and in flat water), though on a good day it's 8 amps or so can't hurt if it wants to kick in and push a little more. After all, conservatively speaking, how could a little over 400 watts (an extra .54 HP) not hurt?
Or, how about some wildly dreaming "pie in the sky" numbers? How about throwing the MPPT controller numbers into the equation? 72V panels x 9.3A MPPT output = 669.7 watts! That's only 76.4 watts shy of 1 HP!
Not much help? Food for thought eh?

Cheers!
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