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Old 24-01-2017, 09:54   #61
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Re: Generating electricity - water around the hull/keel

"My little boat might note the equivalent of 2.4 HP in drag however a big vessel in the trade winds is a very different creature and these systems have a history of success in such boats."
2.5 hp will drive my 10M sloop at 4-5 knots.
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Old 24-01-2017, 10:38   #62
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Re: Generating electricity - water around the hull/keel

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Originally Posted by John Holbrook View Post
Interesting questions and I have no expertise here so this a question as much as a suggest. How about a tube running from a point of the hull where there is high pressure (in front of the keel?) to a point where these is low pressure (stern?) with a small turbine and alternator. If the opening was shaped hydrodynamically would this have Nader the performance of the boat?
Aside from all the reasons presented before that keel or hull mounted generators have significant down sides, this idea would be prohibitively expensive both to retro fit to an existing boat or to add as the design in a new one. When doing a cost/benefit analysis of the potential power generated against the costs: financial costs in design and construction plus costs in lost boat performance the numbers do not add up.
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Old 24-01-2017, 11:13   #63
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Re: Generating electricity - water around the hull/keel

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Originally Posted by John Holbrook View Post
Interesting questions and I have no expertise here so this a question as much as a suggest. How about a tube running from a point of the hull where there is high pressure (in front of the keel?) to a point where these is low pressure (stern?) with a small turbine and alternator. If the opening was shaped hydrodynamically would this have Nader the performance of the boat?
Ok, right against the hull there is something called the boundary layer. This is a few atoms thick of non-moving water. Just microns out from this is the friction layer where water is passing over water and this is where the friction drag it. A little out from this is the disturbed area (let's say an inch) this is the area where you can get attached release, but it is small. Further out from this is the ocean undisturbed by the boat.

The fastest velocity difference is between the hull and the ocean, so if possible that's the water we want to use to scavenge power from. Everything inside the boundary layer is disturbed and is moving proportionately slower.


Modern hydrogens like the watt&sea use a drive leg to drop the prop below the boundary layer and into the free flow. Towed behind generators are far enough back they are also in the open ocean. So they pretty much both see the same amount of velocity difference. So they see the maximum possible water velocity, no contraption can be better than this.

But let's assume we build a tube so we don't have any projections from the hull. Well the same flow characteristics apply, the same boundary layer of attached water, the same disturbed area, so a large percentage of our tube is creating friction, which is going to slow down the boat all the time, but worse it's going to create a lot of turbulent slow water just before it hits the turbine, because the flow of water in the tunnel is going to be slower than the boats speed thru the water.



Here the simple answer really is just use a drive leg to push the prop into clean flowing water and accept the moderate drag penalty from the leg. If you want to get really fancy you could use different size and pitch props optimized for the specific speed the boat is moving, but most don't. Below about 5kn there just isn't that much power available, above 5kn there is enough that a mismatched prop isn't that important. When you hit 20kn you have so much power almost anything will work.

For really high speed boats like the VOR and maxi trimarans they actually do have smaller high pitched props for high speed operation. It just isn't relavent for most of us.


Fundamentally it just comes down to speed then the water is king. If you can average 6kn a hydrogen can make more power than you will ever need. If you average 4kn it won't. Sadly most cruisers average between 4 and 5kn, which is why hydrogens typically are thought of as being moderately effective with a long history of disappointing (though legitimate) performance. Most boats just don't see high enough speeds to make them work.

The answer of course is a larger prop. But the larger the prop the larger the drag, and you get into a negative spiral. Big prop means lot of drag, which means you sail slower, which means you need a bigger prop which means more drag.....
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Old 24-01-2017, 21:35   #64
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Re: Generating electricity - water around the hull/keel

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"My little boat might note the equivalent of 2.4 HP in drag however a big vessel in the trade winds is a very different creature and these systems have a history of success in such boats."
2.5 hp will drive my 10M sloop at 4-5 knots.
But those bigger boats have even bigger power demands. The guy putting down a few million on an 80-100' yacht isn't going to want ice in his drinks and he doesn't want to worry about leaving a light on. In practice by the time you get to mega yachts they just crank up the generator not to mention they have room for 5000-6000w of solar panels if they want to display how eco-friendly they are.
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Old 24-01-2017, 21:51   #65
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Re: Generating electricity - water around the hull/keel

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This is what is obtained coupling an EWOL prop to a electrical engine used as a generator

http://www.naviwatt.fr/wp-content/up...-HPOWERMAX.jpg
Excellent example. Here's a company pushing the idea.

On a small boat (28') boat, you can typically fit 300-400w of solar without any great difficulty and they will produce that output for a few hours each day under way, at anchor, at a dock, etc...

Hull speed will be somewhere around 6.75kts, so at hull speed, this system might put out 375w but unlike the solar panels that will be producing their rated power 20-25% of the time in a fairly predictable manner (sunrise & sunset are pretty well understood), you will only get 375w when you are under sail at hull speed and you have enough wind that you can maintain hull speed while the prop is essentially applying around 1hp in reverse (remember, the system will be no where close to 100% efficient converting drag into energy). What percentage of the time do you run at hull speed and have enough extra wind that it can maintain it even with 1hp push backward?

My guess is for the average sailor that is under 0.5% of the time.

Now you do get some power at slower speeds but at a more typical 4-5kts, it's down around 150w or well below the rating of the solar panels. Even at more moderate speeds with a heavily used boat might reach 5% of the time.

Then you have to account for the fact this is test data presumably with a perfectly clean hull and prop. In the real world, the output can be cut in half with just a thin layer of growth that can show up in a week or two. If you start growing a reef, forget about it. So if you want to see these kinds of results, plan on weekly dives to clean the hull and prop.

Yes, the system puts out more power at higher speeds and a tiny percentage of high performance boats can occasionally reach those speeds but those really fast boats tend to have room for even larger solar arrays. On a large cat that could see 10kts on a regular basis, its easy to find room for a 1000w of solar.
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Old 25-01-2017, 04:47   #66
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Re: Generating electricity - water around the hull/keel

Stumble thank you for taking the time to give me an informed and clear answer

Back to the drawing board...


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Ok, right against the hull there is something called the boundary layer. This is a few atoms thick of non-moving water. Just microns out from this is the friction layer where water is passing over water and this is where the friction drag it. A little out from this is the disturbed area (let's say an inch) this is the area where you can get attached release, but it is small. Further out from this is the ocean undisturbed by the boat.

The fastest velocity difference is between the hull and the ocean, so if possible that's the water we want to use to scavenge power from. Everything inside the boundary layer is disturbed and is moving proportionately slower.


Modern hydrogens like the watt&sea use a drive leg to drop the prop below the boundary layer and into the free flow. Towed behind generators are far enough back they are also in the open ocean. So they pretty much both see the same amount of velocity difference. So they see the maximum possible water velocity, no contraption can be better than this.

But let's assume we build a tube so we don't have any projections from the hull. Well the same flow characteristics apply, the same boundary layer of attached water, the same disturbed area, so a large percentage of our tube is creating friction, which is going to slow down the boat all the time, but worse it's going to create a lot of turbulent slow water just before it hits the turbine, because the flow of water in the tunnel is going to be slower than the boats speed thru the water.



Here the simple answer really is just use a drive leg to push the prop into clean flowing water and accept the moderate drag penalty from the leg. If you want to get really fancy you could use different size and pitch props optimized for the specific speed the boat is moving, but most don't. Below about 5kn there just isn't that much power available, above 5kn there is enough that a mismatched prop isn't that important. When you hit 20kn you have so much power almost anything will work.

For really high speed boats like the VOR and maxi trimarans they actually do have smaller high pitched props for high speed operation. It just isn't relavent for most of us.


Fundamentally it just comes down to speed then the water is king. If you can average 6kn a hydrogen can make more power than you will ever need. If you average 4kn it won't. Sadly most cruisers average between 4 and 5kn, which is why hydrogens typically are thought of as being moderately effective with a long history of disappointing (though legitimate) performance. Most boats just don't see high enough speeds to make them work.

The answer of course is a larger prop. But the larger the prop the larger the drag, and you get into a negative spiral. Big prop means lot of drag, which means you sail slower, which means you need a bigger prop which means more drag.....
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Old 25-01-2017, 08:14   #67
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Re: Generating electricity - water around the hull/keel

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While we are doing a little "blue sky" analysis, I wonder if one could harness galvanic corrosion using the abundance of seawater flowing over whatever dissimilar metals were appropriate to generate electricity using some sort of electrochemical reaction or harnessing some form of generated magnetism using a steel hull or keel. I'm no scientist (obviously) but wonder what might be possible.


You could. That is after all how a battery works. But you'll use up your boat quickly. Quite an expensive way to generate electricity.
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Old 25-01-2017, 08:20   #68
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Re: Generating electricity - water around the hull/keel

A "tidal movement" type of generator, no larger than a 5 gallon bucket, could be used at the end of say a 10 Ft long spinnaker pole out the beam of the boat. One on each side. If the boat rocks maybe 2" at the waterline at anchor from wind wavelets, the pole and gen will move up and down much more than that... .. Might be a flopper stopper at the same time...
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Old 25-01-2017, 12:14   #69
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Re: Generating electricity - water around the hull/keel

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Originally Posted by valhalla360 View Post
Excellent example. Here's a company pushing the idea.

On a small boat (28') boat, you can typically fit 300-400w of solar without any great difficulty and they will produce that output for a few hours each day under way, at anchor, at a dock, etc...

Hull speed will be somewhere around 6.75kts, so at hull speed, this system might put out 375w but unlike the solar panels that will be producing their rated power 20-25% of the time in a fairly predictable manner (sunrise & sunset are pretty well understood), you will only get 375w when you are under sail at hull speed and you have enough wind that you can maintain hull speed while the prop is essentially applying around 1hp in reverse (remember, the system will be no where close to 100% efficient converting drag into energy). What percentage of the time do you run at hull speed and have enough extra wind that it can maintain it even with 1hp push backward?

My guess is for the average sailor that is under 0.5% of the time.

Now you do get some power at slower speeds but at a more typical 4-5kts, it's down around 150w or well below the rating of the solar panels. Even at more moderate speeds with a heavily used boat might reach 5% of the time.

Then you have to account for the fact this is test data presumably with a perfectly clean hull and prop. In the real world, the output can be cut in half with just a thin layer of growth that can show up in a week or two. If you start growing a reef, forget about it. So if you want to see these kinds of results, plan on weekly dives to clean the hull and prop.

Yes, the system puts out more power at higher speeds and a tiny percentage of high performance boats can occasionally reach those speeds but those really fast boats tend to have room for even larger solar arrays. On a large cat that could see 10kts on a regular basis, its easy to find room for a 1000w of solar.
Those power generation figures are quite impressive, but they do not include drag data so it's impossible to calculate (or even guess) how much it would impair the performance of any boat.

But as to your ruminations about the usefulness of such a device...

We had a home brew drag generator on our previous boat. Nothing fancy, just a shaft with a 6 hp Johnson o/b prop, some 12 mm double braid and a surplus tape drive permanent mag 32 V motor. On that 36 foot ex-IOR one tonner, we averaged (really averaged, not guessed) 140 m/day in the trades. That's a speed average just under six knots, and at 6 knots that rig put out 10 amps at the usual 12.5-13.5 volts required to start charging the batteries, or simply taking the house loads directly. So, that's on the order of 120 watts, available 24/7 under those conditions... and coupled with a 50 watt solar panel, we had power to burn... so much so that we typically would only run the troller during the night hours! That was a simple boat by today's standards, small fridge, incandescent lighting, wind vane, some ham radio usage, no computers, not much electrical load.

Our estimate of performance loss wasn't very scientific, but it appeared to knock off around 1/2 knot when deployed at a boat speed of 6 knots. That was quite acceptable to us then, and would be today... and I'd sure like to have that extra power available to feed our hungry autopilot!

Obviously, the troller is of no use when at anchor, but then for us, our electrical loads are smaller then and solar (on our current boat) keeps up ok, at least in the summer. Some cruisers spend little time at sea,and for them solar is clearly better, but for those that voyage much, a reliable power source like a troller is quite useful.

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Old 25-01-2017, 13:09   #70
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Re: Generating electricity - water around the hull/keel

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I'm a newb when it comes to sailing (although I've been reading a tremendous amount for the past 5 years) so the answer may be obvious to some of you old salts. However I'm hoping some of you can help me with a question I have.

Obviously generating electricity for a boat, specifically without using a combustion engine, is one of the great challenges that boaters and manufacturers have been stymied with for decades.

I've often wondered why it is that manufacturers have not yet figured out how to harness the energy of the water that flows around the hull - and most specifically around the keel - in order to generate and store energy while the boat is under sail.

Yes, we have wind generators and solar panels, and we've seen prop generators that can be towed behind the boat. However it seems to me that the most kinetic power available in the environment surrounding a sailboat at any given time would be generated from the forces of the water as it flows around the keel while the boat is under a stiff breeze above water.

I do not know the physical calculations at all, but I have to believe that the power availed by water flowing over the keel must be significant when there is enough breeze to move a 15 tonne sailboat. How is it that this cannot be harnessed? Even if it is at the expense of boat performance (at least when energy production is induced) does it matter - the boat can only travel at a certain hull speed in most instances anyways. And surely if we can generate power its a sacrifice some sailors who are cruising would happily trade wouldn't it?

Could some of you smarter people out there help me with this question I've been struggling with?

Thank you all in advance!

Rob
Rob,
Even if you invent your magic generator that delivers power comparable to the approximately 4HP per ton of displacement needed to reach hull speed it will be no use to a cruiser. We need a reliable energy storage component at greater than 24kWh capacity that can be charged at 24kW for an hour and discharged (and enjoyed) at 1kW for the rest of the day.
The inferior 12V energy storage systems we have cannot be charged at 2000 Amps. This is why cruisers cannot enjoy the comforts available in a house even if it was a house with the lowest electricity usage.
Battery technology is the weakest link. It is my belief that the average cruiser while on the hook would not mind running the engine for one hour if it could be operated at full load to charge the batteries with 24kWh.
The batteries have all this bulk state, absorption state, sulfating, equalizing, balancing and a bunch of other BS that not even 10% of the engine operating time can be utilized as efficiently as when pushing the boat at hull speed.
Again, the battery technology is the weakest link.
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Old 25-01-2017, 18:23   #71
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Re: Generating electricity - water around the hull/keel

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Those power generation figures are quite impressive, but they do not include drag data so it's impossible to calculate (or even guess) how much it would impair the performance of any boat.

But as to your ruminations about the usefulness of such a device...

We had a home brew drag generator on our previous boat. Nothing fancy, just a shaft with a 6 hp Johnson o/b prop, some 12 mm double braid and a surplus tape drive permanent mag 32 V motor. On that 36 foot ex-IOR one tonner, we averaged (really averaged, not guessed) 140 m/day in the trades. That's a speed average just under six knots, and at 6 knots that rig put out 10 amps at the usual 12.5-13.5 volts required to start charging the batteries, or simply taking the house loads directly. So, that's on the order of 120 watts, available 24/7 under those conditions... and coupled with a 50 watt solar panel, we had power to burn... so much so that we typically would only run the troller during the night hours! That was a simple boat by today's standards, small fridge, incandescent lighting, wind vane, some ham radio usage, no computers, not much electrical load.

Our estimate of performance loss wasn't very scientific, but it appeared to knock off around 1/2 knot when deployed at a boat speed of 6 knots. That was quite acceptable to us then, and would be today... and I'd sure like to have that extra power available to feed our hungry autopilot!

Obviously, the troller is of no use when at anchor, but then for us, our electrical loads are smaller then and solar (on our current boat) keeps up ok, at least in the summer. Some cruisers spend little time at sea,and for them solar is clearly better, but for those that voyage much, a reliable power source like a troller is quite useful.

Jim
As I previously said, if you are at sea running at hull speed for a few months at a year, it's a viable option but even for most circumnavigators, those days are a rarity in the course of a 3-5yr trip.

You had 120w of hydro and it cost you almost 10% of your speed. If extracting 120w cost you 1/2kt think how much extracting 300-400w is going to cost you.

I'm guessing you only had 50w solar because this was several years ago. People usually start with 150w as the minimum solar today with 300-400w as more typical, so having more than enough power on a low power usage boat is easy to do.

Also, your home brew system has an advantage over the OP's idea of a permanently mounted unit in that you can retrieve it and negate the speed loss when it's not needed. Also makes it easy to keep it clean so it functions near it's peak efficiency.

They are viable and they aren't anything new. It's just the rare use case where they are the most effective option.
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Old 25-01-2017, 20:02   #72
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Re: Generating electricity - water around the hull/keel

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As I previously said, if you are at sea running at hull speed for a few months at a year, it's a viable option but even for most circumnavigators, those days are a rarity in the course of a 3-5yr trip.

You had 120w of hydro and it cost you almost 10% of your speed. If extracting 120w cost you 1/2kt think how much extracting 300-400w is going to cost you.

I'm guessing you only had 50w solar because this was several years ago. People usually start with 150w as the minimum solar today with 300-400w as more typical, so having more than enough power on a low power usage boat is easy to do.

Also, your home brew system has an advantage over the OP's idea of a permanently mounted unit in that you can retrieve it and negate the speed loss when it's not needed. Also makes it easy to keep it clean so it functions near it's peak efficiency.

They are viable and they aren't anything new. It's just the rare use case where they are the most effective option.
Can't disagree with much of that, but the percent usage idea doesn't play. It is true t hat we didn't use it but a few percent of the days we owned that boat, but when in use it was quite important to us. Kinda like an EPIRB, which is typically used 0% of the time, but is carried by most cruisers!

And we were not at or even very near hull speed when making those 140 mile days... rather the circa 80 -85% of hull speed that Evans and Beth reckon is what most cruisers average (IIRC). I failed to mention that on those occasions where we went faster, the prop would start jumping out of the water (my bad design) and we would pull it in.

finally, you were right in that this was a "few" years ago... like 25! We bought that first solar panel in either '89 or'90, thought it was magic!

Oh... I dunno how speed loss scales with increasing generator power. I suspect that it is somewhat complex but it is obvious that more electricity means more drag. If the presence of the troller meant one didn't have to fit a gen set (and that is a stretch, I'll admit) the overall performance might be improved!

And we haven't touched upon the Gordian knots that sometimes were formed in the line to t he prop... they were quite difficult to unravel at times!

Jim
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Old 29-01-2017, 11:11   #73
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Re: Generating electricity - water around the hull/keel

Thank you so very much to everyone who has contributed productively to this thread - many of you have provided some incredibly insightful and knowledgeable information which has certainly highlighted some of the complexities involved when it comes to subjects like electricity generation.


After reviewing all your replies I am certainly beginning to understand the challenges involved in the question I asked, and that these challenges are multifaceted - clearly fluid dynamics, lift, drag, fouling of equipment, maintenance, battery storage capacity etc. would all cause massive complications on a number of fronts in trying to generate electricity in this manner while under sail.

With that in mind can I ask all you scientific types to discuss this simple question:

If you took a given boat, with a given displacement, with a given sail plan, when the wind conditions are such that it can power your boat up to its hull speed (whatever that may be), what is the theoretical power output being captured by this boat?

It seems to me that the amount of power being generated per second or per hour isn't necessarily trivial.

Where am I going with this? I wonder if I've been thinking about this question in terms differently than what it might be typically discussed by most. Rather than trying to capture a small amount of electricity which could be generated by decreasing the boat's speed marginally over a lengthy trip, rather, I've often wondered if maybe there is a way to generate a much larger amount of electricity over a a much shorter period of time - this of course would be done when their is ample wind available, and by decreasing the boat's speed dramatically during this period, but could be done at either the start or at the end of a voyage.

Let's not even discuss all the myriad of other problems...just curious what the potential is that is not being harnessed right now in terms of units of measure.

Thank you so much.




p.s. -


And to all of you who were offended by my snarky remark to the ONE guy whose reply I found offensive - my apologies to you that I don't do well with arrogant, dismissive "old salts" regardless of their experience and knowledge. If they can't share that knowledge in a useful manner but instead reply in terms that make the question sound stupid without providing any meaningful substance then I have zero time for them. I suppose that's a fault I won't reconcile any time soon.
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Old 29-01-2017, 11:58   #74
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Re: Generating electricity - water around the hull/keel

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Thank you so very much to everyone who has contributed productively to this thread - many of you have provided some incredibly insightful and knowledgeable information which has certainly highlighted some of the complexities involved when it comes to subjects like electricity generation.


After reviewing all your replies I am certainly beginning to understand the challenges involved in the question I asked, and that these challenges are multifaceted - clearly fluid dynamics, lift, drag, fouling of equipment, maintenance, battery storage capacity etc. would all cause massive complications on a number of fronts in trying to generate electricity in this manner while under sail.

With that in mind can I ask all you scientific types to discuss this simple question:

If you took a given boat, with a given displacement, with a given sail plan, when the wind conditions are such that it can power your boat up to its hull speed (whatever that may be), what is the theoretical power output being captured by this boat?

It seems to me that the amount of power being generated per second or per hour isn't necessarily trivial.

Where am I going with this? I wonder if I've been thinking about this question in terms differently than what it might be typically discussed by most. Rather than trying to capture a small amount of electricity which could be generated by decreasing the boat's speed marginally over a lengthy trip, rather, I've often wondered if maybe there is a way to generate a much larger amount of electricity over a a much shorter period of time - this of course would be done when their is ample wind available, and by decreasing the boat's speed dramatically during this period, but could be done at either the start or at the end of a voyage.

Let's not even discuss all the myriad of other problems...just curious what the potential is that is not being harnessed right now in terms of units of measure.

Thank you so much.




p.s. -


And to all of you who were offended by my snarky remark to the ONE guy whose reply I found offensive - my apologies to you that I don't do well with arrogant, dismissive "old salts" regardless of their experience and knowledge. If they can't share that knowledge in a useful manner but instead reply in terms that make the question sound stupid without providing any meaningful substance then I have zero time for them. I suppose that's a fault I won't reconcile any time soon.
You're new to sailing and clearly want to make your mark in the energy generation field. If you went sailing, you might appreciate that the questions yo're asking are interesting but not really important to people who have sailed a lot. They have seen many gimmicks come and go and have learned that they are less important than the simple act of getting on a boat and going for a sail.
Go down to your local marina and offer to crew on a boat, buy a dinghym get sailing.

On your question, a boat needs less than 10 kw to travel at 4 knots in dead calm, Any generator in the water will create much less energy than that. Why do you imagine that sailors wouldn't mind going slowly at the beginning and end of a journey? I usually am using the motor for the first and last half hour, When the port comes into view, the last thing I usually want to do after sailing for say 8 hours, it to go slow. I just want to be tied up in port, sitting on the quay with a nice cold beer at my lips. Remember that water powered generation is the same as trying to stop the boat moving. That might be OK if you're overpowered, but, as has been pointed out, that is not often the case. As well, If I'm coming into port, I'm often coming in to power and having fully charged batteries becomes irrelevant. I don't think there would be many sailors who would want to sail slowly just to get some charge in their batteries. One function of a sailboat is to try to achieve maximum ( Not often above 6 -7 knots) speed by using wind alone, That is the joy of sailing.
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Old 29-01-2017, 11:59   #75
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Re: Generating electricity - water around the hull/keel

Carogan,

It's very difficult to say for sure, but to push my boat close to hull speed my boat demands about 35hp from the engine, so let's asssume that's close enough for what you will suggest, that works out to be about 25kw or so.

If the idea is a large prop, keep in mind that appreciably slowing down the boat also greatly effects the power generated. So using a larger prop may actually generate less power (power goes up with the square of the swept area, but the cube of the velocity). So you have to balance drag and swept area to find a reasonable compromise.

I think few cruisers would prefer a massive gain over a short period than a moderate one over a longer period. Boats while underway don't normally see massive changes in power consumption just long duration loads. Secondly, any conditions where you will average close to hull speed are likely going to last a while (days not hours) so when conditions are suitable there is rarely a hurry.
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- If animals weren't meant to be eaten then they wouldn't be made of food.
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