Generating electricity - water around the hull/keel

[Telesail]

I am not sure I understand what you mean when you ask about "power generated per second or per hour". Power is the Energy generated per unit of time (Joules per second = Watts).

The best way for you to think about trying to capture power from the relative movement of the boat and the water is that power is force * distance/time. Distance/time is speed.

When a boat reaches hull speed, there is no "extra power" in the water available to harness. You cannot push harder against the water (i.e. have extra power from the sail because the wind is whistling") and have no extra speed unless the water is "pushing back" equally hard. In other words, the relative velocity of the boat through the water is unchanged.

I hope this helps but since I am not sure I understand what you are really trying to achieve - for example, where you would store this extra electrical energy because you will still use it at the rate you would normally consume regardless of how you generated it? - I am not sure I am responding to your real question.

[buzzstar]

Originally Posted by Carogan

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. ....

The question as I understand it, it how much power is required to drive your boat under the described conditions. IMO it is impossible to determine "scientifically," but perhaps can be done by engineering. There are too many variables, ranging from hull design, to hull cleanliness, and even further to minor variations in the hull due to garfs or even paint. Any mechanical device would change the conditions, but perhaps it can be done by calculations and electronics external to the vessel. One thing for sure, there would be no excess power to collect and store since the act of doing do would slow the vessel. I am not including solar just so the position of the panel or other collection device remains unchanged. Got it? Under the postulated facts all available power is being used to move the vessel, there is none to harness because if you do so the postulated facts are not achieved.

[topmast]

What you need to consider is 'How much power to drive the vessel to hull speed.? Not very practical to try to go faster. My old fat bottomed girl would go faster under sail than under power.(95 hp Isuszu) So at the top end of sailing there would be little effect on speed by dragging some power out of the passing water as there is still excess power pushing against the bow wave. As soon as the wind drops to below that nessesary for hull speed ,speed will be effected big time. Assume your "device' requires 3 hp and hull needs 30 hp to go hull speed ,anything less than big wind will mucho detrimental .Unless you can haul it up ,disengage or get the dammthing out of the water you live with the drag. Not an engineer but my dog likes it.

[dlymn]

Originally Posted by Shrew

What a weird post. Nothing like arguing with everyone trying to discuss your topic.



When you say 'manufacturer's what do you mean (e.g. Boat manufacturers, alternative energy business?) Boat manufacturers are not in the business of making generators. They can provide options for installing 3rd party Diesel or gas generators, solar panels or wind generators. It would not be cost effective for a boat manufacturer to allocate R&D when there are companies out there dedicated solely to this type of manufacturing.

The amount of energy yielded would need to be at least comparable to other options out there. If the cost is high, and the energy yield is low, it will not be marketable. It's tough to justify cost of R&D for something as yet unmarketable.

Your point was to the water forces around the keel. These forces would only occur as a result of the hull moving through the water, or the water moving around a hull at rest. Thus the parallels to tide generators were made.

However anything that can harvest the water forces moving around a hull will need to capture those forces through movement of their own. That method of capturing hydrodynamic forces can't itself impede sailing performance.

Newton tells us that any action has an equal and opposite reaction. Anything attached to a boat that requires the force of the water moving g past the boat will logically slow the boat down. A propeller spinning creates drag which cause a retarding force on the hull.
The only time that generating power as you sail is important is when you consume electricity as you sail. This assume that your batteries weren't charged when you left port, your motor and other charging devices didn't fully charge and that you won't have access to power or power generation in the next port. These circumstances combined are not so common and spending g thousands on a device is just not justified. My diesel with 2x 80 amp alternators give me all the daily energy I need just going in and out of port

[StuM]

Originally Posted by Carogan

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.

Assuming that you are looking at getting energy from the boat moving through the water, this is self defeating. The more you reduce the speed, the less energy there is available for capture. (And it's not linear either, half the speed and there is a LOT less than half the energy available). If you manage to stop the boat completely, there is NO energy to capture.

[valhalla360]

It's a practical issue.


In theory, as long as the sails can provide enough power, you can generate an unlimited amount of electrical power.


In practice, it quickly falls down.


The power you need to extract from the wind is:
Power to push the boat to Hull Speed + Power to overcome Drag induced by the Generator


So in theory, if you need 30kw to keep the boat at hull speed and you have turbine that produces 2kw at 25% efficiency, you need 38kw(30kw + 2kw/.25) of power from the sails.


In theory, you could generate 100kw but you need 430kw (30kw +100kw/.25) of power from the sails. If you are lucky, the sails will shred extracting that kind of power. If they don't, your next best hope is to be dismasted. If the mast holds up expect more serious problems.


The bigger issue is if you design the turbine to extract large amounts of power at very high wind speeds, it will kill the performance even more at lower wind speeds.
- In conditions where the boat would normally do 6kts and a small generator might knock off 0.5-1.0kts, it might knock off 2-3kts and power generation might only be around 0.25kw.
- In conditions where the boat could just make hull speed, again, it might knock off 2-3kts and only produce 0.5kw


Again, it comes back to the point that cruising boats are only rarely running at hull speed and even when they do run at hull speed, they often won't have a lot of extra power available. In the end, it's the rare situation where you will actually have these large power generation numbers but the drag from a fixed generator will be large all the time.

[captlloyd]

I see lots of numbers, theories , formulas being thrown around here. I come from Akron Ohio where Walt and Art Arfons were from. The engineers were constantly telling them how fast they could go with their land speed cars cause they had formulas, computers and what-not. Problem was the Arfons didn't know anything about all that stuff, they just knew how to put big engines into small cars. Every time the Arfons set a new speed record the engineers would tell them they could not go any faster. The Arfons didn't pay much attention to the experts, the experts were not the ones setting the speed records. But wait a minute, who were the real experts? Maybe it was the ones who were ready to try something everyone else said could'nt be done. There is a major difference between constructive critisizem and critisizem. A lot of you folks just can't seem to get past the fact that the OP does not mind trading off some speed in exchange for power generation.

[dlymn]

Originally Posted by captlloyd

I see lots of numbers, theories , formulas being thrown around here. I come from Akron Ohio where Walt and Art Arfons were from. The engineers were constantly telling them how fast they could go with their land speed cars cause they had formulas, computers and what-not. Problem was the Arfons didn't know anything about all that stuff, they just knew how to put big engines into small cars. Every time the Arfons set a new speed record the engineers would tell them they could not go any faster. The Arfons didn't pay much attention to the experts, the experts were not the ones setting the speed records. But wait a minute, who were the real experts? Maybe it was the ones who were ready to try something everyone else said could'nt be done. There is a major difference between constructive critisizem and critisizem. A lot of you folks just can't seem to get past the fact that the OP does not mind trading off some speed in exchange for power generation.

Interesting except many of the people who are giving advice here are the Arfons. They are people who have travelled thousands of miles under sail, who have experienced first hand the matter of generating electricity, who know that storage is far more important than generation. Boating is full of gimmick makers; people who have a better way, but often have no real experience of the destructive forces of nature, corrosion, organism that attach themselves everywhere underwater, the need to be able to service and repair without lifting the boat and especially the need to be safe and reliable.. Sailors spend hours trying to maximise the output from sails and to garner as much energy as possible to push their boat forward as.efficiently as possible. When something comes along that improves efficiency, sailors will adopt it. LEDs, solar panels etc. But these are about improving efficency not sacrificing sailing power to generate a few extra watts. When a non-stop round the world sailor uses a water turbine generator it's done because there is no other way to generate electricity without sacrificing something else like precious fuel. Cruisers are rarely more than a day or two from the next port, they have generators, solar panels, wind turbines. Harvesting a few extra watts using sailing power is not as important as sailing itself.
I enjoy reading the information provided by experts, people who've been around sailing long enough to know what works and what doesn't. I suggest that like the Arfons, some people should go out and get some real sailing experience, say a thousand hours of sailing and then come back to the forum with the wisdom that hands on experience teaches.

[Stumble]

Originally Posted by captlloyd

I see lots of numbers, theories , formulas being thrown around here. I come from Akron Ohio where Walt and Art Arfons were from. The engineers were constantly telling them how fast they could go with their land speed cars cause they had formulas, computers and what-not. Problem was the Arfons didn't know anything about all that stuff, they just knew how to put big engines into small cars. Every time the Arfons set a new speed record the engineers would tell them they could not go any faster. The Arfons didn't pay much attention to the experts, the experts were not the ones setting the speed records. But wait a minute, who were the real experts? Maybe it was the ones who were ready to try something everyone else said could'nt be done. There is a major difference between constructive critisizem and critisizem. A lot of you folks just can't seem to get past the fact that the OP does not mind trading off some speed in exchange for power generation.

And neither do the thousands of people that have chosen to instal hydro-generators over the years. Burning off a little speed to generate a good bit of power is a pretty sensible trade-off. But putting a large prop in the water to try and harvest a lot of power is contra-indicated. The amount of power available to harvest is a function of the cube of the speed you are going. So doing anything to slow you down hurts the potential. Butting a larger prop off the stern may actually reduce the amount of power harvested because the boat slows down so much. This is a quite classic optimization problem, with a very standard process to resolve.

Up to now the optimizations favored by the industry have centered on slowing a 40' boat at 6kn down by .25-.5kn. As the proper balance between speed and prop size (also read as drag). But you could certainly try to generate the absolute maximum amount of power in the shortest time. It just resolves the optimization process differently. Likely a slightly larger prop optimized for use at a higher boat speed. But it will cost you a lot of production at lower speeds.

[buzzstar]

Originally Posted by captlloyd

I see lots of numbers, theories , formulas being thrown around here. I come from Akron Ohio where Walt and Art Arfons were from. The engineers were constantly telling them how fast they could go with their land speed cars cause they had formulas, computers and what-not. Problem was the Arfons didn't know anything about all that stuff, they just knew how to put big engines into small cars. Every time the Arfons set a new speed record the engineers would tell them they could not go any faster. The Arfons didn't pay much attention to the experts, the experts were not the ones setting the speed records. But wait a minute, who were the real experts? Maybe it was the ones who were ready to try something everyone else said could'nt be done. There is a major difference between constructive critisizem and critisizem. A lot of you folks just can't seem to get past the fact that the OP does not mind trading off some speed in exchange for power generation.

[Fact] Not many computers back in the days when the Arfons were doing their thing. [Opinion and Fact] In the same vein, I've been to Akron, and that does not make me a tire expert. [Opinion and Fact] While your statement is correct that speed can be a tradeoff for power generation, the way the OP has phrased things it seems like the attempt is to generate power without any tradeoff. [Opinion] Let us try to properly identify and distinguish opinion and fact where we can, although perhaps not to the extent I have attempted and the method I have used.

[captlloyd]

Originally Posted by buzzstar

[Fact] Not many computers back in the days when the Arfons were doing their thing. [Opinion and Fact] In the same vein, I've been to Akron, and that does not make me a tire expert. [Opinion and Fact] While your statement is correct that speed can be a tradeoff for power generation, the way the OP has phrased things it seems like the attempt is to generate power without any tradeoff. [Opinion] Let us try to properly identify and distinguish opinion and fact where we can, although perhaps not to the extent I have attempted and the method I have used.

The Arfons were setting records through the 70's when engineers were using computers regularly. I don't think the OP expects there not to be some sort of trade off on speed. Maybe the OP is searching for "what you don't know that you don't know".

[senormechanico]

Bottom line if the OP wants to harvest more energy from the water going past his boat, he needs to install a BIGGER SAIL PLAN (and maybe a bigger hull to hold it).

[valhalla360]

Originally Posted by captlloyd

The Arfons were setting records through the 70's when engineers were using computers regularly. I don't think the OP expects there not to be some sort of trade off on speed. Maybe the OP is searching for "what you don't know that you don't know".

Most of these apocryphal stories are just that "stories".

After the fact they (or an anonymous promoter) make statements saying someone told them it couldn't be done. Say it enough times and maybe get a couple media outlets to repeat it and eventually people believe it to be true.

No engineer ever said the Titanic was unsinkable but lots of people still believe it to be the case because they heard it repeated for decades.

If the OP wants to go out and build a better mouse trap in spite of the simple physics behind the problem, good for him. I'm sure if power generation was the sole and primary purpose, you could build a sailboat that would generate a few hundred KW but it would be a very silly boat that would cost a lot and be horrible for any other use.

PS: In the 1970's, 99.99% of engineer was still with a slide rule (by the late 70's they started coming out with basic calculators but an engineer worth his salt could do the work faster with a slide rule). Yeah there were a few computers and for a few specialized cases, they were used but if you walked into the average engineering firm, you would see rows of drafting tables, not computer work stations.

[hafa]

Originally Posted by valhalla360

...In the 1970's, 99.99% of engineer [sic] was still with a slide rule...

Yep, and look at the quality of the automobiles from that era. Thank the gods for computers...

[valhalla360]

Originally Posted by hafa

Yep, and look at the quality of the automobiles from that era. Thank the gods for computers...

You do realize I wasn't knocking computers?

I was correcting another poster's misinformation suggesting computers were commonly used in engineering during the 70s.