Hydro-electric watermill power system..??

OK, so this might not be the most appropriate thread for a tech question, but it suddenly occurred to me that, as multihulls go pretty quick most of the time, especially on passages, that a small amount of additional drag from a hydro system might not be unwarranted, especially for cruisers rather than racers.

So the questions is: has anyone got any idea how this "might" be done?

I was prompted to ponder this while reading an eco mag that featured adds for low water pressure hydro electricity production - essentially a Pelton wheel inside a casing with the wheel shaft attached to a brushless magnet generator.

Being an engineering ignoramous, I'm not even sure if it's possible, but could a lower-able 'flap' or 'drogue-type' receiver, reasonable wide, and flattish, but tapering according to RAM principles, suck up a small enough amount of water (thereby creating minimal drag) and focus/concentrate the energy of the boat's motion through the water into a narrow pipe that could feed a low-pressure water mill turbine...???

I know from research into airflow that RAM tubes like NACA ducts can concentrate the airflow energy and increase pressure/density of air....and we all know that hauling a bucket dropped overboard on a line requires a significant exertion of energy.....

So could this be worth pursuing as an option to solar panels and wind turbines, especially as the boat is constantly in motion while on passage?

Is there anyone out there with the hydrofynamic smarts to calculate whether this is even possible...???

Or am I off with the koalas, and barking up the wrong gum-tree?

Over to you....

 

hydrogenerators are actually pretty common on racing boats (search up hydrogenerators in the Vendee Globe) it works well if you are racing long distances or making regular long passages. The problem is that cruisers spend more time at anchor than sailing so the wind generator and solar options are more popular.

 

Yeah, I've seen the propeller type generators before - like Watt & Sea, and Ampair....

But my question was specifically about the use of the boat's motion transferred to the water scooped up by a ram tube to drive a Pelton wheel type generator....

Anyone done it before????

 

I think it's a problem of maintenance - you have to keep all the stuff that lives in the ocean and looks for new habitable space out of the system, much easier with an open system (especially when deployed only for use).

 

What purpose do you hope to achieve by separating a stream of water to extract energy instead of leaving it connected with the broader ocean? All I see are frictional losses building up in the system.

 

Well, obviously, the idea is to generate electricity to recharge batteries.....duh!

I doubt friction losses would be an issue, as Pelton wheels are used all over the world fed by pipes which can fall anywhere from 3m to 300m, and being long-ish, would have an issue with friction.....a RAM-type pick up feeding almost directly onto the Pelton wheel should have minimal friction losses.

But I do take the point about marine life, and flotsam too might be an issue.

Still haven't had the primary question answered: is it possible, and if so, what are the techinical parameters...??

 

I think you need a boffin to work out how much energy is available to x diameter hole at y speed.
I see a benefit over an open ocean device in that the energy is contained in the tube, rather like the endplate effect, rather than spilling out of the blades in the open sea.
Since it is an opening in the hull a seacock will be required so maybe a purging fluid could be introduced to stop growth.
It could probably be deployed via a tube within a tube sloping forward ? That way it could bring the working fluid above the waterline keeping the generator from fouling.
If the energy available side stacks up, I think it does have merit.

 

I don't see any reason why it shouldn't work, it comes down to the question if the additional complexity is compensated by the merits over the open generator.
By the way, a set up using the in-tube generator as jet drive is thinkable... .

 

You didn't pick up the basis of my question. Of course I understand you want to generate electricity. I am asking why you think removing a stream of water from the ocean would be better than an immersed propeller?
Friction aside, unless you put a peloton wheel below sea level you will use a portion of the available energy just lifting the water up to the height of the turbine. This will reduce the amount left available for generating power.

I think it is certainly possible that the suggested system could work but I think it would work with lower efficiency than a prop under the water.

After all, didn't the propeller prove itself ages ago over the paddle wheel?

 

RR
Yeah, basically thats what I'm asking for...is there a boffin out there who can give us some stats or an idea if it's viable.

I was imagining a NACA-duct-shaped 'scoop' with a small-ish diameter pipe attached to the narrow end that could be mechanically lowered either from a beam or the transom, which pipe would lead directly into the Pelton wheel chamber.

For example, a set-up similar to this:
http://www.electricmotorsport.com/store/ems_ev_parts_power_ME1112-KIT.php

....but encased in a water-proof casing, of course....

 

Munter
Yeah, OK I see your point....

I'm not suggesting it could be more efficient than the propeller-type designs, but based on the prices of what I've seen available, and hte knowledge around Pelton wheel systems for micro-hydro generation that is available these days (as opposed ot the 19th century), and the competition inherent in many different forms of micro-hydro Pelton wheels on the market, I was wondering if it might prove cheaper to design such a system, and possible even draw up a series of parameters that would enable DIY types to build their own.....

Does that answer the 'purpose' question a bit better..?

 

Just doing some googling and found this:

The Water Baby is a smaller version of Energy System & Design's Stream Engine. This machine is a very small device that converts the energy in water under pressure into electricity. It can operate on heads of 50 feet (15m) to over 500 feet (150m)with flows as low as 3 gpm (11 l/m). At a head of 100 feet (30m) and a flow of 3 gpm (11 l/m) the output is 25 watts; at 24 gpm (90 l/m) the output is 250 watts.

So 250W could generate a cuppla kilowatts a day.

Question is, how to calculate the scoop size and duct profile to generate that kind of pressure and flow.....

 

You could start with the basic physics of converting the minimum head to a flow velocity to see how fast the boat would have to go produce power. I don't think I'd try to include any pressure increase from fancy duct design at this stage because it is too speculative and doesn't change the basic energy balance anyway.
Water at 15m height has potential energy (mgh) Convert that to kinetic energy (1/2 mv^2) to determine to minimum boatspeed required to generate useful power and see if it looks worthwhile.

 

Did I mention I'm no good at math.....

 

Back in mobile range again after a weekend away.

The prevalence of pipe fed turbines in static generating situations doesn’t necessarily indicate that they are more efficient solutions in the moving boat scenario.

I did a couple of quick calcs comparing the head requirements of low head turbines versus the kinetic energy available in the water flow past the hull. For the 15m head required by the first turbine in your link you need a boatspeed of 33 kts to have the equivalent energy in the water flow! A little too much for the average cruising multi. Even an ultra low head machine has a head of some 1.4m which, if you add another 1m to for space for the turbine and equipment to requires a boatspeed of 13 kts.

These figures completely ignore frictional losses which would increase the boat speed required and any clever intake design which might try to accelerate the flow which would lower the required boat speed. Perhaps there is a particular turbine design that could be used for the very low head available to a sail boat but the standard designs would appear wanting.

If I were trying to power a cruising craft I think I’d look more to solar now that panel prices are significantly lower. There is no noise, no moving parts and it makes power in quiet moorings as well as at sea.