Electric yachts recharded by tidal flow?

[Adios]

About the new electric motor equipped yachts that recharge while sailing. Will they trickle charge their batteries while a boat is on a tidal mooring? Other than a bit of slack many boats have tide flowing past the boat the whole time, some places quite fast tide. Not seeing that mentioned as a feature. Bit of a waste if its not possible for some reason. If typical tidal flow is not enough power to turn the prop perhaps a larger prop could be lowered while on the mooring?

 

[sarabande]

At the low speeds (I guess around 3 kts or so on a typical mooring ) you would need a rather large turbine blade area to make a useful electrical contribution. Most of the charging props only start at around 5 kts.

On the hydro electric station I manage, we only start generating when the water past the screw blades reaches around 1 cubic metre a second - that's a tonne of water every second. Ultra low flow generators are available but they are not screw configuration but advanced horizontal water wheel designs with blades in close proximity to each other; again the blade surface area is large, much larger than one could mount on a boat or mooring.

The other problem I can see, from personal experience of keeping my boat on an up to 3 sometimes 4 kt fore and aft mooring is that debris such as weed, old ropes, tree branches quite frequently becomes tangled in the risers and mooring buoys.


Now there is a case to be made for micro sized magneto-hydrodynamics, but the induced drag does pose some interesting design questions which could be incorporated in a boat hull, but which might make it unsailable.

 

[Blueboatman]

The trick is to use the vertical energy from the rise and fall of tide .
Many years ago the forum poster who used to manage Berthon identified this, to give credit due .
A pontoon moored mid river , to which moored boats are attached , has a massive potential to become a plug -in charging station , to harness tidal range and convert it to stored electricity .
As rising tide lifts the tethered pontoon vertically , that is the amount of energy available .
How you decide to convert this linear tidal potential , via mechanics or hydraulics say, into rotational alternator charging ,well , that should keep the amateur busy for a while over his morning cockpit coffee.
The attraction of such a thing , unlike sun or wind, would be its absolute dependability , tide after tide.

 

[AngusMcDoon]

The trick is to use the vertical energy from the rise and fall of tide .

5000 kg boat.
5 m tide range.

Potential energy gain = 5000 * 5 * 9.8
245 kJ

Time to take to rise 5m, 6 hours
6 * 60 * 60 seconds
21,600 s

Power generated on average
245000 / 21600
11 Watts, assuming 100% efficiency. After inefficiency losses you might get 5 Watts. You'd be better off (and save a lot of money) using a solar panel.

Think of a boat hoist. It lifts the same boat the same height in less than a minute. How much diesel does it use to do that? A few cupfulls maybe? If you're going to get significant energy from seawater's tidal height change you need to be working with the mass of cubic km of the stuff like the whole Severn Estuary, not a few boats.

 

[Blueboatman]

I like the math flow, thank you .
Good place to start

So that example is based on a 5 cu metres displaced volume pontoon lifted 5 metres .

5w does seem rather paltry !

Try it this way maybe : 5t pontoon sitting on a hydraulic jack 5 metres in the air then lowered to ground , surely the jack bleeds more than 5w in convertible , electrical energy
I think an old fashioned bicycle wheel rubber dynamo might do that ??
Seriously interested
this forum is awash with engineers ...can we improve it?

 

[AngusMcDoon]

Try it this way maybe : 5t pontoon sitting on a hydraulic jack 5 metres in the air then lowered to ground , surely the jack bleeds more than 5w in convertible , electrical energy.

Only 11 Watts if you lower it over 6 hours, a tide half cycle (approximately).

However you get the energy out you can't get over the potential energy equation...

energy = mass * height * acceleration due to gravity

This forum is awash with engineers ...can we improve it?

Yes, build a Severn barrage.

 

[sarabande]

If the Scotland to Northern Ireland bridge is ever built, it could be populated with sub-surface turbines over a large part of its length to help pay for the cap- and opex.


Boris ? Boris ? Are you listening ?

 

[dom]

Think of a boat hoist. It lifts the same boat the same height in less than a minute. How much diesel does it use to do that? A few cupfulls maybe? If you're going to get significant energy from seawater's tidal height change you need to be working with the mass of cubic km of the stuff like the whole Severn Estuary, not a few boats.

Well that's ruined my morning!

How much bloody lifting do I have to do to burn off this cream cake?

 

[Adios]

Think of a boat hoist. It lifts the same boat the same height in less than a minute. How much diesel does it use to do that? A few cupfulls maybe? If you're going to get significant energy from seawater's tidal height change you need to be working with the mass of cubic km of the stuff like the whole Severn Estuary, not a few boats.

A few cupfuls twice a day could be enough to fill a tank over the long interval many people have between boat uses. May not be economical but perhaps something compact and easily fitted, that clamps to the top of the post with a spring loaded cable bolted to the pontoon. But yes the question will be why bother if a solar panel produces the same for much less cost.

If in effect it is holding back the weight of a number of boats and a pontoon so would it have to be quite a substantial thing? Or the more substantial it is the more resistance to the fall can be got and more benefit gained. If the maximum gain is not great even with a substantial bit of kit its surely not worth it

Could it be enhanced by the falling pontoon building up tension in a spring attached to something with a heavy flywheel which when released spins super fast over a short period. Or is that no better than a geared approach that gives a steady speed? I'm just throwing out probably daft ideas here but it seems like the right crowd to field to

 

[JumbleDuck]

How much bloody lifting do I have to do to burn off this cream cake?

A Tesco Belgian Chocolate Eclair contains 608 kJ which is enough to lift a 2.6 tonne Ford Transit to the top of a two meter hoist twelve times, just about. Of course there would be mechanical losses, to 8 - 10 times would probably be enough.

Or for a boating version, there's enough energy in the eclair to lift a Bavaria 38 almost 8 metres into the air.

 

[Caraway]

I just scribbled this up. Can't see a downside

 

[Biggles Wader]

I love it

I just scribbled this up. Can't see a downside

I love it. I think Im suffering from perpetual emotion.
.

 

[Blueboatman]

Athomson “.... I'm just throwing out probably daft ideas here but it seems like the right crowd to field to “
Oh yes!

 

[Blueboatman]

I love it

I love it. I think Im suffering from perpetual emotion.
.

I’m looking for the Upside

 

[johnalison]

It’s a frescher approach, at least.

 

[dom]

A Tesco Belgian Chocolate Eclair contains 608 kJ which is enough to lift a 2.6 tonne Ford Transit to the top of a two meter hoist twelve times, just about. Of course there would be mechanical losses, to 8 - 10 times would probably be enough.

Or for a boating version, there's enough energy in the eclair to lift a Bavaria 38 almost 8 metres into the air.

Great calculation!

It's interesting how the counterintuitive aspects of this extend to massively overestimating the amount of calories burnt off through exercise.

 

[Concerto]

If the Scotland to Northern Ireland bridge is ever built, it could be populated with sub-surface turbines over a large part of its length to help pay for the cap- and opex.


Boris ? Boris ? Are you listening ?

Bridge? They are talking of a floating tunnel.
Floating tunnel to be assessed for Northern Ireland 'fixed link' - Marine Industry News

Boris listening? He probably is as it was reported in the Daily Mail.

 

[Blueboatman]

In my minds eye now I really really want to attach a solar panel driven 12v motor to 2 gears and a chain drive to deliver an actual 5w to a lift to elevate this 5t pontoon through 5m over 6 hours and see how we get on.. that’s a lot of joules needed surely , converted back into potential energy . Imagine doing it with blocks and tackle or levers or hydraulic jacks ..
Without wishing to try the patience of those who do these calculations all day every day and get paid to do it ... Something doesn’t seem right ... or is it ?

As you all say , things ain’t necessarily what they seem .

Intuition is a very deceptive , wobbly thing. ?

 

[Adios]

In my minds eye now I really really want to attach a solar panel driven 12v motor to 2 gears and a chain drive to deliver an actual 5w to a lift to elevate this 5t pontoon through 5m over 6 hours and see how we get on.. that’s a lot of joules needed surely , converted back into potential energy . Imagine doing it with blocks and tackle or levers or hydraulic jacks ..
Without wishing to try the patience of those who do these calculations all day every day and get paid to do it ... Something doesn’t seem right ... or is it ?

As you all say , things ain’t necessarily what they seem .

Intuition is a very deceptive , wobbly thing. ?

I agree its hard to believe the considerable weight of pontoons and boats wouldn't be able to pull down hard enough to be able to spin something very fast with the right (fairly extreme) gearing. There's not much resistance to a generator rotor is there? The electric boats are able to generate enough to recharge when sailing 7-8 knots. It can be made to generate going up as well so its a pretty constant output entirely independent of the weather. Lunar powered in fact.

 

[AngusMcDoon]

I agree its hard to believe the considerable weight of pontoons and boats wouldn't be able to pull down hard enough to be able to spin something very fast with the right (fairly extreme) gearing.

You can't get more energy out of the system than there is in there. It doesn't matter how much gearing you do. Read about it here...

Gravitational energy - Wikipedia

U = mgh is the relevant line.

In the example I have m is 5000, g is 9.8 and h is 5. The result is in Joules, 245,000 of them. Divide that by the 6 hour tide time, 21,600 seconds, and you get about 11 Joules per second, which is 11 Watts.