Increase efficiency in the cargo ship industry without a propellor

[sophiecentaur]

The most efficient water boats

We're talking about water transport. Efficient hulls are not too good when they need to carry a big load. What you are suggesting is worse than just marginal, as soon as you bring practicalities into the situation. Slow water transport, in the form of a canal network, doesn't fill the bill these days. If you can't carry stuff significantly faster than the 4mph average that canal transport was limited to then it's a non starter. The tugs used on fast moving rivers (like the Rhine) allow short enough journey times for the goods in the barges. Excessive bufferage with fleets of barge flotillas isn't acceptable so speed counts.

 

[sophiecentaur]

The most efficient water boats achieve downwind VMG > 2x windspeed. So in a downstream current of 5kt, they could go upstream at 5kt relative to the shore on a calm day.

etc. etc.
But wouldn't that imply a speed through the water of more than 5kt? What sort of Power would be needed to exceed (double?) that for a loaded barge? I mentioned land yachts in my initial response to sailing upwind. Land yachts have very little drag and so do 'very efficient water boats', which do little more than support a mast and a helmsman.

Actually, this avenue of thought would be a non starter in the case of most inland waters. Even a modest sailing boat mast wouldn't clear bridges on most rivers. I once looked into sailing up the Thames with an air draft of just 10m. Not worth trying except at low tide. Bridges are already established and were chosen to suit existing air drafts.

 

[jbriggs444]

But wouldn't that imply a speed through the water of more than 5kt?

Yes. 10 kts water-relative velocity made good. Which means a water speed even higher than that. So?

 

[sophiecentaur]

Yes. 10 kts water-relative velocity made good. Which means a water speed even higher than that. So?

So what about the drag of the hull? The speed against the wind is not an absolute. Moving a cargo through the water uses massive engines. Upwind experiments are all done with small hulls. I can’t see any equivalence to cargo transport without acres of sail. And that is not possible on rivers with bridges.

 

[jbriggs444]

So what about the drag of the hull? The speed against the wind is not an absolute. Moving a cargo through the water uses massive engines. Upwind experiments are all done with small hulls. I can’t see any equivalence to cargo transport without acres of sail. And that is not possible on rivers with bridges.

The design should be such as to minimize hull drag, yes. The speed against the wind will not be absolute, yes. It will, in particular, depend on wind speed. And likely surface conditions. Yes, I do not see any sweet spot where this is economical for cargo transport. In general, sail fell out of favor for cargo transport long ago.

 

[A.T.]

In general, sail fell out of favor for cargo transport long ago.

Of course. My mention of modern sail boat capabilities was merely a physically interesting side note in reply to the historical account about Cartier sailing up the Saint Lawrence. Not a realistic proposal for cargo shipping.

There is a classic puzzle related to this, which I just posted here:
https://www.physicsforums.com/threa...classical-physics-puzzles.999164/post-6456536

 

[Baluncore]

If the tracked tractor runs on the river bed. Will it be approved by the environment department, or will it stir up too much mud while killing fish.

Track ground pressure will be less underwater due to buoyancy of the tractor. The tractor would need to carry a dense ballast.

A tow line from the tractor to the barge will rise diagonally. As the pull becomes greater, or the water deeper, the tractor will tend to be lifted off the bottom. (A farm tractor hitch or plough is designed so that the drawn load will pull the rear drive wheels down onto the ground, to increase traction).

A light weight underwater, tracked pusher could to be mounted on a rigid arm that hangs below, and rearwards, from near the front of the barge. That way the diagonal compressive force applied by the tracks will increase the track ground pressure, and lift the barge, helpfully reducing the displacement of the hull.

 

[hmmm27]

Unless the canal is actually a submerged concrete road, an underwater tractor will just trash everything, not only in the vicinity, but downstream for a long ways. Even if you're warped enough to think that's a decent tradeoff, it will also stop working after a couple trips, when the tractor starts bottoming out in the ruts.

What about a submerged rail ? Or, overhead, like a trolley bus.

 

[sophiecentaur]

Overhead gets my vote. Underwater would be a nightmare. But overhead would look unsightly.

 

[anorlunda]

There are two ways to interpret the word tracked.

One is tracked like a bulldozer or a army tank.

The other is tracked like a railroad with underwater rails.

Underwater rails would quickly sink in the silt and in my opinion are a nonstarter.

 

[256bits]

Unless the canal is actually a submerged concrete road, an underwater tractor will just trash everything, not only in the vicinity, but downstream for a long ways. Even if you're warped enough to think that's a decent tradeoff, it will also stop working after a couple trips, when the tractor starts bottoming out in the ruts.

What about a submerged rail ? Or, overhead, like a trolley bus.

Right. Churn up the river bottom.
There is the environmental damage to consider, so a dedicated path would be necessary to limit that only during construction of the path.
The infrastructure cost of the dedicated path for the tractor. Grand guess of more than $50 million per mile ( a approximate ( high value ) tramway cost per mile above ground ( don't really know if we can use that as a valid base , but 100 miles of river using that as a base for cost figuring would be a 5$billion dollar investment )

And the incentive for the users to actually move towards the thing while paying a fee.

I can see the Panama Canal having the incentive of saving transit times across the seas, and the St. Lawrence Seaway having the ability to move farther up the river, for cheaper transit.

What would be the incentive for anyone to use this system, besides government decree that all boats/barges must use the tow system, and equip their flotilla for said function.

 

[Vanadium 50]

Underwater rails would quickly sink in the silt and in my opinion are a nonstarter.

Yes, but if the conditions of a towpath are too rough, just think what it's like on the river bottom.

(For most rivers - the Los Angeles River is an exception, being rice and paved)

 

[Baluncore]

There are two ways to interpret the word tracked.
One is tracked like a bulldozer or a army tank.
The other is tracked like a railroad with underwater rails.

The bulldozer is called tracked because it is a "tracklayer" vehicle. It lays track ahead as it advances, continually picking up the track and passing it forwards, to lay it again ahead of the vehicle. A tracklayer advances along the tracks with roller-chain pinions locked to the track chain rollers.

The driven wheels of a railway engine rely on friction between the wheels and the permanent way. Permanent underwater rails, (lubricated with mud), would need to take the form of a gear rack so as to give positive engagement with a tractor drive pinion.

While pinion lubrication by mud would be an advantage, abrasion of the track and pinion by sand and silt would be a problem.

Corrosion of steel track in an oxidising environment would be rapid as the oxide would be removed by each passage of a drive pinion. Stainless steel would corrode rapidly in anaerobic mud. That is the material selection problem.

 

[synch]

A) downstream : go with the flow
B) upstream : use the propeller as a water-driven turbine to drive a winch, and drag the barge/ship against the flow. Maybe use a generator to drive an electric mule. It would be slow but still work.
No fuel cost !

 

[synch]

caveat : it would require a larger turbine than normal ship propellers I guess.

 

[sophiecentaur]

Grand guess of more than $50 million per mile

For a lightweight cable car system, the costs are around $20m per mile so your estimate is on a par but an overhead ship tow would be more chunky than a simple cable car.

Permanent underwater rails, (lubricated with mud),

And abraded by mud and grit. Plus the problem of build up of silt around rails. And there's erosion of the river bed around and under the track.

No fuel cost !

Who pays for the electricity?

 

[jbriggs444]

Who pays for the electricity?

What electricity? The thing is water-powered.

We are talking about something very similar to a tethered turbine that uses the generated power to reel in the tether. And yes, this would likely be even less economically feasible than burning fuel or paying for electricity.

 

[sophiecentaur]

Whoops! So it's a water equivalent off sailing against the wind. Wouldn't the craft also need a regular propellor (when it's traveling elsewhere)? I guess a design that worked both ways would not be too efficient. What sort of speeds could be achieved, I wonder? The capital cost would need to be justified against the existing engine and speed is relevant in transport systems. The Canals died out largely because the railways were quicker. Not relevant for coal transport but, for many items, you can't have idle money during slow journeys.
The economics are very complicated - as complicated as the interesting Engineering factors.

 

[jbriggs444]

Whoops! So it's a water equivalent off sailing against the wind.

Yes, indeed.

Wouldn't the craft also need a regular propellor (when it's traveling elsewhere)?

If the thing needs to nose into a protected and current-free anchorage to load or unload then yes, one would need propellers, maneuvering thrusters, tugboats or some such. A battery and reversible turbine strikes me as the most elegant approach. Make sure not to cut the tow line, Captain Queeg.

If one were to take the craft out on the open ocean, one would need to un-tether and, perhaps, reverse the turbine to act as a propeller. But then one would need sustained power...

For a Rube Goldberg vessel such as this, perhaps one would launch a kite carrying a turbine.