Electric Boats

[Mad Harold]

50 minutes ago, Bargebuilder said:

Ah, but weren't the Hp developed by 'vintage' engines magic Hp, being much more useful than modern Hp, even where a modern engine is gearboxed so it can swing a prop of a similar diameter, pitch and DAR to that of the 'vintage' engine?

The vintage HP was higher torque.

If the same sums apply to boats as motorbikes,horsepower =speed,and torque = accelaration (thrust)

[Bargebuilder]

2 minutes ago, Mad Harold said:

The vintage HP was higher torque.

If the same sums apply to boats as motorbikes,horsepower =speed,and torque = accelaration (thrust)

So, if you have a modern high revving diesel with relatively low torque and swap it's gearbox for one that has a lower gear ratio, at the shaft the torque increases and the revs. reduce and a big grippy propeller like the ones used on low Hp vintage engines can be swung; is that correct?

[tehmarks]

1 hour ago, peterboat said:

Drain and dig it out, spreading it on the fields I suspect?

I have an electric boat nothing is to be gained fitting an undersized motor it will get to hot from working to hard. The correct size motor isn't expensive so buy and fit one plus it uses little or no more electric 

 Apologies, I haven't really explained myself properly. I don't mean a motor that is undersized for propelling the boat when cruising, I mean I don't think I see the point in fitting whatever the equivalent power motor is to a 38hp (in my case engine), for the reasons that mrsmelly mentions.

 

If you can cruise along at a steady pace using 3kW, I don't really see the need to have a another 17kW in reserve to make up for a lack of anticipation. Obviously you do need excess power, but as boats seem to be over-engined to begin with, I'm not convinced you need anywhere near as much excess power as many people are including when designing electric propulsion systems. It's potentially important if you're designing a system around a proprietary battery system that  has a defined peak current that can't be circumvented by throwing more copper at your custom bank of cells.

 

Power seems to be many people's solution (including mine occasionally) to messing up and often even routine manoeuvring; is it not far preferable to just avoid the messing up to begin with, or to think ahead rather than relying on throwing it full aft as you arrive at full speed at the lock landing that was visible quarter of a mile away?

 

Like I said, just a thought, and I'm interested to hear everyone's opinion.

[PCSB]

37 minutes ago, Bargebuilder said:

So, if you have a modern high revving diesel with relatively low torque and swap it's gearbox for one that has a lower gear ratio, at the shaft the torque increases and the revs. reduce and a big grippy propeller like the ones used on low Hp vintage engines can be swung; is that correct?

Not really. Torque is determined by the engine, i.e. it is a chacteristic of the engine only and could be thought of as the turning force of the driveshaft in the engine. It is true that torque does to some extent depend on engine power and revs, but to the best of my knowledge all engines (internal combustion engines) produce maximum toque before they reach maximum power. A low revving (low power) high torque motor can turn more than high revving (high power) low torque motor. caveat - it has been a long (ok, very long) time since I last did any serious physics ... 

[nb Innisfree]

Why not have a larger electric with power in reserve, there's hardly any downside unlike a larger diesel running inefficiently at low speed. As Peter said an electric motor can be be both large and small at the same time. 

[PCSB]

I thought this was interesting ... and hopefully informative too. 

 

[IanD]

12 minutes ago, PCSB said:

Not really. Torque is determined by the engine, i.e. it is a chacteristic of the engine only and could be thought of as the turning force of the driveshaft in the engine. It is true that torque does to some extent depend on engine power and revs, but to the best of my knowledge all engines (internal combustion engines) produce maximum toque before they reach maximum power. A low revving (low power) high torque motor can turn more than high revving (high power) low torque motor. caveat - it has been a long (ok, very long) time since I last did any serious physics ... 

The engine torque curve is pretty much irrelevant when driving a prop, because except at maximum revs (assuming a correctly matched prop) any engine is capable of putting out more power (and torque) than the prop can absorb. Prop torque and power rise rapidly with rpm, at the point where these equal the engine output at that rpm you can't go any faster.

 

The relationship between prop torque and power depends on the prop diameter and pitch (and BAR), for a given prop it makes no difference whether it's driven by a big old slow engine or a geared-down modern high-speed one. 20 old bhp are worth exactly the same as 20 new bhp.

Edited August 18, 2021 by IanD

[Bargebuilder]

15 minutes ago, IanD said:

The engine torque curve is pretty much irrelevant when driving a prop, because except at maximum revs (assuming a correctly matched prop) any engine is capable of putting out more power (and torque) than the prop can absorb. Prop torque and power rise rapidly with rpm, at the point where these equal the engine output at that rpm you can't go any faster.

 

The relationship between prop torque and power depends on the prop diameter and pitch (and BAR), for a given prop it makes no difference whether it's driven by a big old slow engine or a geared-down modern high-speed one. 20 old bhp are worth exactly the same as 20 new bhp.

Thanks for that, very interesting. So given that a 9Hp engine of old was thought to be sufficient in a narrowboat, what Hp rating would be sufficient in a modern engine given the correct gearbox and big grippy propeller to effect an emergency stop if needed?

 

It seems that as the years have gone by, what is deemed as an appropriate number of Hp has risen and risen; perhaps too far?

[David Mack]

3 hours ago, Sea Dog said:

That raises an interesting question (for me anyway): how was dredging done in the horse drawn era?

 

Spoon dredger:

[David Mack]

3 hours ago, Sea Dog said:

That raises an interesting question (for me anyway): how was dredging done in the horse drawn era?

 

Spoon dredger:

[tehmarks]

26 minutes ago, nb Innisfree said:

Why not have a larger electric with power in reserve, there's hardly any downside unlike a larger diesel running inefficiently at low speed. As Peter said an electric motor can be be both large and small at the same time. 

 

43 minutes ago, tehmarks said:

It's potentially important if you're designing a system around a proprietary battery system that has a defined peak current that can't be circumvented by throwing more copper at your custom bank of cells.

 

Originally this thought came about from wondering whether one could design an electric propulsion system around a B-Box LVS/LVL installation. A 'full stack' of LVS modules is remarkably close to the peak current requirements of a Lynch Marlin 8kW, which intuitively seems a bit too weedy for a long steel narrowboat — and certainly if one want equivalence with their existing engine. This got me wondering about how much power one actually needs, because the obvious comparison is the days of horses. It seemed like an interesting thought experiment. The other obvious benefit is a potentially significant cost saving.

 

I'm not suggesting that anyone actually tries to stick a tiny motor in a big boat, more a case of wondering how much reserve power for manoeuvring one actually needs. People constantly seem to rev the whatevers off their engine making routine manoeuvres, and I'm not convinced it's at all necessary.

[dmr]

4 minutes ago, tehmarks said:

 

 

Originally this thought came about from wondering whether one could design an electric propulsion system around a B-Box LVS/LVL installation. A 'full stack' of LVS modules is remarkably close to the peak current requirements of a Lynch Marlin 8kW, which intuitively seems a bit too weedy for a long steel narrowboat — and certainly if one want equivalence with their existing engine. This got me wondering about how much power one actually needs, because the obvious comparison is the days of horses. It seemed like an interesting thought experiment. The other obvious benefit is a potentially significant cost saving.

 

I'm not suggesting that anyone actually tries to stick a tiny motor in a big boat, more a case of wondering how much reserve power for manoeuvring one actually needs. People constantly seem to rev the whatevers off their engine making routine manoeuvres, and I'm not convinced it's at all necessary.

 

Lots of variables but if you want a figure 30hp would be fine, 15 to 20 would be just about ok.

If we had purpose designed boats, shallow drafted and so a fair bit lighter,  then even less would do, but I don't want to go boating in a floating caravan that gets blown all over the place by a little gust of wind.

[ditchcrawler]

1 hour ago, David Mack said:

 

Spoon dredger:

@Rose Narrowboats have one

[Rob-M]

2 minutes ago, ditchcrawler said:

@Rose Narrowboats have one

It's the one on the photo above from David.

[magnetman]

Canals were made for propulsion systems which used the land for traction not the water. 

 

Propellers may in fact be the wrong approach altogether. It might be better to have a great big tractor wheel on an automatically varying depth arrangement in the centre of the boat and driven by an electric motor, for canal use. This would help enormously with general control of the craft and stopping quickly. 

 

Use the land. Not the water. 

 

propellers on canals are a red herring. 

 

 

 

 

 

 

[ditchcrawler]

17 minutes ago, magnetman said:

Canals were made for propulsion systems which used the land for traction not the water. 

 

Propellers may in fact be the wrong approach altogether. It might be better to have a great big tractor wheel on an automatically varying depth arrangement in the centre of the boat and driven by an electric motor, for canal use. This would help enormously with general control of the craft and stopping quickly. 

 

Use the land. Not the water. 

 

propellers on canals are a red herring. 

 

 

 

 

 

 

Interesting thought

[IanD]

2 hours ago, tehmarks said:

 

 

Originally this thought came about from wondering whether one could design an electric propulsion system around a B-Box LVS/LVL installation. A 'full stack' of LVS modules is remarkably close to the peak current requirements of a Lynch Marlin 8kW, which intuitively seems a bit too weedy for a long steel narrowboat — and certainly if one want equivalence with their existing engine. This got me wondering about how much power one actually needs, because the obvious comparison is the days of horses. It seemed like an interesting thought experiment. The other obvious benefit is a potentially significant cost saving.

 

I'm not suggesting that anyone actually tries to stick a tiny motor in a big boat, more a case of wondering how much reserve power for manoeuvring one actually needs. People constantly seem to rev the whatevers off their engine making routine manoeuvres, and I'm not convinced it's at all necessary.

There have been lots of threads about this on the forum. I suspect one reason that modern diesels are so overpowered is they make so much noise and vibration at maximum rpm (almost never used) that nobody ever wants to go there in normal use, not even upstream on rivers.

 

So a typical 40hp engine (at full revs) probably never sees more than half this -- meaning about 20hp, which happens to be what was common for big old slow engines which were happy to run at full power all day without overheating or making you go deaf.

 

This also seems to be what is becoming accepted as standard for electric propulsion on narrowboats, 15kW is 20bhp, which is plenty even for river use or the Ribble Link. If you don't ever intend to do this then lower power would be OK, but builders are presumably reluctant to build boats which are not "go-anywhere" because selling them might be more difficult -- the same reason that a 57' boat typically has a Beta 43 fitted not a Beta 20, it's what the market expects.

[peterboat]

2 hours ago, tehmarks said:

 

 

Originally this thought came about from wondering whether one could design an electric propulsion system around a B-Box LVS/LVL installation. A 'full stack' of LVS modules is remarkably close to the peak current requirements of a Lynch Marlin 8kW, which intuitively seems a bit too weedy for a long steel narrowboat — and certainly if one want equivalence with their existing engine. This got me wondering about how much power one actually needs, because the obvious comparison is the days of horses. It seemed like an interesting thought experiment. The other obvious benefit is a potentially significant cost saving.

 

I'm not suggesting that anyone actually tries to stick a tiny motor in a big boat, more a case of wondering how much reserve power for manoeuvring one actually needs. People constantly seem to rev the whatevers off their engine making routine manoeuvres, and I'm not convinced it's at all necessary.

I have a D135 lynch (real Lynch motor) motor in my boat running at a nominal 72 volts, its rated at 36kw peak 13kw constant its geared at nearly 3 to 1 which multiplies the torque at the propeller shaft by 3. Now stopping and starting is no issue cruising is 3.3kws at 3mph but I have plenty in reserve for those emergencies. 

The motor response is totally different to a diesel engine as its instant torque so no slow buildup to revs its straight there.

The issue with a small modern diesel engine is it would also require high gearing as well so the noise levels would be high in comparison to the electric motor or a larger diesel engine. 

[Sea Dog]

17 hours ago, David Mack said:

 

Spoon dredger:

Interesting. Funnily enough, not surprising... once you've seen it. Thanks David. 

[Mad Harold]

20 hours ago, magnetman said:

Canals were made for propulsion systems which used the land for traction not the water. 

 

Propellers may in fact be the wrong approach altogether. It might be better to have a great big tractor wheel on an automatically varying depth arrangement in the centre of the boat and driven by an electric motor, for canal use. This would help enormously with general control of the craft and stopping quickly. 

 

Use the land. Not the water. 

 

propellers on canals are a red herring. 

 

 

 

 

 

 

Interesting!  Perhaps a large paddle wheel with a tractor tyre around it's circumference.Best of both worlds?

I bet there will be complaints about the canals being too deep then.😃

[ditchcrawler]

I have just fallen onto this blog that may be of some interest http://solarpowerednarrowboat.blogspot.com/

[Mad Harold]

2 hours ago, ditchcrawler said:

I have just fallen onto this blog that may be of some interest http://solarpowerednarrowboat.blogspot.com/

Thanks for posting that.

I found it very interesting.

[Detling]

On 18/08/2021 at 19:40, tehmarks said:

If you can cruise along at a steady pace using 3kW, I don't really see the need to have a another 17kW in reserve to make up for a lack of anticipation. Obviously you do need excess power, but as boats seem to be over-engined to begin with, I'm not convinced you need anywhere near as much excess power as many people are including when designing electric propulsion systems. It's potentially important if you're designing a system around a proprietary battery system that  has a defined peak current that can't be circumvented by throwing more copper at your custom bank of cells.

That power can be useful stopping sharply, instead of ramming the boat coming round the bend on the wrong side. Also used for reversing the boat off the sticky bottom the bow has slid silently onto and is now preventing forward progress.  As both of these are reverse gear maybe a low power motor for one way and a big one for going astern.

 

[MtB]

14 minutes ago, Detling said:

That power can be useful stopping sharply, instead of ramming the boat coming round the bend on the wrong side. Also used for reversing the boat off the sticky bottom the bow has slid silently onto and is now preventing forward progress.  As both of these are reverse gear maybe a low power motor for one way and a big one for going astern.

 

 

Seconded. 

 

And similarly, a big diameter slow revving blade works far better in astern than an egg whisk. 

[nb Innisfree]

1 hour ago, Detling said:

That power can be useful stopping sharply, instead of ramming the boat coming round the bend on the wrong side. Also used for reversing the boat off the sticky bottom the bow has slid silently onto and is now preventing forward progress.  As both of these are reverse gear maybe a low power motor for one way and a big one for going astern.

 

Unlike an ICE a large electric motor can be economical at low output, so it can do the job of both without the need of a reverse gear.