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That's the graph for the motor. It reduces at low speeds because the losses are proportional to current/torque but output power drops as rpm decreases, so at half the rpm but the same torque the percentage loss doubles. But as I tried to explain this doesn't matter for a motor driving a propeller, because you never get into the bad efficiency low-rpm/high-torque corner -- when you follow the prop torque curve down as rpm drops the efficiency actually gets a little better, see the figures I gave.

Which I wouldn't do if I had "lithium-ion" batteries (e.g. NMC chemistry) instead of LFPs. But then I don't think anyone with a boat should touch NMC or similar with a bargepole of any length, even a ten-foot one wouldn't be long enough if they caught fire... You'd hope that insurers will see sense about this, especially with the increasing use of batteries for off-grid/feed-in applications in home -- nobody there suggests that you should not charge them (LFP!) from solar or the mains when you're not in the house, so why should boats be any different? Unlikely to happen, any more than it does in houses with off-grid/feed-in setups with batteries... 😉 It's been pointed out to the BSS (via their technical committee) that though this advice (disconnect after charging) is correct for the batteries in many portable devices (including power banks, ebikes, escooters...) which do pose a fire risk if overcharged, it does not apply to correctly designed inbuilt LFP batteries on boats.

From a discussion on the Electric Narrowboats group on Facebook, for those who don't use it but might be interested... ============================================================================== There's still a lot of misinformation/misunderstanding about prop/motor choice including oft-repeated statements like "they're different to diesels" or "low torque at high speed changes things", so I'd like to try and clear this up. There's no fundamantal difference; to get the full rated power out of a motor (electric or diesel) you need to match the prop size to the maximum power rpm. Overpropping means you can't reach full power/rpm, the rpm stops rising when propeller torque (proportional to rpm^2 -- power rises as rpm^3) hits the maximum motor torque. For a typical electric narrowboat, to keep prop size up and noise down you don't want to go much over 1000rpm at full power, and for a motor rated at 14~15kW/130-143nm (e.g. Torqmar, Engiro) you end up with something close to an 18" x 12" prop (or 16" x 12" 4-blade, which I've got and so has Paul Sumpner -- and this was also the conclusion of the recent Ortomarine trials. (Exact equation : Nm = 9550 * kW/rpm) This is why not just the headline power of the motor matters, but also the rated rpm and torque -- many of the motors being sold for direct drive on canal boats are really too high-speed/low-torque, possibly because high torque at lower speed needs a bigger and more expensive motor, or the main target market for the manufacturer is faster seagoing boats where higher speed props are fine. The reason "low-speed torque" doesn't matter is that propeller torque drops rapidly at lower rpm -- and this also affects efficiency. I've attached the efficiency plot for the Engiro 12013 (14kW/130nm/1080rpm), and this is what happens as rpm drops: 1080rpm : 14kw/130nm/91% 850rpm : 7kW/80nm/92% 650rpm : 3kW/46nm/92.5% 500rpm : 1.4kW/27nm/93% If you put the same size prop on a lower-torque higher-speed motor, this will limit the power and rpm to below the rating of the motor. For example, a 15kW 1500rpm motor (e.g. Bellmarine 15/20kW) has 95nm of continuous torque, so with this prop will top out at 920rpm, at which point power will only be 9.2kW. Of course you can push more than this for short periods (e.g. short-term rating (30 seconds?) is 127nm), but that doesn't help you on a river (see below). For many people with motors like this, such overpropping will be a better choice than the much smaller noisier "egg-whisk" matched prop for normal cruising, so long as you're aware that you can no longer achieve the full rated power -- a bit more than 60% in this case. Which will only matter if you ever need it, for example when travelling upriver against a current for any distance. The more overpropped the motor is, the more that maximum power/rpm drops off -- put an 18" x 14" on the Bellmarine 15kW and it'll top out at about 8.5kW/95nm/850rpm, again fine (and quiet!) for normal canal cruising, but now down to not much over half the rated power should you need it on a river. This downside of overpropping matters more on electric boats than on diesel boats since they have much less power to begin with -- an overpropped Vetus 10kW might end up only able to sustain about 7hp, which is very definitely on the low side for anything other than still water. Of course all this only applies to direct drive motors, but that's what most electric canal boats use for various very good reasons...

African or European?

Several decent beers every time we were there, but I don't recall exactly what. Possibly due to the amount consumed... 😉

Was friendly the last couple of times we were there, with decent pub grub and beer. Not many customers on midweek evenings when we were there, but landlady said it could get packed on Friday/Saturday so if you want to eat there I'd check ahead... 😉

Well colour me surprised... 😉

That's why I know it'll be raining on Saturday... 😞 https://www.facebook.com/Smiffs.W6

I can only assume you think this would make the canals "suitable for navigation" because you can use your fabulously effective anchor and winch to go up and down them? 😉

Of course not, because the government's own figures show that the biggest overall benefit from the waterways is to the much larger number of people who use them for other purposes -- walking, cycling, fishing -- which is how the DEFRA grant is justified. Though strictly speaking they don't have to be *navigable* for those users, meaning working locks and paddles and so on, just kept in water. OTOH it's quite possible that the cost of just this (keeping them navigable, as opposed to in water for the non-boater users) *is* paid for by boaters, including license fees for both private boaters and hire companies, the 9% slice from most marina fees, and direct payments to CART from EOG/farm and online moorings.

<sigh> Ignore the fact it was a literal reply to a snide comment your bestie made, and throw some more fuel onto the fire... 😞 Onto the naughty step again, maybe you'll be happy there together...

I didn't say they *couldn't*, just that they're bred for slow heavy load pulling, but the heavier the animal is the less well suited it is to moving more quickly, and the more quickly it gets exhausted and overheats when doing so -- as I'm sure you're well aware of, even elephants can get a move on if they have to but they're not really built for it... 😉 Getting under bridges is certainly an issue in some places, it's one reason cobs or donkeys were often used on the canals, but whether it is on the Lancaster I don't know.

It's unlikely they'd have used heavy draught horses, these are bred for pulling heavy loads (ploughs, wagons) at walking pace, not trotting at 8-10mph.

Only one beer? I'm truly disappointed... 😞 You mean like you and your bestie BLUNT? 😉

Wow, those are ridiculously light -- at least, when unladen. If Swiftsure was 74' x 5'6" and 32cwt (1.6t) unladen and you put 80 passengers on it that would add another 100cwt (6.6t total) given average weight in the 1800s. Incidentally, if you put those figures into the vicprop calculator and allow 5hp (engine equivalent to 2 flogged horses?) for propulsion, it predicts 11.6mph unladen, 9.6mph with 20 passengers, 8.5mph with 40 passengers, and 7.2mph fully laden with 80 passengers -- which given a normal number of passengers actually stacks up quite well with the historical reports of speed... 🙂

I've been pretty open about what I've found since getting the boat, certainly much more so than most others about things like cost (higher than originally quoted), energy usage (more than expected), solar yield (less than expected), fuel consumption and generator running hours (more than expected), joystick failures (Vetus!!!), charging speed (lower than expected), electrical cooling (needed improvement, now done) -- because this should all be useful for anyone else thinking about going electric. But every time I do post anything some people seem to be just desperately looking for ways to find fault or tell me I've wasted my money -- I'm sure this is in part the good old green-eyed monster, but they'll never admit this. Which is why I've largely stopped posting details, because I'm fed up of this attitude -- and it's always the same people doing it, see this thread for example... 😞 Would love to do the BCN challenge, but this year it just didn't stack up with planned cruises for myself and family. Maybe next year... 😉 More trolling, see above... 😞

You really don't seem to understand what I said, so let me repeat it. All I ever said about running the genny was I preferred doing it when not cruising (e.g. tea in bed in the morning, out shopping at lunch, at the pub in the evening) so I could enjoy complete silence while travelling instead of just quiet (still quieter than any diesel boat I've ever been on) -- why would I do anything else, that would be idiotic? As far as solar is concerned I go out when I want to (and can -- still working remember, and I have lots of other mostly musical events on), and use as much solar as I can get -- but it has no influence on whether I go out or not. Of course like anyone else I'd rather be cruising in the sun (with lots of solar power!) than in the rain but then this is England, you don't always have a choice... I'm not having a go at you or anyone else for asking questions, but your repeated posts about Gybe Ho had zero useful content and were 100% personal attacks -- which by definition makes you a troll. If you don't like being called a troll, stop posting like one... 😉

You really are inventing stuff here... I'm not "struggling to enjoy it", I go out (and love it!) whenever I have enough holiday and no other events that I need to be at home for -- including these and boating plans my next free weekend is in October. I've certainly never stayed in the marina because "I didn't want to listen to the generator" -- all I do is try and arrange it so that if possible the genny runs when I'm not cruising or in the pub, why would I do anything else? Your last line is pure fake concern -- be honest, you don't care a fig, you're just having a dig as usual... Sorry to disappoint you -- I had the boat built because I could afford it (better than having the money sitting in the bank doing nothing!) and didn't want to rent boats any more, and don't regret it -- as far as I'm concerned, more money than sense would be spending it on Art... 😉 As far as water shortages are concerned, I'm in exactly the same boat (ho, ho...) as anyone else -- p*ssed off by all the closures and stoppages, but realise that with the hot summer and water shortages and lack of maintenance these are inevitable. So I've had to change my mind about where to go, it's not a big deal, every trip I've done has still been enjoyable -- so you don't need to feel sorry for me, if that makes you feel any better... 😉

The beer (and food) was fine when we were there recently -- but the Shroppie Fly beer was better, and it's much more of a pub if that's what you're looking for (can't comment on the food, we ate at the Comby not the Fly).

If that's the rhyming slang you came up with after I pointed out that your username spelled out BLUNT, then that's down to your fertile imagination -- maybe you're the one being "cotton wool" here... 😉 Anyway, do explain again how you think these two lines are not in conflict, I must be missing something... 1. "Really basic questions from a totally clueless person. An old man that can’t do anything, totally incompetent by the sound of things." 2. "Members are required to conduct themselves in a civil manner including the use of language when engaging with other members" It's currently impossible to plan any trip much in the future given water shortages and stoppages, next time I'm going out I'll do what I did last time and decide based on the situation at the time -- nothing else makes sense.

You're sure it's not a euphemism for something more personal? 😉

Just like humans, there are a couple of things that limit how much power a horse can put out for how long, the first is muscle/fuel/lactic acid (getting tired), the second is overheating -- and like humans but unlike many other animals, horses sweat to keep cool, so they have better endurance. Like humans they can put out high power for very short periods of sprinting (15hp and 3hp), sustained power over long periods (e.g. a day for a horse, endurance cycling for a human) is much smaller (about 1hp (750W) for a horse and 0.3hp (250W) for athletes) -- that's roughly a factor of 10 lower. For half an hour (towing horses with changeover, running 10000m) humans can average about 400W, so on the same basis you could guess that a horse could sustain about 1.5hp -- about 3hp for a pair of horses. That's about 50% more than the all-day power, not to be sniffed at but not massive either -- it would reduce boat journey times by about 15% compared to not changing horses (boat power is speed^3 -- unless you can catch a ride on a soliton, obviously...). Which was enough to pull a fine-lined shallow-draft light flyboat at 8mph average with horse changes, as the historical facts show 🙂

My "snide remarks" are usually about what posters say, not their personal attributes or intentions. But I make an exception sometimes when people are making especially obnoxious or personal posts, like you regularly do. And you especially don't like this being pointed out, see your last couple of posts -- you don't seem able to resist personal attacks, or to distinguish between attacking what people say (fine) and attacking them personally (not fine). No I'm not "playing the victim", but yet again your posts are not within the rules of the forum. Which you also don't like being pointed out, so I expect you'll come back with more of the same... 😞 To repeat -- if you don't agree with what someone says then dispute what they say instead of name-calling, that's how grown-ups discuss things. That applies equally to GybeHo, me, and anyone else you don't like... 😉 AFAIK the water is fine both in Great Haywood and down here in Lunnon, thank you for asking...🙂