IanD
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Posts posted by IanD
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I'd second the pruning saw suggestion, but you might want to get one with smaller teeth than ones with big deep teeth designed for cutting green wood, these tend to get stuck in the kind of crap you might need to cut off. Yes I've got both types, that's how I know ;-)
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When we went through this summer some of the bridges were pretty much impossible for one person to open, unless they're built like Jonah Lomu.
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She used to serve Marston's Pedigree too - but her customer base wasn't big enough to support two different beers. She used to have to throw a lot away. She chose to keep the 6X going because it was the more popular of the two.
She also keeps a mean boxed cider, but it looks too much like cloudy wee-wee for me to drink it!
And when we went there this summer -- for the first time, based on enthusiastic recommendations -- the 6X was not exactly in the best of condition, we (real ale enthusiasts one and all) had a couple and then went back to the boat. Not actually bad enough to reject it, just stale and old-tasting, not at all what I'd expected (yes I know what 6X ought to taste like). It was especially disappointing since we'd planned the route carefully so we could stop there :-(
Maybe it's not always like this, but having an old pub stuck in a time-warp (the pub and atmosphere were lovely!) isn't such a good thing if the quality of the beer also harks back to the 1970s when "real ale" was often badly kept, leading to the dreaded keg revolution. A pub with limited opening hours and relatively small turnover can often have problems keeping the beer good, especially in summer -- though it wasn't that hot when we were there.
Anybody else had the same experience, or was this a one-off? I wouldn't go there again based on our visit, but maybe (hopefully?) we were unlucky...
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To quote J.E. Gordon:
"Strength and stiffness are not the same; steel is stiff and strong, nylon is flexible and strong, a biscuit is stiff and weak, jelly is flexible and weak..."
(but I agree with Blackrose, for a steel narrowboat hull either can be used)
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In a boat with a steel cabin and roof this together with the hull forms a roughly square-section tube, and any tube like this (a torsion box) is strong in both torsion and bending -- far stronger than a non-closed tube (e.g. an open-topped hull), but weaker than a circular tube.
But if you're then going to bash the sides in by ramming things they're much weaker because they're flat (round tube is much more resistant to this), the gunwales give a big increase in stiffness at gunwale level because they're horizontal.
Above and below this you've only got the stiffness of the material (cabin sides and hull) and any strengthening stringers attached to these -- but these only help if they are a lot stiffer than the underlying material, which depends heavily on their section (I or U are much better than traditional L) and thickness at right-angles to the hull.
Engineering lesson over...
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The problem with tidal energy -- like so many other renewable sources -- is that unlike Norway it can't provide more than a fraction of the UK's energy requirements, though at least it's more predictable than most renewable alternatives. Go and read "Sustainable Enrgy -- Without the Hot Air" by David MacKay (free download) and then have a rethink...
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As was pointed out, unless there are regular charging stations -- which wouldn't be so difficult for the canals compared to roads, but would cost a lot of money to install -- you would need huge (and very expensive) battery banks to be able to travel long distances between occasional charging stations. And given the minute number of boats (and the much smaller fuel usage) compared to cars it makes no environmental sense to do this, unlike cars where motives include reduced energy use and far lower pollution in cities.
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Junckers Rustic Oil was recommended to me by a friend who used to be a high-end cabinetmaker; he used it on his solid wood kitchen worktops, I used on our beech dining table for years, hardwearing, heatproof, waterproof, looks good, easy to refinish.
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Lead acid is used on boats because weight and size aren't so important and they are by far the cheapest battery per kWh at the moment -- about £90/kWh for T-105.
The cost per kWh of (conventional) lightweight compact lithium batteries is dropping due to adoption in cars like the Tesla pushing volumes up, and is now being promoted for home power storage applications like the Tesla Powerwall, but they're still more than £200/kWh.
If the lithium-air cells are even smaller and lighter than conventional lithium, it still remains to be seen whether they're cheaper or not -- probably they'll carry a price premium for the smaller size/weight, at least initially.
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When we moored at Bugsworth a few years back I had to move the boat, because where we'd picked was a nice stretch of grass with a pile of dogshit roughly every foot, it was almost impossible to walk across the grass without stepping in one. Many of them looked the same, as if the same owner had been taking the same dog there daily for a very long time...
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T'would be nice if we could get 1000w/m2 from our solar panels.
Job sorted - who'd need fossil fuels ?
Indeed it would be, if it was possible even in theory.
From the fantastic (free) "Sustainable Energy -- Without the Hot Air" by David MacKay
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The power of raw sunshine at midday on a cloudless day is 1000W per
square metre. That’s 1000W per m2 of area oriented towards the sun, not
per m2 of land area. To get the power per m2 of land area in Britain, we
must make several corrections. We need to compensate for the tilt between
the sun and the land, which reduces the intensity of midday sun to about
60% of its value at the equator (figure 6.1). We also lose out because it is
not midday all the time. On a cloud-free day in March or September, the
ratio of the average intensity to the midday intensity is about 32%. Finally,
we lose power because of cloud cover. In a typical UK location the sun
shines during just 34% of daylight hours.
The combined effect of these three factors and the additional complication
of the wobble of the seasons is that the average raw power of sunshine
per square metre of south-facing roof in Britain is roughly 110W/m2,
and the average raw power of sunshine per square metre of flat ground is
roughly 100W/m2.
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The best commercial solar panels are about 20% efficient, the more cost-effective ones used by most boaters are around 15%.
http://www.theecoexperts.co.uk/which-solar-panels-are-most-efficient
This means about 90W/m2 in the midday summer sun, or 15W/m2 average during daylight hours over the year. Interestingly, tilting them instead of lying them flat only gains about 10%, so it's not really worth the hassle on a boat.
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After Christmas up at Cosgrove with Kate & Snowy in 1985 (when I fell through the ice on Christmas day and did my Excalibur demonstration), we broke ice in Baron all the way back to and through London. By the time we got back the bilges were having to be pumped out every couple of hours because the ice had taken off some rivet heads on the bow (real ones, riverted iron hull). A few weeks later the boat sank overnight in eight feet of water with all their possesions on board because the boatyard fixing the hull forgot to keep the pumps going...
www.steamershistorical.co.uk/Web_FMC_Steamers/BARON.doc
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I had one of those quiet moments on the canal ruined once when someone went by with a supercharged 2000hp engine COMPLETELY unsilenced
Ditto, except it was an F-111 taking off with full afterburner passing just above the roof at 7am -- followed by another one. I thought the end of the world had arrived...
Not going to happen to anyone again though, now that Upper Heyford has closed ;-)
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It is about time the importers took on some responsibility to ensure the quality of the products rather than just making the quickest profit. I have been fortunate to have the resources to ensure quality products from China but there is a cost and its about time other importers did the same
So you spend more money to supply good quality products, which you charge more for -- good for you. Other people don't bother and sell stuff cheaper -- good for them, it's just a different business model, low quality/price as opposed to high qaulity/price.
Joe Public has to choose between cheaper and more expensive products, and very often goes for the cheap option -- and then whinges afterwards when it fails. Boo hoo, what did you expect for that price?
But paying more doesn't guarantee better quality (even if it does in your case) because other vendors push out low-quality crap *and* charge more for it by ripping off the buyer -- they're not out to provide high-quality products and good service to satisfied customers, just make a fast buck.
Doing "the right thing" nowadays only pays off in market areas where a good reputation and satisfied customers (who recommend you) actually pays off. But given the current reliance of most people on unverified reviews and feedback on websites -- a lot of it just plain made up -- it's getting harder to make such a business work, pile 'em high and sell 'em cheap is winning out.
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Factories *everywhere* have always done what they can to keep to production cost down while still passing inspection standards. If you pay a low price (and don't pay for decent QA/QC) you get crap, if you pay more and do things properly you get good quality stuff. It used to be the same when there was a lot of manufacturing in the UK, the cheap stuff churned out here was cheap crap then.
Now all the low-cost manufacturing has gone to places like China so anything left in the UK tends to be decent quality because it's expensive to make, so the cheap crap is made in China -- but it also makes high-quality stuff, often still cheaper than its Western competitors.
So leave out the thinly disguised racism and scaremongering, the simple truth now is the same as it always has been -- you get what you pay for.
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In terms of marine engines that particular unit is quite twee some of the units in the larger ships are 4/5 storeys high (house wise) some u tube videos will give you some idea size wise.
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Tesla have already demonstrated a swappable battery -- admittedly it needs fork-lift type equipment, but there's no reason these couldn't be standardised as well as the batteries. If everyone drove them the grid load would go up, but then there'd be a huge bank of batteries (charged cars) attached to it to charge up the flat batteries. Still the cleanest way of moving vehicles around even if the power comes from fossil fuels, far more so if it comes from renewables. Yes I know the problems of relying on renewables without nuclear to provide baseline load capacity...
The huge Wartsila diesels might seem to have relatively low power (47bhp/ton) but don't forget this is at about 100rpm, the bmep is ridiculously high as well as the thermodynamic efficiency. They can even be pretty clean, but a lot of the techniques they use only work in low-speed diesels, not high-revving ones like in cars.
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It seems to me that the technology of electrical storage is still basically 19th century. Until major advances are made (even Lithium is only scratching the surface) electric storage cars are still going to have big drawbacks.
I believe one avenue of research is to forget chemical storage completely and look harder at the way capacitors work which could be incredibly efficient but also possibly very dangerous (think of a big battery bank that could discharge all its power almost instantly)
They're called supercapacitors and are well known in electronics. On the plus side they can be charged and discharged faster than batteries, which is why some Formula 1 KERS systems use them. On the minus side, their energy density is much lower than batteries, even with some of the latest improvements on the horizon. Chemical energy storage -- effectively at the molecular level -- is just inherently much denser than charge storage.
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According to one source, propellor power is typically proportional to RPM^2.7 -- don't know how accurate this is for low-speed boats...
http://continuouswave.com/whaler/reference/propellerPowerCurve.html
rpm(%) power(%)
100 100
90 75
80 55
70 38
60 25
50 15
40 8
30 4
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Modern aircraft propeller technology has come on a long way too, what with carbon fibre and super accurate balancing. Quite a few turboprop aircraft are now capable of cruising at speeds approaching 400mph and over with a tail wind. For example, certain Beech Super King air, twin turboprop planes and many others such as the Bombardier Dash 8 aircraft another twin turboprop small passenger airliner and indeed probably the type that Nicknorman flies backwards and forwards from Aberdeen on with Flybee.
Whilst on holiday in St Newlyn East near Newquay in Cornwall years ago I was talking to an old chap who was a young lad during WW2 and lived close to what was then RAF St Mawgan ''still in use'', and he told me how he saw an American air force 4 engined Liberator taking off, which left the ground, stalled and sadly promptly crashed straight into a cliff. The investigators discovered that the propellers variable pitch control was set in the course pitch position which is the position for cruising at its cruising altitude when the props should have been set to the fine pitch setting for take off which allows the engines to rev out to their maximum power torque. In course pitch on takeoff the engines would have been struggling big time for revs and power hence the stall and crash. The pilot may have changed to the course pitch far too early, that nobody ever found out, I don't think.
A similar issue is what caused all the problems with the Napier Sabre H24 sleeve-valve aero engine in WW2 -- it had a lot of power and manual pitch control, and the pilots found that by keeping the pitch in coarse the aircraft cruised more quietly and smoothly at lower revs -- but the engines weren't designed to be flogged flat out at low revs all day and regularly seized up, which is not a good thing in a fighter plane. Once the pitch control was made automatic the problems went away.
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You seem somewhat categorical in your statements, whereas in reality what you say is only true if the owner wishes to extract the maximum power from the engine. Many canal boats are over-propped and thus require less rpm to cruise on canals. That they have a slightly reduced top speed on open water may be of no concern to the owners.
They may be secondary effects, but only within a smallish range of parameters. They can become dominant effects further from "normality". Your statement was categorical without any bounds, hence my disagreement with it.
I'm an engineer, and always concentrate on the most important things first because they dominate the design. Assuming you're not silly enough to design/run a prop so far away from the norm that it cavitates badly or has a pitch double the diameter, all the curves for things like prop efficiency are pretty smooth -- they may have an optimum, but the performance difference isn't significant unless you go a long way away from this.
Maybe next time I'll prefix any statement with "except for really stupid designs"... ;-)
In many waterways a boat with a 24" prop would be called a plough! A modern(!) canal is a shallow waterway with no room for deep draught boats with big props. As the mud comes up something has to go and it's now usually boat draught and prop size.
Agreed, this is one reason modern boats don't start and stop as well as old ones with much bigger slower-turning props -- it's always better to have the biggest prop you can fit in for slow boats, pushing a lot of water slowly is better than pushing less water faster. . But since a lot of the engines started off life in tractors, maybe ploughing the canal is just returning to their roots...
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OK I'll rephrase that -- if you want to make the best use of the engine power (which you've paid for, after all...) for situations like venturing out onto rivers, the boat should be [...].
As you say this doesn't matter in many cases so overpropping means lower rpm when cruising. Though to be honest, the real reason this is an advantage is the frankly rubbish noise and vibration reduction on many boats, the engine would often be happier (more efficient, better battery charging) running a couple of hundred rpm faster -- say around 1400-1500rpm instead of the 1200-1300rpm that many boats are propped for.
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I guess one of the reasons is that while most modern engines will rev well past 2000rpm, hence meaning a 2:1 ratio box would give over 1000rpm prop speed, in practice they are often powerful enough and prop'ed such they they cruse all day at 1700rpm. At least the hireboat I was on last weekend this was the case.
Second question is likely to be cost, a 2:1 box and an 18x18 prop is a lot cheaper than a 3:1 and a 25x28 prop!
Daniel
Boats should be propped so that the engine reaches maximum revs in open water, in this case about 8 knots at 43bhp/2800rpm for a Beta 43. Required power drops very rapidly as speed drops, to keep a narrowboat moving at normal speeds typically takes less than 10bhp which would typically mean less than 1400rpm engine revs.
I don't think there's any difference in gearbox cost but there sure is in prop cost -- but unless you can fit a bigger diameter prop in (which most modern boats can't) the issue goes away anyway...
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No I disagree. That is how a screw works when screwed into a solid thing like a lump of wood, but a propellor is moving in a fluid, which can result in all sorts of strange effects like cavitation, stalling, recirculation, vortexing etc.
These are all second-order effects, go and look at documents or online calculators for prop size. But I did make a calculation error, at 2/3 the speed you need more than 50% extra pitch because thrust goes as square of RPM, not linearly. Using the calculator here http://www.vicprop.com/displacement_size.php and putting in a 55' x 7' boat drawing 2 feet with a Beta 43, I get the following:
2:1 gearbox 1400rpm at prop 7.94 knots max using 3 blade 17.3" x 10.6" (pitch ratio 0.61)
2.8:1 gearbox 1000rpm at prop 7.94 knots max using 3 blade 21.2" x 14.8" (pitch ratio 0.70)
Since thrust at a given rpm is proportional to blade area (square of diameter) x pitch and (21.2/17.3)^2 is 1.5, you'd get similar results with a 2.8:1 gearbox and a 17.3" X 22.2" prop -- but this is a very big pitch ratio (1.3) so would have lower efficiency than the recommended one, so would need even bigger pitch to compensate, which would have lower efficiency, which...
In other words I've answered my own question about why a 2:1 gearbox is used -- unless you can fit a much bigger diameter prop in (which most modern boats can't, 18" is typically the limit) it's the best choice :-)
Bolt Cutters ?
in Boat Equipment
Posted
I think you know exactly what I meant -- some pruning saws have small regular teeth (usually cut on pull only), some have the big "W" shaped deep teeth (often cut both ways) -- these cut bigger diameter soft green wood faster but also jam much more easily when cutting other stuff.