MoominPapa

In my experience, experts are not the answer. If you ask one, you have no way of knowing if they are giving you good advice (or even if they understood the question) If you ask more than one and get contradictory advice you're worse off than when you started. The only safe way is to understand the problem enough to decide which expert to believe. Once you've done that you don't really need the expert in the first place! An expert who'll just answer a question is useless, someone with expertise who'll pass on his or her knowledge is invaluable. On that score, Gibbo wins. He must spend hours on the well-written explanations he posts here and we are all in his debt. MP.

A water bottle might be better keep the boots for feet. MP.

This known in Moomin circles as "lurking". There's nothing more irritating than seeing the gates start to open and setting off to get into the lock with perfect timing, then finding that the relevant shore crew is too busy yakking and doesn't get the other gate open in time. MP.

They're also possibilties. There may be enough current to weld the control cables, or worse, the thrust bearing in the gearbox. It's the same principle here, but with 240v around much more potentially dangerous. The biggest danger, pre-RCD, was that the total resistance of the circuit via the earthed hull was too high for the fuse to blow. That could lead to kilowatts being disipated in unlikely and dangerous places and shock hazards that didn't get disconnected. In the era of the compulsory RCD, the dangers of a high-impedance earth are less. MP.

The reason for using two studs is to eliminate the failure mode where the stud becomes detached from the Hull, but the DC and AC cables are still connected together because they're still attached to the stud. If that happens and then there's an AC earth fault (ie a live cable touches the hull) then the fault current will get as far as the DC negative system and then find its way to the hull via any stray negative-to-hull connections. This leads to "interesting" effects like the braid of the co-axial cable of the radio aerial glowing red hot. The reason for having only one connection to the hull is to make sure that the electrical system cannot create a current flowing through the hull. The hull has low resistance, but not zero resistance, and the water has high resistance but not infinite resistance. This means that a very small proportion of any current flowing in the hull will infact leave the hull, flow through the water and then re-enter the hull. That causes electrolysis which causes corrosion. The best compromise for these two competing requirements is two studs, mechanically distinct, but very close to each other on the steelwork. MP.

I realise that it may not be possible because of the hospital situation, but there are some great free public moorings at Ferry Meadows. They're on small lake accessed via a cut from the river. clicky There are also some moorings off-river downstream on the other side by the rowing lake, which I've been told are good, but never used. Hope your poorly crew-member gets better soon. MP.

Advice seconded. Compared to the canals or the Ouse, the Middle Level is virtually deserted. You should be able to find spots in the middle of nowhere to party without disturbing anyone. MP.

Ah, sorry, I thought from your previous post that you'd been 'scoping around...... MP.

Fascinating, that makes perfect sense. What value is the peak current whilst the plunger is moving? That's what we need to size the fuse. MP.

Great minds, and all that! That's exactly what I've got. I plan to use one switch (with safety cover) as the "ignition" switch and the other (with cover removed) to control the Adverc controller on the alternator. It's useful to be able to switch that out when the engine is cold or under heavy load. MP.

That makes sense, thanks Sir Nibble, yer honour. Since the pull-in winding has inductance, that will slow the rise of the current through it for a while. I wonder if the time-constant works out for the solenoid contacts to close and shut-down the pull-in winding before its current has risen to the steady-state value? I have a feeling that the inductance will be too low and the pull-in time too long, but maybe not. Time to add one of those "turn your PC into an oscilloscope" boxes to my christmas list........ MP.

Well Creek is shallower for further and narrower too, but is fairly weed free. For weed, you need to go West from Bill Fen towards Holme Fen, but take plenty of strong crew for bow-hauling. A boat from the marina got stuck for three hours a week or two ago. I miss the Slough Arm (a bit). MP.

Those would all work well. I already have the switches and panel, so I have to fit the wiring to the panel. All good fun. MP.

The engine controls I'm planning are a simple toggle switch and a push-button for the starter. The aim it to make sure that if someone comes along and presses the starter button when the engine is running, it doesnt engage the starter again. Doing that makes nasty grinding noises and may damage the starter or ring-gear. This is less relevant for engines which have keyswitches because that tend to have mechanical locks to achieve the same thing and even if they don't, people are more familiar with ignition switches and less likely to do the wrong thing. The rest is voodoo, best ignored. MP.

Brilliant, thanks Gibbo. MP.

In the spirit of recycling, when I asked on here about sealant for diesel, I was recommended this stuff: clicky Note that this recycled advice is brand new and unused, I've not found the necessary round tuits to actually buy and try this stuff yet. It looks good though. I guess to apply it you would have to drain the tank. MP.

I had a similar experience on Well Creek. (Except the other boat's crew were very nice about it.) We were going ludicrously slowly and there was nothing I could do about it. I let our tail pass us at Outwell town moorings, only to catch them again at Marmont Priory Lock. Mrs Norton, the lock-keeper, knew we were coming and that both boats would fit in the lock together so there was no way she was going to waste two lockfulls! Half a mile below Marmont Priory lock, the Old River Nene opens out and it would be possible to run a convoy of five narrowboats abreast and still not bother boats coming the other way. MP.

Hmm, computers are great at doing signal analysis, but I'm not sure I'd like to put the contents of a petrol engine ignition system anywhere near my computer, except through a very carefully designed interface, preferably including opto-isolators. Them chips are not known for liking kilo-volts up 'em. MP.

Agreed, and unless you have some active system in the shower to keep the flow rate contsant, it makes yo-yo ing temps in the shower inevitable too. I thought that accumulator-less pumps worked with a calibrated feed-back from output to input. The pressure at the outlet rises until the flow through the tap + the flow through the feedback equals the pump flow rate at the balanced pressure, and then stays there. At least in theory, that should be better for the morco-driven shower. Argh, there's no escape from differential equations, even in boats! MP.

We have a non-thermotstic mixer tap, (just hot and cold taps feeding the shower head), Morco and accumulator. It's not ideal. The fundamental problem is that the energy output from the Morco is fixed, apart from the two big and small flame settings. Therefore to control the shower temperature, in the end _all_ you can do it control the water flow: more water for colder, less water for hotter. With an accumulator, the pressure changes all the time, it increases when the pump is running, then the pump shuts off and it decreases. There's a corresponding change in water flow, and the shower gets hotter, colder, hotter, colder. If you can arrange a water pump without an accumulator which provides a steady pressure, that may well be much better. I'm planning to try a thermostatic shower mixer. MP.

The VDO tach I'm planning to use has a combination of switches to set a division ratio, and a trimmer for fine adjustment, according to the manual I downloaded. Of course to do the twiddling requires _another_ way to measure the engine speed. Those shine-a-laser-on-the-flywheel tachos would be ideal, but I don't have one. A cunning plan I'm thinking of trying, (not done yet, so no idea if it will work) is to record the engine sound on the laptop. On my thumper, the ignition events should be blindingly obvious on a waveform display using something like Audacity, and I can just measure the time between them off the X-axis and do the maths. It's either so cunning, you could put a tail on it and call it a weasel, or a mad scheme that will never work. MP.

Cosmetically difficult - I have the panel already with matching SPST switches I think that's the winner. As I said, the NO contact of the alternator-controlled relay makes a great place to connect the hours counter, I'll feed the common contact via the iginition switch and the start button from the NC contact. All this is low-current stuff. Start button feeds the coil of a second relay which switches the higher-current solenoid circuit. The engine room layout means that by having a second relay I'll be able to make the higher current circuit shorter and keep it away from the engine panel too - added bonus. Understood. The alternator is a bog-standard A127. No idea about wattage of light - I'd guess quite small. Not at the moment, just a big brass bourdon gauge in the engine room. I'm seriously considering an idiot-light visible from the steering position. Thanks again for your help. MP.

OK, you asked. I'm trying to arrange things so that all the circuits have a suitably sized fuse close to the battery terminal. I don't yet know what size fuse I need to protect the starter solenoid, but I do know that it's much larger than that needed for the engine charging and instruments. I'm therefore planning two fuses close to the engine battery, the low-rated one will feed the ignition switch (just a single pole toggle switch - not a keyswitch) and that switch will then feed the instruments and the charge light and the oil light and the Adverc. The original plan was to have a relay which was energised when the charge light is lit, the larger fuse feeds the starter solenoid via the NO contacts and the "start" push-button. That disables the start button when the engine is running _and_ when the ignition switch is off - perfect. The new plan uses a relay from the D+ alternator terminal to ground, and NC contacts. That disables the start button once the engine is running, but it doesn't do so whilst the ignition switch is off. I will need a second relay to do that. Actually this is not all bad, since it lets me generate a signal for the hours counter which enables it only when the engine is running, rather than when the ignition switch is on. It's interesting: making this stuff work is easy. Making it so it doesn't catch fire if an arbitrary wire shorts to the hull, without making every wire finger-thick, is difficult. Boating, I believe, like all sensible boaters at this time of year. MP.

Getting a good signal inside a metal tube is difficult, so a radio with an external aerial is good. 12v rather than 240v is likely to use less battery juice, after inverter losses are taken into account. Most boat have limited space and get bumped from time to time, so a compact box which can be built in, rather than a free standing one which ends up on the floor when you misjudge a lock entrance, helps. All in all it seems to me that car radios win. MP.