Col_T

I don't know about "well chuffing dull" - any thread that gives "zygote" an airing must have some value, even if only for using such a great Scrabble word?

Very many thanks for a fine body of answers, and I think I even understand most them! However . . . . Am I right that the alternator never completely stops outputting, even when the battery has decided it's had enough, it just drops the output to a float charge voltage. Sometimes that just ain't enough and a soul wants to know why they do. I didn't think you were a doctor?!!!

I have an imperfect understanding of 12v electrical generation, so some questions to try and improve that a little. Alternator output - this is typically rated in Amps e.g. our boat has two alternators, a 70A for the domestics and lower rated one for the engine start battery. I know that the battery bank limits the amount of charge, in Amps, that it will accept during charging but what determines the maximum output of the alternator - is this defined by the design, or 'imposed' by internal circuitry? Just a high-level answer will be fine; I wouldn't understand anything detailed! Regulator - I think this is that part of the alternator that controls the actual voltage output, preventing the alternator from exceeding a 'designed in' maximum voltage, but does it also sense when the battery has decided enough is enough, and if so, how? Alternator output (2) - our boat spends most of it's time connected to a land-line with the battery charger keeping the batteries topped-up, so what does the alternator 'do' when we go cruising and pretty much the first thing the alternator sees are fully charged domestics? Yes, I know it stops generating electricity but, if I understand it correctly, the actual generation is the product of a mechanical operation - copper windings spinning is a magnetic field produce the electricity, so where does the electricity 'go' if the batteries are fully charged? Or are is the magnetic field electrically generated? All answers gratefully received, especially those that don't get too technical !!

A few possibilities:- hotter summers increasing evaporation; warmer, wetter winters reducing snow-fall, and therefore snow-melt; water management - extraction for agriculture, industry, human consumption, etc; someone left a paddle up! BTW - I have no expertise in this area, but the above seem likely candidates, except for the last one, of course.

Thanks for the responses chaps, and for answering all my questions, including the one I hadn't asked e.g. where would the probe be sited - between, or against, the batteries!

We have recently had 300w of solar panels installed, with a Tracer 3215BN solar charge controller and MT50 remote meter. I can get a battery temperature monitoring probe as an optional extra for the 3215BN which raises a couple of questions:- Is it worth getting the temperature probe? Whereabouts on the battery pack would it be located if I did get one? Without the probe the 3215 assumes the batteries are at 25C and bases it's charging on that. If I understand correctly, the 3215 will try to increase the amps delivered to charge the batteries, if there is enough sun-light to support this, so possibly not hugely relevant during a typical British winter?

Which leads me to a question about the best way to leave a boat over winter. With electric heaters and a de-humidifier, presumably you leave windows closed - but what about the rest of the ventilation. Is that all blocked up, to prevent the warmth from the heaters escaping - would that increase condensation? If the normal ventilation is not blocked up, then surely the warmth from the heaters will get ventilated out of the boat? All education gratefully received.

And as MtB has mentioned the K & A, are there any stretches of Armco?

I have heard it said, on this very forum, that surface charge is just part of the charge in the battery - it may be used more quickly than charge that has to come from deep within the cells, but it's charge none the less. So, two things:- is this actually correct - can't think why it shouldn't be, but I have a lot to learn; if this is correct, all that will happen is that Smartgauge SoC will fall rapidly while the surface charge is 'burned off'?

Okay, thanks for that, Alan.

Thanks to all who contributed to this, many useful opinions and a good link. Yes, it is a fairly cheap, standard cool-box, rather than any kind of fridge, and the thought was to use this on a one week camping holiday, rather than as a permanent refrigeration solution on the boat - we already have a 12v fridge on that, though no solar panels -yet. Thanks to all who reminded me about the efficiency aspect e.g. to assume that 50% efficiency is all one can reasonably expect from solar panels at our latitude and with our, usual, weather! I happily accept that I over-looked that point. However, and accepting that the original numbers need amending to accommodate the 50% efficiency point, were the original calculations about right, and if not, why not? Why am I asking again? Well, it's a way of checking my understanding and / or bettering my education!

I have a 12v cool box rated at 50 watts in operation. I reckon this will draw about 4.2 amps, and about 100Ah from a 12v battery bank over a 24 hour period. There is a thought that we might be able to run this from a solar array, so I have attempted to size the array we would need. The array would need to generate 100 amps (to replace the amps used over the previous 24 hour period), plus a further 15 amps to cover assumed charging inefficiencies, so a total of 115 amps. Assuming 8 hours of useful sun-light a day at this time of year, that's 115 / 8 = about 14.5 amps. Volts x amps = watts, so I'd need a 12 x 14.5 = 174 watt panel and a 20 amp charge controller. So that's how I think the calculation works - is that anywhere close to being correct, or have I missed something? All tips / pointers / guidance welcomed. For clarity, this above calculations suggest the minimum size of the battery bank will be 200Ah, which is probably enough to torpedo this little dream!

Thanks for the comments, Paul and Alan. Alan, Your solution looks particularly appealing, being discrete and, hopefully, comparatively easy to do. Thanks, also, for posting the photo as it means I don't have to try and interpret what you were saying. Pictures and lots of words spring to mind!!

Yup, it's a Jonathan Wilson, so thanks for that!!

We have a 57' boat which has a 150 gallon water tank at the bow, just behind the gas locker, and a 50 gallon diesel tank at the stern. The handrails are square section, integral to the hull (so it's not possible to wrap fingers right round), with scuppers / drain points cut into the handrail about 12' from the stern-end of the cabin. The way the boat is trimmed at present, the scupper is about 3' too far forward and rust is starting to 'bubble' the paintwork were water pools as it is not draining away via the scuppers. I could get new scuppers cut into the handrails at the appropriate place, leaving a decision about whether or not to fill-in the originals, or I could just re-trim the boat so that water drains via the scuppers instead of pooling. A couple of questions: 1: Should the boat be trimmed with both water and diesel tanks empty, or does it not really matter? 2: Presumably the boat should be trimmed so that the underside of the counter is slightly under water at all times? Thanks in advance.

Er, but it does say 47RJ. To be precise, it says "47RJ CY 1W" - which may mean it is rated at 1 watt, not the 5 watts suggested by Boater Sam?

Or, better still, ban pump outs and make composting toilets mandatory!!

Ah, okay. Penny slow to drop, but it has now! Thanks for the explanation.

Quite right, Alan, but in both the cases you cite, the metal that is heated will expand in three dimensions. My question is, if a steel tank is heated, and therefore all sides expand in three dimensions, would the capacity of the tank actually decrease slightly?

Sorry to backtrack, but there are a couple of things I don't understand here, mainly around the 'expansion' topic. Firstly, get a block of steel, heat it enough to measure how much it has expanded and you will find that all three dimensions have increased e.g. it is wider, and deeper and higher. If that is case, wouldn't heating a tank cause it's volume to decrease a little? Secondly, in the scenario where a mooring dolly includes a fuel breather, and a tube extends down from the dolly into the tank. If I've understood it correctly, the suggestion is that expansion of air within the tank will cause a noticeable amount of diesel to be ejected through the fuel breather. Doesn't this require an amount of fuel to be trapped above the air so it can be expelled? If so, how does that fuel get trapped above the pocket of air in the first place?

Your first post says " I have 4 X 6v batteries and I check them to see if fully charged and it seems so.... They are reading at close to 6v when I checked them." The state of charge table, below, suggests that your batteries are not fully charged which may well explain why the Combi is permanently showing charger on fast mode. There is the chance that, if the batteries have not been fully charged for a long period, their capacity has been permanently, severely reduced, through a process known as sulphation. The only heavy load you talk about is the domestic, not 12v, fridge. When you are on shore-power, this will be powered from the shore-power, via the Combi, as long as the Combi has pass-through functionality built in. When not on shore-power, you will need the inverter function of the Combi switched on, to convert the 12v from the batteries to the 240v the fridge requires. The inverter is another load, and is not 100% efficient so will get hotter the longer that it has to work. Given that the fan is now on almost permanently, it's reasonable to say that the Combi thinks it's working pretty hard pretty much permanently - this may not be good for the life expectancy of the Combi. There is a chance that your little trip to Bath and back has taken a set on batteries that were dubious to start with and finished them off. I'm no expert in this electrical stuff, so hopefully the thoughts above will prompt someone who knows what they are talking about to intervene and educate us both! Hope this helps. There you are - Wotever and Old Goat beat me to it, and both know far more than I. Rejoice.

First time we came back leaving Bristol moorings at 8:30 and moored on the BOA side of Bathampton Bridge (183) at about 19:00. That included lunch on the hoof, but about 30 minutes for tea by the bus station in Bath. I thought that we were pushing on a bit, going against the stream at about 1600 revs, BETA 1505, but then I'm a bit of a wuz (that spelling looks well dodgy!) when it comes to flogging the engine!! Unless something has changed pretty radically, you'll encounter moored boats pretty much solid from BOA to Avoncliff Aqueduct, clumps of CCers between Avoncliff and Dundas Aqueducts, with the section between Dundas and Claverton seeming to be nothing but moored boats. After that, well, it's just Bathampton and Bathwick to look forward to! I think your best bet might be to get onto the river at Bath, and see the time is like, at least you'll have done the deep lock, the gates of which are flippin' heavy, and folk like watching but not helping! Have fun!

We've only done that section twice, but from our experience there is a short pontoon (3 boats?) just under the Bitton Railway Bridge (no. 211) on your right as you head towards Bristol. There is another short pontoon on your left, which also has water and Elsan (I think) but I neglected to make a note of exactly where in our copy of Nicholsons, so that's not much use, I'm afraid. There is also moorings at Hanham Lock, but these were occupied by what looked like long-termed a when we went past last year. On the two occasions we've gone down to Bristol, we've done the deep lock late in the afternoon, and moored by Bath bus station (pretty much opposite what look like old warehouses, which'll be on your left after four bridges) overnight so that we have all day to get to Brizzle. We motor on down to Hanham, phone the keeper at Netham Lock, which is where you pay and get a key, for the water points if I remember correctly. The Netham keepers will point out the mooring spots, opposite the Great Britain being our preferred spot, and you'll be on your way. We prefer Bristol to Bath - we think it has a better feel to it, and there's only so much sandstone this old fogey can stand!! Hope this helps, and that you enjoy your trip.

Not quite sure if I'm being sarcastic, pedantic, or humourless, but you'll be wanting a question mark at the end of your second sentence.