Bavaria wiring

[hairbox]

Hi is there anyone out there who can explain the wiring on bavaria's for example all the books I read and advice I have been given on boat wiring says that you must have an isolator switch between the + side of the battery to starter and consumers this is also the case in the volvo engine manual. However looking at the wiring diagram in the owners handbook it shows an isolator switch on the - side of the battery. How come?

any advice much apprieciated


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[Twister_Ken]

Ja, zatz ze vay ze robotz sint programmiert to vire zem op.

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[MainlySteam]

As long as the DC negative is not grounded, so that a positive to ground short cannot occur upstream of the switch, then I don't think that the electricity much cares which side is switched.

Best practice would have the switch be double pole and break both the positive and negative conductors, but that is either down the learning path for Ken's robots or else Bav are saving their pennies.

John

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[pvb]

Probably down to economics...

You can isolate the battery by disconnecting either the positive or the negative, although conventionally it's done in the positive lead. In some installations, it might be possible to use less battery cable if the isolator is in the negative lead, and this may well be the reason in Bavaria's case. A few metres of cable here or there might not sound much, but multiply it by thousands of boats and that's a lot of copper!

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[boatmike]

Can't be sure without seeing your wiring diagram but I have seen similar even on quite large installations and it is really bad practice.
I have heard it said that if there is a blocking diode on the supply (positive) side that acts as an isolator to an extent, then to fully isolate the battery one only needs a switch on the ground (negative). I don't agree with this philosophy and believe that it is poor practice and does not protect your boats wiring from a short to earth as well as isolating the positive terminal does. Nothing will.
Are you sure the switch you are talking about is an isolator switch not a changeover switch though? Does it only have two positions, on an off? Is it connected to only one battery terminal? How many batteries do you have?
(Sorry this is not as simple as it sounds!) Often changeover switches are fitted without battery isolator switches on the grounds that in the off position they isolate the batteries. This is also dubious practice.
Regardless of how your boat is wired I would have a seperate isolator on the positive terminal of every battery you have as a minimum. If you don't have this my advice would be fit them ASAP. It can have no negative effect whatsoever regardless of how your boat is wired and may just save your life one day!
Sometimes the terminal itself can incorporate a switch and these can be bought at chandlers and retrofitted easily which I would certainly consider in your case. As I say it can't hurt. Only one word of warning however. Beware of cheap switches. Especially the rotary ones. I have seen Taiwanese nasties that are a bigger risk than not having one at all. Make sure they are proper Marine quality and especially on the traction (engine starting) battery or any battery that can be switched over to engine starting make sure it is rated to the full current draw of the starter motor.




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[andyball]

I wired my boat like this since the isolator was far enough away from the battery to make a short from the + cable to ali.hull a faint possibility.

By taking -'ve wire to switch, once isolated, both wires wd have to short out at once for there to be a problem.




Don't know why it'd be bad practice, except that it's unusual & might confuse the unwary.

Remove the negative batt. terminal or switch off an isolator in the -'ve cable......what can go wrong?, how would a short in the +'ve side cause current to flow in this situation?



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[hairbox]

Hi Boatmike, I am not sure what the difference is between an isolator and change over switch, but the switch I have has either on or off poles controlling 3 batteries 55ah starting batt and 2x140ah domestic all connected in series also I have an isolating diode in the circuit. I have looked at the wiring diagram of a brand new Bav and this is wired identically, surelly Bav are not endangering life by using bad pracitice if so this is quite a worrying

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[MainlySteam]

As others are saying, I would be pretty confident that you do not have a problem. If it were my own boat I would not be inclined to rush out and buy a pile of switches and reengineer what Bav have done.

If you have any remaining concerns and you need your mind put at rest on the matter, you could get a competent marine electrician to look at the wiring diagram but I suspect he will only confirm what Bav's own designers have come up with.

John

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[boatmike]

Hi Hairbox!
I think we are illustrating the impossibility of analysing a wiring diagram without having it in front of us. If you would like to send it to me for further comment I will send you a PM with my address)
I have worked for a number of boatbuilders and shipbuilders on small craft and have also experience of Naval vessels from Frigates to Patrol Craft. The only thing this experience has really taught me (and this site is illustrating it) is that there are as many opinions and ways of doing things as there are people to express such opinions.
You cannot change the laws of Physics though. Neither can you stop boatbuilders from cutting corners to achieve lower costs. As far as endangering life by adopting poor practices is concerned this is probably getting over emotional.
Bavaria yachts achieve a fantastic value for money package and have achieved extraordinary success in reducing the cost of their product. Much of this has been done by adopting volume production techniques like SCRIMP moulding for the hull which not only reduces cost but produces a very good moulding. They have also looked very carefully at value analysis in other areas and could well carry this over to the electrical system. Having said this I would add that I have a great deal of respect for their product but don't expect them to fit anything that costs money and does not help them to sell their boats. If isolator switches are not demanded by the buyer (and they should be) they won't fit them. Simple as that. There is unfortunately at this time no international code of practice they have to comply with unless you ask for them to achieve Lloyds or DNV registry (not just a hull moulding certificate where I think they have Germanischer Lloyd already?) which will cost you a lot of money even if they are prepared to do it.
As far as Isolator switches are concerned the difference between isolating the Positive and Negative is clear.
In the case of a battery short circuit caused for instance by flooding (note that on a LLoyds or DNV registered vessel the battery needs to be in a watertight box vented above the waterline and on many small boats it is not) if the battery positive is isolated (note that this requires a WATERPROOF switch or a switch mounted well above the waterline) the complete wiring of the boat is protected and cannot short out. The battery of course will fry but the rest of your wiring won't as it is disconnected. If only the negative pole is isolated THE COMPLETE WIRING OF THE WHOLE BOAT IS STILL LIVE and can short out anywhere the water gets to and in the case of a battery that is not in a waterproof box it will run straight back to earth at the negative terminal even if an isolator is fitted. Think of it in reverse. It is not the BATTERY you are isolating. It is the vessels WIRING. If this is positively disconnected from the battery at the positive terminal it is out of the circuit completely. It is not if you just remove the earth.
Therefore in the case of damage and water ingress, anywhere in the boat if the battery positive is isolated there is LESS chance of writing off all of your boats wiring than if only the negative is isolated. Note I did not say NO chance. LESS chance. Anything that increases safety and reduces risk is worthwhile in my philosophy.
Fitting isolator switches on the positive terminal is not NECESSARY but DESIRABLE
There are lots of things on the boat that are in this catagory that are equally not supplied by the boatbuilder. EPERBS, VHF, Liferafts, Lifejackets, even basic navigation equipment. These are not supplied by the boatbuilder either but I would not go to sea without them. Neither would I avoid fitting an isolator switch on my positive battery terminal. As I said before it can do no harm and increases safety. The only argument I can see for not doing it is that it is too much bother or too expensive. Switches are in the last analysis cheap items. Personally I would also (and have on my own boat) adopt LLoyds recommendation and ensure that the batteries are in watertight boxes (also cheaply available) and vented over the side from the top of the box above the waterline. (Hydrogen gas is lighter than air). You can then sleep at night safe in the knowledge that any water leak into the boat cannot short your battery. Your wiring from the battery is disconnected fully when not in use. There will also be no dangerous build up of explosive gas.
If you want to read up on this subject I would recommend Dag Pikes book "Boat Electrical Systems" (Adlard Coles) It is very simple and straightforward book. There are also some other publications by HMSO that are thought provoking such as the IMO code for High Speed Passenger Ferries that outline the statutary requirements for these vessels. Para 19.6.4 of this code states " Any traction or service battery........ must be fitted in a suitable watertight compartment vented to atmosphere at least 1.5 metres above the passenger deck and be fitted with suitable means of isolation. Para 19.8.14 states "In cases of permanently grounded (non isolated) battery banks the positive feed terminal of each seperate bank must as a minimum requirement be isolated by means of a suitable waterproof switch to IMO etc.etc....."
There are similar paragraphs in other codes for vessels over 20 metres OAL that carry passengers.
Why should we be any less safe at sea than a larger vessel?
As you say yourself this is what OEM's expect to see so why not just do it and be safe?
Either way enjoy your sailing and don't worry too much about regulations. No ones boat in our size range complies totally anyway as there are very few regs to comply with. There are new EC regs coming in, some of which are already in force but they are as yet not as rigourous as passenger craft and probably never will be. Good practice however does not change just because the regulations don't apply.....

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