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Topic Title: Installations on Boats
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Created On: 20 March 2017 09:08 AM
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 20 March 2017 09:08 AM
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SDN8BD

Posts: 46
Joined: 05 January 2017

Morning,

I will be helping out a friend in the near future with the installation on his new narrow boats. Just wanted to get a few opinions really. I assume with the regards to the regs I just treat it as a caravan in the most parts as I don't recall seeing anything in the regs regarding boats.

The installation will broadly consist of:
-Bank of 12v lead acid batteries in the hull
-Invertor unit supplying the 230v AC equipment and sockets
-12V charge regulator (battery charging from 230v shore power and possibly solar trickle charging)
-12v lighting and other ancillaries etc.

I assume the earthing arrangement is usually TN-S for the shore power supply with everything being cross bonded as it would in a normal installation but also including the metallic hull of the boat.

When not connected to the shore power but moored the invertor based 230v system will be operating and there is an obvious danger that someone could be stood on the muddy bank and touch the hull. Does this mean a TT earth rod is needed when moored up off grid?

Cheers,
Steve
 20 March 2017 09:22 AM
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rocknroll

Posts: 9534
Joined: 03 October 2005

Read this,

Here

It gives you the necessary standards that apply.

Regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 20 March 2017 09:39 AM
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AJJewsbury

Posts: 15632
Joined: 13 August 2003

I assume the earthing arrangement is usually TN-S for the shore power supply

Could be anything other than PME - but TT is probably most likely. See section 709 of BS 7671.

When not connected to the shore power but moored the invertor based 230v system will be operating and there is an obvious danger that someone could be stood on the muddy bank and touch the hull. Does this mean a TT earth rod is needed when moored up off grid?

If you have a local TN-S system from the inverter with the hull as the generator's electrode, there shouldn't be a voltage difference between the hull and the bank even during fault conditions - there's no circuit for the person to complete so no shock risk (unless someone runs an extension lead from the boat to the shore and somehow gets a live conductor in contact with the ground - and even then the 30mA RCD should intervene before it becomes life threatening).
- Andy.
 20 March 2017 09:44 AM
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SDN8BD

Posts: 46
Joined: 05 January 2017

Thanks both.

Plenty more research to be done.

Steve
 20 March 2017 09:59 AM
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AJJewsbury

Posts: 15632
Joined: 13 August 2003

-12V charge regulator (battery charging from 230v shore power and possibly solar trickle charging)

I'd also expect the 12V batteries for the inverter to be charged from the engine - otherwise you'll be limited to about one evening away from shore power (or have a very large battery!)
- Andy.
 20 March 2017 10:58 AM
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SDN8BD

Posts: 46
Joined: 05 January 2017

Andy,

Yes I missed that bit,

As the hull isn't yet built I am not sure on the arrangement yet but I believe there will be two 100A alternators on the engine to charge the batteries. Whether I will install a small capacity battery just for engine starting duties I am not yet sure.

Steve
 20 March 2017 11:18 AM
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AJJewsbury

Posts: 15632
Joined: 13 August 2003

I'd definitely expect a separate battery for engine starting - it's far too easy to run the inverter batteries down (5 min of microwave cooking and a TV for couple of hours used to do it on the one I stayed on for a week once, despite a very impressive looking collection of lead and acid) - it would not have been good to have been dead in the water next morning too.
- Andy.
 20 March 2017 11:32 AM
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SDN8BD

Posts: 46
Joined: 05 January 2017

Cheers Andy,

A fair point. I am fairly familiar with split starting and auxiliary load battery and alternator systems from overland expedition vehicles and recovery vehicles.

I will use a voltage sensing system on the engine battery which ensure the engine battery is fully charged before connecting the alternator to the battery bank. Will have to have a bit more of a think how this links into the shore connection and allows the engine battery to also be charged in that direction too. I am sure there must be a smart regulator system that allows this for camper vans.

Cheers,
Steve
 20 March 2017 11:56 AM
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GeoffBlackwell

Posts: 3790
Joined: 18 January 2003

Both of the small craft electrical standards mentioned in RNR's link where updated in 2012.

The AC standard included a major change to the requirements for bonding the AC and DC systems.

Boat systems can be complex and you should assume nothing.

The Boat Safety Scheme - given in RNR's link - is a very good place to start as the vessel will have to obtain a safety certificate issued by them.

You might also try canal boat forums.

Regards

Geoff Blackwell
 20 March 2017 11:47 PM
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broadgage

Posts: 2317
Joined: 07 August 2007

For a boat used only in inshore waters, I would suggest two battery banks.
One for domestic purposes and a separate battery for engine starting. A handful of essential circuits should have a changeover switch such that they are powered from the domestic battery normally but can be switched to the starter battery if needed.
Such as navigation lights, VHF radio, bilge pump, and basic internal lighting.

A boat intended for offshore cruising should preferably have two engines, each with 2 alternators, and a total of 3 batteries.
Domestic battery, charges from both engines
Port engine starting battery
Starboard engine starting battery.
With duplicated starting batteries, the essential loads could be taken from either starter battery via a changeover switch.

If only a single engine is fitted then an alternative means of propulsion is needed such as sails or an outboard engine.
 21 March 2017 06:20 AM
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GeoffBlackwell

Posts: 3790
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I will be helping out a friend in the near future with the installation on his new narrow boats.


Is this meant to be boats or boat?

If the former is this a commercial venture?

Note that if you are involved in any design work most professional indemnity insurance policies excluded boats, ships, marinas, harbours, etc.

Here are some links to previous posts that might be of interest.

Link 1

Link 2

Link 3

Link 4


Also look at - Wiring Matters 2008 No 29.


Regards

Geoff Blackwell
 21 March 2017 09:03 AM
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SDN8BD

Posts: 46
Joined: 05 January 2017

Thanks both. It is boat (singular) which he will be living on himself. it is also an inland only vessel.

Cheers,
Steve
 21 March 2017 10:17 AM
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mapj1

Posts: 9107
Joined: 22 July 2004

Be careful if mixing mains from an inverter with mains from shore power - in some ways it is easier if the shore power charges the batteries and the AC on board is always from the inverter, but it is not sensible if there is much high wattage load.
Note that many inverters do not generate a sine wave, more of a stepped square wave, and while this means that both the peak and RMS voltages are more or less in the right relation, not everything likes this,and the sharp edges can give interference to radio and TV reception and similar . And many inverters don't like mains filters where the first element is a capacitor, as the peak currents that flow during the edges of the steps are many times the average current.
Also, like all paralleling of generators there is the vexed question of the N-E bond - there ought to be one in or near the inverter, or the RCD wont work. (but again, care some inverters are not isolated between the battery and the output, so on alternate half cycles of the output, the battery negative is either 'live' or 'neutral' - the only way to be sure is to run the inverter and measure volts L-E and N-E and then remeasure with a low wattage load in parallel with the meter - if it is isolated output, then you see about 100V with the meter alone, collapsing to not a lot with the load in parallel.)
Equally when on shore power, you don't want that NE link to appear across the shore supply - or the shore side RCD wont stay on.
The usual fix is a double pole change-over switch.

-------------------------
regards Mike
 31 March 2017 11:35 AM
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ericmark

Posts: 329
Joined: 12 February 2008

Cathodic protection is a real consideration, when I did it diodes were used in the earth. I would have preferred to have used an isolation transformer.

Both my son and I are electricians and it was his boat, now sold, major problem was getting a shore supply big enough to run the washing machine. Inverters seemed the answer but we got cheap rubbish which failed. We were also at that time unaware you can get an inverter designed to top up the shore supply. So 4 amp from shore and 9 amp from batteries.

However the design we used was sound, it was just we used a poor quality inverter. 24 volt reduces current to inverter and if not already fixed to 12 you should look at 24 volt it halves cable sizes.

Anyway idea was to use a large class II battery charger, the shore supply would only feed the battery charger nothing else, so no need it import earth so no cathodic protection problem. Everything would then run from the inverter.

But second problem is charging the batteries fast enough, there are in basic terms three types of battery charger, fixed voltage which is what most engine alternators give, pulse charging which is what most solar panels use, and stage charging however the latter has a problem.

The three stage charger works well when the battery is not in use, idea is simple, as much charge as the charger can give until (using 12 volt values here) the voltage hits 14.8 volt (14.4 volt with VRLA) that is stage 1, then it maintains the 14.8 volt until the current drops to a preset figure with ours it was 5.6 amp at that point it considers the battery 80% charged and it drops the voltage to a float voltage of around 13.4 volt for the last 10% of the charge other wise it could buckle the plates.

The 5.6 amp is the problem, if your using lights which draw say 4 amp then before it goes into the last stage the battery is charging at 1.6 amp not 5.6 amp so it is being stressed. So either you need two banks one in use with float charge only and one on rapid charge, or a completely different method of charging.

The pulse charge does not have this problem, I will not pretend to understand fully, but it seems it works out charge rate required by voltage decay curve. Sterling do some special products which takes the output from two alternators kids the alternator that the voltage is below 14.2 volts to get full output then boosts the voltage and uses the pulse charge method of regulation.

This means instead of 16 hours to recharge batteries it's down to 9 hours, And cruising in a narrow boat you would be hard pressed to run the engine for more than 7 hours per day.

Again although 9 hours for fully discharged battery for a half charged battery it is clearly a lot less, so although calculations may show you need 330 Ah battery capacity to charge in time you may need 660 Ah capacity.

I hunted for a 600 amp isolator for the battery, I could not find one of a reasonable size, so I used welding connectors, mainly for supply to inverter.

Depending on the inverter type, standard residual current devices may not work, written in full as RCD stands for recreational craft directive with narrow boats.

With mainly maria use the requirements are different from continual cruising, the lead acid battery needs to be fully charged once a month, so sitting in a maria most of its life having special regulators in the alternator or external units to combine alternator outputs are not really required, on the other hand with mainly cruising you don't need special power top up inverters. So step one is to work out what you need.

Except for special washing machines the only one which would work with simulated sine wave was the LG when we were doing it, there are more inverter washing machines now, in spite of rating at 2.4kW it would run from a 6A MCB but not a 4A MCB. Many marinas rather than meter the supply have different changes based on if a 4, 6, 10 or 16 amp MCB is used. Sorry lost link to special inverters all I can tell you is they are made.
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