Boat Electrics - The Basics?

conks01

conks01

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Hi,

Can anyone provide me with a basic overview of boat electrics please.

I own a 19ft bilge keel and have found out today that the electrics appear to need updating.

Power requirements are merely mast light and depth sounder. There is no onboard and bilge pump is manual.

I know very little regarding electrics. Can you please recommend cable type and size I might need together with connector types, whether I will have to run with a new fused switch panel and bus bars etc. ?

My other query is where to locate all the cables.

Any help greatly appreciated.

Thanks.
 
Hi

More info please

Why do you think the systems needs updating

Do you have a battery and how is it charged ?

Do you have an On / Off switch

What sort of engine (inboard or outboard)

Regards
 
You're thinking along the right lines about cable sizes. The required size will depend on the length of cable required and the rating of your starter motor. Lights, etc will only have a much lower current draw.

The basics are that you should aim to had a dedicated starter battery and one or more house batteries. Your boat's alternator will charge these when running and it's a good idea to have a diode or relay charging system. These make it easy to charge both battery sets at once and will isolate them wen not charging. The batteries should be connected to isolator switches using the heavy duty cables, ideally with crimped connectors. Any lights and instruments should be connected in to a fused switch panel which in turn is connected to the batteries with heavier duty cable.

An automatic, electric bilge pump or two are worth fitting.
 
Baddox said:
I managed that in a 15 footer so why not?
Click to expand...

Well, of course you could, but it seems rather excessive. The OP clearly doesn't know a great deal about the subject so could easily end up believing he needs huge amounts of stuff that just aren't necessary in a small, simple boat. He says he just wants to run a single nav light and a depth sounder, for which a 20Ah gel-cell in a box would do fine, taken home to charge or with a small solar panel. Or get a bit more serious with a 60Ah leisure battery and an off-the-shelf 4 or 6 way panel. But multiple battery banks for such a boat definitely seems unusual.

What electric-start outboard did you have on a 15-footer? I didn't think you got that much below 20hp?

Pete
 
Last edited:
OP requires a very simple system. A battery presumably he has one, if not one light enough to take home for charging although he might want to progress to a small solar charging panel. Wiring should be somewhat heavier than really needed for voltage drop considerations simply for robustness and resistance to corrosion etc.
A single fuse in an in line holder will suffice for protection near the battery +ve terminal. This should be rated at 5 amps. Best is a spade type auto fuse with appropriate crimp on lugs for connection.
You will need a box to hold a switch for the mast head light. I mounted mine within easy reach just inside the main entrance to cabin. Make room for another switch for a cabin light either now or later. These little guys can be brilliant stuck to cabin roof. http://www.banggood.com/3W-24led-COB-LED-Chip-220mA-WhiteWarm-White-For-DIY-DC-12V-p-959064.html.
Regarding mast head light. Unless it is fitted and working I would not have any wiring in the mast if you can avoid it. So LED port and starboard on cabin sides and a stern light will have all wiring inside the boat and easily accessible.
Wiring can be usefully run in conduit plastic tubing making it easy to add wires or replace them. I have also used large bore fibreglass insulating flexible tubing glued to the hull and cabin walls and roof. Or you can just glue the wires to the ceiling or walls. Use hot melt glue or contact cement to hold them in place then finish with epoxy or similar.
PS look towards fitting a VHF radio in future as a most useful addition to safety gear.
good luck olewill
 
Sea dog - because it's over 30 years old, in places has been badly spliced, certain wires cut but not terminated, none of lights actually work and most are chaffed.

Battery charge is from ashore. I remove it to charge etc.

Engine is an outboard.

Power requirements are for a to be fitted depth sounder/log, lights and a 12v outlet, other than that not much else.

Thanks.
 
Baddox - Yes, I appreciate where you're coming from but Pete has pretty much said it all. It's small power requirements on a very basic boat etc.

The battery is a 75 and was poorly charged, now topped up. I would believe that I need to go down the 4 way panel with a 12v outlet (for charging hand held VHF etc.) but it's the cable type, size and whether I need bus bars that's confusing me not to mention how I go about concealing all.

Thanks
 
conks01 said:
Hi,

Can anyone provide me with a basic overview of boat electrics please.

I own a 19ft bilge keel and have found out today that the electrics appear to need updating.

Power requirements are merely mast light and depth sounder. There is no onboard and bilge pump is manual.

I know very little regarding electrics. Can you please recommend cable type and size I might need together with connector types, whether I will have to run with a new fused switch panel and bus bars etc. ?

My other query is where to locate all the cables.

Any help greatly appreciated.

Thanks.
Click to expand...
Boat Owners Illustrated Electrical Handbook, by Charlie Wing, this gives you all the info you need and much more. Quite pricey but I borrowed one from our library.
Also if you Google for 12volt wiring calculation tables you will be able to calculate what size wires you need. For starters have a look at 12voltplanet.co.uk, but there are many other easy to use calculators on other sites
 
conks01 said:
Baddox - Yes, I appreciate where you're coming from but Pete has pretty much said it all. It's small power requirements on a very basic boat etc.

The battery is a 75 and was poorly charged, now topped up. I would believe that I need to go down the 4 way panel with a 12v outlet (for charging hand held VHF etc.) but it's the cable type, size and whether I need bus bars that's confusing me not to mention how I go about concealing all.

Thanks
Click to expand...

Hi Conks -

Ahh that simple a system

If you don't understand the existing system and the wires look doggy rip them all out.

Then -
I would sugest that you mount a board, close to the battery box to mount , - 1) a negative busbar (or ccould be just a simple bolt through the board) and connect it to the battery neg using black battery cable with a snap on fastener on the battery post and 2) mount a simple On/ Off keyswitch and lead a red battery cable to a battery snap connector to the battery Posative (+) post.

Then get a simple fused switch pannel (Force 4 chandlers have them) with as many switches as you need and connect the busbar using 20amp rated red wire to the on/off keyswitch. You now have a fused distribution pannel.

Then take a pair of wires (5 amp rated should cope with lighting circuits) from each device with the red wire connected to the fused swith pannel output and the black wire taken to the negative busbar.

Soldered joints insulated with heat shrink sleeve is better than connectors (unless you use expensive marine rated stuff) and keep all of the runs of wire neat and pinned down.

Then lable each switch !

I would also sugest that you install a solar pannel, attached directly to the battery (via a fuse) even a small 10 Watt one wold keep your battery topped up.

The above is basically the system I had on my 20ft Kingfisher.

also I buy as many parts and wire as I can from an auto parts shop.

Good luck - Seadog
 
conks01 said:
Baddox - Yes, I appreciate where you're coming from but Pete has pretty much said it all. It's small power requirements on a very basic boat etc.

The battery is a 75 and was poorly charged, now topped up. I would believe that I need to go down the 4 way panel with a 12v outlet (for charging hand held VHF etc.) but it's the cable type, size and whether I need bus bars that's confusing me not to mention how I go about concealing all.

Thanks
Click to expand...

I would start with the devices you intend to run.
You have stated 1 mast head light, a depth sounder and maybe a 12v socket ( I assume cigarette lighter style) .

I would buy the smallest panel you can find - 4 switches should be fine but rather than a cigarette lighter socket, give thought to a USB socket or wiring the HH VHF charger directly in ( some cradles have wires.) That then gives you the ability to charge more things

Depending on the panel the only bus you might need would be a common return - wire all the - to that then back to the battery- I would expect the panel to have an + and if you only have one thing connected to each switch then no bus needed but no harm fitting any in advance if you think you might expand the system later - e.g. more instruments.
Wiring size depends on length of run and current - tables already given, but given the simplicity I would possibly just buy one reel of the larger size needed and use for all. being over specced never hurt. If money is ok I would go with marine tinned as it lasts longer.

I assume that the Masthead light has an LED bulb in. if not change it as the power consumption is much less. 75 ah should be ok but ideally you should work out how much you will draw in 24 hours. multiply the current in amps of each piece of kit by the time it will be running. Remember that the battery should never be discharged below 50% of charge and getting above 80% takes sophisticated charging equipment and time so you only really have about 1/3 of the batteries nominal capacity available to you.

I would also give consideration to a small solar panel. 5W will not need a controller and will stop the batteyr discharging. If you go up to say 20W ( which will need a controller) then you may be able to leave the battery in situ during the summer and come back to it every weekend pretty much fully charged. Depends on conditions of course and won't apply at the end and beginning of the season. but it adds to the ability to just turn up and sail.

As for hiding the wiring, that is the hard part. The general situation is to run it behind headlining, furniture, in lockers etc, even in the bilge ideally in conduits but that may not be possible. If not then consider using some nice wooden mouldings with recesses behind from local DIY emporium and use those to disguise the run. Stick to corners, edges etc of the cabin rather than up the middle and try and make the moulding symmetrical and it probably won't be noticed. failing that - just go for a neat finish and don't worry about it.
 
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