Electrical Project

[teoman]

Hey guys,
I am planning on setting up the electrical system of my new boat myself.

The boat is a 36 foot wooden built riva/lobster boat type. Planned engine are dual 150 HP.

Here is a first template of my drawing. I would appreciate any comments and recommendations...

Thanks a lot.

[KnottyBuoyz]

Just a quick glance but I think the charge lead from your alternator has to go to the ACR. IIRC you'd need two ACR's one for each lead from the two engines. This would eliminate one battery switch. Some of the others more experienced with twin engines can probably help.

[capt littlelegs]

Yes that looks well thought out with all the permutations taken care of. The only thing you might like to consider is an isolated negative return system but this is only possible if the starter, alternator and engine electrics are also the isolated type. I'm wondering why you need 300hp unless this is a planning boat. If they are oversized on a displacement hull they run too slow and create bore glazing and smoke.

[capt littlelegs]

Originally Posted by KnottyBuoyz

Just a quick glance but I think the charge lead from your alternator has to go to the ACR. IIRC you'd need two ACR's one for each lead from the two engines. This would eliminate one battery switch. Some of the others more experienced with twin engines can probably help.

The split charge relay I think you are refering to is voltage sensed so needs no other connection. It could be simplified with only two battery banks then you don't need anything splitting and it would save one switch... unless an isolated neg return is used.

Originally Posted by capt littlelegs

I'm wondering why you need 300hp unless this is a planning boat. If they are oversized on a displacement hull they run too slow and create bore glazing and smoke.

This seems to be one of the very popular (in Turkey) semi displacement vessels.
Otherwise sure 300 horses are overkill and wo´nt last long. Except he fits a CPP to them instead of a gearbox. Then he would have a win / win situation. But thats valid for a semidispl. vessel too...................

Regards
Richard

[CDK]

Teoman, draw the complete circuit, including color coding and cable sizes and post that on the forum.
That may result in useful comments and recommendations, but even then you still need to filter out a lot of static.

[capt littlelegs]

Originally Posted by CDK

Teoman, draw the complete circuit, including color coding and cable sizes and post that on the forum.
That may result in useful comments and recommendations, but even then you still need to filter out a lot of static.

Static?

[teoman]

Actually then engine horsepower is drawed from the design hp/speed graphic.
at about 270HP, I get about 18.5 knots speed. But I didn t buy the engines yet. Its going to take me a while to get to this point anyway.

CDK, thanks I will do that and get a more detailed drawing. I wanted to know if I am on the right way.

Actually I need 2 seperate batteries for the engines, and a 3rd bank for service.
I would appreciate if you can detail a little more the isolated negative return system.
Also can I use the same grounding plate for AC and DC (connecting the grounding plate to both negative bus ?

Thanks

[Stumble]

I would highly recommend looking at something like the Capi2 distributed power bus system. In my eyes it is really only worth doing on new boats, or complete refits, but in those instances I wouldn't think twice about adding it to my boat.

What they do is allow you to run one main trunk line down the middle of the boat, and tap that line for any of your power draw items directly. Thus resulting in significantly easier instalation of almost all of your electrical draws. And the cost savings in using less wire pays for the system itself, not to mention all of the labor trying to chase wires throughout the boat.

[capt littlelegs]

Originally Posted by teoman

Actually then engine horsepower is drawed from the design hp/speed graphic.
at about 270HP, I get about 18.5 knots speed. But I didn t buy the engines yet. Its going to take me a while to get to this point anyway.

CDK, thanks I will do that and get a more detailed drawing. I wanted to know if I am on the right way.

Actually I need 2 seperate batteries for the engines, and a 3rd bank for service.
I would appreciate if you can detail a little more the isolated negative return system.
Also can I use the same grounding plate for AC and DC (connecting the grounding plate to both negative bus ?

Thanks

It's not a problem having two starter batteries, one could also be for the bilge pump but you only really need one with the house battery as back up.

An isolated return means that no part of the low voltage system is in contact with external metal parts of the boat so that is a floating system... in more ways than one!

The obvious reason for this could be thought of as eliminating any possibility of inducing galvanic current but the main reason is that if any fault occurs to the hull, engine or metal parts then that equipment does not fail as a first fault by blowing fuses, trips or burning out cables when under way, unlike an AC safety system, instead the fault remains safe until a regular test is made by a pair of permanently fixed lamps or meters connected from the earth, hull, engine etc. and each side of the battery. If a lamp or meter doesn't work then there is a fault to be fixed... or a failed lamp. This is a Lloyds recommended system. An overload or short across both lines would still blow fuses etc. to protect cables.

The hull, engines, shafts, anodes, skin fittings etc. are still bonded to the low voltage earth point, either on the hull if metal or an engine. The AC earth point should ideally be separate and adjacent to the low voltage earth point to avoid disturbing one or other and losing the earth if worked on. The negative battery terminal should not be used directly for an AC or DC earth for the same reason whatever system is used.

[capt littlelegs]

Originally Posted by Stumble

I would highly recommend looking at something like the Capi2 distributed power bus system. In my eyes it is really only worth doing on new boats, or complete refits, but in those instances I wouldn't think twice about adding it to my boat.

What they do is allow you to run one main trunk line down the middle of the boat, and tap that line for any of your power draw items directly. Thus resulting in significantly easier instalation of almost all of your electrical draws. And the cost savings in using less wire pays for the system itself, not to mention all of the labor trying to chase wires throughout the boat.

As someone who has chased a lot of wires through boats and buildings I really can't see the practical benefit, you still need wires and now you've got even bigger cables to try to get in and connect to, even so, you can still do most of this a lot simpler with local fuseboards and switches if needed without the potentially troublesome electronics. The wire and labour saved must be really expensive or the system really cheap to be worthwhile, somehow I don't think it is!

[SuenosAzules]

All written so far are good points. Be sure to stick to marine grade cable with 16 AWG minimum. See ABYC E-11 standards for wiring standards and A-28 of that book for galvanic isolation standards. Just in case you want to insure it or sell it in the future a little easier.

http://www.abycinc.org

[CDK]

Originally Posted by capt littlelegs

Static?

Yes, static.

The noise from a shortwave radio garbling important messages.
Women chattering through your phone call.
Ignorant fools posing as experts on a forum.

[capt littlelegs]

Originally Posted by CDK

Yes, static.

The noise from a shortwave radio garbling important messages.
Women chattering through your phone call.
Ignorant fools posing as experts on a forum.

Just as I though then!

[CDK]

Originally Posted by teoman

I would appreciate if you can detail a little more the isolated negative return system.
Also can I use the same grounding plate for AC and DC (connecting the grounding plate to both negative bus ?

Thanks

Like I said, you need to filter out the static!

An isolated negative return is utter nonsense.
First of all, negative is not the return but the source of all electrical energy, but that misunderstanding is so widespread we have to live with it.

You cannot isolate DC ground. Don't pay attention to anybody who says you can. Your starter motor has internal ground connections and so does your alternator. Sensors for temperature and pressure use engine block ground, just like the ignition parts.
You simply cannot isolate a starter motor from the engine block because using plastic washers and bushings would displace it physically and there still remains the steel shaft and bendix.
It also serves no purpose at all and would double the wiring.

So all boats, cars, tractors, tanks and planes on this planet have the battery negative connected to the engine block with short, heavy cables, crimp terminals, sealed with a sleeve )*. For boat engines I recommend the use of liquid neoprene under the sleeve so capillary water invasion is impossible.
The engine block and anything bolted on is your rock of safety, your reference point for the whole electrical system. A strap connects it to the stern tube, ground plate and zinc anodes.

The AC circuit is a completely different chapter. We'll discuss it when the need arises.

)* The French recognized the "negative return" misconception and connected the + to ground. But they lost that battle and surrendered.