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The reason for connecting to the engine vs. the battery, is for lightening strikes. You really dont want lightening thinking the battery is earth ground.
I have owned lots of boats and been on lots of other boats. The ones I have been on I cant say as to how they were grounded. But all of the boats I have owned have been grounded thru the engine. Again due primarily to lightening strikes. It may blow a prop off but the chances of it blowing a hole in the bottom of the boat trying to get to the water are lessened considerably.
No Loran that I have owned (6 before converting to gps) has ever had problems using the engine for grounding.
Considering the chassis ground and the engine block and the battery's negative terminal are at the same potential (remember the 4 gauge cable that runs from the battery to the engine?), it would be pretty much impossible to get stray current hooking to the engine and not get the same stray current hooking to the battery. The resistance of the negative battery cable is too low to present any type of isolation.
quote:Originally posted by Sea_Dad:
The reason for connecting to the engine vs. the battery, is for lightening strikes. You really dont want lightening thinking the battery is earth ground.
I have owned lots of boats and been on lots of other boats. The ones I have been on I cant say as to how they were grounded. But all of the boats I have owned have been grounded thru the engine. Again due primarily to lightening strikes. It may blow a prop off but the chances of it blowing a hole in the bottom of the boat trying to get to the water are lessened considerably.
No Loran that I have owned (6 before converting to gps) has ever had problems using the engine for grounding.
Considering the chassis ground and the engine block and the battery's negative terminal are at the same potential (remember the 4 gauge cable that runs from the battery to the engine?), it would be pretty much impossible to get stray current hooking to the engine and not get the same stray current hooking to the battery. The resistance of the negative battery cable is too low to present any type of isolation. How do you provide for a chassis ground if the electronic component doesn't have a chassis ground? Thanks Bob
If its all plastic, you cant, and most likely its fully plastic on the front as well. Hopefully it will have a metal plate in the rear that you could use.
Sea_Dad...as always you make a good point on going to the engine with boat ground Vs the battery. Lightening strikes! I had a buddy of mine get hit, five aboard, all safe, but all the electronics went dead and the boat stopped. Other boats saw it and were next to him immediately...the marina was waiting to haul the boat. There was a soft spot in the hual about 5" in diameter that you could have put you hand through (mush). Fiberglass. Everybody 'got lucky' that day.
"Never enough time to do it right; ALWAYS enough time to do it over." Boston Whaler, "MUMBLER", 24' Outrage (1996), twin 175 HP Evinrude Ocean Pros. Snowball, the cat...
My boat is in storage so I can't look at it right now but was hoping to get some clarification on the seperation of Engine battery ground vs. Engine chassis ground. If I recall I have a black (4 AWG) wire going from the engine to battery ground and all electronics have black wire going to negative ground on the battery as well. I also have seen the green chassis ground from some electronics. From what I gather you are saying these should be tied to the Engine's chassis ground (metal) along with other metal such as gas tank etc. and grounding plate if you have one. How do you identify the engines chassis ground. Is it a green wire as well?
The green chassis wire is used to identify it as chassis ground. There is no engine chassis ground, nor is there really an engine ground.
The engine is metallic making it electrically conductive. The engines starter circuit (plus the rest of the engines components) use it for ground reference, it saves wire.
The battery bolts to the engine with its black starter cable. This then ties the engine to the boats ground. The engine also sits in the water, and thus the boats ground circuit is "earth grounded" by means of the engine.
You can tie chassis ground to any point on the boats ground and achieve grounding of the unit's chassis. However, if you pick a point thats not the engine (which is directly contacting the water), but still ships ground, then you are hoping a lightening strike will pick the least damaging path to the water not become bored trying to find the water and just go ahead and punch a hole in the bottom of the boat to get to it.
Disclaimer:
The engine is not the ideal way to protect the boat against lightening. Using a corona (or ionizing) wand designed specifically for lightening protection is the best way. But if you dont have one, then second best is better than 3rd best.
I am going to install a loran within the next couple of weeks.The loran(northstar 800x) has three wires, positive, negative, and ground. The manual says DO NOT connect the ground to the same place as the negative wire. So where do I connect it to. I do not have a Dynaplate. I did locate some "green" wires which come from the fuel fill and fuel tank and one hooked up to negative battery terminal.Should I install a Dynaplate?? Thanks
Thanks for the reply but I'm still not exactly clear on one this grounding plate issue (I do have an electronics background but been a long time since I've used it). From previous posts it sounded to me like the engine ground was seperate from the battery ground (which is why I was confused). Now the questions...If the engine ground is tied to the battery ground, are they not the same ground? I guess what I'm getting at is if I installed a grounding plate to run a true "chassis ground" for my electronics that require it would it need to be isolated from the engine/battery ground? I realize there is a potential difference in grounds and that ideally you would want lightning to follow a path to ground (preferably not through the engine I would think but through the grounding plate). Should these two grounds be isolated from one another and is a grounding plate usually installed through the hull so it has a direct path to water? I recall seeing a large sportfish in Islamorada a few years back that got a direct strike from lightning. It smoke all electronics and somewhat melted some fiberglass if I recall. I guess there is no guarantee the lightning will always go where you want it to.
Look folks, what we are talking about here are three different circuits. In a perfect world the three would never be connected to each other in any way, but that's not possible. Its still desirable to isolate each of the three from the others to the extent possible. Here are what the three are:
1. Your power system, which has a negative side which somewhere somehow will be connected to your battery. This one is here to complete the circuits and without it none of your electrical devices will work. That one is pretty straight forward and I think virtually everyone understands it. These wires are black more often than not
2. The chassis grounds, which will be connected to mother earth. The purpose of this one is twofold. First it gives a path to disapate stray electrical charges. The second is that it allows electrical energy that is attendent to the use of your individual pieces of electronics to be disapated without interfering with other electronic devices. Think of it as a way to move static, and other charges resulting from the operation of the devices, from your electronics to the ocean and you'll have graped enough of its purpose to take care of your needs. The wires that are used for this are often actually braided shielding.
3. The bonding system, which is that set of wires by which various metal stuff on the boat is connected to other metal stuff on the boat. This third one is the least understood. Let me try to make its purpose simple. The bonding wires are there to give the means of least resistance to connect things of different electrical potential. If those wires did not exist the potential will find other paths to equalize, and if the other path includes an electrolite (salt water for instance) it will lead to the movement of material from one thing to another - and that means that parts will disappear before your very eyes. The wires that constitute the bonding system are often either bare copper or green wires.
There is a fourth possible system as well, but most of our small boats do not have AC electrical systems so I'm not going to confuse the issue with any mention of it.
Does that help at all?
Thom
"The amount S&P 500 corporations owe to their employee's retirement benefits plans for which they have set aside no funds: $458,000,000,000"
joe l, try hooking it to the engine first. ABYC says any connection to the engine must be on the same grounding post as the battery is hooked to. If it locks on to the signal and you have no signal strength issues, then your done. I consider grounding plates as a last resort. I personally dont want thru holes in the hull below the waterline that may not really need to be there.
Back in the early days of loran (Thom may remember Loran-A, vs. the now loran-C signal), if you didnt use a grounding plate of some type you wouldnt pick up squat. But with the newer designs, namely active antennas, the need for a grounding plate dissappeared.
The reason they want you to ground somewhere other than the negative side of the battery (preferebly to the water (earth ground)) is because of the loran signal itself. Its wavelength is really damn big (it's a 100khz carrier signal). So you need all the effective ground you can get to make the antenna effective.
As for a lightening strike, I would much rather have soft glass or even a hole punched through the glass in the transom long before I would want that to happen to the area around the grounding plate, considering the grounding plate is always under water. This is the main reason I ground to the engine.
[This message was edited by Sea_Dad on 03-14-03 at 11:38 PM.]
quote: If the engine ground is tied to the battery ground, are they not the same ground?
yes they are, just as soon as you bolt the negative battery cable to the engine.
Grounding plates connect to the water, the boats ground circuit also connects to the water by way of the engine. Therefore you will never achieve isolation between the two.
Grounding plates are a much more effective way to connect to earth ground than the engine. But grounding plates require thru holes below the waterline. They also create drag and turbulence if they are the brass gazillion pores type.
The engine is a grounding plate by virtue of it's touching the water.
The engine also allows you to create a single point which to ground all equipment to the earth. By creating a single point grounding system you can minimize or altogether eliminate ground loops that can wreak havoc on electronics.
When it comes to a lightening strike, the engine is also way way beefier than the hull itself is. Remember, that grounding plate is bolted thru the hull and those small thru holes will become huge after the lightening bores through them. This is why they recommend a 4 gauge wire connected to a wand and running over the side of the boat and sitting in the water.
Ok, this has been puzzling me on my boat. It appears to have a bonding system - fairly heavy (#8 or 10) wire running from metal on the t-top to a thru-hull fitting. None of the existing electronics appears to be tied into it, it seems more like it's just grounding the t-top frame. I was wondering if was there for dissipating electrical charges.
Anyway, I'm adding a lot of metal to the top of my hardtop roof - handrails, rocket launchers, radar pedastal, etc and was wondering should I connect them to this wiring? The only device I have that has a seperate chasis ground is my raymarine radar, and I plan to tie that in, but what about all the other metal up there?
Sorry for taking the topic slightly askew, it didn't seem to warrant it's own question.
to create a separate ground could you attach your grounding plate to a thru-hull fitting? I thought I read that one should not use a bronze thruhull as a ground is that true?
Heres what I did when I installed my electronics on my new boat this past weekend, for the chassis ground, I found that the forward bilge pump had one on it. The grounding plate was too far away and a pain to get to, so I took the wire from that grounding plate that went to the forward bilge pump off of the bilge pump and connected it too a ground Bus that I installed in forward bilge. Then I ran my electronic'
s chassis grounds to it and connected a new chassis ground for the forward bilge pump. Now all thats left to do is attach the NMEA cable for the Furuno 600L (they really should include that in the box) and my electronics will be completely installed.
You have a grounding tab on a bilge pump? You sure about that?
I've got to ask you all a question. Where are you buying these thru hull fittings, water inlets or outlets I assume, that have some sort of attachement tab for use as grounding devices? I only ask because I wasn't aware that the manufacturer's of those plumbing fittings felt that they would make fine ground plates as well. Dunk says that when he does surveys he can tell from the outside of the boat if the thru hulls have been used as grounding points - they take on a tint of red color because of metal loss .......
Thom
"The amount S&P 500 corporations owe to their employee's retirement benefits plans for which they have set aside no funds: $458,000,000,000"
Grounding plate? 
sort all of this out 
"Never enough time to do it right; ALWAYS enough time to do it over." Boston Whaler, "MUMBLER", 24' Outrage (1996), twin 175 HP Evinrude Ocean Pros. 
Snowball, the cat... 
