Electrical Question - Grounding The Auto Pilot

Dan Johnson · Apr 5, 2009

Stu, Dave, and Donaflex...

Stu, we're talking about a Raymarine S1 autopilot here. Those are quotes from the SmartPilot Series Commissioning Guide dated Sep 2006--mine says the same thing. It does not mention a keel specifically; the exact cautionary notation reads "S1 system MUST be connected to ships ground." They supply a 1/4" tab female crimp-on for this (yellow barrel = 10-12 AWG wire) to make this connection to the computer board's lug.

They call the wire the "earth strap" and say it should be connected to metal that is in contact with the water (now THAT says "keel" to me). They add that if that's not possible, it can be connected to the negative pole of the battery "(ideally at the battery itself)". Lastly they caution to keep the earth strap as short as possible.

Given the distance from where I intend to mount the computer, it's about 10 feet to the nearest keel bolt and less than 4 feet to a battery negative post, hence a 10AWG wire to the battery is in order.

Dave: thanks for the update regarding X-5. There must be some differences between it and the S-1. Bill Roosa may have touched on that--possibly a change in componentry. All the surface mountings tell me that there are a lot of components that may have been fried with conventional solder heat application instead of wave soldering.

A comparison to the ground plane for an SSB radio was mentioned. I suspect that an SSB radio's grounding need is significantly different than for this autopilot.

Donaflex: the case is molded plastic, with no likely electronic field impact. The unit has a separate, dedicated plus/minus power source connection. There is a cautionary note also about interferring with other electonic components, causing things to "function incorrectly". Raymarine also supplies "suppression ferrites" to be used with non-supplied cables, placed nearest the Raymarine device.

Ron20324 · Apr 5, 2009

Dan, Unless the keel is bare metal, it is not an "earth" ground like a Dynaplate would be. Layers of glass cloth/paint/epoxy/bondo and such insulate the keel from "earth".

Damauny already told us the 1/4 strap is 12 guage, though he does not list his source or circular mills. You already know you need a 30-amp wire, so why can't you just get your wire on that basis? It's not rocket science. And I agree with Stu: if the book says put it on the battery, then put it there. The neg buss probably behind the circuit breaker panel is GROUNDED, but it is not "GROUND" and can produce ground loops. The neg post of the battery IS ground.

All to often someone posts a question that the book says XXX, but why can't I do YYY? All too often the replies are opinions, not facts, which is what the original poster wants. And that is why you got 5 different wire sizes: opinions. The A in AWG means American, so you won't find mm without a cross-reference. Google wire sizes and fiind a cross-reference from AWG to mm if you really want to know.

It doesn't help that some posts are the S-1, some are the X-5 with different manuals. And if you own a 34-foot boat, you need to become an electrician...and a plumber... and an engine mechanic...and a...

Dan Johnson · Apr 6, 2009

Hey Ron--Thanks for the input...

that's the point I was trying to make regarding the keel. Mine's steel, well painted, and not likely to be in good electrical contact with the water (if the barrier coat is holding up!). Therefore the battery negative terminal is the best ground reference point for this digital circuitry.

Again, the metric specs and braided wire references are predominantly English (UK) in origin. For as large a manufacturer as Raymarine is, one would think that their technical writers could create a domestic US market-oriented manual. Dealing with metrics isn't our forte in the US. Over the years of being in the telecom business I've had to translate Nipponglish into meaningful instructions that made sense. This is no different.

Don12364 · Apr 7, 2009

For Dan

I had to go through it - why shouldn't you suffer too!
Rgds,
Donalex
..................................................

744 - Statement on Signing the Metric Conversion Act of 1975.
December 23, 1975

Gerald R. Ford
1975: Book II

I AM today signing H.R. 8674, the Metric Conversion Act of 1975.
This legislation establishes a national policy of coordinating and planning for the increased use of the metric measurement system in the United States.
To say that this legislation is historic is an understatement. The question of a common measurement language is, in fact, nearly as old as our country. President George Washington raised the issue in his first message to Congress on January 8, 1790. He called at that time for a uniform system of currency and weights and measures. He repeated his request several times thereafter.
President James Madison also urged Congressional action on a measurement system. Fifty years later--in July 1866--Congress did pass legislation making it legal to use the metric system in U.S. trade and commerce.
In 1875, the United States was one of the 17 countries which signed the Treaty of the Meter. In spite of that, the country retained its old measurement system. There have been expressions of legislative interest from time to time since 1875, but no further definitive statement of national policy has been forthcoming.
We should learn from this brief history that legislation cannot solve all our problems. Indeed, if the legislation is not founded on public acceptance, it will have less than no effect at all.
That is why I think this bill is so interesting--because the real impetus came from the private sector, from people in the business of buying and selling American products here and overseas. U.S. industry in this regard is miles ahead of official policy. American companies already are making great use of metric measurements. Many areas of our industry--such as pharmaceuticals, cameras, and space exploration--already are entirely or largely metric. In addition, many of the country's largest retailers are finding it is good business to deal metrically with their customers.
The truth is that our continued use of the English system of measurement was making us an island in a metric sea. In 1965, Great Britain renounced its old system of measurement in favor of metric. It was followed by the Commonwealth countries. Today, more than 90 percent of the world's people uses metric measurement in their everyday lives.
A few years ago, the Congress asked the Secretary of Commerce to determine what impact the increasing worldwide use of the metric system was having on the United States and whether it was desirable to increase the use of metric weights and measures here. The National Bureau of Standards, which conducted that study, urged wider use of the metric measurement language. NBS also proposed a coordinated national program to bring this about. The legislation before us today implements that NBS finding.
It is important to stress that the conversion contemplated in this legislation is to be a completely voluntary one. The Government's function, through a U.S. Metric Board that I shall appoint, will be to coordinate and synchronize increasing use of metric measurement in the various sectors of our economy.
I sign the bill with the conviction that it will enable our country to adopt increasing use of this convenient measurement language--both at home in our schools and factories and overseas with our trading partners.
Note: As enacted, H.R. 8674 is Public Law 94-168 (89 Stat. 1007). The statement was released at Vail, Colo.

Dan Johnson · Apr 7, 2009

Donaflex...

you oughta know by now that you can't trust American politicians!

I've been working in metrics for years on Japanese cars and bikes. Aha, but give me the good old days of working on Whitworth stuff with good ole' spanners! Now there's a set of conversion tables for ya! :dance:

RAD · Apr 7, 2009

Whitworth and Lucas brings back memory's working on the 650 Bonneville and BSA bikes

Dan Johnson · Apr 8, 2009

RAD...

Yep, a 441 and MG-TC's and TD's among others...