microwave almost drove me into a piling!

[diver dave]

Here's a good one, with a happy ending.
So, initial cruise for us on this boat. Lots of AICW running. I have autopilot on, running the ditch. At the helm, I notice the boat headed directly for a channel marker. I take over the helm. Turns out the fluxgate heading sensor is located about 3' forward of the battery/electrical area. The 2/0 inverter feed cables, about 3' long had a bit of a loop, or more exactly, were not run very close together. With the 10A ac load, they were carrying over a hundred Amps, and generating a significant magnetic field, thereby picked up by the heading sensor, thereby sending the AP off by 10 degrees. Only with the microwave on. I twisted the 2/0 Plus and Minus cables together, and reduced the effect down to 1 to 2 deg of error. And, new rule. Manual steering under bridges.

 

[Ski in NC]

I too learned long ago, no AP under bridges. Depending on the bridge, lots of steel there, it screws up the natural flux lines and boat will make a turn right under the bridge.

 

[diver dave]

I didn't think of that one. Yes, steel can hold a magnetic "charge".
I guess this is why the mil has huge degaussing coils to control ship's mag field. And, big boats that know better have gyro compasses.

 

[fryedaze]

We experienced a similar response when our Instapot ( pressure cooker) was placed in storage that is next to the flux gate in the bildge.

 

[Jeff F]

I collided with a big steel barge a couple of years ago. Was running parallel to it about 30 feet away on AP and the boat suddenly changed course 40 degrees. Learned my lesson the hard way.

 

[DCDC]

Have not had AP interference issues but a low oil pressure alarm sounds every time the microwave is powered from the inverter.

 

[diver dave]

Have not had AP interference issues but a low oil pressure alarm sounds every time the microwave is powered from the inverter.

Sounds like a more complex alarm system than a simple oil pressure switch to the block feeding a lamp/buzzer directly.

 

[wkearney99]

This talk of magnetic interference.. makes me glad to have switched to an up-mast satellite compass unit for heading and position data.

 

[GoneFarrell]

I'll stick with the chunk of magnetite I got floating on oil in a wood bowl. Worked for the Vikings!

Gal's 100 watt ham radio amp would turn on the stern thruster on my boat when she keyed Morse code.

 

[DDW]

I did the dockside commission of an autopilot while side tied to a dock that turned out to have steel pipe floats. The compass error was about 40 degrees.

 

[diver dave]

I’m sure most of u know this, but ur mobile phone with its built in flux sensor is a splendid tool for tracking down these magnetic gremlins.
Really handy for surveying a spot on the dash for a mag compass.

 

[Alisske]

Glad it did not end badly. Another “What the hell!?!” Another Fact to add to the boating rolodex.

I had a similar issues with AP delivering a boat. I was in georgia ICW. No no one around, single handed, nice cool morning, having coffee. Had to take a dump, ran down to head, threw pants down, then the boat went hard to starboard!

Clinched my cheeks, ran up to helm holding pants up, boat corrected its course. All clear. Let my blood pressure drop, then went back down to head.

Sure enough, SAME THING HAPPENED!!! It was a cold morning so I had pants on with a metal big belt buckle. When i threw down my pants, the buckle landed on the flux compass. (I was not that familiar with boat and did not notice it’s location). Probably not the best place

Glad it worked out for you

 

[diver dave]

Glad it did not end badly. Another “What the hell!?!” Another Fact to add to the boating rolodex.



I had a similar issues with AP delivering a boat. I was in georgia ICW. No no one around, single handed, nice cool morning, having coffee. Had to take a dump, ran down to head, threw pants down, then the boat went hard to starboard!



Clinched my cheeks, ran up to helm holding pants up, boat corrected its course. All clear. Let my blood pressure drop, then went back down to head.



Sure enough, SAME THING HAPPENED!!! It was a cold morning so I had pants on with a metal big belt buckle. When i threw down my pants, the buckle landed on the flux compass. (I was not that familiar with boat and did not notice it’s location). Probably not the best place



Glad it worked out for you

Well shoot. Every mariner knows not to wear iron buckles. Brass! [emoji851]

 

[GoneFarrell]

I’m sure most of u know this, but ur mobile phone with its built in flux sensor is a splendid tool for tracking down these magnetic gremlins.
Really handy for surveying a spot on the dash for a mag compass.

Thanks, did not know that. Will wave that around on the boat!

 

[Cheechako]

I’m sure most of u know this, but ur mobile phone with its built in flux sensor is a splendid tool for tracking down these magnetic gremlins.
Really handy for surveying a spot on the dash for a mag compass.

Could you explain how to use a phone to survey for magnetic interference? Are your referring to using the Compass app built into most phones and watching for deviations as you move it about in the cabin?

 

[diver dave]

You can either look at the built in compass. Or, download any of a number of gaussmeter apps, Most are free or 99 cents.

 

[toocoys]

I'm really interested in hearing how you run auto-pilot in the ditch. Not sure what the ACW is like, but the ICW here on the Texas coast is rather narrow, bendy/turny, and full of traffic. Of course I have no auto-pilot, but I have navigated our ICW from Galveston to Port Arthur, and I would think AP would be dangerous.

And I really am interested in hearing about it, that wasn't mean to be a dismissive type of post, just in case it comes across that way.

 

[diver dave]

Places like Mosquito Lagoon and almost the entire length of the Indian River are a mile or so wide. And little depth change over that mile. Of course, there are other areas, like the ditch in Boca Raton, and most of Broward county, where it is a dig, and is narrow. Huge diversity here in FL on width and driving “precision” required.

 

[FoxtrotCharlie]

I'm really interested in hearing how you run auto-pilot in the ditch. Not sure what the ACW is like, but the ICW here on the Texas coast is rather narrow, bendy/turny, and full of traffic. Of course I have no auto-pilot, but I have navigated our ICW from Galveston to Port Arthur, and I would think AP would be dangerous.

And I really am interested in hearing about it, that wasn't mean to be a dismissive type of post, just in case it comes across that way.

We primarily use the 'heading hold' function on our autopilot while on the rivers or ICW - very easy to set, &/or put on standby for turns/curves.

 

[toocoys]

Places like Mosquito Lagoon and almost the entire length of the Indian River are a mile or so wide.

Ah! I've only experienced the ICW on the Texas and Louisiana coasts, so when I think about the ICW I only think about that 125 foot width. But I guess I can see where it could be used. Especially in places like Galveston Bay that are wide open and only marked by channel markers. I don't ever think about it being open like that because I've never gone west, only east.

 

[Unclematt]

After I read post this I experimented by going through a bridge on AP. About 1/2 way through the boat took a solid right hand turn. I always hand steer whenever I am in narrow areas or close quarters.

 

[diver dave]

Easy fix. [emoji41]

https://www.sperrymarine.com/navigat-2500-gyro-compass

We are not using true heading sensors. We are using magnetic field sensors.

 

[DCDC]

Have not had AP interference issues but a low oil pressure alarm sounds every time the microwave is powered from the inverter.

Alarm is from a gearbox oil pressure transmitter.

 

[psneeld]

It must depend on things I can't guess to be important from outside the boat. Internal appliances and wiring are more predictable


I have used AP through bridges with no problem.(if I had a reaction, I think it was high voltage lines more than the steel). I also use it though long narrow canals/ICW waterways where I sit back and change heading a few degrees at a time with the remote. So most of the other ICW parts are easy to use it except the narrow, shallow parts that are full of sharp turns.


Occasionally it has gone wacky on me, sometimes because a connection has loosened or maybe overheating the computer part (sun beating in a bad way). My one radio if I transmit more than 5-10 seconds, the AP starts a turn. But none of these unexpected turns at 6.3 knots....are really a nail biter.

 

[Jeff F]

I’m sure most of u know this, but ur mobile phone with its built in flux sensor is a splendid tool for tracking down these magnetic gremlins.
Really handy for surveying a spot on the dash for a mag compass.

Good idea. I mounted a heading sensor in my new boat and after relocating it twice finally figured out the interference was related to inverter use, and hence highly variable.

So you'd place the phone in a proposed mounting location and then monitor while cycling through onboard electrical systems? Could have saved me some minor grief.

 

[diver dave]

Remember the kids science experiment that used a battery, coil of wire, a nail, and some iron dust. We noticed that adding the nail to the middle of the coil seemed to increase the power of the magnet.

As we proceed under the bridge, the large steel span, or the tons of steel rebar in a fixed bridge, all are diverting the earth’s magnetic field; actually changing the perceived north pole to be in a different direction.

 

[Jeff F]

Easy fix. [emoji41]

https://www.sperrymarine.com/navigat-2500-gyro-compass

We are not using true heading sensors. We are using magnetic field sensors.

These days we're using magnetic plus acceleration plus satellite, which when combined with some good software can provide remarkable and reliable performance.

My bad experiences have all been with old simple fluxgate compasses and 20+ year old AP systems. I doubt that a modern AP would suddenly turn the boat due to a brief flux change, because the other sensors would indicate that the course hadn't changed.

 

[psneeld]

Remember the kids science experiment that used a battery, coil of wire, a nail, and some iron dust. We noticed that adding the nail to the middle of the coil seemed to increase the power of the magnet.

As we proceed under the bridge, the large steel span, or the tons of steel rebar in a fixed bridge, all are diverting the earth’s magnetic field; actually changing the perceived north pole to be in a different direction.

In my experience with many different boats..is it is the rarity that it affects APs than the rule...maybe I am just lucky.


or......



I know the theory...but there isn't current in the rebar and it isn't all aligned the same way.... so has anyone seen an article published about compasses and bridges? I have had a few but again after many transits of the ICW, I have never thought it much of an issue.


While I am always prepared for an AP failure or inadvertent turn...it's not something I worry about at slower hull speeds. Unless in heavy traffic...and I don't mean ports, I mean lot's of small crazies zooming under bridges or in canals while I am.

 

[diver dave]

No electrical current is necessary in a piece of iron to deflect the earths natural field.

Putting a mag compass in a steel vessel normally requires some pretty healthy compensating magnets to reduce deviation. Just due to the hull. Now, adding high dc current appliances just adds to that.

 

[L Erie Tugger]

Several years ago a friend of ours was going north on the St. Clair River running on autopilot. He went down for a quick lunch (bad idea anytime you're in restricted waterways) while passing the large Detroit Edison power plant. Before he realized what was happening the boat rammed the unloading dock with considerable damage both to the boat and to him when thrown into the bulkhead.

We use our autopilot actively when running the canals (Erie, Trent, Rideau) and use a handheld remote to maintain position. It works very well and lets you get a bit back from the wheel in a more relaxed position.