Magnetic compass

[Bmarler]

KVH sailcomp still has electronic compasses available. This is similar to the one I have: https://www.marineelectronics.com/products/product/103ac-sailcomp

 

[tpbrady]

I find that the heading sensor with my Raymarine autopilot is very good at displaying the magnetic heading that is usually dead on with COG from the GPS. If I wanted to create a compass deviation card, that is what I would use for calibration. The only time that the GPS and heading sensor don’t agree is when I leave a tool box in the pilot house right over the heading sensor below it, or run into a chart location where a note says possible magnetic disturbances.

Tom

 

[Hippocampus]

Depending upon how you set up your MFD if you set a waypoint the boat should end up at the waypoint. No set will be displayed or occur. Most people use gps determined waypoints and most APs will end up exactly at that waypoint as the electronics continuously compensates for set.
In order to show set you need to set up your AP to follow a compass course , place a waypoint via gps input only along the projected line of the compass course. The distance from the spot on the projected spot and your actual spot is the set.

https://en.wikipedia.org/wiki/Set_and_drift

Note you need two datum. Where you are predicted to go if no set existed and where you end up with set operative. Using one waypoint won’t serve. You need the other as well. Above I offered a simple way to do this with what’s on most peoples boat. It doesn’t matter how you get the two points. Magnetic compass or satellite or gps. One predicted with no set occurring.One with.

 

[psneeld]

What I posted will show set in little or no time...but as set changes often it's just a wasted exercise to calculate it until you need to...just use nav on the AP and enjoy modern nav.

 

[Hippocampus]

Pretty happy with compass in my phone and pad. They go in the oven if there’s an electric storm nearby.

 

[RickyD]

Ensure that the COG is magnetic, not True, to be used to compare with a magnetic compass. Then as mentioned ensure allowance for wind and current as COG will be correct when the compass is affected by a boat crabbing.

I have true north markers in my harbor. I'd probably check declination with that. I also have the Furuno SX20 so I should be able to get my compass close. I have been meaning to swing my compass. I do have the two adjustment magnets. I hate looking at my mag compass and seeing 10 degrees off. It's on the to do list but.....

 

[HeadedToTexas]

Here's some info on electrical circuits and compass deviation.

https://www.wired.com/story/can-your-electronic-gadgets-interfere-with-your-compass/

Outstanding article. Clear and practical. Very nice.

 

[rgano]

From your comments it seems likely the compass and plotter were in place when you bought the boat in which case the PO never bothered with the compass. I like the compass to be as close to the electronic indications of heading as possible because I can imagine the plotter going out on a trip leaving me only the compass to steer by, even if for only a short time. As I usually have paid attention to the plotter's indications, I would know what the compass should read and not end up going around in a circle in the dark.

I have a 1943 US Army Corps of Engineers sun compass designed for tanks in the desert that I take along to generate a real compass deviation table for other boats, but I don't get the impression that you are looking for the sine qua non here.

As mentioned above find that calm day with no currents to speak of. Make sure you know which of the compass' adjusting screws is which (one is N-S and one is E-W). Set the Garmin to read magnetic and not true and the variation to be automatic. Get a good helmsman or a have a very tight autopilot and run N as indicated by the plotter. Adjust the compass with a brass or other non-magnetic screwdriver to read N. Turn and steady up on S as indicated by the plotter. Note how many degrees off S the compass reads and use the adjuster to take out half off that amount. Next, turn N as indicated by the plotter and note the new reading on the compass, hopefully as far off N as you were off of S. Now do the same thing with the E-W adjuster before checking N-S again. When you are as well adjusted as the think you can get (your compass, not your mind), you can make up your own table for as many increments as you like, plotter on one side and compass on the other.

My own small helm compass is typically within 2 degrees of the magnetic reading chart plotter using this method, so I don't bother with a table.

 

[RickyD]

Short story here. I decided to take my 19' ski boat to Catalina Island from Dana Point. That's quite a long ride. But, while I had a handheld GPS, I didn't have a back up mag compass. So, I bought this little stick on compass just in case. I checked it for deviation by raising it up and down over the dashboard and it stayed good. Well I should have checked the batteries in the GPS because once I started I saw the batteries were dying so I turned it off and used the mag compass. Quite some time later, and after I figured to be at Avalon, through the fog I could see the oil platforms in the middle of the channel. I had missed the Island. I turned on the gps, got my mark to Avalon, made 110 degree adjustment and got there ok. Never told my wife who was with me. Of course bought new batteries. So upon arriving home I checked the compass. It was only the last 1/4 inch down to the the dash the deflected the compass. I guess my finger was under it initially.

 

[RT Firefly]

Greetings,


STILL can't post MY pictures!!!! From the net is fine. Just not the ones I take.

 

[rgano]

Short story here. ............... Never told my wife who was with me. Of course bought new batteries. So upon arriving home I checked the compass. It was only the last 1/4 inch down to the the dash the deflected the compass. I guess my finger was under it initially.

Ya know, RickyD, we are not usually persnickety about punctuation here, but a comma can make a lot of difference in a marriage:

"Never told my wife who was with me."

versus

I never told my wife, who was with me.

Actually, I'm now wondering which is correct.

 

[ScottC]

Reminds me of the cute title of a book on punctuation...
https://www.amazon.com/Eats-Shoots-...d=1700422559&sprefix=Eats+shoo,aps,148&sr=8-1

 

[rgano]

Armed pandas! What's next?

 

[RickyD]

Ya know, RickyD, we are not usually persnickety about punctuation here, but a comma can make a lot of difference in a marriage:

"Never told my wife who was with me
versus

I never told my wife, who was with me.

Actually, I'm now wondering which is correct.

Your correction is the correct one. I'm usually one who complains about punctuation. This time I was just typing faster than my brain can work. You see I should have said : My wife was with me but I never told her. I started typing "I never told my wife" But then realized I needed to make it clear she was with me. But then, as you pointed out, I didn't.

 

[rgano]

Your correction is the correct one. I'm usually one who complains about punctuation. This time I was just typing faster than my brain can work. You see I should have said : My wife was with me but I never told her. I started typing "I never told my wife" But then realized I needed to make it clear she was with me. But then, as you pointed out, I didn't.

Thanks for the laugh my wife and I got out of it!

 

[Brooksie]

Had a boat with wiper motor close over compass. Motor was in steel housing but still caused compass to turn when activated although compass was fine when wiper off.
Friend of mine recommended I wrap the motor in Muntz Metal and got me a small sheet of it from, at the time, Carpenter Steel Co. Problem solved.

 

[Endeavor GB 32]

We had a 42 Grand Banks, we were on our first cruise, autopilot steering a course, when my wife turned on the microwave. The boat made an immediate 90 degree turn to port. Never made that mistake again! It was funny after the fact, fortunately...
Be safe out there!
Regards,
Scott

 

[Hippocampus]

Never owned a steel boat. Often wondered about the details of using an old school magnetic compass on them.