Association Forum - Magnets in a Marine Environment

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Magnets in a Marine Environment

New Topic

Topic Locked

Printer Friendly

Author

Topic

waterbaby
Navigator

Member Avatar

USA
168 Posts

Initially Posted - 01/21/2012 : 06:33:46

I'm working on some new curtains for my boat and have been considering alternatives to the original design and hardware. Does anyone know if magnets will corrode in the slightly humid interior of the boat?

1986 TR/SK #5250 Sunshine

Edited by - on

DaveR
Master Marine Consultant

Members Avatar

USA
2015 Posts

Response Posted - 01/21/2012 : 06:54:36

Did a search, They're made from iron and will corrode, but it's easily remedied by cleaning and dipping in epoxy or a rubber dip, etc.

Edited by - on

waterbaby
Navigator

Members Avatar

USA
168 Posts

Response Posted - 01/21/2012 : 08:14:08

Duh. Thanks Dave, I should have done that search myself. Maybe I'll just use snaps... I don't know anything about epoxy or rubber. I just thought the magnets would be easier to open and close.

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9080 Posts

Response Posted - 01/21/2012 : 08:34:16

I recall some little magnetic "pucks" in the bottom of a shower curtain that I don't recall corroding, although they were certainly in the environment to do so. I suspect they were ceramic-based, and maybe coated with something. (A little polyurethane spray might do the trick.)

Edited by - on

Steve Milby
Past Commodore

Members Avatar

USA
5902 Posts

Response Posted - 01/21/2012 : 09:05:49

Velcro works well for that purpose.

Edited by - on

Prospector
Master Marine Consultant

Members Avatar

Canada
3159 Posts

Response Posted - 01/21/2012 : 10:30:11

How close will te magnets and steel plates be to your compass?

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5376 Posts

Response Posted - 01/21/2012 : 18:30:09

Chris - good point. Any time you add any steel objects or permanent magnets (e.g.: loudpeakers) to your boat you will distort your compass' magnetic deviation.

Each season when I recommission Passage, one of my on-the-water rituals is to re-orient my compass using my GPS. I sail North (000M) for some period of time, the sail South (180M) and tweak the N-S setscrew, then sail West (270M) and East (090M) and tweak the other one. I repeat N-S and W-E.

There are several charted natural ranges that I can use to double-check the calibration around Milford Harbor. These consist of daymarks or breakwaters in the foreground with smokestacks, steeples or large buildings behind.

Edited by - on

Ryan L
Navigator

Members Avatar

USA
230 Posts

Response Posted - 01/22/2012 : 00:05:07

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 Chris - good point. Any time you add any steel objects or permanent magnets (e.g.: loudpeakers) to your boat you will distort your compass' magnetic deviation.

Each season when I recommission Passage, one of my on-the-water rituals is to re-orient my compass using my GPS. I sail North (000M) for some period of time, the sail South (180M) and tweak the N-S setscrew, then sail West (270M) and East (090M) and tweak the other one. I repeat N-S and W-E.

There are several charted natural ranges that I can use to double-check the calibration around Milford Harbor. These consist of daymarks or breakwaters in the foreground with smokestacks, steeples or large buildings behind.
<hr height="1" noshade id="quote"></blockquote id="quote">

Heads up to anyone doing this to not confuse magnetic headings with true.

Edited by - on

bigelowp
Master Marine Consultant

Members Avatar

USA
1776 Posts

Response Posted - 01/22/2012 : 06:41:47

Bruce - over the course of an off season how much adjustment does your compass require to be properly calibrated? Intuition tells me very little if any unless a change/addition to closely located electronics/metal objects. That said if significant adjusting is called for this is a good wake up call for at least some of us less so diligent folk.

Edited by - on

waterbaby
Navigator

Members Avatar

USA
168 Posts

Response Posted - 01/22/2012 : 10:18:51

LOL! You've tickled my funny bone! Not your fault to be sure, but still funny from my point of view. IF I had a compass I'd likely place it somewhere in the cockpit cause I doubt on this little boat I doubt we'll be doing much navigating from inside the cabin. I said if because I actually don't own a compass.

The magnets I'm thinking of would be simular to the type Dave B mentions, a simple small puck type and I doubt they would be able to make any signicant difference to a compass unless I put it near my windows, kinda unlikely, at least for me. Now for the really funny part. I've had a very nice garmin sitting in a box in the galley sink for nearly a year. Someday I'm going to get that durned thing installed and figure out how to use it. So far with the advantage of the fact that we are sailing on a river we haven't really needed it, we just try to keep track of whether we turned left or right as we left the marina. I've been known to get lost in my own back yard, but even I can keep track of that.

Someday we hope to sail to Ocracoke and you can bet, I'll be hitting you folks up on how to install a compass and calibrate it with my garmin. Notice there's a lot of 'Someday's in these paragraphs. Sigh...

BTW, here's kinda what I'm thinking of:
http://video.sailrite.com/Thermozite-Window-Panels/youtube.html
I love the idea of getting a little insulation along with my curtains, but I wanted to be able slap them up there and get them down without fussing with snaps, also I think I'll try to finish them a little differently so that they look more like curtains and less like window wrappers. :)

Edited by - on

Steve Milby
Past Commodore

Members Avatar

USA
5902 Posts

Response Posted - 01/22/2012 : 11:09:44

Thanks for the tip on Thermozite, Andre. The heat coming through my portlights works the AC much too hard in midsummer, and Thermozite covers should reduce the heat and make it much more comfortable, whether in the slip or on the hook. Of course, this does mean I'll have still another project for this spring. Darn!

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9080 Posts

Response Posted - 01/22/2012 : 12:33:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 Each season when I recommission Passage, one of my on-the-water rituals is to re-orient my compass using my GPS. I sail North (000M) for some period of time, the sail South (180M) and tweak the N-S setscrew, then sail West (270M) and East (090M) and tweak the other one. I repeat N-S and W-E.<hr height="1" noshade id="quote"></blockquote id="quote">Bruce: Just a thought... This might be easier motoring rather than sailing. Under sail, your bow (and compass) are not pointed exactly in the direction you are actually traveling (GPS), due to leeway. And the slower you go, the more leeway you have. Your tidal currents can similarly complicate things, especially going north and south. (They drove me crazy around here--trying to fill and empty your Long Island Sound twice a day!)

Edited by - Stinkpotter on 01/22/2012 12:40:49

Voyager
Master Marine Consultant

Members Avatar

USA
5376 Posts

Response Posted - 01/22/2012 : 13:23:11

Ryan,
Thanks for pointing out about magnetic versus true. Magnetic variation in most of the US (except for a north-south trending line running through parts of Florida, Atlanta, Ohio and central Ontario) is non-zero, meaning that your compass reading will be "incorrect", or rather must be corrected by up to 20 degrees variation one way or the other to arrive at "true" direction.

Handy thing is that variation is listed on charts of your area. In LI Sound where I sail, the variation is about -15 degrees. So when my compass points 000M or north, I'm really heading toward 345 true, or a little to the west of north. When I sail easterly towards Old Saybrook from Milford, once I clear the headlands of Woodmont, I generally set my compass for 065M which puts me on a course for Falkner's Island, passing Long Sand Shoal. See NOAA chart 12372.

Including me, many sailors use magnetic for all course piloting including using setting their GPS for Magnetic (you'll find that in the setup menu). The other school of thought is to use True for everything, and make corrections for your compass' variation. Some in this camp do not use a compass at all, except as a backup when electronics fail.

Karen, my compass is mounted on the port bulkhead, which is about 30" from where one of the puck magnets you described would be. This will affect my magnetic deviation (vs variation) by a few degrees on certain headings. Trick about deviation is it is devious - not consistent from heading to heading.

Getting to Peter's question, I recently installed a new VHF radio and it changed my deviation. Same time, I added new speakers for my radio/CD/MP3 player, so had to tweak the compass adjustments by approx 1/2 a turn. As mentioned, it requires successive approximations on several north/south and east/west passes, so the exact amount of rotation is not easy to say. Suffice it to say, if you rely on compass readings primarily with a GPS backup, any time you move metal around inside your cabin (pots & pans, new stove, heater, speakers, new radio, etc), you should at least check your compass' deviation on several known GPS courses.

Many people who rely on their compasses do not adjust them themselves, only note the deviation and variation on several headings. Professionals can be hired to come to your boat to make the required adjustments. Like a piano tuner, you can let them do the precision work.

Dave Bristle's comment about motoring vs sailing is good advice, that's why I usually perform the tweaks in several passes and use my GPS as well as ranges to set the compass. Current around Milford is at most 1 knot, while in the Mystic area, 2-3 knots are common.

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9080 Posts

Response Posted - 01/22/2012 : 19:25:48

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 ...Current around Milford is at most 1 knot...<hr height="1" noshade id="quote"></blockquote id="quote">If it is running at one knot and you are sailing or motoring perpendicularly to it at 5 knots, you're course is affected by 9 degrees.

Edited by - on

redviking
Master Marine Consultant

Members Avatar

USA
1771 Posts

Response Posted - 01/23/2012 : 08:07:11

OK, I am befuddled... While I too have played with my compass, it was the worst idea I ever had. I had to hire a true compass adjuster to fix it properly. There is a lot to it and once it is done, why do you need to do it every year? There is not a lot of stray magnetic fields on a C25, bigger yachts, sure. Electronics play a big part. Guess where most plotters are mounted? Right next to the compass. SO, when they do this stuff to correct the idiot who knew about adjustment screws, but tried anyway, they have you run with all your stuff going, including the engine, inverter if applicable, radar - ditto, and whatever else might cause a deviation. Not an adjustment for the faint of heart....

sten

Edited by - on

waterbaby
Navigator

Members Avatar

USA
168 Posts

Response Posted - 01/23/2012 : 19:40:00

Bruce,
Thank you for so patiently and kindly trying educate me on what is clearly a very complicated topic. When it comes time to install the compass I'll at least know it's not as straight forward as it migh seem. Forgive me if for now I bury my head in the sand and try to pretend I didn't see any of this. It sounds so very complicated, and it's making my head hurt.

Edited by - on

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.