[PSUBS-MAILIST] gyro compass

Tue Jun 28 00:04:19 EDT 2016

Hank,

The compass that you are using looks to be a low end boat compass which typically do not have adjusting magnets installed.  Although it's oil filled there may be an air bubble in it that compresses at depth and causes the compass card to hang up.  

Perhaps an aircraft magnetic compass mounted inside would be of help.  All aircraft must have an aviation magnetic compass by law, and they seem to be all the same whether installed in a Boeing or a Cessna.  My old Stinson 108-2 had the usual example.  It needed to be "swung" annually wherein the plane with all power on was lined up on a compass rose painted on the tarmac and a brass screw driver was used to remove the compass error with the plane pointed on each point on the rose.  There is a published procedure for this task.  The errors could never be completed removed so a compass correction card was filled in and attached to the compass.  The aircraft directional gyro would then be aligned to match the compass prior to departure and also about every half hour as the gyro tended to precess off course.  My old Stinson was steel truss with aluminum skin and it was tricky to swing the compass.  Most aircraft are mostly aluminum so slightly easier.  Note that any charged wire, regardless of being terminated, will affect the overall magnetic deviation.  The aircraft directional gyro is near useless due to precession unless you can reset it from time to time.  Jim, I trust that you would agree with the foregoing.

On a related note, I tried following a heading with my dive compass while operating a Sea Doo DPV and it was way off when the DPV was running.  Pathetic.  As well, diving anywhere near concrete (likely ferro-cement) or steel debris on the bottom would deviate the dive compass.

Quote from http://uboat.net/articles/61.html: On the British Royal Navy submarines of Type A (1903) the magnetic compass was located out of the submarine hull, on the submarines' command bridge. The compass was closed inside impermeable stand. Inside the submarine it was possible to keep the submarine's course by means of telescope. The compass and the telescope were improved by the time, but one problem remains. Classic magnetic compasses were not able for navigation on submarines because of the submarines' magnetic shell effect. Because of that, the magnetic compasses' deviations were too big.

Another form of navigation is by time-speed-distance-terrain following where you navigate by bottom contour at a known speed and accurate chart.  Water currents will throw off your dead reckoning meaning so you will need some way to "take a fix".  Since you may not be able to remain in visual contact with the bottom you will need a decent depth sounder.

Perhaps a dive compass mounted on a pole (an aft fin) behind and above the hull with a video camera instead of the "telescope"?  You could even tow your marker buoy from the aft fin.

I believe that the effect of deviation follows the inverse square law.  That is: if the compass was placed twice as far away from the ferrous material, then that material would then have one quarter of the deviating effect.  My forestry engineer Dad taught me that before taking a bearing in the bush, always take the axe off your belt and put it at least 10 feet away.  I still have his compass and his altimeter.

Vance, what were the solutions that Perry used?

Tim

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of hank pronk via Personal_Submersibles
Sent: Monday, June 27, 2016 2:06 PM
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] gyro compass

Its Aliens, Alan,

I tried it inside the sub and it tries to work but is totally off.  I did squeeze it with the body off to simulate depth and it worked fine in the shop being squeezed.  

Hank

On Monday, June 27, 2016 2:39 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hank,

I think your theory about the UFO is looking good at this stage.

It didn't work at 10ft, that's about 5psi; So have you tried squeezing

it in various places to replicate that? Or what about mounting it

inside the hull on a pole in the center of the dome area, as far

as possible from the hull. If it worked it would eliminate any Alien

influences & indicate that the water pressure was the problem.

Alan

  _____  

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> >
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 
Sent: Monday, June 27, 2016 11:26 PM
Subject: Re: [PSUBS-MAILIST] gyro compass

Alan,

I took my compass apart and it is perfect, it works perfect in my shop etc.  I put it in the lake and it is stuck on N most of the time.  Occasionally it will move. I think there is some mineral interference or an old sunken UFO messing with it.  

Hank

On Monday, June 27, 2016 5:11 AM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hank, 

why would you want a turn & bank indicator above some sought of compass?

There are a multitude of inexpensive underwater compasses that scuba divers use,

although they may be a bit small to be read at a distance. Possibly there is some

issue with the compression of the oil stopping your compass from functioning?

Mounting the compass outside the hull seems to be standard practice & I haven't

heard of any failing. Perhaps someone with previous issues with them could comment.

Alan

  _____  

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> >
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 
Sent: Monday, June 27, 2016 10:37 PM
Subject: Re: [PSUBS-MAILIST] gyro compass

Kieth,

I stand corrected, a turn and bank indicator is just the ticket and tons of them on eBay for cheap.  I was focusing on compass only, but these indicators are much cheaper and more available.  

Thanks' for the tip

Hank

On Sunday, June 26, 2016 6:25 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hi Kieth,

My understanding is the aircraft units are noisy, I assume that is the air units.  They are hard to find in guaranteed working condition for a price that works for me.  If you know of any for a descent price-please let me know.

Hank

On Sunday, June 26, 2016 6:16 PM, k6fee via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Hank, 

Try using a gyro compass ( or atifical horizon) from an aircraft. They sre either air, vaccum or electric  powered.

Keith 

Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Date: 6/26/16 4:11 PM (GMT-08:00) 

To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 

Subject: [PSUBS-MAILIST] gyro compass 

I am going to try to make a gyro compass, looks doable.  I don't care about what direction I am going-I just want to go in a strait line.  I will point the sub in the direction I want to go at the surface, then turn on the gyro and sink.   Then I can just follow the gyro.

Hank

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