RIN Blog
Blog Home All Blogs

Reverse Polarity in Compasses

Posted By Administration, 04 July 2018

Reverse Polarity in Compasses

Author: Nigel Williams

Reverse polarity is where the magnetism in the compass needle becomes permanently reversed such that the red end of the needle points south instead of north. This is different to the magnetic needle being temporarily deviated a little when near a metal object or weak magnet and correcting itself as soon as it is moved away. It can affect any brand of compass.

Working in the military and outdoor industry for 40 years, I had never come across a reversed polarity compass until about 10 years ago. Since then I have personally seen about 40 and heard of many more cases, at least 2 of which ended in a mountain rescue call out for competent navigators. This problem is unlikely to be caused by proximity to ordinary metal, a penknife for instance (how would the military survive with all their armoured vehicles and weaponry?). I have a box of about 20 assorted compasses all mixed together, they are strongly affected by each others magnetic needle yet once separated they have never reversed as their magnetism is actually quite weak. So what is going on?

Could it be batteries? Many of us will have had normal batteries in a head torch or GPS for instance adjacent to our compass in the rucksack over many years without effect. Pass these items by your compass, it hardly affects the needle, in fact less affect than another compass would. So that does not explain the sudden increase of incidents. Mobile phone batteries are different being rechargeable, but remove it from your phone and put it by your compass, it has little or no affect, now try the mobile phone without the battery - it has a strong affect from a magnet in the speaker system. This also illustrates that whether the phone is switched on or off is irrelevant.

Mountain rescuers and sea kayakers carry radios with a speaker with a strong magnet in it which will cause a change in polarity if left rubbing together in a rucksack or kayak hatch regardless of whether switched on or having a battery in. For a sea kayaker in poor visibility this could be a very serious situation as they may have no other features to support their navigation decisions in sea fog. Walky talky devices will do the same thing (I used one recently in the field to correct a reversed polarity compass by stroking the speaker area of it along the needle). Most digital cameras also now have a speaker in.

The guilty culprit seems to be anything with a speaker in it. Additionally, some phone cases have a small magnet in that puts the phone into a hibernate mode, that too will change needle polarity. An experiment of stroking one of these devices on a compass reversed the polarity after just a few minutes. It is not hard to envisage this happening quite by accident with a phone and compass lying together in the lid of a rucksack or jacket pocket on a days walk.

Outdoor equipment manufacturers have recently been using magnets in belts, chin straps, drinking tube clips for rucksack water containers which keep the tube attached to the front of the sac and fingerless gloves with a fold over mitten piece which is attached out of the way to the back of the hand with a magnet. Potentially a worrying thought if you are compass in hand trying to follow a bearing. Gloves also get stuffed into pockets where a compasses may be.

A conscious effort is required to keep the compass isolated from other gadgets, from phones and radios, to digital cameras, GPS, avalanche transceivers and SPOT devices. Try experimenting with all your devices near your compass so that you are aware of the ones that have a significant affect and keep them apart whether using them or storing them. A challenge for MR personnel with suggestions that transceivers can be affected by phones as well, they are often carrying a phone, a radio, a transceiver and a compass!

Trying to use a reversed walkers compass knowing the white end of the needle is pointing to the north is not really an option. The white end is about 1mm longer than the red end to counter the dip of the north (red end of the needle). Once polarity is reversed, not only is the north end now heavier it is also wanting to dip. This results in the end of the needle brushing against the compass capsule floor and not being stable or reliable.

Consider carrying a simple spare compass or have at least 2 in the party. If alone and you suspect your compass has reversed then compare it with one that you may have on your GPS, phone, or watch, or think of other natural signs such as the expected wind direction or position of the sun.

The magnetism in a compass needle is very small and can be reversed if the needle can be held still by stroking the north pole of a good bar magnet repeatedly along the needle from the intended north to south of the needle.
However, there is no guarantee as to the strength of the re-magnetised needle and how easily it might reverse again. The compass manufacturers will usually rectify the problem if the compass is returned to them.

A reverse polarity compass could have a life threatening consequence; try to treat it as a delicate scientific instrument.

Tags:  Compass  Education  Land Navigation  Navigation On Foot 

Share |
PermalinkComments (0)

Securing Positioning, Navigation & Timing: 14 June 2018 Event Report

Posted By John Pottle, 21 June 2018

The recently published Blackett report “Satellite-Derived Time and Position: A Study of Critical Dependencies” concludes “we must take steps to increase the resilience of our critical services in the event of Global Navigation Satellite System (GNSS) disruption, including by “adopting potential back-up systems where necessary”.

Implementation of the Blackett recommendations is being overseen by a UK Cabinet Office Blackett Review Implementation Team (BRIG). The technical aspects of implementing the recommendations are being led by a Positioning, Navigation and Timing Technical Group (PNTTG), reporting to the BRIG.

Three organisations represented on PNTTG – Innovate UK Knowledge Transfer Network (KTN), Royal Institute of Navigation (RIN) and The General Lighthouse Authorities – hosted a seminar on 14 June 2018 to review user needs and the status of two possible RF back-up options to GNSS mentioned in the London Economics report on the economic impact of a GNSS disruption.

The event attracted strong interest, with more than 100 delegates, including representation from user communities requiring assured and accurate position or time. Presenter organisations included UK Space Agency, RIN, Spirent, Imperial College Institute for Security Science and Technology, Ursanav and Orolia. Nick Lambert of NLA International facilitated and chaired the event.

The status of two possible RF back-up systems was presented and discussed: enhanced Loran (eLoran) by Chuck Schue, CEO Ursanav, and Satellite Time and Location (STL) by John Fischer, CTO Orolia. Orolia also demonstrated a static STL system as a back-up to GNSS, generating considerable interest amongst delegates.

STL, which is operational and undergoing user trials and evaluation at present, uses the existing Iridium global satellite constellation’s paging channel to enable a positioning and timing capability on a global basis. Power levels are 1000x (30dB) higher than GNSS, meaning that use indoors becomes possible. STL is currently being evaluated for provision of precise time to financial and government institutions in USA, UK, Italy and Japan. The system uses a narrow-band signal just above the GNSS L-band frequencies. As the signals are encrypted it is practically impossible to spoof STL. The higher power level also offers potential resiliency advantages to GNSS.

eLoran is a ground-based system for time and position, operating in internationally protected frequency bands. The combination of high power and low frequency enables wider coverage than GNSS including indoors and even limited capability under water. eLoran stations are operational to enable precise time in USA (East Coast) and UK. Positioning from eLoran would require additional stations to be made live, noting however that each ground station offers very broad geographic coverage. As well as the USA and UK, other regions offering or considering eLoran type services include Russia, Asia (4 countries including China), Middle East (3 countries) and Australia.

As well as the possibility to consider back-up systems to GNSS on a discrete basis, Orolia and STL shared a white paper on the benefits of an holistic approach to resilient GNSS. The link is provided below.

The seminar concluded by considering some key questions, including how to set up a single UK point of contact for industry and users to increase awareness, share insights and knowledge, and develop a roadmap towards standards and accreditation for resilient systems. This work is being further considered by the organisers, who will report to the next BRIG and PNTTG meetings. Comments and views are invited, please contact RIN or KTN.


Links to referenced documents:




Tags:  GNSS  Navigation  Resilience  Safety  Trinity House 

Share |
PermalinkComments (0)

On Foot - Navigation or Map Reading?

Posted By Administration, 20 June 2018

On Foot - Navigation or Map Reading?


Author: Nigel Williams


Several articles in the last edition of the magazine raise issues of what, when, how and who should teach basic map and compass navigation skills.

So how are we taught navigation, is there a universal methodology and are those teaching it trained to do so?

The Geography teacher has to get pupils through an exam which usually involves a 1:50 000 scale map, plotting skills, symbols and grid references among other things - in other words, a static map reading process. Those involved with outdoor activities require students to navigate on the move, a completely different set of skills and level of confidence because the outcome of an error will have a direct consequence.

Who gets the pupils first may have an impact on their learning to navigate, which is a good reason to start in primary school. Both British Orienteering and the National Navigation Award Scheme (NNAS) have materials and training to support that. However, there is no formal course within the UK education system where a teacher can learn to teach navigation. As a result, there is no universal UK system to benchmark the process of either teaching or pupil outcomes.

Most user organisations such as schools, youth organisations and outdoor training organisations came into being before the 1970/1980s when British Orienteering developed a simple and successful teaching process. However, orienteering was viewed sceptically by others as not being relevant to their established methods and aims. The wearing of something akin to pyjamas, running and perceived club membership probably enhanced that view.

Understanding contours

Navigation is taught randomly across many organisations in the UK, largely based on an 80-year-old military methodology. The original focus being to teach accurate plotting skills to pin point trenches and gun positions, accuracy of angles and magnetic variation were vital to avert shelling your own side. Prismatic compasses and mils instead of degrees gave a much greater level of accuracy than our current base plate compasses. The methodology was never designed for outdoor recreation and on the move navigation.

Much of the old teaching requires numeracy skills and is designed to enable the communication of information, little of which is relevant to navigation for recreation. When did you last use a grid reference during a walk in the countryside or need to communicate a bearing? We tend to point at the map and then the direction we want to go in. A simple compass needle to set the map when following linear features is generally sufficient.

Numeracy as a starting point for learning the subject can be a barrier for many learners and later in life may impact people’s confidence to get active outdoors. It may also be a reason why people opt for using a GPS/phone, because it appears to get around the perceived complexities that the teaching methodology has thrown at them in the past. We can’t dismiss grid references but as a starting point it is not going to enthuse.

Magnetic variation currently in the UK is less than the stated accuracy of a standard baseplate compass which according to the manufacturers can be up to 2.5 degrees out. It is irrelevant for beginners and simply adds complexity and confusion. Beginners usually plan to follow tracks and paths where dial turning bearings are not required.

In recent years the orienteering map and its availability has become a huge asset in teaching navigation skills and British Orienteering now have around 560 maps from across the UK on their website which can be down loaded, some free, some for a small payment. Availability of these maps are a game changer for every age group and level of learning. The amount of navigation skills learning and practice that can be achieved in a short space of time is far greater than on any other mapping.

Map setting

Instead of learning 1:50 000 symbols by rote in the class room, imagine giving children an orienteering map of the school /local park grounds without the key on it. Then invite them to go and discover what the symbols are - active learning and building map confidence within their known environment.

Orienteering maps don’t have grid numbers on and competitors use compasses without rotating dials or numbers on and they are arguably the best on foot navigators in the world. The teaching process is not numeracy based, it keeps things simple, fun and as practical as possible with a teaching methodology and progressions that are consistent and can be benchmarked nationally.

NNAS uses a similar approach of developing skills with orienteering map scales and exercises. Ultimately the aim is to develop the skills needed to become confident and competent with standard recreation scale maps 1:25 000, 1: 40 000 and 1:50 000 as well as combining a GPS or altimeter if required.

The key things both these organisations embrace is a simple set of progressions written on one side of A4 and tutors are required to be trained to teach the subject, a 1-day course usually meets most tutor needs. This is absent in virtually all the other major organisations involved with navigation or the teaching of it. The NNAS awards are also being accredited on the Scottish Credits and Qualifications Framework endorsing tutor competence and a clear structure to teaching the subject.

If a simple UK navigation teaching methodology were to be established and tutors trained to deliver a similar approach, the benefits could be wide ranging from supporting the health and obesity agenda and reducing Mountain Rescue call outs to benchmarking between the many outdoor qualifications and youth skills awards.

Learning skills with an orienteering scale map provides many learning and feedback opportunities without having to walk long distances. The environment is often less intimidating than being in the hills and therefore also supports the learning process.

Tags:  education  land  Navigation  on foot  orienteering 

Share |
PermalinkComments (0)

Note of meeting of the IMO Maritime Safety Committee MSC99 – 16 to 25 May 2018

Posted By Administration, 05 June 2018

Note of meeting of the IMO Maritime Safety Committee MSC99 – 16 to 25 May 2018

Author: Kim Fisher

This was an 8 day meeting of the Maritime Safety Committee under the chairmanship of Mr Bradley Groves (Australia). The Maritime Safety Committee meets three times in a two year cycle nominally for 5 days but is permitted a longer meeting when the period between meetings exceeds 6 months.

A substantive issue at the meeting concerned a regulatory scoping exercise for the use of Maritime Autonomous Surface Ships (MASS). This was new work which was progressed in a Working Group. A framework was developed including the aim and objective, the preliminary definition of MASS and degrees of autonomy, the list of mandatory regulations to be considered and the applicability in terms of type and size of ships. This will be further developed by a correspondence group for the next meeting.

A further Working Group discussed the issue of safety measures for non-SOLAS ships operating in polar waters as an extension to the Polar Code. This proved to be a difficult topic and will be further discussed at the next meeting. Meanwhile the Sub-committee on Ship Design and Construction (SDC) was tasked with developing recommendatory safety measures for fishing vessels over 24 m in length and pleasure yachts over 300 gross tonnage.

Limited changes to Chapter IV (Radiocommunications) of the International Convention for the Safety of Life at Sea (SOLAS) to replace references to “Inmarsat” by “recognized mobile satellite service” were adopted to enter into force on 1 January 2020. This facilitates the introduction of other satellite operators to provide Global Maritime Distress and Safety System (GMDSS) services. The Iridium system had been proposed for recognition and after some debate this was agreed. Further work on its implementation will be carried out by the International Maritime Satellite Organization (IMSO). An initial application for the BeiDou messaging service to be recognised as a further service was accepted.

New work items were agreed for the Japanese Quasi-Zenith Satellite System (QZSS) to be considered as a future component of the World-Wide Radionavigation System (WWRNS) and for a revision of the guidelines for Vessel Traffic Services.

The workload of the Sub-committee on Navigation Communications and Search and Rescue (NCSR) was discussed as it has been proving difficult to achieve all the work. This resulted in a proposal to extend the length of the meeting from 5 to 8 days for the next two years.

The next meeting of MSC is scheduled to take place from 3 to 7 December 2018. A meeting of the Joint IMO/ITU Experts Group is planned for 3 to 7 September 2018 and a meeting of the ICAO/IMO Joint working group is planned for 17 to 21 September 2018. The meeting of the IMO/IHO Harmonization Group on Data Modelling (HGDM) is planned for 29 October to 2 November 2018. A meeting of NCSR is planned for 16 to 25 January 2019.

Tags:  IMO  Maritime  Report  Safety 

Share |
PermalinkComments (0)
Page 4 of 4
1  |  2  |  3  |  4