Prismatic Compass's

[ranger]

Not that I can afford one right (but it is on my wants list), but I was wondering if any of you have or have ever used Prismatic Compass's and can comment on their ease of use. I know a good one will cost approx £200, but so does a GPS and at least this won't let you down due to battery failure.

SIRS Navigation Ltd do one, the G150

http://www.sirs.co.uk/G150 Marching Compass.htm

There is also the M-73 by Pyser - SGI Ltd

http://www.pyser-sgi.com/products/4.htm

Lastly, there is the SILVA Mark IV

http://www.silva.se/outdoor/index.htm

Can any of you comment on any of these? I have read the review of the Traser one on this site, but don't like the look of it.

 

[johnboy]

Hi,

Prismatic compasses if they are well made are an excellent bit of kit.

If you buy one ensure that it's in Degrees. The militray use MILS which is fine if you want to super accuracy to shoot rockets at people. But is a little fussy when you are trying to follow a bearing at night.

If you plan on walking on lots of set bearings, taking lots of super accurate sightings then they are superb. I have found however that translation of bearings from the map or vice versa is difficult. (but not impossible) and you end up using a plastic roamer for accurate grid referances. Hence the popularity of all of the SILVA base plate compasses.

A SILVA type 4 or SUNNTO RA69 with a built in roamers and fairly instinctive method of taking bearings from the map to ground and ground to map. Will be sufficent for all navigation needs in a temperate climate. If you are heading off to Desert or Arctic conditions then a sighting compass could possibly be useful it depends what you are doing when you get there.

Then there is the cost. £200.00 for a decent prismatic and about £20.00 for a excellent Base plate compass.

Prismatics are: heavier, require looking after, cost more. Using one you will stand out from the crowd that's for sure.

It's a classic example of form over function Prismatics look great.
SILVA types work better.

If you are dead set on a Prismatic I'd advise you buy the following book.

The Manual of Map Reading. Available from HMSO. It's the MOD map reading course and covers Prismatic compasses in detail. As well as sun compasses, interpreting Air photos.

Interesting however that the largest section of this excellent manual is given over to navigation with a SILVA type compass.

It beats me why anybody with decent navigation skills would need to use a GPS in the UK???? With a relevent OS map and working compass and basic navigation skills you should be fine.

cheers

John

 

[Jon]

I have to agree with Johnboy in that the Silva type compasses are far more practical for 99% of map work. The other name they are known as is a "protractor Compass". They work as a protractor and as a compass. To apply the readings from a sighting compass to your map you would need another piece of kit, a protractor.

If you really need the accuracy of a sighting compass take a look at the Silva Expedition 54. It is a normal baseplate compass but has a fancy little viewing system built in that allows very accurate sightings to be taken when you need to. The quoted accuracy is +/- 0.5 of a degree. I think that is the same as the claims for sighting compasses.

You get the best of both worlds and the Expedition 54 will set you back about £60. But if you don't need the very accurate sightings go for the Silva Expedition 4, about £20, its been around for years and is very respected.

Hope this helps

Jon.

 

[ChrisKavanaugh]

A few observations might help your decision. One degree of error in a compass reading works out to 92 feet per mile. I found this bit of information in THE 2 OZ. BACKPACKER by Robert S.Wood, Ten Speed Press www.tenspeed.com This is a marvelous little book with great tips ( and a few points to disagree with.) The finest tools of navigation are complemented with a developed sense of direction and landmarks through observation. In unfamiliar country we quickly create a "mental template" of our new surroundings, ie. The first time tourist to Paris recognises the Eiffel Tower and the direction and side of the river he/she is on. The compass must always be trusted. People get disoriented and decide it is broken or affected somehow. As an example: I live a short walk from a freeway that can take me south to San Diego or North to San Francisco. The signs even refer to the freeway as south bound/northbound. Yet my stretch actually follows the coast on a East/West axis!

 

[gurushaun]

I can thouroughly recommend the Silva type 54, I've had one for over 12 years and its never let me down once, back bearings become a piece of cake as both bearings appear in the Window as you take a sighted bearing. A light, robust, accurate piece of kit at a fraction of the price of an equivalent prismatic...no contest :-D .

Cheers

Shaun

 

[sargey]

i was trying to find a picture of my old trusty recta DP10, it's the matchbox style compass with prismatic system, clinometer and a mirror with luminous aiming marks. because it has a see-through capsule like a baseplate compass it an also be used as a protractor. although not quite as easy as a real baseplate compass. it is/was the issue swiss army compass.

cheers, and.

 

[ranger]

Thanks for all the feedback, looks like I'll be better of sticking with my trusty SILVA compass.

 

[Nod]

Try E-bay, I've seen the British Army Prismatic compasses on there for about £30. Couldn't vouch for their condition though so you'd have to take a gamble that it was in full working order.