Shortcomings of Orienteering (land) compass - SailNet Community
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post #1 of 15 Old 10-15-2010 Thread Starter
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Shortcomings of Orienteering (land) compass

How is a marine hand bearing compass (ie Iris 50) superior to a bearing compasses for land navigation (ie Silva Type 20)? I have a couple of the latter, but am wondering how the marine compasses may be superior.

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Dave
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post #2 of 15 Old 10-15-2010
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Well, first the marine ones usually are designed to float... second, they're designed to be read at eye level while sighting on the target. Third, they're probably better stabilized/damped than the terrestrial ones.

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post #3 of 15 Old 10-15-2010
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The Iris 50 (and the military types of hand bearing compasses) have a prism/lens which simultaneously splits the view: one view is the compass scale (degrees), the other view is the object to which you are looking at.

The Silva type of compasses do not have such a prism (or lens / 'gun-sight' as with the military type compass) with which to 'split' the view, so your eyeball has to alternately 'focus' between the 2 views.

You typically use the Silva type by holding such at some distance from your eyeball (to view the 'pointer'), the prism types are held next-to-the-eyeball and therefore are vastly more 'sensitive' and more accurate.
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While the IRIS 50 does have a prism, it doesn't split the view. It merely allows you to read the compass without having to look down at the compass card.



If you look at the compass, you can clearly see that you can not view through the prism...the outboard end is covered by rubber.

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The Iris 50 (and the military types of hand bearing compasses) have a prism/lens which simultaneously splits the view: one view is the compass scale (degrees), the other view is the object to which you are looking at.

The Silva type of compasses do not have such a prism (or lens / 'gun-sight' as with the military type compass) with which to 'split' the view, so your eyeball has to alternately 'focus' between the 2 views.

You typically use the Silva type by holding such at some distance from your eyeball (to view the 'pointer'), the prism types are held next-to-the-eyeball and therefore are vastly more 'sensitive' and more accurate.

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post #5 of 15 Old 10-15-2010
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SD - correct on all counts, as usual

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Looks like another item to add to my wish list. Now to decide between the Iris, Vion, and W&P.
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In the end tho, will the Silva work? the simple answer is probably yes it will. But it may not be as accurate due to less dampening vs the Iris model(s). or other equal. BUT, I personally feel, if that is all you have, ie a Silva. use it!

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Originally Posted by Hewie View Post
Looks like another item to add to my wish list. Now to decide between the Iris, Vion, and W&P.
Dave
They're basically the same in terms of function. The Iris 50 is the least expensive at about $75 or so. Get it in the Yellow, not the Blue, since if you drop it into the water, the yellow is a lot easier to spot.

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Quote:
Originally Posted by Hewie View Post
Looks like another item to add to my wish list. Now to decide between the Iris, Vion, and W&P.
Dave
I currently use a Plastimo Iris 50 and a Morin, but it is not usable at night any more; it is more stable that the Plastimo. The Morin gets more day time use.

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Quote:
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T Get it in the Yellow, not the Blue, since if you drop it into the water, the yellow is a lot easier to spot.
Damn - I bought the blue one.

I always use the neck strap.

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