# Those round things in ships' bridge windows

**URL:** <https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790>\
**Category:** Factual Questions\
**Created:** [May 28, 2001, 5:57pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790 "2001-05-28T17:57:34Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\
**Post date:** [May 28, 2001, 5:57pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790/1 "2001-05-28T17:57:34Z")

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On most large ships and many large boats I’ve noticed a round transparent disc about a foot across in the front bridge window. I seem to remember seeing a vertical radius in them. What is this? I assume it is some sort of navigation device whereby an object’s position can be identified as so-many degrees off of the bow. Is that right? What is it called?

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**Author:** ![Rayne\_Man](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Rayne\_Man](https://boards.straightdope.com/u/Rayne_Man)\
**Post date:** [May 28, 2001, 6:11pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790/2 "2001-05-28T18:11:52Z")

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On some ships that disk is a type of windscreen(shield) wiper. What happens is that the disk spins at high speed and throws all the water off. Thus the crew on the bridge always have an clear area to look through even in very heavy rain or spray

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**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\
**Post date:** [May 28, 2001, 6:31pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790/3 "2001-05-28T18:31:03Z")

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[Here’s](http://www.speich.com/clear-view-screens.htm) a picture of one for those who are curious.

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<div class="post-metadata">

**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\
**Post date:** [May 28, 2001, 6:31pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790/4 "2001-05-28T18:31:50Z")

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That makes sense. They have the same sort of thing for movie cameras.

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**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\
**Post date:** [May 28, 2001, 7:43pm UTC](https://boards.straightdope.com/t/those-round-things-in-ships-bridge-windows/66790/5 "2001-05-28T19:43:55Z")

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The same things are used on the enclosures of some high-speed production milling machines, so the operator can see what’s going on through the “rainstorm” of coolant.