The Straight Dope

Go Back   Straight Dope Message Board > Main > General Questions

Reply
 
Thread Tools Display Modes
  #1  
Old 03-25-2004, 07:40 AM
Johnny L.A. Johnny L.A. is offline
Charter Member
 
Join Date: Jan 2000
Location: NoWA
Posts: 48,686
What's a minus tide?

I hear people around here talking about "minus tide", especially as it relates to clamming and oystering. What's a "minus tide"? It seems to be an especially low tide, but what is it "minus" in relation to? Average low tide?
__________________
'Never say "no" to adventure. Always say "yes". Otherwise you'll lead a very dull life.' -- Commander Caractacus Pott, R.N. (Retired)

'Do not act incautiously when confronting a little bald wrinkly smiling man.' -- Lu-Tze
Reply With Quote
Advertisements  
  #2  
Old 03-25-2004, 07:54 AM
pipper pipper is offline
Guest
 
Join Date: Oct 2002
Minus tides refer to low tides that drop below the "Mean Low Water" level. This generally occurs around the full and new moons when the tidal changes are greatest. It's important for mariners because nav charts generally list depths in relation to Mean Low water depths. It's probably important to clammers because it means that seabed that is usually underwater is exposed during these very low tides.
Reply With Quote
  #3  
Old 03-25-2004, 08:31 AM
pipper pipper is offline
Guest
 
Join Date: Oct 2002
Doh... slight correction. Tide levels (including minus tides) and nautical charts are based on a reference point of "Mean Lower Low Water," which is a bit lower than the "Mean Low Water" point. Here's the definition of the two terms:

Mean Low Water (MLW)
The average height of all low water at a reference station over a 19 year cycle.


Mean Lower Low Water (MLLW)
The average height of the low water spring waters over a 19 year cycle. ["Spring waters" refers to spring tides which occur during the full and new moons. Neap tides occur during the first and third quarters of the moon]

Here's a pretty good article explaining tides in general:

http://www.sailnet.com/collections/a...leid=sexton056
Reply With Quote
Reply



Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 09:00 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@chicagoreader.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Publishers - interested in subscribing to the Straight Dope?
Write to: sdsubscriptions@chicagoreader.com.

Copyright 2013 Sun-Times Media, LLC.