Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 03-11-2010, 13:20   #31
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,580
Images: 240
Ship Squat
http://www.pomorci.com/Skole/Stabili...2031,32,33.pdf
__________________

__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 04-11-2010, 14:27   #32
Registered User

Join Date: Feb 2010
Location: Seattle
Boat: Work: Ships/Tugs Play: Grand Banks 36
Posts: 76
When I was sailing tankers on the West Coast, we routinely had to discharge ballast to clear Pinole Shoal in San Pablo Bay (at least 3' UKC, IIRC), then immediately take on ballast to clear the Carquinez Bridge. This took coordination between the bridge team and C/M in the CCR to accomplish. Even then, we had to lower the signal masts and still only cleared the bridge by a few feet. There was only a certain tidal stage this would work so that also added a variable. The pilot was also very careful to make sure the house passed under the highest point of the bridge, but off to the side just enough so as to not take out the lights and/or RACON. On some bridges, these hang quite a few feet below the bridge structure.

Also, I'm pretty sure the QM2 needs to transit The Narrows in NY Harbor at only certain stages of tide so as to clear the Verrazano Bridge. Exciting? Yes. Fairly Routine, though? Yup.

And yes, squat is most definitely taken into account for these types of transits. However, the amount of squat is determined not only by the speed of the vessel, but also greatly by the UKC. Therefore, small vessels are unlikely to see any benefit of taking advantage of squat to reduce their effective mast heights.

Quote:
Originally Posted by Arch Stanton View Post

The "20 inches" figure makes for a good headline but it's misleading: 20 inches isn't the clearance, it's the known margin of error in the draft calculation.
That's a pretty big margin of error. Like David M said, an inch or two is typical. If a calculated draft and actual, observed draft differ by more than three of four inches, something is not right. Twenty inches is enough to exceed bending limits and cause some very bad damage if you're off in the wrong direction. BTW, the same ship I was referring to above would routinely have about 17" of sag after loading in Valdez.

Passenger vessels typically have much more static loads and whatever minor changes in trim or list do occur, they can be corrected with small ballast tanks or fuel transferring, if necessary.
__________________

__________________
Watermann is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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 On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What do I really need on a new 42 foot yacht? anne claydon Monohull Sailboats 28 27-06-2011 02:39
Eight-Foot Draft irwinsailor Monohull Sailboats 21 26-08-2010 22:40
Clipper Cove Reportedly Cleared of Derelicts TaoJones General Sailing Forum 6 31-03-2010 19:16
Want To Buy: 39 to 45 Foot Sailboat NorthernneckLon Classifieds Archive 2 12-01-2010 19:30



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 23:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.