What class is your vessel under? Can you quote/give more detail on this class rule? If they have now revised the rules, I am positive that they have, sound & valid reason.

Hi, refer to IMO MSC/Circ.645(6 June 1994) Annex Page7 Item 3.2.4, it says "Bustie breakers should be open during equipment class 3 operations unless equivalent integrity of power operation can be accepted according to 3.1.3"

Thank you. That is what I wanted to know. Let me look-up.

http://www.imca-int.com/documents/divisions/marine/docs/IMCAM113.pdf

This is in order to provide better redundant distribution of power. Also it will help to discuss same with your Class surveyor, during his next visit to your vessel.

Hi, this is not real vessel. We are under concept design period, we want to know the difference between an open bustie and a close bustie during DP. I have all the rules we need, but I just want to know in what aspect, this will influence our design.

Please see DNV Rules for classification of ships, Special equipments & systems, Additional class, Part 6, Chapter 7, PP-19, here:

http://doc.baidu.com/view/159a345d3b3567ec102d8ad7.html

Addendum: The required info. is in Section 5- PP-19, of Part 6, Chapter 7

"When the system is designed to operatedwith closed bus-tie breaker in DP mode, this breaker shall be acircuit breaker capable of breaking the maximum short circuitcurrent in the system, and which is selective in relation to gen-erator breakers to avoid total loss of main power (black-out) "

Is this the only difference?

Well you have three classes which divide the designs by robustness of DP system which would depend on the critical nature of use....The system has more redundancy as the class distinction increases, ie; should one component fail the bus-tie opens automatically and isolates the failed system to safeguard the redundant system/s....should one water tight compartment fail the components in that compartment should have redundancy in another water tight compartment, and so on....Each of these requirements is dictated by the class of your vessel, which is dictated by the critical nature of the positioning system...

Check the publication here for free download that deals with the specifics of power redundancy schemes for your class of vessel...

http://www.imca-int.com/documents/publications.html

Also please go into what is available here for a better understanding of the subject:

http://www.google.co.in/#hl=en&output=search&sclient=psy-ab&q=closed+bus+tie&oq=Closed+Bustie&gs_l=hp.1.0.0i13i30.42331.42331.0.46974.1.1.0.0.0.0.345.345.3-1.1.0.les%3B..0.0...1c.1j2.zE_ip5frt0k&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=1d90548ed80c812d&biw=972&bih=476

This is comparison between bus tie & ring bus:

http://www.google.co.in/#hl=en&sclient=psy-ab&q=compare+ring+bus++with+bus+tie+&oq=compare+ring+bus++with+bus+tie+&gs_l=serp.3...0.0.3.3548.0.0.0.0.0.0.0.0..0.0.les%3B..0.0...1c.1.1HTbknYj4-Y&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=1d90548ed80c812d&biw=972&bih=476