Portable Second Deck Design

Dear friends
i know my question is not about boat design but i like to use experience of good naval architects of this forum.
i want to design a portable second deck for a ship which i have attached it's midship section. please give me an idea or necessary class requirements about this issue.
ship particulars
L=55
B=9.5
H=5.34

kind regards

 

The various class societies will differ somewhat in their approach, but your best shot is to get the rules of the particular society with which this vessel will be classed. There should be a section in these class rules about sizing the scantlings for portable hatch covers (below deck) or portable hatch beams. These rules should be located in the section covering hull scantlings, unless there is a special section or guide devoted to hatch covers.

It basically comes down to this: With the portable cover loaded to the design spec, make sure the stress in the cover beams is below allowable, and use some type of stiffening bar around the edge of the cover to keep it from deflecting when the cover is removed, opened, or closed. If the cover is designed to be lifted, you need to check the stresses to make sure the cover is not overloaded by its own weight when suspended.

There may be other loading and design considerations, like the loadings from wheeled vehicles running around on the cover.

 

that would actually stiffen the hull when it is in place. biggest issue I can see is the loading might affect the stability, so cargo would have to be scheduled to place heavier cargo down below, and lighter cargo above to keep CG at an acceptable height.

 

is there some special fittings to keep the moveable deck in it's position?
if i weld a fixed support in cargo hold then i will have some problems with bulk cargoes in the bags.

 

It's not clear what you are talking about. The portable decks provide extra deck area onto which to load cargo in the hold. The strength calculation of the vessel does not consider the use of portable hatch beams or portable decks as strength members since they generally lack effective shear connection to the rest of the hull. The hole in the deck is still there; the portable deck just keeps the crew and cargo from falling thru it into the lower hold.

All hatch beams and portable decks are designed with a certain maximum loading which can be carried on them. Class societies are very careful about this, which is why they have a section in the rules governing the design of hatch covers in general, and hatch beams and portable decks in particular. These maximum loadings will be noted in the vessel's stability documents, to allow the crew to properly plan the cargo stowage.

 

Portable hatch beams are generally designed to be lifted out of the hold and placed out of the way to facilitate cargo loading, and once loading of the lower hold is completed, then they are lifted back into place. The same can hold true for a portable deck, but some ships with particularly large openings may use portable decks which are composed of articulated sections which can be opened up accordion-style.

Because of the danger of performing hot work in a hold filled with potentially flammable vapor or dust, welding of the beams or portable decks closed is generally not recommended.

The portable hatch beams and portable cargo decks may be secured by a variety of means. Check a supplier like Macgregor for details:

http://www.cargotec.com/en-global/macgregor/hatch-covers/Pages/default.aspx

 

You should pay for this technical advice