Ship stability after redesign

[jimmymc90]

I know this is probably a simple question for most of you but I would appriciate any help.
As part of a college project I have redesigned a ro-ro ferry to comply with MARPOL Annex 1 regulation 12a. This hos been done by reducing the height of the six double bottom tanks by 1.17m and the space where the reduction has taken place is now a void space double bottom. The added steel is roughly 50 tonnes and the reduction in fuel capacity is 300 Tonnes.

Im now working on calculating the ships stability. What im unsure of is how the draft of the ship will be effected by this redesign. The draft before was 5.5m.
Also any suggestions on how the ships, deadweight, lightweight etc and ships stabilty will be affected would be greatly appreciated.

cheers,
James

[Ad Hoc]

James

I assume you ahve the orginal data to begin with? (Otherwise how can you change it?)

If you know what the draft is of the parent hull, do you also have its displacement?...if so, then all you do is a simple "weights on" and "weights off" table. And compare displacement before and after.

If you don't have the hydrostatics, you can 'guesstimate' by the simple TPC of the hull.

[jimmymc90]

Ad Hoc

I have the parent ships desplacement and am in the process of getting a copy of the ships hydrostatic data. Would it just be a case of doing a break down of the ships displacement then reading the corresponding draft of the hydrostatic tables? also is the ships displacement calculated for when the ship is carrying cargo, fuel, water etc or is the displacement calculated it its unloaded condition?

[Ad Hoc]

Originally Posted by jimmymc90

Would it just be a case of doing a break down of the ships displacement then reading the corresponding draft of the hydrostatic tables?

Yes. But not displacement, weight.

You do a weight breakdown, of "on's" and "off's" then read off on the hydro tables what the draft is, at the corresponding displacement, for that new calculated full load weight. The weight = the displacement from hydro tables of course.

[jimmymc90]

That makes a bit more sense now, cheers for your help Ad Hoc