Hydrostatic Curves of ship

Hey friends,

I want to write scientific article about hydrostatic curves extrapolation. Many times it can not be done by simply generation of regression line (it can be for small intervals like 0.1m, situation becomes complex once there is a need to extrapolate for larger draught interval like 1m ), for this purpose i would like train MLP with hydrostatic curves of other vessels, especially focusing on LCF, LCB, MTcm and many more. Once MLP is trained with hydrostatic curves of the ship then it could predict the missing parts of hydrostatic curves for other ships.

Does anyone can share with me with some hydrostatic curves of ships? especially with bulk carriers or tankers, it could be good to deal with ship with Cb between 0.65 - 0.80.

With best regards.

 

What do you mean by missing parts of hydrostatic curves?

 

It means that for my vessel hydrostatic curves are prepared from draught from 4.00 m up to 10.00 m. So hydrostatics are missing from draught 0m up to 4 m.
So if I dont have body lines plan maybe then MLP methods may estimate hydrostatic parameters.
But for that i need some data to train with.

 

Draught 0 would be drydock. Most likely under 4 m the vessel would have no stability and capsize. However, without the body lines, how can you calculate the curves? There are infinite possible shapes.

 

Multilayer perception method may estimate hydrostatic curves based on similiar hydrostatic curves of the ships, esspecialy in case of missing data.

 

What gonzo said.

The concept, while having mathematical plausibility, is in and of itself unuseful. By the time a $40 million panamax bulker is all said and done; designed, classed, built, and insured; there are no missing hydrostatic curves. Those needed are required just for the ship to become operational. It is far more useful to select a specific vessel to compare to rather than polish the data from a sh*t-ton of unsimiliar vessels. Futhermore, modern block design and construction concepts already sorts the majority of a specific type of commerical vessel into distinct "family trees", each vessel only having small perturbations from those before and those after. (Reallistically, all the worlds commerical ship design only needa handful of design offices; who, in todays economic market, are going to reuse (honestly or not) successful design/build schemes).

What would, and has been, useful, would be the ability of a data base to flag "similiar" vessels for specific comparison. But even before going there....can you come up with one plasuable reason you would need this information for an already designed and built commericial vessel. (Warships are a whole other ball game where things like this are regularly done).

 

Let's suppose a large ship (a bulk carrier, for example) has to be raised onto the floating dock for one of its five-year inspections. A study of the ship's stability would need to be carried out as the dock rises. Several critical moments arise in this process. One of them is, for example, when the ship's hull begins to rest on the dock supports. But there are other moments that must be studied.
Knowing the hydrostatic properties at drafts less than the dock entry draft is not just convenient, it's essential.

 

Thats the one purpose which justify the need of research, the second one may be with stability assessment when grounding.
Volume of the ship as well displacement may be linearly aproximated - same tendency is observed for many ships, however LCF as well LCB are complex - there is a need for a source data.
What to do if you dont have that data? calculations based on bodylines plan requires software, or engineer to prepare spreadshet including appendages which is not so easy to solve for non engineers. So maybe MLPs trained on the base of similiar hydrostatic curves may solve the problem of extrapolation.

But anyway that a project - without hydrostatic curves there is no possibility even to verify this concept.

 

Yes, that's exactly the same case I was referring to with the floating dock example.
Do you have the body lines plan? I think you said no, but perhaps I can get it. With it, I'll calculate the hydrostatic values. Perhaps if you give us the main dimensions and the type of vessel, we can, as you suggest, obtain more data on a similar hull.
I know it's very difficult, but we're here to see what can be done and how. We already know what can't be done.

 

Can you imagine any ship without a complete set of lines? If a ship is aground, calculations can be done with the existing body plan. There is no need to guess.

 

And that, @gonzo, is it different from what we're saying here?. What do you mean by "complete set of lines"?, because for me, the longitudinal profile and 10 or 12 cross-sections are enough.
Would anyone like to contribute something constructive to this discussion?

 

Yeah, but that is all in the Intact Stability Booklet....an original document (with updates) mandated to be onboard all vessels over 24m by SOLAS (Chapt II-1). And extending that to the damaged case, all updated original Damage Control Booklets and plans are also required by SOLAS, and in some cases MARPOL, to also be onboard.
That only leaves us with two cases: I) the vessel is damaged in such a way that the ISB and DCB onboard originals were destroyed or II) the vessel is so heavily damaged (broke in half anyone?) that the updated originals are no longer relevant.

In Case I the owner/operator can immediatly replace the destroyed documents with shoreside copies ( If there are NO shoreside copies we are into our third critical failure in the chain and no amount of extra data manipulation is going to recover from that, as it begs the barratry question).

In Case II you are going to have to work it up from scratch anyway, just like all the WWII ships docked with extensive damage.

If you look at recent modern cases where ships were damaged (Tanker War, Yemen Attacks, MV RUBY, MAERSK MAGELLAN, etc) you see a trend where nobody wants them. See this article: gCaptain Article: Fire-hit Ships Stuck at Sea for Months as Ports Refuse Entry - Merchants Exchange https://www.pdxmex.com/gcaptain-article-fire-hit-ships-stuck-at-sea-for-months-as-ports-refuse-entry/

 

Frankly, I think you're going off on a tangent. What do SOLAS, MARPOL, COLREG, the West Coast Lighthouse Guide, etc., etc., Yemen Atack .... have to do with the need for complete hydrostatic set of values?. You, I can't think why, suggested they weren't necessary at all, and I think it's now clear that having them is indeed advisable.
The issue is, and let's not beat around the bush, how could we help the OP obtain their complete hydrostatic curves?

 

Many times during operations as an officer on board, the ship’s body line plans are missing, and hydrostatic data is only available for certain draught values, which I will paste below. However, the main question is how to derive the missing data. The idea was to achieve this by training an MLP (Multi-Layer Perceptron) using hydrostatic data from similar ships.

If you take volume as a function of draught, it can be extrapolated using regression in MS Excel with a close fit (R² ≈ 1). However, the shape of the LCF (Longitudinal Center of Flotation) curve is more complex and needs to be modeled using data from similar ships, depending on their draught, and i guees it can be done instead of time consuming calculation based on body lines plan - especially once there are missing or not available on board of the ship

 

Extrapolating is not advisable if you need to perform any "delicate" calculations. I believe the only thing you could do is, given the curves of a similar ship, if the curves in the common areas are similar, perform an affine transformation of the model hull and deduce the curves in the missing draughts.