How to make a GZ curve if you know GM?

The one that is always used, since there is no term of “small angle metacentre” that you have used. Historically it is correctly Transverse metacentric height, but later the “transverse” has been omitted since “GM” has been taken to mean transverse metacentric height. A subtle change in its definition. If one is referring to “initial metacentre” it is understood that one is referring to a vessels initial stability and shall at some time later refer to its large angle stability where such a definition of metacentric height is no longer valid and another is used.

In naval architecture there are many definitions which use the same word to define "something", however, they are sometimes contrary to each other. Thus one must be sure to understand the context of the definition and not cross over into a different condition or discipline.

As noted above, and to that comment. When you actually design a boat and start referring to its “stability” you need to be very clear and very precise what aspect and which definition one is referring to. Each definition is very well understood by the recipient of the stability analysis, whether it be the chief designer, Flag authority or the Master. The context is either added or understood by both, hence just the term being used has only one definition; in said context. Quoting from reference books does not put the definition into context until used. Otherwise you’re just referring to endless different definitions which may or may not explain each other and appear contrary and not know why.

It’s like going into a shop and asking for asparagus. The shop keeper passes you the asparagus, and you complain I wanted sausages. Huh…well “I” always have sausages with my asparagus, so it is obvious “I” wanted sausages not asparagus. Context is everything in definitions.

Thus, unless you have designed and assessed its stability, for various 3rd parties, of a vessel for real your understanding of “stability” shall constantly be at odds with itself and your understanding. Each definition needs context.

 

If it is of any help, I can add that the OP is being judged in Norway with a stability test that adds weights, 5 cm off centre in increasing incriments measuring roll angle along the way. Presumably, the smallest numbers score the highest points.

Paul (OP), would that be correct?

-Tom

 

Guys, this is why it is important to use right (no simplified) definitions. From classic naval architecture, metacentre is centre of curvature of line drawn by centre of buoyancy during inclination.

 

What is the source of the "right" definitions in general?

 

DISCLAIMER: Post below is provided for humor only. I am not endorsing the definition contained in it.

A somewhat bizzare definition of metacentre:

metacentre (plural metacentres)
1.(physics, shipbuilding) A midway point between a ship's centre of buoyancy when upright and its centre of buoyancy when tilted; it must be above the centre of gravity to enable a tilting ship to return to an upright position.

It's in the Wiktionary. http://en.wiktionary.org/wiki/metacentre No idea where it came from. No attribution and no citation. Interestingly the diagram which accompanies the definition is fine.

Clearly Widtionary is no a reliable source for definitions of naval architecture terminology.

 

Approved textbook or reference book on Ship Theory. The ones I used during my studies - Blagoveshensky, Holodilyn 'Ships Statics and Dynamics'; Rojdestvensky, Lugovsky 'Ship Statics'. Those have full mathematical definition of metacentre, etc.,

I have studied stability from both naval architectures side and from navy, and also taught stability for ship operators; would say that definitions are different and navy/operators tend to simplify them.

 

Would these be good sources?

Principles of Naval Architecture including the new edition which is appearing as a series of separate volumes.

ITTC Dictionary of Hydromechanics

Basic Ship Theory by Rawson and Tucker

 

David, I am somewhat confused.

You say you're a degree qualified NA...did you not use these books as references or buy them when you were a student? If so, you would know the esteem in which they are held...if you do not have them (or used them)...begs the question why not?

These were first NA books i bought over 25years ago...still have them on my bookshelf.

 

Never said I'm a naval architect and don't consider myself to be one. Just said that I have a degree in naval architecture.

I know the esteem I hold them in, wondering about others.

 

How does this help the OP?

Isn't one of the rules to stay on topic?

-Tom

 

Submarine, the OP's problem was resolved in posts 2 and 4. Then, for some reason, the discussion moved into chatting and arguing about the terminology used here and in naval architecture in general. Anyways, it is a quite usual dynamics of bd.net discussions, and I believe it will end up becoming pretty informative for readers of the topic.
Cheers

 

Oh no, not that old chestnut of definitions again

 

LOL!!!
Well, when it comes to discussions, I prefer dynamics to statics.

 

Thats correct. Let people discuss whatever they want. I think I got my answer in post 2 and 4. Thank you again.