inclining experiment

[Alik]

On one of boats we tested GM was 14m.

[mizkuzi]

Originally Posted by Alik

Traditional inclining experiment might not be accurate enough for catamaran. There are notes on that in ISO12217-1.

Hi Alik, do u have a softcopy of that ISO rules? If you dont mind I would like to have a copy of it. You can email it to me at tajanheaven_40787@yahoo.com. Thanks. Im very new to catamaran boat building and we will be hopefully having our inclining experiment by mid july.. I suppose that ISO rules would help me a lot then. Or maybe u can tell me if theres a downloadable softcopy of that. thanks a lot!

[mizkuzi]

Hi where can i find a softcopy of this ISO12217-1 rules or is there any downloadable file for this? i need it so badly.

[mizkuzi]

Hi,

1.) I would like to ask how much degrees should be the ''initial heel'' during inclining experiment of a catamaran sailing craft? (note: craft is made of composites) i have read from a reference but its for barge and it says initial heel should be less than 0.5 deg., how about catamarans made of composites?

2.) How about TRIM? from my reference on barge it says that trim should be less than 1% of LBP and if not, hydrostatics should be used for calculations. What about for catamarans?

I need ideas from the experts of catamaran boatbuilders and designers! It would be much appreciated. Thanks a lot! ^_^

[Eric Sponberg]

Mizkuzi,
If you are a naval architect, you should know this stuff because it is basic naval architecture that you learn in college or even at a design trade school.

That said, the ISO-standards must be purchased--there are no free copies. If you Google the standard by its number, you will find sources where it is for sale. Have your credit card ready, and once you pay for it, you can download a copy.

In general, and regardless of the type of craft, during an inclining experiment, the angle of heel should be between about 2 degrees and 4 degrees of heel. This gives you enough heeling moment simply to do the calculations, but not so much that the metacenter changes dramatically. Here's what happens: As you know, the inclining experiment results in a measurement of GM, the distance between the center of gravity and the metacenter. G, the center of gravity, should be reliably estimated from the weight study, but the inclining experiment confirms this number. The metacenter is calculated as BM, the distance that M (metacenter) is from B (center of buoyancy), and BM is equal to Iwp/Vol of displacement. KB is the distance from the keel (or baseline reference). KB, Iwp, B, and BM all come from the lines plan or hydrostatic calculations from your computer model. Volume does not change during the test--the displacement is constant, and so the volume of displacement is constant. However, the center of buoyancy changes ever so slightly, moving sideways with the angle of heel, but you don't want it to move too far, because then it might also move up or down or fore and aft, and you don't want that to happen. Also, as the boat heels or trims, Iwp (moment of inertia of the waterplane) changes ever so slightly, and you don't want that to change too much either during the test. So that is why we keep the angle of heel down to between 2 to 4 degrees, regardless of the type of hullform, and why you do not want the trim to change during the test. It does not matter what type of craft it is--this applies to ALL craft.

It also does not make any difference what material the boat is built out of because the problem of stability is primarily a problem of the geometry of free-floating bodies.

It would be worthwhile for you to study these principles again in your textbooks on stability.

I hope that helps.

Eric

[mizkuzi]

Originally Posted by Eric Sponberg

Mizkuzi,
If you are a naval architect, you should know this stuff because it is basic naval architecture that you learn in college or even at a design trade school.

That said, the ISO-standards must be purchased--there are no free copies. If you Google the standard by its number, you will find sources where it is for sale. Have your credit card ready, and once you pay for it, you can download a copy.

In general, and regardless of the type of craft, during an inclining experiment, the angle of heel should be between about 2 degrees and 4 degrees of heel. This gives you enough heeling moment simply to do the calculations, but not so much that the metacenter changes dramatically. Here's what happens: As you know, the inclining experiment results in a measurement of GM, the distance between the center of gravity and the metacenter. G, the center of gravity, should be reliably estimated from the weight study, but the inclining experiment confirms this number. The metacenter is calculated as BM, the distance that M (metacenter) is from B (center of buoyancy), and BM is equal to Iwp/Vol of displacement. KB is the distance from the keel (or baseline reference). KB, Iwp, B, and BM all come from the lines plan or hydrostatic calculations from your computer model. Volume does not change during the test--the displacement is constant, and so the volume of displacement is constant. However, the center of buoyancy changes ever so slightly, moving sideways with the angle of heel, but you don't want it to move too far, because then it might also move up or down or fore and aft, and you don't want that to happen. Also, as the boat heels or trims, Iwp (moment of inertia of the waterplane) changes ever so slightly, and you don't want that to change too much either during the test. So that is why we keep the angle of heel down to between 2 to 4 degrees, regardless of the type of hullform, and why you do not want the trim to change during the test. It does not matter what type of craft it is--this applies to ALL craft.

It also does not make any difference what material the boat is built out of because the problem of stability is primarily a problem of the geometry of free-floating bodies.

It would be worthwhile for you to study these principles again in your textbooks on stability.

I hope that helps.

Eric

I would like to say thank you for the help u have given me. About the ISOrules, it was sad to tell that i've never learned about it from school and its a shame then or perhaps i only heard about it back then. The school more focuses on cargo ships and i think thats because cargo ships are more popular in the philippines and they only introduced as ABS and classNK which is oftenly used by japanese shipbuilding companies here and thats what weve used throughout the year.

Anyways, it feels like a new world to me to be working on catamaran boatbuilding company in BV class now coz its good to learn more than what ive learnt from school. Problem is i dont have anyone else where i could ask if theres something i dont understad since im the only naval architect and i dont have a senior naval in this french-owned company, so it is really a challenge to me since i know that im new to boatbuilding and i believe that i got a long way to go to be fully called a great naval architect.

It was a great help from you Sir and thank you for making me understand.
^_^

[Eric Sponberg]

Glad to help. Good luck!

Eric