War vessels seakeeping

[akuamare]

I need to write a "short" paper about war ships' seakeeping (particularly for a frigate)... but I only found general information.

The main point of the paper is broachig: causes, mathematical prediction, consequences, ...

Could anyone help me ?

Smoothy waves

[jehardiman]

Modern or sailing?

Do you understand what broaching is and what the difference would be between a modern frigate and a sailing one?

[Guillermo]

Hola, akuamare!
Here you have something about broaching:
http://www.mariecurie.org/annals/volume1/spyrou.pdf
http://web02.webb-institute.edu/stab..._Hashimoto.pdf
http://web02.webb-institute.edu/stab...da-Peters).pdf

[jehardiman]

To quote from one of the papers above:

While a ship in waves normally experiences a periodic motion, broaching is a transition from a stable periodic motion to a non-periodic motion. This transition can be explained as hetero- or homoclinic bifurcation by executing invariant manifold analysis of an unstable surf-riding equilibrium as a saddle. (Umeda, 1999) The trajectories connecting two saddles in different wave slopes, which appears only at heteroclinic bifurcation point, looks like a periodic orbit but has a period of infinity because the velocity on a saddle in eigen direction asymptotically tends to zero.

That about sums it up for the modern frigate.

[mmd]

I understand the need for the specificity of technical language, John, but the quote in your post above is beyond the pale.

[Bergalia]

Originally Posted by mmd

I understand the need for the specificity of technical language, John, but the quote in your post above is beyond the pale.

I think he means 'Don't let the waves hit you side on....'

[akuamare]

First of all... THANKS for your help (specially GG... regards from Madrid. And yes, the "paper" is for the ETSIN)


I'll "study" those proceeds, sure. I'm thinking to include and specific application, based on a X m frigate and a range of speeds and 0º-360º wave directions...


Thanks again

Smoothy waves


PS, a sailing frigate would be too much vessel for me... but it's an idea for the future

[jehardiman]

Originally Posted by mmd

I understand the need for the specificity of technical language, John, but the quote in your post above is beyond the pale.

mmd, one of my problems is that I DO understand it.....

akuamare;
It may be a better paper if you only looked at waves from say 315 to 045 relative (i.e. a wave with a relative direction of 000 is from the stern, 090 from the port to stbd, 180 is on the bow, etc.) but varied the wave length from 1/3 the length of the vessel to 4 times the length of the vessel. Then look to see if ships speed has any effect on the answer. Because a frigates length is about 1/2 the wavelength of common 11-13 second seaways, they really have trouble with broaching in following seas.

[safewalrus]

Or to put it into Seamans terms they're pigs to steer with a following sea! Don't I know it! And JEH how long is a 'frigate?' these days - some look like light cruisers (they are but they build 'em that way to con the politician and get bigger ships!)

[jehardiman]

Originally Posted by safewalrus

And JEH how long is a 'frigate?' these days - some look like light cruisers (they are but they build 'em that way to con the politician and get bigger ships!)

They are slightly smaller than the size of a WWII light cruiser at say 500' and 5000 t's. FFG-7 and La Fayette classes are ~450' LOA and ~4300 t's full load. Older ones were smaller; ~ 380' and 3300 t's full load (USCG 378's and Type 21).

For comparison, a US Fletcher class WWII DD was 376' and 2900 t's, a UK WWII Tribal class DD was 344' and 1900 t's, a German WWII Z class was 384' and 1900 t's, and Japanese WWII Kagero was 364' and 2000 t's.