Ship's speed effect on stability

Hello everybody,

I have a question. How, speed of a ship effect on stability. In actualy, on a cruise ship. So for a cruise ship, how speed of the ship effect on stability? Thanks for your answer ^^

 

In general (very general terms) the greater the speed the greater the accelerations. Less comfortable ride.

But anything apart from that, and you'll have to be more specific.

 

you got me confused ldigas, first thought was my own ex now 27 express cruiser
that could dance quite a bit at sea but trotling up to plane boot became way more straightlined
most cruizeships use water stabilisers at speed that dont work floating around
yet for real bad weather all boats have to slow down, even change course, hmm..

 

Yes, I agree, not one of my best moments

But to answer it properly, it would really need to be asked more precise. What exactly does he mean
by "stability"? I presumed seakeeping properties, movements and accelerations in main directions,
vertical, rolling and pitching being the most uncomfortable ones.

He is interested in cruise ships (I assume he means big cruise ships, not the 20m ones that carry tourists
around the islands on daytours), and they're rather stable by themselves. Most of the time they go
at economic speed, and increasing the speed in their cases will in most cases increase the motions.
The fact that they have a variety of means of controlling and damping those motions makes them rather comfortable
ships.

In smaller vessels, things differ a lot. They're rarely optimized for one speed, more for a range of speeds,
and going below that range puts them at the mercy of the sea, and above that range (if they can, in terms
of power) usually gives them larger motions.
Sailboats are usually better fitted since the sail "stabilizes" them a bit, so to say.

I'm not sure what you mean by "straightlined" - do you mean it holds the course better at larger speed?

 

Another possibility is stability as in the amount a vessel will heel when subject to a heeling moment.

 

Generally speaking speed increases stability... cruise ships, dinghies...

 

True for sailboats and boats with a keel, where aerodynamic forces on sails and/or hydrodynamic forces on the keel dampen rolling motions.
However, not always true for powerboats, because some of them see their waterplane beam decreased when running close to hull speed. It will strongly depend on the boat's hull geometry, of course.
See, for example, this paper for more info: http://www.marine.osakafu-u.ac.jp/~lab07/kata-laboHP/katayama_PP/STWS96.pdf

 

That's same with hard chines as with keels in this regard. True what you said about planing boats. Chears Teddy

 

Yep,...which stability? Static transverse stability, small angle transverse stability, large angle transverse stability, ultimate transverse stability, dynamic stability, coursekeeping stability, longitudinal stability, with active control, passive speed effects, etc.; ....there are lots of them