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Would a set of very massive spinning disks on the lowest points of a ship increase its inertia to ocean waves? As ships are filled with an enormous mass of balast water which is not enviroment friendly should this idea possibly make a change? How to fix the issue that the center of rotation of such disk would feel a very strong torque when a huge wave strikes the ship?

Janko Bradvica
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  • Why is ballast water not environmentally friendly? – Jon Custer Jun 01 '21 at 12:35
  • @JonCuster I just mentioned that because, when released, the water from one part of the ocean that contains flora and fauna could ruin the equilibrium of another part og the ocean..... – Janko Bradvica Jun 01 '21 at 13:27

2 Answers2

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If the mounting of the spinning disk is fixed then it will be no good.

However, in the market of luxury motor yachts there are systems available that apply gyroscopic effects with a responsive mounting. You can internet search with search terms such as 'stabilizer', 'gyro' and/or 'gyroscopic'

Strong actuators are in place that tilt the fast spinning gyro wheel.



Use case:
The mounting to the frame of the boat is such that on a flat sea the gyro system can cause the boat to roll from from side to side.

When the boat is in a swell that is causing the boat to roll from side to side the gyro system can diminish that side-to-side roll to a large extent.

Incidentally, a boat fitted with a gyro stabilizer still needs to be well trimmed in order to not have any list. If you would try to counteract a list with the gyro system then quite quickly the gyro system will be saturated.

Ideally the gyro stabilizer system should remain close to it's unsaturated home position. That way the system has room to spare. A swell causes oscillation with respect to the trimmed state. So the gyro stabilizer system will perform best when operating on a well trimmed boat.



[Later addition]

Initially I opted to only mention the existence of gyro stabilizers. A quick search will find that the operating principle of gyro stabilizers is gyroscopic precession. Gyroscopic precession is discussed here on physics.stackExchange in a 2012 answer written by me.

(Well, the question 'what is gyroscopic precession?' has many duplicates here on physics stackexchange, because people keep asking that same question over and over again. (Yeah, duplicates are supposed to be flagged, but with gyroscopic precession questions that isn't happening.))

The gyro stabilizers on luxury yachts are set up as follows: the spin axis points vertical. There are actuators that can force a pitching motion of the spinning gyro wheel. (I'm using the standard names for ship motions )

When the ship is on calm water:
When the gyro wheel is in pitching motion then in response the gyro wheel will tend to roll. The gyro wheel is mounted in such a way that roll motion of the gyro wheel is transferred to the entire ship.

So on calm water:
Forcing a pitching motion of the gyro wheel causes roll of the ship as a whole.

When there is a swell then the gyro stabilization system is used to counteract the effect of that swell on the ship.

Here is what would happen if the gyro wheel is mounted in such a way that the spin axis is fixed relative to the frame of the ship.

In that case: when there is a swell it causes the ship to roll from side to side. In order to counteract that rolling the gyro wheel must perform a pitching motion. But a ship is much longer than it is wide; pitching motion of a ship requires a far far larger force than rolling motion.

When pitching motion is denied to the gyro wheel the spinning gyro wheel offers no opposition to rolling of the ship.

So that is a circumstance that is unique to the case of mounting a gyro wheel, for the purpose of attitude control, on a ship.

With a gyro stabilizer system the purpose of the actuators is to force the pitching motion that is required to elicit the desired response from the gyro wheel.

Cleonis
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  • Why would a fixed mounting be no good? It's going to try to resist any change to the ships attitude either way. Like a top. – DKNguyen May 31 '21 at 21:33
  • @DKNguyen If that is what you believe then by all means you should start a gyro-stabilizer-for-luxury-yachts company. The actuators make the device more expensive. Your idea, if it works, will be much lower cost. I strongly encourage you to build a scale model, the bigger the better. Operating an actual scale model is when the rubber meets the road. – Cleonis May 31 '21 at 22:00
  • OP has already defined the question as "very massive spinning wheels". And the system the OP seems to describe to me would not correct for list so much as it provides additional (open-loop) resistance to it. Besides, I think my idea is actually more expensive since the wheels would have to be on par with the ship itself and if the wheel explodes, the entire ship will too. By the way, the system you describe, are you referring to a Control Moment Gyroscope? – DKNguyen May 31 '21 at 22:12
  • @DKNguyen Yeah, the gyro stabilizer technology for luxury yachts is Control Moment Gyroscope type. The other type of attitude control technology is reaction wheel. When I read the OP it did not occur to me that the OP might have reaction wheels in mind. Reading again: there is no indication, in my opinion, that the question author had a responsive system in mind, and reaction wheels for attitude control must be implemented as a closed loop system. There is a 2012 answer by me discussing how gyroscopic precesssion works – Cleonis Jun 01 '21 at 15:25
  • I wasn't really thinking about reaction wheels in my first comment. I was more thinking something along the lines of a top, or where you spool up a bicycle wheel in your hands and try to turn it. It tries to resist moving out of its plane. – DKNguyen Jun 01 '21 at 17:06
  • @DKNguyen I added a section with discussion of the specific circumstances of operating a gyro stabilization system on a ship. – Cleonis Jun 01 '21 at 20:15
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There is another way to accomplish this which does not require big rotating masses, as follows:

In the ship is mounted a small gyroscope with roll and pitch sensors attached to it, just like in the attitude gyro in an airplane's autopilot.

Sticking out of the sides of the hull are large fins whose pitch is controlled with accordingly large servomotors.

The servomotor control system is connected to the roll and pitch sensors in the gyro, so that when the gyro senses roll or pitching movement of the hull from wave action, the servomotors adjust the pitch of the fins to produce a countertorque which cancels the rolling and pitching induced by the waves.

As such, this system works in exactly the same way as the autopilot system in the airplane: when engaged, it holds the hull level and horizontal in the roll and pitch axis.

Systems like this can be retrofitted to ships originally intended for cargo use when they are converted to passenger use, to increase passenger comfort. However, engaging the automatic roll-and pitch control lock has the effect of slowing down the ship, so even if it is available, it is not always used if the captain is in a hurry.

niels nielsen
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