How does a boat stabilizer work? A boat stabilizer works by using various methods to counteract the rolling motion of the boat due to the waves.
Even the smoothest sea will have waves moving across it and these can make a boat move. This causes two problems. Firstly, everything is much easier to go on a surface that is not moving. Be it fishing, transporting something, or hauling in crab, if the deck is moving up and down it becomes much more difficult. And, secondly, the motion causes a lot of people to get seasick.
Seasickness is caused because of a disparity in signals between the eyes and the vestibular system. The vestibular system is the part of our inner ears that controls our balance. It is made of tubes with microscopic hairs and liquid. When we move our head, the liquid moves, this moves the hairs, and they send an electrical signal to our brain. Seasickness is caused when our vestibular system tells us that we are moving, but our eyes tell us that we are not.
Boats roll in the sea because they can float and because of gravity. If the sea is perfectly still with not a single wave, all boats and ships will be completely upright. They are designed to have their center of gravity right at the bottom. All of the heavy items, such as the engines, are as low down in the ship as they can be. This helps pull the bottom of the ship down and counteract the upward force of buoyancy. Ships with tall masts, such as yachts, often have a weight attached to the bottom of keel called ballast. If the heavier items in the ship were high up, or if much more of the ship was above water than below it, the ship would tip over.
When a wave comes from the side, it carries a lot of energy and lifts the side of the boat it reaches first. This makes the boat tilt, with that side going up and the other side going down. As the wave passes underneath the boat, the slope of the water changes. The first side starts to drop and the other side rises. The boat then tries to return to an upright position, but its momentum carries it past upright and it tilts in the opposite direction. As waves continue to pass underneath, the boat rocks from side to side. This motion is called rolling, and it can cause problems on a boat.
There are basically three types of ship stabilizers. The first are called bilge keels. They are fixed rims on the keel of the boat. They are usually long, narrow strips that run along both sides of the keel of the boat. Their job is to resist the push of the waves. When the wave rolls the ship, it moves to one side. The rim in the sea has a large surface area and it pushes against the water as the boat tries to move. It is like when you pull your open hand through the water. This resistance is enough to stop the boat rolling and when it rolls back, the rim pushes against that as well. Bilge heels are extremely cheap and easy to make. A lot of large ships, such as cruise ships, use them. They need no power and they have no moving parts. However, they are not enormously powerful and they create drag on the boat.
The second type are called active fin stabilizers. These are much more sophisticated, but also much more expensive. They function like underwater airplane wings. Water moving over the wing produces lift, just like air moving over an airplane wing does. The lift on the active fin stabilizers can be directed to be up or down. When the boat starts to roll, sensors on board direct the computer to change the angle of the stabilizers. This produces force in the opposite direction to the ship’s roll and cancels it out. When the ship rolls back, the angle changes and the same thing happens. They are effective but they are very expensive, they have a lot of moving parts, and they need power. They also only work when the ship is moving because they need water to be passing over the wings. Although, modern systems can overcome this by being able to flap their wings to create stability when the boat is stationary.
And the third stabilizer is a gyroscope. A spinning object has angular momentum, which means that when it spins, it resists movement. Think about the spinning bicycle wheel experiment. If you hold a bicycle wheel and someone spins it, it is very difficult to angle the wheel away from the plane it is spinning on. This happens on a boat. A very large and heavy flywheel is spun at an enormous speed. When the boat starts to roll, the angular momentum of the flywheel counteracts it and the boat doesn’t move. These are very effective and work whether the boat is moving or not. However, they are very big, create a lot of noise and heat, need a lot of power, and are very expensive. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Stabilizer_(ship)
https://quantumstabilizers.com/whitepapers/how-does-yacht-stabilization-work