Why Do Boats Need Ballast For Stability? (Explained)

Boats need balance in order to stay afloat, but even more to keep things stable up on deck.

Why Do Boats Need A Ballast For Stability?

Sailboats primarily utilize a ballast – or weight in the hull of the ship – to maintain stability in rough waters or high winds. Furthermore, a ballast keel, or fin-like blade on the bottom of the boat, will help keep the craft from tipping when the sails are pushed by the wind.

Without a ballast, most boats would never be able to navigate treacherous waters.

What is Boat Ballast?

A boat’s ballast is usually a metal weight or other heavy cargo placed in the hull of a ship that is sealed off and allows the vessel to have weight on the bottom.

This provides stability in that it pulls the boat downwards toward the water, and displacing the more dense water out and to the sides of the ship. As the ship sails, the weight keeps it steady.

Think for a moment of a beach ball in a pool. If you blow up a beach ball and place it in the water, you could easily tap the ball, and it would twist, turn, and possibly even go upside down from the force.

However, if you taped a rock to the bottom of the beach ball on the inside and attempted to twist it, the rock would try to keep the ball steady, always facing the rock down toward the water, and not allow it to twist, turn or flip.

This is a very watered-down explanation to show how ballast can create a weight to function as a way to keep a boat balanced in the water.

How Much Ballast do Boats Need?

Boats, especially sailboats, do require ballast in order to prevent them from altogether tipping over in certain situations – but these boats can still tip over.

Therefore it is essential to know how much ballast a boat needs.

While it is difficult to put a number to it, the way that ballast works in many modern boats is that ballast is made with a water tank. This means that specific sizes of boats are going to require different amounts of water for their water tanks.

Larger boats will need a larger tank and vice versa with smaller boats.

For example, a cargo ship that hauls thousands of tons of shipping containers is going to need a complex system of piping and pumping of water in and out of the ballast water tank at the bottom of the ship in order to keep it as steady as possible.

While a smaller sailboat is going to have a less complex, but still as relevant, system for the ballast.

Most larger fixed keel sailboats have ballast that weighs up to half of the weight of the boat– that’s a lot of added weight that is part of the boat’s design.  With water ballast, the amount or size of the water tank is designed by the manufacturer of that boat.

What is a Water Ballast System?

A water ballast system is how water is regulated and filtered through the tank to make sure that the proper amount of water is continuously being used during specific situations.

For example, as we have mentioned in our article about water in the bilge, boats will need to have that water filtered out, changed, cleaned, or otherwise checked continuously to make sure that the boat is not rotting or sinking.

The same goes for the ballast.

Many water ballast systems will filter new water through, filter gray water out, and raise or lower the quantity of water in the tank.

The boat ballast system is crucial to maintaining a proper balance on board as well as keep the ship from rotting in the hull with stagnant water.

Why is it Called a “Ballast”?

“Ballast” is a mid-16th century word that is derived from possibly Germanic or Scandinavian in origin.

The ballast was used in early shipbuilding by using rocks, gravel, or sand in the bottom of a boat in order to keep that weight distribution properly managed.

Until modern technology created the water tank and piping system, shipbuilders had to be very careful about how much weight they put into the bottom of a boat and with materials that wouldn’t damage the hull of the ship over time.

Sometimes ballast is simply the cargo or the crew of the boat if the boat is small enough.

What is a Ballast Keel?

The ballast keel is a “fin” or flat blade under a sailboat or large vessel.

It prevents the sailboat from being blown from side to side by tough winds, and it also holds the weight of the ballast – whether that is a water tank, lead, or other weight – that the ship needs to stay upright.

The ballast, especially on a sailboat, compensates for the top-heavy weight of the mast and forces on the sails.

The keel is incredibly essential on a sailboat because it keeps the boat from sliding sideways from the wind in the sails, and keeps it moving forward.  The ballast in the keel keeps the boat from tipping or heeling drastically from the forces of the wind.  These are two separate but important functions.

How Else Can You Improve a Boat’s Stability?

Improving your boat’s stability comes from understanding your boat’s center of gravity and what you have onboard that may affect it.

For example, cargo and bulky items, as well as people, must be distributed evenly throughout the boat in order to maintain good stability.

In another example, steering your boat properly against or into waves, rather than dipping on one side into deep valleys of waves, is crucial to preventing the boat from tipping far to one end or another.

You also want to be sure that anything you have in the bilge, such as an excess of water or oil, is adequately flushed out and filtered. Too much water could pull your ship downward too far, and not enough can make you too light to resist the waves.

At the end of the day, you want to make sure you are not overloading your boat with people or cargo, and that while the boat is in motion or on rough waters, your weight distribution is even and safe for everyone.