Decide
Where does a ballasted keelboat get most of her stability at large angles?
The lesson in plain words
- Ballasted monohull
- A keelboat is a monohull: a boat with one hull.
- It carries ballast, weight placed low for stability, in its keel.
- Low ballast helps preserve a righting lever at large heel, within the boat’s range of positive stability.
- Most recover from a knockdown, when the mast is in the water.
- A big breaking wave can still roll her over.
- Multihull
- Catamarans have two hulls; trimarans have three.
- Their wide hull spacing provides stability.
- Cruising multihulls may give little warning through heel.
- They can remain stable upside down after capsize and normally cannot self-right.
- Reef early: reduce the sail area using the builder’s wind-speed guidance.
- Dinghies and planing boats
- A sailing dinghy has little ballast.
- Hull shape and crew weight help keep it upright.
- Sitting out means leaning your weight over the side.
- Most sailing dinghies are designed to be righted after capsize.
- Planing boats have hulls that lift partly out of the water at speed.
- Small planing motorboats rely mainly on hull shape and width.
- Rigid inflatable boats (RIBs) also have buoyant tubes.
- Crew and load position matter in both.
- Heel tells you different things
- On a keelboat 20° of heel is normal sailing.
- On a cruising catamaran, a hull lifting clear of the water is a serious warning.
- In a dinghy, heel is controlled by the crew’s weight moment to moment.
- Learn what is normal for your boat.
Key data
- Keelboat
- Ballast low in the keel: usually self-rights from a knockdown
- Catamaran
- Hull spacing gives stability; can remain stable inverted
- Sailing dinghy
- Crew weight and hull shape; most are designed to be righted
Key points
- Keelboats rely on low ballast; most recover from a knockdown.
- Cruising multihulls rely on hull spacing and can remain stable inverted.
- Sailing dinghies rely on shape and crew weight; most are designed to be righted after capsize.
- Reef a multihull early; she gives little warning by heeling.
Check what you have read
What is the main stability risk of a cruising catamaran?
True or false?
Decide each statement before you see the answer.
Sailing dinghies rely on shape and crew weight; most are designed to be righted after capsize.
Reef a multihull early; she gives little warning by heeling.
A keelboat cannot roll over.
A catamaran does not heel, so she cannot capsize.
Practice case & exam keys
Situation
You usually sail a 10 m keelboat. A friend asks you to sail her 12 m catamaran in a freshening Force 5. She is barely heeling. Do you carry full sail as long as she stays flat?
Show the answer
No. Heel gives little warning on a cruising catamaran. Cruising multihulls can remain stable inverted after capsize. Follow the builder’s reefing guide, using true or apparent wind as specified.
Exam keys
- Keelboat: weight stability from low ballast; usually self-rights from a knockdown.
- Cruising multihull: form stability from hull spacing; can remain stable inverted.
- Sailing dinghy: shape and crew weight; most are designed to be righted after capsize.
- Cruising multihull: reef using the builder’s wind-speed limits and specified wind reference.