Use this handy **hull speed calculator** to determine the maximum speed of a **displacement hull vessel**/**boat** using **Hull Speed (in knots) = 1.34 × √(LWL)** formula.

For instance:

- A
**25-foot boat**: Hull Speed ≈ 6.70 knots - A
**50-foot boat**: Hull Speed ≈ 9.48 knots

## Hull Speed Calculator

Waterline Length (ft) | Hull Speed (knots) | Hull Speed (mph) |
---|---|---|

10 | 4.20 | 4.83 |

15 | 5.19 | 5.97 |

20 | 6.00 | 6.90 |

22 | 6.29 | 7.24 |

25 | 6.70 | 7.71 |

30 | 7.34 | 8.45 |

35 | 7.93 | 9.12 |

40 | 8.48 | 9.76 |

45 | 9.00 | 10.36 |

48 | 9.28 | 10.68 |

50 | 9.48 | 10.91 |

55 | 10.00 | 11.51 |

60 | 10.38 | 11.94 |

65 | 10.81 | 12.44 |

70 | 11.22 | 12.89 |

75 | 11.60 | 13.35 |

80 | 12.00 | 13.80 |

## Hull Speed Formula

The **Hull Speed Formula** is:

`Hull Speed (in knots) = 1.34 × √(LWL)`

Where

LWLrepresents theLength of the Waterlinein feet.

Let’s apply this formula to our **30-foot sailboat**:

**Hull Speed = 1.34 × √30
≈ 1.34 × 5.48
≈ 7.34 knots**

## What is Hull Speed?

**Hull speed** is the speed at which a displacement hull boat’s bow wave becomes equal to its waterline length. At this point, the boat essentially tries to climb its own bow wave, requiring significantly more power to increase speed further.

## Hull Speed Chart

Waterline Length (ft) | Hull Speed (knots) |
---|---|

20 | 6.00 |

30 | 7.34 |

40 | 8.48 |

50 | 9.48 |

60 | 10.38 |

## What is the hull speed of a boat with a 16 waterline?

Let’s calculate the hull speed for a boat with a **16-foot waterline**:

**Hull Speed = 1.34 × √16
= 1.34 × 4
= 5.36 knots**

This means a boat with a **16-foot waterline** has a theoretical maximum speed of about **5.36 knots** or approximately **6.17 mph**.

To visualize this, imagine a small daysailer or a modest cabin cruiser, at **5.36 knots**, it would take about **11.2 minutes** to travel one nautical mile.

## How much horsepower does it take to reach the hull speed?

**Horsepower ≈ (Displacement in pounds / 550) × Hull Speed^3**

**A boat with:**

**16-foot waterline****3,000 lbs displacement**- Hull speed of
**5.36 knots**(as calculated earlier)

**Horsepower ≈ (3000 / 550) × 5.36^3
≈ 5.45 × 153.93
≈ 839 HP**

## Sources / References

- U.S. Naval Institute – Understanding Hull Speed
- BoatUS Foundation – Hull Speed
- Royal Yachting Association – Understanding Boat Speed

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