Hull Speed Calculator / Chart / Formula

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

LWL represents the Length of the Waterline in 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

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